[compiler] Revert error description

[compiler] Simplify ref mutation validation to single forward pass
Rewrites ValidateNoRefAccessInRender to use a simpler single-pass algorithm that only validates ref mutations (reads are now handled separately by ValidateNoImpureValuesInRender). The new approach: - Tracks refs and ref values through the function - Identifies functions that mutate refs (directly or transitively) - Only errors when ref-mutating functions are called at the top level - Supports null-guard exception: mutations inside `if (ref.current == null)` are allowed for the initialization pattern This reduces ~700 lines of complex fixpoint iteration to ~400 lines of straightforward forward data-flow analysis.
2026-01-14 13:18:15 -08:00 · 2026-01-14 13:11:17 -08:00 · 2026-01-13 18:57:40 -08:00 · 2026-01-13 18:56:35 -08:00 · 2026-01-12 16:38:51 -08:00 · 2026-01-12 16:38:51 -08:00
86 changed files with 2286 additions and 1555 deletions
--- a/compiler/.claude/settings.json
+++ b/compiler/.claude/settings.json
@@ -1,11 +0,0 @@
-{
-  "permissions": {
-    "allow": [
-      "Bash(yarn snap:*)",
-      "Bash(yarn snap:build)",
-      "Bash(node scripts/enable-feature-flag.js:*)"
-    ],
-    "deny": [],
-    "ask": []
-  }
-}
--- a/compiler/.claude/settings.local.json
+++ b/compiler/.claude/settings.local.json
@@ -0,0 +1,16 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(node scripts/enable-feature-flag.js:*)",
+      "Bash(yarn snap:*)",
+      "Bash(for test in \"error.invalid-access-ref-during-render\" \"error.invalid-ref-in-callback-invoked-during-render\" \"error.invalid-impure-functions-in-render-via-render-helper\")",
+      "Bash(do)",
+      "Bash(echo:*)",
+      "Bash(done)",
+      "Bash(cat:*)",
+      "Bash(sl revert:*)"
+    ],
+    "deny": [],
+    "ask": []
+  }
+}
--- a/compiler/.gitignore
+++ b/compiler/.gitignore
@@ -8,9 +8,7 @@ dist
 .vscode
 !packages/playground/.vscode
 testfilter.txt
-.claude/settings.local.json

 # forgive
 *.vsix
 .vscode-test
-
--- a/compiler/CLAUDE.md
+++ b/compiler/CLAUDE.md
@@ -10,8 +10,7 @@ This document contains knowledge about the React Compiler gathered during develo
  - `src/Validation/` - Validation passes that check for errors
  - `src/Entrypoint/Pipeline.ts` - Main compilation pipeline with pass ordering
  - `src/__tests__/fixtures/compiler/` - Test fixtures
-    - `error.todo-*.js` - Unsupported feature, correctly throws Todo error (graceful bailout)
-    - `error.bug-*.js` - Known bug, throws wrong error type or incorrect behavior
+    - `error.*.js` - Fixtures that should produce compilation errors
    - `*.expect.md` - Expected output for each fixture

 ## Running Tests
@@ -20,30 +19,21 @@ This document contains knowledge about the React Compiler gathered during develo
 # Run all tests
 yarn snap

-# Run tests matching a pattern
-# Example: yarn snap -p 'error.*'
+# Run specific test by pattern
 yarn snap -p <pattern>

-# Run a single fixture in debug mode. Use the path relative to the __tests__/fixtures/compiler directory
-# For each step of compilation, outputs the step name and state of the compiled program
-# Example: yarn snap -p simple.js -d
-yarn snap -p <file-basename> -d
-
-# Update fixture outputs (also works with -p)
+# Update fixture outputs
 yarn snap -u
 ```

 ## Version Control

-This repository uses Sapling (`sl`) for version control. Sapling is similar to Mercurial: there is not staging area, but new/deleted files must be explicitlyu added/removed.
+This repository uses Sapling (`sl`) for version control. Unlike git, Sapling does not require explicitly adding files to the staging area.

 ```bash
 # Check status
 sl status

-# Add new files, remove deleted files
-sl addremove
-
 # Commit all changes
 sl commit -m "Your commit message"

@@ -183,17 +173,69 @@ const UseEffectEventHook = addHook(

 **Key insight:** If a hook is missing an `aliasing` config, it falls back to `DefaultNonmutatingHook` which includes a `Render` effect on all arguments. This can cause false positives for hooks like `useEffectEvent` whose callbacks are not called during render.

-## Feature Flags
+### Effect Inference Pipeline

-Feature flags are configured in `src/HIR/Environment.ts`, for example `enableJsxOutlining`. Test fixtures can override the active feature flags used for that fixture via a comment pragma on the first line of the fixture input, for example:
+Effects are populated by `InferMutationAliasingEffects` (runs before validation):

-```javascript
-// enableJsxOutlining @enableChangeVariableCodegen:false
+1. For `Date.now()`, `Math.random()` etc. - adds `Impure` effect (controlled by `validateNoImpureFunctionsInRender` config)
+2. For `ref.current` access - adds `Impure` effect (controlled by `validateRefAccessDuringRender` config)
+3. For return terminals - adds `Alias` from return value to `fn.returns`
+4. For component/JSX returns - adds `Render` effect
+5. For function expressions - adds `CreateFunction` effect with captures

-...code...
-```
+### Validation: validateNoImpureValuesInRender

-Would enable the `enableJsxOutlining` feature and disable the `enableChangeVariableCodegen` feature.
+Located at `src/Validation/ValidateNoImpureValuesInRender.ts`
+
+**Purpose:** Detect when impure values (refs, Date.now results, etc.) flow into render context.
+
+**Algorithm:**
+1. Track impure values in a Map<IdentifierId, ImpureEffect>
+2. Track functions with impure returns separately (they're not impure values themselves)
+3. Fixed-point iteration over all blocks:
+   - Process phi nodes (any impure operand makes result impure)
+   - Process instruction effects
+   - Process terminal effects
+   - Backwards propagation for mutated LoadLocal values
+4. Validate: check all Render effects against impure values
+
+**Key patterns:**
+- `Impure` effect marks the target as impure
+- `Capture/Alias/etc` propagates impurity from source to target
+- `Apply` propagates impurity from args/receiver to result
+- `CreateFunction` propagates impurity from captured values (but NOT from body effects)
+- If a value has both `Render` and `Capture` in same instruction, only error on Render (don't cascade)
+
+**Tracking functions with impure returns:**
+- Separate from the `impure` map (function values aren't impure, just their returns)
+- Populated when analyzing FunctionExpression bodies
+- Used when:
+  1. Calling the function - mark call result as impure
+  2. Capturing the function - mark target as impure (for object.foo = impureFunc cases)
+
+**Backwards propagation:**
+- When `$x = LoadLocal y` and `$x` is mutated with impure content, mark `y` as impure
+- This handles: `const arr = []; arr.push(impure); render(arr)`
+
+## Known Issues / Edge Cases
+
+### Function Outlining
+After `OutlineFunctions` pass, inner functions are replaced with `LoadGlobal(_temp)`. The validation runs BEFORE outlining, so it sees the original FunctionExpression. But be aware that test output shows post-outlining HIR.
+
+### SSA and LoadLocal
+In SSA form, each `LoadLocal` creates a new identifier. When a loaded value is mutated:
+- `$x = LoadLocal y`
+- `mutate($x, impure)`
+- `$z = LoadLocal y` (different from $x!)
+- `render($z)`
+
+The impurity in $x must propagate back to y, then forward to $z. This requires backwards propagation in the fixed-point loop.
+
+## Configuration Flags
+
+In `Environment.ts` / test directives:
+- `validateNoImpureFunctionsInRender` - Enable impure function validation (Date.now, Math.random, etc.)
+- `validateRefAccessDuringRender` - Enable ref access validation

 ## Debugging Tips

@@ -201,21 +243,3 @@ Would enable the `enableJsxOutlining` feature and disable the `enableChangeVaria
 2. Look for `@aliasingEffects=` on FunctionExpressions
 3. Look for `Impure`, `Render`, `Capture` effects on instructions
 4. Check the pass ordering in Pipeline.ts to understand when effects are populated vs validated
-
-## Error Handling for Unsupported Features
-
-When the compiler encounters an unsupported but known pattern, use `CompilerError.throwTodo()` instead of `CompilerError.invariant()`. Todo errors cause graceful bailouts in production; Invariant errors are hard failures indicating unexpected/invalid states.
-
-```typescript
-// Unsupported but expected pattern - graceful bailout
-CompilerError.throwTodo({
-  reason: `Support [description of unsupported feature]`,
-  loc: terminal.loc,
-});
-
-// Invariant is for truly unexpected/invalid states - hard failure
-CompilerError.invariant(false, {
-  reason: `Unexpected [thing]`,
-  loc: terminal.loc,
-});
-```
--- a/compiler/packages/babel-plugin-react-compiler/src/CompilerError.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/CompilerError.ts
@@ -132,6 +132,12 @@ export class CompilerDiagnostic {
    return new CompilerDiagnostic({...options, details: []});
  }

+  clone(): CompilerDiagnostic {
+    const cloned = CompilerDiagnostic.create({...this.options});
+    cloned.options.details = [...this.options.details];
+    return cloned;
+  }
+
  get reason(): CompilerDiagnosticOptions['reason'] {
    return this.options.reason;
  }
--- a/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Pipeline.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Pipeline.ts
@@ -96,7 +96,6 @@ import {propagateScopeDependenciesHIR} from '../HIR/PropagateScopeDependenciesHI
 import {outlineJSX} from '../Optimization/OutlineJsx';
 import {optimizePropsMethodCalls} from '../Optimization/OptimizePropsMethodCalls';
 import {transformFire} from '../Transform';
-import {validateNoImpureFunctionsInRender} from '../Validation/ValidateNoImpureFunctionsInRender';
 import {validateStaticComponents} from '../Validation/ValidateStaticComponents';
 import {validateNoFreezingKnownMutableFunctions} from '../Validation/ValidateNoFreezingKnownMutableFunctions';
 import {inferMutationAliasingEffects} from '../Inference/InferMutationAliasingEffects';
@@ -107,6 +106,7 @@ import {nameAnonymousFunctions} from '../Transform/NameAnonymousFunctions';
 import {optimizeForSSR} from '../Optimization/OptimizeForSSR';
 import {validateExhaustiveDependencies} from '../Validation/ValidateExhaustiveDependencies';
 import {validateSourceLocations} from '../Validation/ValidateSourceLocations';
+import {validateNoImpureValuesInRender} from '../Validation/ValidateNoImpureValuesInRender';

 export type CompilerPipelineValue =
  | {kind: 'ast'; name: string; value: CodegenFunction}
@@ -271,10 +271,6 @@ function runWithEnvironment(
      assertValidMutableRanges(hir);
    }

-    if (env.config.validateRefAccessDuringRender) {
-      validateNoRefAccessInRender(hir).unwrap();
-    }
-
    if (env.config.validateNoSetStateInRender) {
      validateNoSetStateInRender(hir).unwrap();
    }
@@ -296,8 +292,15 @@ function runWithEnvironment(
      env.logErrors(validateNoJSXInTryStatement(hir));
    }

-    if (env.config.validateNoImpureFunctionsInRender) {
-      validateNoImpureFunctionsInRender(hir).unwrap();
+    if (
+      env.config.validateNoImpureFunctionsInRender ||
+      env.config.validateRefAccessDuringRender
+    ) {
+      validateNoImpureValuesInRender(hir).unwrap();
+    }
+
+    if (env.config.validateRefAccessDuringRender) {
+      validateNoRefAccessInRender(hir).unwrap();
    }

    validateNoFreezingKnownMutableFunctions(hir).unwrap();
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/Globals.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/Globals.ts
@@ -38,7 +38,7 @@ import {
  addObject,
 } from './ObjectShape';
 import {BuiltInType, ObjectType, PolyType} from './Types';
-import {TypeConfig} from './TypeSchema';
+import {AliasingSignatureConfig, TypeConfig} from './TypeSchema';
 import {assertExhaustive} from '../Utils/utils';
 import {isHookName} from './Environment';
 import {CompilerError, SourceLocation} from '..';
@@ -626,11 +626,136 @@ const TYPED_GLOBALS: Array<[string, BuiltInType]> = [
  // TODO: rest of Global objects
 ];

+const RenderHookAliasing: (
+  reason: ValueReason,
+) => AliasingSignatureConfig = reason => ({
+  receiver: '@receiver',
+  params: [],
+  rest: '@rest',
+  returns: '@returns',
+  temporaries: [],
+  effects: [
+    // Freeze the arguments
+    {
+      kind: 'Freeze',
+      value: '@rest',
+      reason: ValueReason.HookCaptured,
+    },
+    // Render the arguments
+    {
+      kind: 'Render',
+      place: '@rest',
+    },
+    // Returns a frozen value
+    {
+      kind: 'Create',
+      into: '@returns',
+      value: ValueKind.Frozen,
+      reason,
+    },
+    // May alias any arguments into the return
+    {
+      kind: 'Alias',
+      from: '@rest',
+      into: '@returns',
+    },
+  ],
+});
+
+const EffectHookAliasing: AliasingSignatureConfig = {
+  receiver: '@receiver',
+  params: ['@fn', '@deps'],
+  rest: '@rest',
+  returns: '@returns',
+  temporaries: ['@effect'],
+  effects: [
+    // Freezes the function and deps
+    {
+      kind: 'Freeze',
+      value: '@rest',
+      reason: ValueReason.Effect,
+    },
+    {
+      kind: 'Freeze',
+      value: '@fn',
+      reason: ValueReason.Effect,
+    },
+    {
+      kind: 'Freeze',
+      value: '@deps',
+      reason: ValueReason.Effect,
+    },
+    // Deps are accessed during render
+    {
+      kind: 'Render',
+      place: '@deps',
+    },
+    // Internally creates an effect object that captures the function and deps
+    {
+      kind: 'Create',
+      into: '@effect',
+      value: ValueKind.Frozen,
+      reason: ValueReason.KnownReturnSignature,
+    },
+    // The effect stores the function and dependencies
+    {
+      kind: 'Capture',
+      from: '@rest',
+      into: '@effect',
+    },
+    {
+      kind: 'Capture',
+      from: '@fn',
+      into: '@effect',
+    },
+    // Returns undefined
+    {
+      kind: 'Create',
+      into: '@returns',
+      value: ValueKind.Primitive,
+      reason: ValueReason.KnownReturnSignature,
+    },
+  ],
+};
+
 /*
 * TODO(mofeiZ): We currently only store rest param effects for hooks.
 * now that FeatureFlag `enableTreatHooksAsFunctions` is removed we can
 * use positional params too (?)
 */
+const useEffectEvent = addHook(
+  DEFAULT_SHAPES,
+  {
+    positionalParams: [],
+    restParam: Effect.Freeze,
+    returnType: {
+      kind: 'Function',
+      return: {kind: 'Poly'},
+      shapeId: BuiltInEffectEventId,
+      isConstructor: false,
+    },
+    calleeEffect: Effect.Read,
+    hookKind: 'useEffectEvent',
+    // Frozen because it should not mutate any locally-bound values
+    returnValueKind: ValueKind.Frozen,
+    aliasing: {
+      receiver: '@receiver',
+      params: ['@value'],
+      rest: null,
+      returns: '@return',
+      temporaries: [],
+      effects: [
+        {kind: 'Assign', from: '@value', into: '@return'},
+        {
+          kind: 'Freeze',
+          value: '@value',
+          reason: ValueReason.HookCaptured,
+        },
+      ],
+    },
+  },
+  BuiltInUseEffectEventId,
+);
 const REACT_APIS: Array<[string, BuiltInType]> = [
  [
    'useContext',
@@ -644,6 +769,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        hookKind: 'useContext',
        returnValueKind: ValueKind.Frozen,
        returnValueReason: ValueReason.Context,
+        aliasing: RenderHookAliasing(ValueReason.Context),
      },
      BuiltInUseContextHookId,
    ),
@@ -658,6 +784,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      hookKind: 'useState',
      returnValueKind: ValueKind.Frozen,
      returnValueReason: ValueReason.State,
+      aliasing: RenderHookAliasing(ValueReason.State),
    }),
  ],
  [
@@ -670,6 +797,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      hookKind: 'useActionState',
      returnValueKind: ValueKind.Frozen,
      returnValueReason: ValueReason.State,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -682,6 +810,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      hookKind: 'useReducer',
      returnValueKind: ValueKind.Frozen,
      returnValueReason: ValueReason.ReducerState,
+      aliasing: RenderHookAliasing(ValueReason.ReducerState),
    }),
  ],
  [
@@ -715,6 +844,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      calleeEffect: Effect.Read,
      hookKind: 'useMemo',
      returnValueKind: ValueKind.Frozen,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -726,6 +856,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      calleeEffect: Effect.Read,
      hookKind: 'useCallback',
      returnValueKind: ValueKind.Frozen,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -739,41 +870,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        calleeEffect: Effect.Read,
        hookKind: 'useEffect',
        returnValueKind: ValueKind.Frozen,
-        aliasing: {
-          receiver: '@receiver',
-          params: [],
-          rest: '@rest',
-          returns: '@returns',
-          temporaries: ['@effect'],
-          effects: [
-            // Freezes the function and deps
-            {
-              kind: 'Freeze',
-              value: '@rest',
-              reason: ValueReason.Effect,
-            },
-            // Internally creates an effect object that captures the function and deps
-            {
-              kind: 'Create',
-              into: '@effect',
-              value: ValueKind.Frozen,
-              reason: ValueReason.KnownReturnSignature,
-            },
-            // The effect stores the function and dependencies
-            {
-              kind: 'Capture',
-              from: '@rest',
-              into: '@effect',
-            },
-            // Returns undefined
-            {
-              kind: 'Create',
-              into: '@returns',
-              value: ValueKind.Primitive,
-              reason: ValueReason.KnownReturnSignature,
-            },
-          ],
-        },
+        aliasing: EffectHookAliasing,
      },
      BuiltInUseEffectHookId,
    ),
@@ -789,6 +886,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        calleeEffect: Effect.Read,
        hookKind: 'useLayoutEffect',
        returnValueKind: ValueKind.Frozen,
+        aliasing: EffectHookAliasing,
      },
      BuiltInUseLayoutEffectHookId,
    ),
@@ -804,6 +902,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        calleeEffect: Effect.Read,
        hookKind: 'useInsertionEffect',
        returnValueKind: ValueKind.Frozen,
+        aliasing: EffectHookAliasing,
      },
      BuiltInUseInsertionEffectHookId,
    ),
@@ -817,6 +916,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      calleeEffect: Effect.Read,
      hookKind: 'useTransition',
      returnValueKind: ValueKind.Frozen,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -829,6 +929,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      hookKind: 'useOptimistic',
      returnValueKind: ValueKind.Frozen,
      returnValueReason: ValueReason.State,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -842,6 +943,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        returnType: {kind: 'Poly'},
        calleeEffect: Effect.Read,
        returnValueKind: ValueKind.Frozen,
+        aliasing: RenderHookAliasing(ValueReason.HookCaptured),
      },
      BuiltInUseOperatorId,
    ),
@@ -866,27 +968,8 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      BuiltInFireId,
    ),
  ],
-  [
-    'useEffectEvent',
-    addHook(
-      DEFAULT_SHAPES,
-      {
-        positionalParams: [],
-        restParam: Effect.Freeze,
-        returnType: {
-          kind: 'Function',
-          return: {kind: 'Poly'},
-          shapeId: BuiltInEffectEventId,
-          isConstructor: false,
-        },
-        calleeEffect: Effect.Read,
-        hookKind: 'useEffectEvent',
-        // Frozen because it should not mutate any locally-bound values
-        returnValueKind: ValueKind.Frozen,
-      },
-      BuiltInUseEffectEventId,
-    ),
-  ],
+  ['useEffectEvent', useEffectEvent],
+  ['experimental_useEffectEvent', useEffectEvent],
  ['AUTODEPS', addObject(DEFAULT_SHAPES, BuiltInAutodepsId, [])],
 ];

--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/HIR.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/HIR.ts
@@ -1879,7 +1879,15 @@ export function isRefValueType(id: Identifier): boolean {
 }

 export function isUseRefType(id: Identifier): boolean {
-  return id.type.kind === 'Object' && id.type.shapeId === 'BuiltInUseRefId';
+  return isUseRefType_(id.type);
+}
+
+export function isUseRefType_(type: Type): boolean {
+  return (
+    (type.kind === 'Object' && type.shapeId === 'BuiltInUseRefId') ||
+    (type.kind === 'Phi' &&
+      type.operands.some(operand => isUseRefType_(operand)))
+  );
 }

 export function isUseStateType(id: Identifier): boolean {
@@ -1890,6 +1898,13 @@ export function isJsxType(type: Type): boolean {
  return type.kind === 'Object' && type.shapeId === 'BuiltInJsx';
 }

+export function isJsxOrJsxUnionType(type: Type): boolean {
+  return (
+    (type.kind === 'Object' && type.shapeId === 'BuiltInJsx') ||
+    (type.kind === 'Phi' && type.operands.some(op => isJsxOrJsxUnionType(op)))
+  );
+}
+
 export function isRefOrRefValue(id: Identifier): boolean {
  return isUseRefType(id) || isRefValueType(id);
 }
@@ -2058,4 +2073,23 @@ export function getHookKindForType(
  return null;
 }

+export function areEqualSourceLocations(
+  loc1: SourceLocation,
+  loc2: SourceLocation,
+): boolean {
+  if (typeof loc1 === 'symbol' || typeof loc2 === 'symbol') {
+    return false;
+  }
+  return (
+    loc1.filename === loc2.filename &&
+    loc1.identifierName === loc2.identifierName &&
+    loc1.start.line === loc2.start.line &&
+    loc1.start.column === loc2.start.column &&
+    loc1.start.index === loc2.start.index &&
+    loc1.end.line === loc2.end.line &&
+    loc1.end.column === loc2.end.column &&
+    loc1.end.index === loc2.end.index
+  );
+}
+
 export * from './Types';
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/HIRBuilder.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/HIRBuilder.ts
@@ -988,7 +988,7 @@ export function createTemporaryPlace(
    identifier: makeTemporaryIdentifier(env.nextIdentifierId, loc),
    reactive: false,
    effect: Effect.Unknown,
-    loc: GeneratedSource,
+    loc,
  };
 }

--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/ObjectShape.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/ObjectShape.ts
@@ -5,7 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {CompilerError} from '../CompilerError';
+import {CompilerError, ErrorCategory} from '../CompilerError';
 import {AliasingEffect, AliasingSignature} from '../Inference/AliasingEffects';
 import {assertExhaustive} from '../Utils/utils';
 import {
@@ -190,14 +190,22 @@ function parseAliasingSignatureConfig(
          };
        }
        case 'Impure': {
-          const place = lookup(effect.place);
+          const into = lookup(effect.into);
          return {
            kind: 'Impure',
+            into,
+            category: ErrorCategory.Purity,
+            description: effect.description,
+            reason: effect.reason,
+            sourceMessage: effect.sourceMessage,
+            usageMessage: effect.usageMessage,
+          };
+        }
+        case 'Render': {
+          const place = lookup(effect.place);
+          return {
+            kind: 'Render',
            place,
-            error: CompilerError.throwTodo({
-              reason: 'Support impure effect declarations',
-              loc: GeneratedSource,
-            }),
          };
        }
        case 'Apply': {
@@ -1513,6 +1521,11 @@ export const DefaultNonmutatingHook = addHook(
          value: '@rest',
          reason: ValueReason.HookCaptured,
        },
+        // Render the arguments
+        {
+          kind: 'Render',
+          place: '@rest',
+        },
        // Returns a frozen value
        {
          kind: 'Create',
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/PrintHIR.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/PrintHIR.ts
@@ -1009,7 +1009,7 @@ export function printAliasingEffect(effect: AliasingEffect): string {
      return `MutateGlobal ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.reason)}`;
    }
    case 'Impure': {
-      return `Impure ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.reason)}`;
+      return `Impure ${printPlaceForAliasEffect(effect.into)} reason=${effect.reason} description=${effect.description}`;
    }
    case 'Render': {
      return `Render ${printPlaceForAliasEffect(effect.place)}`;
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/TypeSchema.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/TypeSchema.ts
@@ -185,11 +185,29 @@ export const ApplyEffectSchema: z.ZodType<ApplyEffectConfig> = z.object({

 export type ImpureEffectConfig = {
  kind: 'Impure';
-  place: string;
+  into: string;
+  reason: string;
+  description: string;
+  sourceMessage: string;
+  usageMessage: string;
 };

 export const ImpureEffectSchema: z.ZodType<ImpureEffectConfig> = z.object({
  kind: z.literal('Impure'),
+  into: LifetimeIdSchema,
+  reason: z.string(),
+  description: z.string(),
+  sourceMessage: z.string(),
+  usageMessage: z.string(),
+});
+
+export type RenderEffectConfig = {
+  kind: 'Render';
+  place: string;
+};
+
+export const RenderEffectSchema: z.ZodType<RenderEffectConfig> = z.object({
+  kind: z.literal('Render'),
  place: LifetimeIdSchema,
 });

@@ -204,7 +222,8 @@ export type AliasingEffectConfig =
  | ImpureEffectConfig
  | MutateEffectConfig
  | MutateTransitiveConditionallyConfig
-  | ApplyEffectConfig;
+  | ApplyEffectConfig
+  | RenderEffectConfig;

 export const AliasingEffectSchema: z.ZodType<AliasingEffectConfig> = z.union([
  FreezeEffectSchema,
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/AliasingEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/AliasingEffects.ts
@@ -5,7 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {CompilerDiagnostic} from '../CompilerError';
+import {CompilerDiagnostic, ErrorCategory} from '../CompilerError';
 import {
  FunctionExpression,
  GeneratedSource,
@@ -162,7 +162,15 @@ export type AliasingEffect =
  /**
   * Indicates a side-effect that is not safe during render
   */
-  | {kind: 'Impure'; place: Place; error: CompilerDiagnostic}
+  | {
+      kind: 'Impure';
+      into: Place;
+      category: ErrorCategory;
+      reason: string;
+      description: string;
+      usageMessage: string;
+      sourceMessage: string;
+    }
  /**
   * Indicates that a given place is accessed during render. Used to distingush
   * hook arguments that are known to be called immediately vs those used for
@@ -222,6 +230,14 @@ export function hashEffect(effect: AliasingEffect): string {
      return [effect.kind, effect.value.identifier.id, effect.reason].join(':');
    }
    case 'Impure':
+      return [
+        effect.kind,
+        effect.into.identifier.id,
+        effect.reason,
+        effect.description,
+        effect.usageMessage,
+        effect.sourceMessage,
+      ].join(':');
    case 'Render': {
      return [effect.kind, effect.place.identifier.id].join(':');
    }
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/ControlDominators.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/ControlDominators.ts
@@ -8,7 +8,7 @@
 import {BlockId, computePostDominatorTree, HIRFunction, Place} from '../HIR';
 import {PostDominator} from '../HIR/Dominator';

-export type ControlDominators = (id: BlockId) => boolean;
+export type ControlDominators = (id: BlockId) => Place | null;

 /**
 * Returns an object that lazily calculates whether particular blocks are controlled
@@ -23,7 +23,7 @@ export function createControlDominators(
  });
  const postDominatorFrontierCache = new Map<BlockId, Set<BlockId>>();

-  function isControlledBlock(id: BlockId): boolean {
+  function isControlledBlock(id: BlockId): Place | null {
    let controlBlocks = postDominatorFrontierCache.get(id);
    if (controlBlocks === undefined) {
      controlBlocks = postDominatorFrontier(fn, postDominators, id);
@@ -35,24 +35,24 @@ export function createControlDominators(
        case 'if':
        case 'branch': {
          if (isControlVariable(controlBlock.terminal.test)) {
-            return true;
+            return controlBlock.terminal.test;
          }
          break;
        }
        case 'switch': {
          if (isControlVariable(controlBlock.terminal.test)) {
-            return true;
+            return controlBlock.terminal.test;
          }
          for (const case_ of controlBlock.terminal.cases) {
            if (case_.test !== null && isControlVariable(case_.test)) {
-              return true;
+              return case_.test;
            }
          }
          break;
        }
      }
    }
-    return false;
+    return null;
  }

  return isControlledBlock;
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingEffects.ts
@@ -27,11 +27,13 @@ import {
  InstructionKind,
  InstructionValue,
  isArrayType,
-  isJsxType,
+  isJsxOrJsxUnionType,
  isMapType,
+  isMutableEffect,
  isPrimitiveType,
  isRefOrRefValue,
  isSetType,
+  isUseRefType,
  makeIdentifierId,
  Phi,
  Place,
@@ -70,6 +72,7 @@ import {
  MutationReason,
 } from './AliasingEffects';
 import {ErrorCategory} from '../CompilerError';
+import {REF_ERROR_DESCRIPTION} from '../Validation/ValidateNoRefAccessInRender';

 const DEBUG = false;

@@ -569,14 +572,32 @@ function inferBlock(
      terminal.effects = effects.length !== 0 ? effects : null;
    }
  } else if (terminal.kind === 'return') {
+    terminal.effects = [
+      context.internEffect({
+        kind: 'Alias',
+        from: terminal.value,
+        into: context.fn.returns,
+      }),
+    ];
    if (!context.isFuctionExpression) {
-      terminal.effects = [
+      terminal.effects.push(
        context.internEffect({
          kind: 'Freeze',
          value: terminal.value,
          reason: ValueReason.JsxCaptured,
        }),
-      ];
+      );
+    }
+    if (
+      context.fn.fnType === 'Component' ||
+      isJsxOrJsxUnionType(context.fn.returns.identifier.type)
+    ) {
+      terminal.effects.push(
+        context.internEffect({
+          kind: 'Render',
+          place: terminal.value,
+        }),
+      );
    }
  }
 }
@@ -749,17 +770,7 @@ function applyEffect(
      break;
    }
    case 'ImmutableCapture': {
-      const kind = state.kind(effect.from).kind;
-      switch (kind) {
-        case ValueKind.Global:
-        case ValueKind.Primitive: {
-          // no-op: we don't need to track data flow for copy types
-          break;
-        }
-        default: {
-          effects.push(effect);
-        }
-      }
+      effects.push(effect);
      break;
    }
    case 'CreateFrom': {
@@ -1061,6 +1072,17 @@ function applyEffect(
            reason: new Set(fromValue.reason),
          });
          state.define(effect.into, value);
+          applyEffect(
+            context,
+            state,
+            {
+              kind: 'ImmutableCapture',
+              from: effect.from,
+              into: effect.into,
+            },
+            initialized,
+            effects,
+          );
          break;
        }
        default: {
@@ -1966,6 +1988,11 @@ function computeSignatureForInstruction(
          value: ValueKind.Primitive,
          reason: ValueReason.Other,
        });
+        effects.push({
+          kind: 'ImmutableCapture',
+          from: value.object,
+          into: lvalue,
+        });
      } else {
        effects.push({
          kind: 'CreateFrom',
@@ -1973,6 +2000,20 @@ function computeSignatureForInstruction(
          into: lvalue,
        });
      }
+      if (
+        env.config.validateRefAccessDuringRender &&
+        isUseRefType(value.object.identifier)
+      ) {
+        effects.push({
+          kind: 'Impure',
+          into: lvalue,
+          category: ErrorCategory.Refs,
+          reason: `Cannot access ref value during render`,
+          description: REF_ERROR_DESCRIPTION,
+          sourceMessage: `Ref is initially accessed`,
+          usageMessage: `Ref value is used during render`,
+        });
+      }
      break;
    }
    case 'PropertyStore':
@@ -2137,6 +2178,15 @@ function computeSignatureForInstruction(
          into: lvalue,
        });
      }
+      if (value.children != null) {
+        // Children are typically called during render, not used as an event/effect callback
+        for (const child of value.children) {
+          effects.push({
+            kind: 'Render',
+            place: child,
+          });
+        }
+      }
      if (value.kind === 'JsxExpression') {
        if (value.tag.kind === 'Identifier') {
          // Tags are render function, by definition they're called during render
@@ -2145,29 +2195,23 @@ function computeSignatureForInstruction(
            place: value.tag,
          });
        }
-        if (value.children != null) {
-          // Children are typically called during render, not used as an event/effect callback
-          for (const child of value.children) {
-            effects.push({
-              kind: 'Render',
-              place: child,
-            });
-          }
-        }
        for (const prop of value.props) {
-          if (
-            prop.kind === 'JsxAttribute' &&
-            prop.place.identifier.type.kind === 'Function' &&
-            (isJsxType(prop.place.identifier.type.return) ||
-              (prop.place.identifier.type.return.kind === 'Phi' &&
-                prop.place.identifier.type.return.operands.some(operand =>
-                  isJsxType(operand),
-                )))
-          ) {
-            // Any props which return jsx are assumed to be called during render
+          const place =
+            prop.kind === 'JsxAttribute' ? prop.place : prop.argument;
+          if (isUseRefType(place.identifier)) {
+            continue;
+          }
+          if (place.identifier.type.kind === 'Function') {
+            if (isJsxOrJsxUnionType(place.identifier.type.return)) {
+              effects.push({
+                kind: 'Render',
+                place,
+              });
+            }
+          } else {
            effects.push({
              kind: 'Render',
-              place: prop.place,
+              place,
            });
          }
        }
@@ -2203,6 +2247,11 @@ function computeSignatureForInstruction(
            value: ValueKind.Primitive,
            reason: ValueReason.Other,
          });
+          effects.push({
+            kind: 'ImmutableCapture',
+            from: value.value,
+            into: place,
+          });
        } else if (patternItem.kind === 'Identifier') {
          effects.push({
            kind: 'CreateFrom',
@@ -2384,15 +2433,46 @@ function computeSignatureForInstruction(
      });
      break;
    }
+    case 'BinaryExpression': {
+      effects.push({
+        kind: 'Create',
+        into: lvalue,
+        value: ValueKind.Primitive,
+        reason: ValueReason.Other,
+      });
+      effects.push({
+        kind: 'ImmutableCapture',
+        into: lvalue,
+        from: value.left,
+      });
+      effects.push({
+        kind: 'ImmutableCapture',
+        into: lvalue,
+        from: value.right,
+      });
+      break;
+    }
+    case 'UnaryExpression': {
+      effects.push({
+        kind: 'Create',
+        into: lvalue,
+        value: ValueKind.Primitive,
+        reason: ValueReason.Other,
+      });
+      effects.push({
+        kind: 'ImmutableCapture',
+        into: lvalue,
+        from: value.value,
+      });
+      break;
+    }
    case 'TaggedTemplateExpression':
-    case 'BinaryExpression':
    case 'Debugger':
    case 'JSXText':
    case 'MetaProperty':
    case 'Primitive':
    case 'RegExpLiteral':
    case 'TemplateLiteral':
-    case 'UnaryExpression':
    case 'UnsupportedNode': {
      effects.push({
        kind: 'Create',
@@ -2423,7 +2503,7 @@ function computeEffectsForLegacySignature(
  lvalue: Place,
  receiver: Place,
  args: Array<Place | SpreadPattern | Hole>,
-  loc: SourceLocation,
+  _loc: SourceLocation,
 ): Array<AliasingEffect> {
  const returnValueReason = signature.returnValueReason ?? ValueReason.Other;
  const effects: Array<AliasingEffect> = [];
@@ -2436,20 +2516,18 @@ function computeEffectsForLegacySignature(
  if (signature.impure && state.env.config.validateNoImpureFunctionsInRender) {
    effects.push({
      kind: 'Impure',
-      place: receiver,
-      error: CompilerDiagnostic.create({
-        category: ErrorCategory.Purity,
-        reason: 'Cannot call impure function during render',
-        description:
-          (signature.canonicalName != null
-            ? `\`${signature.canonicalName}\` is an impure function. `
-            : '') +
-          'Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)',
-      }).withDetails({
-        kind: 'error',
-        loc,
-        message: 'Cannot call impure function',
-      }),
+      into: lvalue,
+      category: ErrorCategory.Purity,
+      reason: 'Cannot access impure value during render',
+      description:
+        'Calling an impure function can produce unstable results that update ' +
+        'unpredictably when the component happens to re-render. ' +
+        '(https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)',
+      sourceMessage:
+        signature.canonicalName != null
+          ? `\`${signature.canonicalName}\` is an impure function.`
+          : 'This function is impure',
+      usageMessage: 'Cannot access impure value during render',
    });
  }
  if (signature.knownIncompatible != null && state.env.enableValidations) {
@@ -2748,7 +2826,23 @@ function computeEffectsForSignature(
        }
        break;
      }
-      case 'Impure':
+      case 'Impure': {
+        if (env.config.validateNoImpureFunctionsInRender) {
+          const values = substitutions.get(effect.into.identifier.id) ?? [];
+          for (const value of values) {
+            effects.push({
+              kind: effect.kind,
+              into: value,
+              category: effect.category,
+              reason: effect.reason,
+              description: effect.description,
+              sourceMessage: effect.sourceMessage,
+              usageMessage: effect.usageMessage,
+            });
+          }
+        }
+        break;
+      }
      case 'MutateFrozen':
      case 'MutateGlobal': {
        const values = substitutions.get(effect.place.identifier.id) ?? [];
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingRanges.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingRanges.ts
@@ -19,6 +19,7 @@ import {
  ValueReason,
  Place,
  isPrimitiveType,
+  isUseRefType,
 } from '../HIR/HIR';
 import {
  eachInstructionLValue,
@@ -28,6 +29,9 @@ import {
 import {assertExhaustive, getOrInsertWith} from '../Utils/utils';
 import {Err, Ok, Result} from '../Utils/Result';
 import {AliasingEffect, MutationReason} from './AliasingEffects';
+import {printIdentifier, printType} from '../HIR/PrintHIR';
+
+const DEBUG = false;

 /**
 * This pass builds an abstract model of the heap and interprets the effects of the
@@ -104,7 +108,6 @@ export function inferMutationAliasingRanges(
    reason: MutationReason | null;
  }> = [];
  const renders: Array<{index: number; place: Place}> = [];
-
  let index = 0;

  const errors = new CompilerError();
@@ -197,14 +200,12 @@ export function inferMutationAliasingRanges(
          });
        } else if (
          effect.kind === 'MutateFrozen' ||
-          effect.kind === 'MutateGlobal' ||
-          effect.kind === 'Impure'
+          effect.kind === 'MutateGlobal'
        ) {
          errors.pushDiagnostic(effect.error);
          functionEffects.push(effect);
        } else if (effect.kind === 'Render') {
          renders.push({index: index++, place: effect.place});
-          functionEffects.push(effect);
        }
      }
    }
@@ -214,10 +215,6 @@ export function inferMutationAliasingRanges(
        state.assign(index, from, into);
      }
    }
-    if (block.terminal.kind === 'return') {
-      state.assign(index++, block.terminal.value, fn.returns);
-    }
-
    if (
      (block.terminal.kind === 'maybe-throw' ||
        block.terminal.kind === 'return') &&
@@ -227,23 +224,31 @@ export function inferMutationAliasingRanges(
        if (effect.kind === 'Alias') {
          state.assign(index++, effect.from, effect.into);
        } else {
-          CompilerError.invariant(effect.kind === 'Freeze', {
-            reason: `Unexpected '${effect.kind}' effect for MaybeThrow terminal`,
-            description: null,
-            details: [
-              {
-                kind: 'error',
-                loc: block.terminal.loc,
-                message: null,
-              },
-            ],
-          });
+          CompilerError.invariant(
+            effect.kind === 'Freeze' || effect.kind === 'Render',
+            {
+              reason: `Unexpected '${effect.kind}' effect for MaybeThrow terminal`,
+              description: null,
+              details: [
+                {
+                  kind: 'error',
+                  loc: block.terminal.loc,
+                  message: null,
+                },
+              ],
+            },
+          );
        }
      }
    }
  }

  for (const mutation of mutations) {
+    if (DEBUG) {
+      console.log(
+        `[${mutation.index}] mutate ${printIdentifier(mutation.place.identifier)}`,
+      );
+    }
    state.mutate(
      mutation.index,
      mutation.place.identifier,
@@ -255,8 +260,16 @@ export function inferMutationAliasingRanges(
      errors,
    );
  }
+  if (DEBUG) {
+    console.log(state.debug());
+  }
  for (const render of renders) {
-    state.render(render.index, render.place.identifier, errors);
+    if (DEBUG) {
+      console.log(
+        `[${render.index}] render ${printIdentifier(render.place.identifier)}`,
+      );
+    }
+    state.render(render.index, render.place, errors);
  }
  for (const param of [...fn.context, ...fn.params]) {
    const place = param.kind === 'Identifier' ? param : param.place;
@@ -515,6 +528,13 @@ export function inferMutationAliasingRanges(
  const ignoredErrors = new CompilerError();
  for (const param of [...fn.params, ...fn.context, fn.returns]) {
    const place = param.kind === 'Identifier' ? param : param.place;
+    const node = state.nodes.get(place.identifier);
+    if (node != null && node.render != null) {
+      functionEffects.push({
+        kind: 'Render',
+        place: place,
+      });
+    }
    tracked.push(place);
  }
  for (const into of tracked) {
@@ -577,7 +597,6 @@ export function inferMutationAliasingRanges(
 function appendFunctionErrors(errors: CompilerError, fn: HIRFunction): void {
  for (const effect of fn.aliasingEffects ?? []) {
    switch (effect.kind) {
-      case 'Impure':
      case 'MutateFrozen':
      case 'MutateGlobal': {
        errors.pushDiagnostic(effect.error);
@@ -612,10 +631,74 @@ type Node = {
    | {kind: 'Object'}
    | {kind: 'Phi'}
    | {kind: 'Function'; function: HIRFunction};
+  render: Place | null;
 };
+
+function _printNode(node: Node): string {
+  const out: Array<string> = [];
+  debugNode(out, node);
+  return out.join('\n');
+}
+function debugNode(out: Array<string>, node: Node): void {
+  out.push(
+    printIdentifier(node.id) +
+      printType(node.id.type) +
+      ` lastMutated=[${node.lastMutated}]`,
+  );
+  if (node.transitive != null) {
+    out.push(`  transitive=${node.transitive.kind}`);
+  }
+  if (node.local != null) {
+    out.push(`  local=${node.local.kind}`);
+  }
+  if (node.mutationReason != null) {
+    out.push(`  mutationReason=${node.mutationReason?.kind}`);
+  }
+  const edges: Array<{
+    index: number;
+    direction: '<=' | '=>';
+    kind: string;
+    id: Identifier;
+  }> = [];
+  for (const [alias, index] of node.createdFrom) {
+    edges.push({index, direction: '<=', kind: 'createFrom', id: alias});
+  }
+  for (const [alias, index] of node.aliases) {
+    edges.push({index, direction: '<=', kind: 'alias', id: alias});
+  }
+  for (const [alias, index] of node.maybeAliases) {
+    edges.push({index, direction: '<=', kind: 'alias?', id: alias});
+  }
+  for (const [alias, index] of node.captures) {
+    edges.push({index, direction: '<=', kind: 'capture', id: alias});
+  }
+  for (const edge of node.edges) {
+    edges.push({
+      index: edge.index,
+      direction: '=>',
+      kind: edge.kind,
+      id: edge.node,
+    });
+  }
+  edges.sort((a, b) => a.index - b.index);
+  for (const edge of edges) {
+    out.push(
+      `  [${edge.index}] ${edge.direction} ${edge.kind} ${printIdentifier(edge.id)}`,
+    );
+  }
+}
+
 class AliasingState {
  nodes: Map<Identifier, Node> = new Map();

+  debug(): string {
+    const items: Array<string> = [];
+    for (const [_id, node] of this.nodes) {
+      debugNode(items, node);
+    }
+    return items.join('\n');
+  }
+
  create(place: Place, value: Node['value']): void {
    this.nodes.set(place.identifier, {
      id: place.identifier,
@@ -629,6 +712,7 @@ class AliasingState {
      lastMutated: 0,
      mutationReason: null,
      value,
+      render: null,
    });
  }

@@ -681,9 +765,9 @@ class AliasingState {
    }
  }

-  render(index: number, start: Identifier, errors: CompilerError): void {
+  render(index: number, start: Place, errors: CompilerError): void {
    const seen = new Set<Identifier>();
-    const queue: Array<Identifier> = [start];
+    const queue: Array<Identifier> = [start.identifier];
    while (queue.length !== 0) {
      const current = queue.pop()!;
      if (seen.has(current)) {
@@ -691,11 +775,34 @@ class AliasingState {
      }
      seen.add(current);
      const node = this.nodes.get(current);
-      if (node == null || node.transitive != null || node.local != null) {
+      if (node == null || isUseRefType(node.id)) {
+        if (DEBUG) {
+          console.log(`  render ${printIdentifier(current)}: skip mutated/ref`);
+        }
        continue;
      }
-      if (node.value.kind === 'Function') {
-        appendFunctionErrors(errors, node.value.function);
+      if (
+        node.local == null &&
+        node.transitive == null &&
+        node.value.kind === 'Function'
+      ) {
+        const returns = node.value.function.returns;
+        if (
+          isJsxType(returns.identifier.type) ||
+          (returns.identifier.type.kind === 'Phi' &&
+            returns.identifier.type.operands.some(operand =>
+              isJsxType(operand),
+            ))
+        ) {
+          appendFunctionErrors(errors, node.value.function);
+        }
+        if (DEBUG) {
+          console.log(`  render ${printIdentifier(current)}: skip function`);
+        }
+        continue;
+      }
+      if (node.render == null) {
+        node.render = start;
      }
      for (const [alias, when] of node.createdFrom) {
        if (when >= index) {
@@ -709,6 +816,12 @@ class AliasingState {
        }
        queue.push(alias);
      }
+      for (const [alias, when] of node.maybeAliases) {
+        if (when >= index) {
+          continue;
+        }
+        queue.push(alias);
+      }
      for (const [capture, when] of node.captures) {
        if (when >= index) {
          continue;
--- a/compiler/packages/babel-plugin-react-compiler/src/Utils/utils.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Utils/utils.ts
@@ -167,6 +167,14 @@ export function Set_filter<T>(
  return result;
 }

+export function Set_subtract<T>(
+  source: ReadonlySet<T>,
+  other: Iterable<T>,
+): Set<T> {
+  const otherSet = other instanceof Set ? other : new Set(other);
+  return Set_filter(source, item => !otherSet.has(item));
+}
+
 export function hasNode<T>(
  input: NodePath<T | null | undefined>,
 ): input is NodePath<NonNullable<T>> {
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoImpureFunctionsInRender.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoImpureFunctionsInRender.ts
@@ -1,59 +0,0 @@
-/**
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- */
-
-import {CompilerDiagnostic, CompilerError} from '..';
-import {ErrorCategory} from '../CompilerError';
-import {HIRFunction} from '../HIR';
-import {getFunctionCallSignature} from '../Inference/InferMutationAliasingEffects';
-import {Result} from '../Utils/Result';
-
-/**
- * Checks that known-impure functions are not called during render. Examples of invalid functions to
- * call during render are `Math.random()` and `Date.now()`. Users may extend this set of
- * impure functions via a module type provider and specifying functions with `impure: true`.
- *
- * TODO: add best-effort analysis of functions which are called during render. We have variations of
- * this in several of our validation passes and should unify those analyses into a reusable helper
- * and use it here.
- */
-export function validateNoImpureFunctionsInRender(
-  fn: HIRFunction,
-): Result<void, CompilerError> {
-  const errors = new CompilerError();
-  for (const [, block] of fn.body.blocks) {
-    for (const instr of block.instructions) {
-      const value = instr.value;
-      if (value.kind === 'MethodCall' || value.kind == 'CallExpression') {
-        const callee =
-          value.kind === 'MethodCall' ? value.property : value.callee;
-        const signature = getFunctionCallSignature(
-          fn.env,
-          callee.identifier.type,
-        );
-        if (signature != null && signature.impure === true) {
-          errors.pushDiagnostic(
-            CompilerDiagnostic.create({
-              category: ErrorCategory.Purity,
-              reason: 'Cannot call impure function during render',
-              description:
-                (signature.canonicalName != null
-                  ? `\`${signature.canonicalName}\` is an impure function. `
-                  : '') +
-                'Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)',
-              suggestions: null,
-            }).withDetails({
-              kind: 'error',
-              loc: callee.loc,
-              message: 'Cannot call impure function',
-            }),
-          );
-        }
-      }
-    }
-  }
-  return errors.asResult();
-}
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoImpureValuesInRender.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoImpureValuesInRender.ts
@@ -0,0 +1,307 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import prettyFormat from 'pretty-format';
+import {CompilerDiagnostic, CompilerError, Effect} from '..';
+import {
+  areEqualSourceLocations,
+  HIRFunction,
+  IdentifierId,
+  InstructionId,
+  isJsxType,
+  isRefValueType,
+  isUseRefType,
+} from '../HIR';
+import {
+  eachInstructionLValue,
+  eachInstructionValueOperand,
+} from '../HIR/visitors';
+import {AliasingEffect} from '../Inference/AliasingEffects';
+import {createControlDominators} from '../Inference/ControlDominators';
+import {isMutable} from '../ReactiveScopes/InferReactiveScopeVariables';
+import {Err, Ok, Result} from '../Utils/Result';
+import {
+  assertExhaustive,
+  getOrInsertWith,
+  Set_filter,
+  Set_subtract,
+} from '../Utils/utils';
+import {printInstruction} from '../HIR/PrintHIR';
+
+type ImpureEffect = Extract<AliasingEffect, {kind: 'Impure'}>;
+type RenderEffect = Extract<AliasingEffect, {kind: 'Render'}>;
+type FunctionCache = Map<HIRFunction, Map<string, ImpuritySignature>>;
+type ImpuritySignature = {effects: Array<ImpureEffect>; error: CompilerError};
+
+export function validateNoImpureValuesInRender(
+  fn: HIRFunction,
+): Result<void, CompilerError> {
+  const impure = new Map<IdentifierId, ImpureEffect>();
+  const result = inferImpureValues(fn, impure, new Map());
+
+  if (result.error.hasAnyErrors()) {
+    return Err(result.error);
+  }
+  return Ok(undefined);
+}
+
+function inferFunctionExpressionMemo(
+  fn: HIRFunction,
+  impure: Map<IdentifierId, ImpureEffect>,
+  cache: FunctionCache,
+): ImpuritySignature {
+  const key = fn.context
+    .map(place => `${place.identifier.id}:${impure.has(place.identifier.id)}`)
+    .join(',');
+  return getOrInsertWith(
+    getOrInsertWith(cache, fn, () => new Map()),
+    key,
+    () => inferImpureValues(fn, impure, cache),
+  );
+}
+
+function processEffects(
+  id: InstructionId,
+  effects: Array<AliasingEffect>,
+  impure: Map<IdentifierId, ImpureEffect>,
+  cache: FunctionCache,
+): boolean {
+  let hasChanges = false;
+  const rendered: Set<IdentifierId> = new Set();
+  for (const effect of effects) {
+    if (effect.kind === 'Render') {
+      rendered.add(effect.place.identifier.id);
+    }
+  }
+  for (const effect of effects) {
+    switch (effect.kind) {
+      case 'Alias':
+      case 'Assign':
+      case 'Capture':
+      case 'CreateFrom':
+      case 'ImmutableCapture': {
+        const sourceEffect = impure.get(effect.from.identifier.id);
+        if (
+          sourceEffect != null &&
+          !impure.has(effect.into.identifier.id) &&
+          !rendered.has(effect.from.identifier.id) &&
+          !isUseRefType(effect.into.identifier) &&
+          !isJsxType(effect.into.identifier.type)
+        ) {
+          impure.set(effect.into.identifier.id, sourceEffect);
+          hasChanges = true;
+        }
+        if (
+          sourceEffect == null &&
+          (effect.kind === 'Assign' || effect.kind === 'Capture') &&
+          !impure.has(effect.from.identifier.id) &&
+          !rendered.has(effect.from.identifier.id) &&
+          !isUseRefType(effect.from.identifier) &&
+          isMutable({id}, effect.into)
+        ) {
+          const destinationEffect = impure.get(effect.into.identifier.id);
+          if (destinationEffect != null) {
+            impure.set(effect.from.identifier.id, destinationEffect);
+            hasChanges = true;
+          }
+        }
+        break;
+      }
+      case 'Impure': {
+        if (!impure.has(effect.into.identifier.id)) {
+          impure.set(effect.into.identifier.id, effect);
+          hasChanges = true;
+        }
+        break;
+      }
+      case 'Render': {
+        break;
+      }
+      case 'CreateFunction': {
+        const result = inferFunctionExpressionMemo(
+          effect.function.loweredFunc.func,
+          impure,
+          cache,
+        );
+        if (result.error.hasAnyErrors()) {
+          break;
+        }
+        const impureEffect: ImpureEffect | null =
+          result.effects.find(
+            (functionEffect: AliasingEffect): functionEffect is ImpureEffect =>
+              functionEffect.kind === 'Impure' &&
+              functionEffect.into.identifier.id ===
+                effect.function.loweredFunc.func.returns.identifier.id,
+          ) ?? null;
+        if (impureEffect != null) {
+          impure.set(effect.into.identifier.id, impureEffect);
+          hasChanges = true;
+        }
+        break;
+      }
+      case 'MaybeAlias':
+      case 'Apply':
+      case 'Create':
+      case 'Freeze':
+      case 'Mutate':
+      case 'MutateConditionally':
+      case 'MutateFrozen':
+      case 'MutateGlobal':
+      case 'MutateTransitive':
+      case 'MutateTransitiveConditionally': {
+        break;
+      }
+    }
+  }
+  return hasChanges;
+}
+
+function inferImpureValues(
+  fn: HIRFunction,
+  impure: Map<IdentifierId, ImpureEffect>,
+  cache: FunctionCache,
+): ImpuritySignature {
+  const getBlockControl = createControlDominators(fn, place => {
+    return impure.has(place.identifier.id);
+  });
+
+  let hasChanges = false;
+  do {
+    hasChanges = false;
+
+    for (const block of fn.body.blocks.values()) {
+      const controlPlace = getBlockControl(block.id);
+      const controlImpureEffect =
+        controlPlace != null ? impure.get(controlPlace.identifier.id) : null;
+
+      for (const phi of block.phis) {
+        if (impure.has(phi.place.identifier.id)) {
+          // Already marked impure on a previous pass
+          continue;
+        }
+        let impureEffect = null;
+        for (const [, operand] of phi.operands) {
+          const operandEffect = impure.get(operand.identifier.id);
+          if (operandEffect != null) {
+            impureEffect = operandEffect;
+            break;
+          }
+        }
+        if (impureEffect != null) {
+          impure.set(phi.place.identifier.id, impureEffect);
+          hasChanges = true;
+        } else {
+          for (const [pred] of phi.operands) {
+            const predControl = getBlockControl(pred);
+            if (predControl != null) {
+              const predEffect = impure.get(predControl.identifier.id);
+              if (predEffect != null) {
+                impure.set(phi.place.identifier.id, predEffect);
+                hasChanges = true;
+                break;
+              }
+            }
+          }
+        }
+      }
+
+      for (const instr of block.instructions) {
+        const _impure = new Set(impure.keys());
+        hasChanges =
+          processEffects(instr.id, instr.effects ?? [], impure, cache) ||
+          hasChanges;
+      }
+      if (block.terminal.kind === 'return' && block.terminal.effects != null) {
+        hasChanges =
+          processEffects(
+            block.terminal.id,
+            block.terminal.effects,
+            impure,
+            cache,
+          ) || hasChanges;
+      }
+    }
+  } while (hasChanges);
+
+  fn.env.logger?.debugLogIRs?.({
+    kind: 'debug',
+    name: 'ValidateNoImpureValuesInRender',
+    value: JSON.stringify(Array.from(impure.keys()).sort(), null, 2),
+  });
+
+  const error = new CompilerError();
+  function validateRenderEffect(effect: RenderEffect): void {
+    const impureEffect = impure.get(effect.place.identifier.id);
+    if (impureEffect == null) {
+      return;
+    }
+    const diagnostic = CompilerDiagnostic.create({
+      category: impureEffect.category,
+      reason: impureEffect.reason,
+      description: impureEffect.description,
+    }).withDetails({
+      kind: 'error',
+      loc: effect.place.loc,
+      message: impureEffect.usageMessage,
+    });
+    if (!areEqualSourceLocations(effect.place.loc, impureEffect.into.loc)) {
+      diagnostic.withDetails({
+        kind: 'error',
+        loc: impureEffect.into.loc,
+        message: impureEffect.sourceMessage,
+      });
+    }
+    error.pushDiagnostic(diagnostic);
+  }
+  for (const block of fn.body.blocks.values()) {
+    for (const instr of block.instructions) {
+      const value = instr.value;
+      if (
+        value.kind === 'FunctionExpression' ||
+        value.kind === 'ObjectMethod'
+      ) {
+        const result = inferFunctionExpressionMemo(
+          value.loweredFunc.func,
+          impure,
+          cache,
+        );
+        if (result.error.hasAnyErrors()) {
+          error.merge(result.error);
+        }
+      }
+      for (const effect of instr.effects ?? []) {
+        if (effect.kind === 'Render') {
+          validateRenderEffect(effect);
+        }
+      }
+    }
+    if (block.terminal.kind === 'return' && block.terminal.effects != null) {
+      for (const effect of block.terminal.effects) {
+        if (effect.kind === 'Render') {
+          validateRenderEffect(effect);
+        }
+      }
+    }
+  }
+  const impureEffects: Array<ImpureEffect> = [];
+  for (const param of [...fn.context, ...fn.params, fn.returns]) {
+    const place = param.kind === 'Identifier' ? param : param.place;
+    const impureEffect = impure.get(place.identifier.id);
+    if (impureEffect != null) {
+      impureEffects.push({
+        kind: 'Impure',
+        into: impureEffect.into,
+        category: impureEffect.category,
+        reason: impureEffect.reason,
+        description: impureEffect.description,
+        sourceMessage: impureEffect.sourceMessage,
+        usageMessage: impureEffect.usageMessage,
+      });
+    }
+  }
+  return {effects: impureEffects, error};
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoRefAccessInRender.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoRefAccessInRender.ts
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoSetStateInEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoSetStateInEffects.ts
@@ -202,10 +202,10 @@ function getSetStateCall(
    );
  };

-  const isRefControlledBlock: (id: BlockId) => boolean =
+  const isRefControlledBlock: (id: BlockId) => Place | null =
    enableAllowSetStateFromRefsInEffects
      ? createControlDominators(fn, place => isDerivedFromRef(place))
-      : (): boolean => false;
+      : (): Place | null => null;

  for (const [, block] of fn.body.blocks) {
    if (enableAllowSetStateFromRefsInEffects) {
@@ -224,7 +224,7 @@ function getSetStateCall(
          refDerivedValues.add(phi.place.identifier.id);
        } else {
          for (const [pred] of phi.operands) {
-            if (isRefControlledBlock(pred)) {
+            if (isRefControlledBlock(pred) != null) {
              refDerivedValues.add(phi.place.identifier.id);
              break;
            }
@@ -337,7 +337,7 @@ function getSetStateCall(
                 * be needed when initial layout measurements from refs need to be stored in state.
                 */
                return null;
-              } else if (isRefControlledBlock(block.id)) {
+              } else if (isRefControlledBlock(block.id) != null) {
                continue;
              }
            }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-ref-accessing-function-to-object-property-if-not-mutated.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-ref-accessing-function-to-object-property-if-not-mutated.expect.md
@@ -1,52 +0,0 @@
-
-## Input
-
-```javascript
-import {useRef} from 'react';
-import {Stringify} from 'shared-runtime';
-
-function Component(props) {
-  const ref = useRef(props.value);
-  const object = {};
-  object.foo = () => ref.current;
-  return <Stringify object={object} shouldInvokeFns={true} />;
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: Component,
-  params: [{value: 42}],
-};
-
-```
-
-## Code
-
-```javascript
-import { c as _c } from "react/compiler-runtime";
-import { useRef } from "react";
-import { Stringify } from "shared-runtime";
-
-function Component(props) {
-  const $ = _c(1);
-  const ref = useRef(props.value);
-  let t0;
-  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
-    const object = {};
-    object.foo = () => ref.current;
-    t0 = <Stringify object={object} shouldInvokeFns={true} />;
-    $[0] = t0;
-  } else {
-    t0 = $[0];
-  }
-  return t0;
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: Component,
-  params: [{ value: 42 }],
-};
-
-```
-      
-### Eval output
-(kind: ok) <div>{"object":{"foo":{"kind":"Function","result":42}},"shouldInvokeFns":true}</div>
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.assign-global-in-component-tag-function.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.assign-global-in-component-tag-function.expect.md
@@ -5,6 +5,7 @@
 function Component() {
  const Foo = () => {
    someGlobal = true;
+    return <div />;
  };
  return <Foo />;
 }
@@ -26,9 +27,9 @@ error.assign-global-in-component-tag-function.ts:3:4
  2 |   const Foo = () => {
 > 3 |     someGlobal = true;
    |     ^^^^^^^^^^ `someGlobal` cannot be reassigned
-  4 |   };
-  5 |   return <Foo />;
-  6 | }
+  4 |     return <div />;
+  5 |   };
+  6 |   return <Foo />;
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.assign-global-in-component-tag-function.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.assign-global-in-component-tag-function.js
@@ -1,6 +1,7 @@
 function Component() {
  const Foo = () => {
    someGlobal = true;
+    return <div />;
  };
  return <Foo />;
 }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.assign-global-in-jsx-children.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.assign-global-in-jsx-children.expect.md
@@ -5,6 +5,7 @@
 function Component() {
  const foo = () => {
    someGlobal = true;
+    return <div />;
  };
  // Children are generally access/called during render, so
  // modifying a global in a children function is almost
@@ -29,9 +30,9 @@ error.assign-global-in-jsx-children.ts:3:4
  2 |   const foo = () => {
 > 3 |     someGlobal = true;
    |     ^^^^^^^^^^ `someGlobal` cannot be reassigned
-  4 |   };
-  5 |   // Children are generally access/called during render, so
-  6 |   // modifying a global in a children function is almost
+  4 |     return <div />;
+  5 |   };
+  6 |   // Children are generally access/called during render, so
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.assign-global-in-jsx-children.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.assign-global-in-jsx-children.js
@@ -1,6 +1,7 @@
 function Component() {
  const foo = () => {
    someGlobal = true;
+    return <div />;
  };
  // Children are generally access/called during render, so
  // modifying a global in a children function is almost
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.capture-ref-for-mutation.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.capture-ref-for-mutation.expect.md
@@ -32,33 +32,22 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error

 ```
-Found 2 errors:
+Found 1 error:

-Error: Cannot access refs during render
+Error: Mutating refs during render is not allowed

-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
+React refs are mutable containers that should only be mutated outside of render, such as in event handlers or effects. Mutating a ref during render can cause bugs because the mutation may not be associated with a particular render. See https://react.dev/reference/react/useRef.

-error.capture-ref-for-mutation.ts:12:13
+error.capture-ref-for-mutation.ts:9:4
+   7 |     const position = currentPosition.current;
+   8 |     const nextPosition = direction === 'left' ? addOne(position) : position;
+>  9 |     currentPosition.current = nextPosition;
+     |     ^^^^^^^^^^^^^^^ Cannot mutate ref during render
  10 |   };
  11 |   const moveLeft = {
-> 12 |     handler: handleKey('left')(),
-     |              ^^^^^^^^^^^^^^^^^ This function accesses a ref value
-  13 |   };
-  14 |   const moveRight = {
-  15 |     handler: handleKey('right')(),
+  12 |     handler: handleKey('left')(),

-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.capture-ref-for-mutation.ts:15:13
-  13 |   };
-  14 |   const moveRight = {
-> 15 |     handler: handleKey('right')(),
-     |              ^^^^^^^^^^^^^^^^^^ This function accesses a ref value
-  16 |   };
-  17 |   return [moveLeft, moveRight];
-  18 | }
+Refs may be mutated during render if initialized with `if (ref.current == null)`
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.hook-ref-value.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.hook-ref-value.expect.md
@@ -20,30 +20,26 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error

 ```
-Found 2 errors:
+Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

-error.hook-ref-value.ts:5:23
+error.hook-ref-value.ts:5:22
  3 | function Component(props) {
  4 |   const ref = useRef();
 > 5 |   useEffect(() => {}, [ref.current]);
-    |                        ^^^^^^^^^^^ Cannot access ref value during render
+    |                       ^^^^^^^^^^^^^ Ref value is used during render
  6 | }
  7 |
  8 | export const FIXTURE_ENTRYPOINT = {

-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
 error.hook-ref-value.ts:5:23
  3 | function Component(props) {
  4 |   const ref = useRef();
 > 5 |   useEffect(() => {}, [ref.current]);
-    |                        ^^^^^^^^^^^ Cannot access ref value during render
+    |                        ^^^^^^^^^^^ Ref is initially accessed
  6 | }
  7 |
  8 | export const FIXTURE_ENTRYPOINT = {
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-during-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-during-render.expect.md
@@ -17,15 +17,23 @@ function Component(props) {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

+error.invalid-access-ref-during-render.ts:5:9
+  3 |   const ref = useRef(null);
+  4 |   const value = ref.current;
+> 5 |   return value;
+    |          ^^^^^ Ref value is used during render
+  6 | }
+  7 |
+
 error.invalid-access-ref-during-render.ts:4:16
  2 | function Component(props) {
  3 |   const ref = useRef(null);
 > 4 |   const value = ref.current;
-    |                 ^^^^^^^^^^^ Cannot access ref value during render
+    |                 ^^^^^^^^^^^ Ref is initially accessed
  5 |   return value;
  6 | }
  7 |
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-in-reducer-init.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-in-reducer-init.expect.md
@@ -28,7 +28,7 @@ export const FIXTURE_ENTRYPOINT = {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

@@ -36,7 +36,16 @@ error.invalid-access-ref-in-reducer-init.ts:8:4
   6 |     (state, action) => state + action,
   7 |     0,
 >  8 |     init => ref.current
-     |     ^^^^^^^^^^^^^^^^^^^ Passing a ref to a function may read its value during render
+     |     ^^^^^^^^^^^^^^^^^^^ Ref value is used during render
+   9 |   );
+  10 |
+  11 |   return <Stringify state={state} />;
+
+error.invalid-access-ref-in-reducer-init.ts:8:12
+   6 |     (state, action) => state + action,
+   7 |     0,
+>  8 |     init => ref.current
+     |             ^^^^^^^^^^^ Ref is initially accessed
   9 |   );
  10 |
  11 |   return <Stringify state={state} />;
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-in-reducer.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-in-reducer.expect.md
@@ -24,7 +24,7 @@ export const FIXTURE_ENTRYPOINT = {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

@@ -32,7 +32,16 @@ error.invalid-access-ref-in-reducer.ts:5:29
  3 | function Component(props) {
  4 |   const ref = useRef(props.value);
 > 5 |   const [state] = useReducer(() => ref.current, null);
-    |                              ^^^^^^^^^^^^^^^^^ Passing a ref to a function may read its value during render
+    |                              ^^^^^^^^^^^^^^^^^ Ref value is used during render
+  6 |
+  7 |   return <Stringify state={state} />;
+  8 | }
+
+error.invalid-access-ref-in-reducer.ts:5:35
+  3 | function Component(props) {
+  4 |   const ref = useRef(props.value);
+> 5 |   const [state] = useReducer(() => ref.current, null);
+    |                                    ^^^^^^^^^^^ Ref is initially accessed
  6 |
  7 |   return <Stringify state={state} />;
  8 | }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-in-render-mutate-object-with-ref-function.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-in-render-mutate-object-with-ref-function.expect.md
@@ -20,18 +20,26 @@ function Component() {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

-error.invalid-access-ref-in-render-mutate-object-with-ref-function.ts:7:19
-   5 |   const object = {};
+error.invalid-access-ref-in-render-mutate-object-with-ref-function.ts:8:15
   6 |   object.foo = () => ref.current;
->  7 |   const refValue = object.foo();
-     |                    ^^^^^^^^^^ This function accesses a ref value
-   8 |   return <div>{refValue}</div>;
+   7 |   const refValue = object.foo();
+>  8 |   return <div>{refValue}</div>;
+     |                ^^^^^^^^ Ref value is used during render
   9 | }
  10 |
+
+error.invalid-access-ref-in-render-mutate-object-with-ref-function.ts:6:21
+  4 |   const ref = useRef(null);
+  5 |   const object = {};
+> 6 |   object.foo = () => ref.current;
+    |                      ^^^^^^^^^^^ Ref is initially accessed
+  7 |   const refValue = object.foo();
+  8 |   return <div>{refValue}</div>;
+  9 | }
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-in-state-initializer.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-access-ref-in-state-initializer.expect.md
@@ -24,7 +24,7 @@ export const FIXTURE_ENTRYPOINT = {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

@@ -32,7 +32,16 @@ error.invalid-access-ref-in-state-initializer.ts:5:27
  3 | function Component(props) {
  4 |   const ref = useRef(props.value);
 > 5 |   const [state] = useState(() => ref.current);
-    |                            ^^^^^^^^^^^^^^^^^ Passing a ref to a function may read its value during render
+    |                            ^^^^^^^^^^^^^^^^^ Ref value is used during render
+  6 |
+  7 |   return <Stringify state={state} />;
+  8 | }
+
+error.invalid-access-ref-in-state-initializer.ts:5:33
+  3 | function Component(props) {
+  4 |   const ref = useRef(props.value);
+> 5 |   const [state] = useState(() => ref.current);
+    |                                  ^^^^^^^^^^^ Ref is initially accessed
  6 |
  7 |   return <Stringify state={state} />;
  8 | }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-aliased-ref-in-callback-invoked-during-render-.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-aliased-ref-in-callback-invoked-during-render-.expect.md
@@ -21,17 +21,27 @@ function Component(props) {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

-error.invalid-aliased-ref-in-callback-invoked-during-render-.ts:9:33
-   7 |     return <Foo item={item} current={current} />;
+error.invalid-aliased-ref-in-callback-invoked-during-render-.ts:7:37
+   5 |     const aliasedRef = ref;
+   6 |     const current = aliasedRef.current;
+>  7 |     return <Foo item={item} current={current} />;
+     |                                      ^^^^^^^ Ref value is used during render
   8 |   };
->  9 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
-     |                                  ^^^^^^^^^^^^^^^^^^^^^^^^ Cannot access ref value during render
+   9 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
  10 | }
-  11 |
+
+error.invalid-aliased-ref-in-callback-invoked-during-render-.ts:6:20
+  4 |   const renderItem = item => {
+  5 |     const aliasedRef = ref;
+> 6 |     const current = aliasedRef.current;
+    |                     ^^^^^^^^^^^^^^^^^^ Ref is initially accessed
+  7 |     return <Foo item={item} current={current} />;
+  8 |   };
+  9 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-assign-current-inferred-ref-during-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-assign-current-inferred-ref-during-render.expect.md
@@ -27,7 +27,7 @@ React refs are values that are not needed for rendering. Refs should only be acc
  4 | component Example() {
  5 |   const fooRef = makeObject_Primitives();
 > 6 |   fooRef.current = true;
-    |   ^^^^^^^^^^^^^^ Cannot update ref during render
+    |   ^^^^^^ Cannot update ref during render
  7 |
  8 |   return <Stringify foo={fooRef} />;
  9 | }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-capturing-ref-returning-function-in-rendered-object.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-capturing-ref-returning-function-in-rendered-object.expect.md
@@ -0,0 +1,51 @@
+
+## Input
+
+```javascript
+import {useRef} from 'react';
+import {Stringify} from 'shared-runtime';
+
+function Component(props) {
+  const ref = useRef(props.value);
+  const object = {};
+  object.foo = () => ref.current;
+  return <Stringify object={object} shouldInvokeFns={true} />;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{value: 42}],
+};
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: Cannot access ref value during render
+
+React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
+
+error.invalid-capturing-ref-returning-function-in-rendered-object.ts:8:28
+   6 |   const object = {};
+   7 |   object.foo = () => ref.current;
+>  8 |   return <Stringify object={object} shouldInvokeFns={true} />;
+     |                             ^^^^^^ Ref value is used during render
+   9 | }
+  10 |
+  11 | export const FIXTURE_ENTRYPOINT = {
+
+error.invalid-capturing-ref-returning-function-in-rendered-object.ts:7:21
+   5 |   const ref = useRef(props.value);
+   6 |   const object = {};
+>  7 |   object.foo = () => ref.current;
+     |                      ^^^^^^^^^^^ Ref is initially accessed
+   8 |   return <Stringify object={object} shouldInvokeFns={true} />;
+   9 | }
+  10 |
+```
+          
+      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-ref-accessing-function-to-object-property-if-not-mutated.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-ref-accessing-function-to-object-property-if-not-mutated.js
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-disallow-mutating-ref-in-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-disallow-mutating-ref-in-render.expect.md
@@ -26,7 +26,7 @@ error.invalid-disallow-mutating-ref-in-render.ts:4:2
  2 | function Component() {
  3 |   const ref = useRef(null);
 > 4 |   ref.current = false;
-    |   ^^^^^^^^^^^ Cannot update ref during render
+    |   ^^^ Cannot update ref during render
  5 |
  6 |   return <button ref={ref} />;
  7 | }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-disallow-mutating-refs-in-render-transitive.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-disallow-mutating-refs-in-render-transitive.expect.md
@@ -27,14 +27,14 @@ Error: Cannot access refs during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

-error.invalid-disallow-mutating-refs-in-render-transitive.ts:9:2
-   7 |   };
-   8 |   const changeRef = setRef;
->  9 |   changeRef();
-     |   ^^^^^^^^^ This function accesses a ref value
-  10 |
-  11 |   return <button ref={ref} />;
-  12 | }
+error.invalid-disallow-mutating-refs-in-render-transitive.ts:6:4
+  4 |
+  5 |   const setRef = () => {
+> 6 |     ref.current = false;
+    |     ^^^ Cannot update ref during render
+  7 |   };
+  8 |   const changeRef = setRef;
+  9 |   changeRef();
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-indirect-via-mutation.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-indirect-via-mutation.expect.md
@@ -0,0 +1,47 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+
+import {arrayPush, identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const getDate = () => Date.now();
+  const now = getDate();
+  const array = [];
+  arrayPush(array, now);
+  return <Foo hasDate={array} />;
+}
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: Cannot access impure value during render
+
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render-indirect-via-mutation.ts:10:23
+   8 |   const array = [];
+   9 |   arrayPush(array, now);
+> 10 |   return <Foo hasDate={array} />;
+     |                        ^^^^^ Cannot access impure value during render
+  11 | }
+  12 |
+
+error.invalid-impure-functions-in-render-indirect-via-mutation.ts:6:24
+  4 |
+  5 | function Component() {
+> 6 |   const getDate = () => Date.now();
+    |                         ^^^^^^^^^^ `Date.now` is an impure function.
+  7 |   const now = getDate();
+  8 |   const array = [];
+  9 |   arrayPush(array, now);
+```
+          
+      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-indirect-via-mutation.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-indirect-via-mutation.js
@@ -0,0 +1,11 @@
+// @validateNoImpureFunctionsInRender
+
+import {arrayPush, identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const getDate = () => Date.now();
+  const now = getDate();
+  const array = [];
+  arrayPush(array, now);
+  return <Foo hasDate={array} />;
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-indirect.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-indirect.expect.md
@@ -0,0 +1,46 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const getDate = () => Date.now();
+  const array = makeArray(getDate());
+  const hasDate = identity(array);
+  return <Foo hasDate={hasDate} />;
+}
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: Cannot access impure value during render
+
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render-indirect.ts:9:23
+   7 |   const array = makeArray(getDate());
+   8 |   const hasDate = identity(array);
+>  9 |   return <Foo hasDate={hasDate} />;
+     |                        ^^^^^^^ Cannot access impure value during render
+  10 | }
+  11 |
+
+error.invalid-impure-functions-in-render-indirect.ts:6:24
+  4 |
+  5 | function Component() {
+> 6 |   const getDate = () => Date.now();
+    |                         ^^^^^^^^^^ `Date.now` is an impure function.
+  7 |   const array = makeArray(getDate());
+  8 |   const hasDate = identity(array);
+  9 |   return <Foo hasDate={hasDate} />;
+```
+          
+      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-indirect.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-indirect.js
@@ -0,0 +1,10 @@
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const getDate = () => Date.now();
+  const array = makeArray(getDate());
+  const hasDate = identity(array);
+  return <Foo hasDate={hasDate} />;
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-function-call-2.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-function-call-2.expect.md
@@ -0,0 +1,52 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const now = () => Date.now();
+  const f = () => {
+    // this should error but we currently lose track of the impurity bc
+    // the impure value comes from behind a call
+    const array = makeArray(now());
+    const hasDate = identity(array);
+    return hasDate;
+  };
+  const hasDate = f();
+  return <Foo hasDate={hasDate} />;
+}
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: Cannot access impure value during render
+
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render-via-function-call-2.ts:15:23
+  13 |   };
+  14 |   const hasDate = f();
+> 15 |   return <Foo hasDate={hasDate} />;
+     |                        ^^^^^^^ Cannot access impure value during render
+  16 | }
+  17 |
+
+error.invalid-impure-functions-in-render-via-function-call-2.ts:6:20
+  4 |
+  5 | function Component() {
+> 6 |   const now = () => Date.now();
+    |                     ^^^^^^^^^^ `Date.now` is an impure function.
+  7 |   const f = () => {
+  8 |     // this should error but we currently lose track of the impurity bc
+  9 |     // the impure value comes from behind a call
+```
+          
+      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-function-call-2.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-function-call-2.js
@@ -0,0 +1,16 @@
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const now = () => Date.now();
+  const f = () => {
+    // this should error but we currently lose track of the impurity bc
+    // the impure value comes from behind a call
+    const array = makeArray(now());
+    const hasDate = identity(array);
+    return hasDate;
+  };
+  const hasDate = f();
+  return <Foo hasDate={hasDate} />;
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-function-call.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-function-call.expect.md
@@ -0,0 +1,50 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const now = Date.now();
+  const f = () => {
+    const array = makeArray(now);
+    const hasDate = identity(array);
+    return hasDate;
+  };
+  const hasDate = f();
+  return <Foo hasDate={hasDate} />;
+}
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: Cannot access impure value during render
+
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render-via-function-call.ts:13:23
+  11 |   };
+  12 |   const hasDate = f();
+> 13 |   return <Foo hasDate={hasDate} />;
+     |                        ^^^^^^^ Cannot access impure value during render
+  14 | }
+  15 |
+
+error.invalid-impure-functions-in-render-via-function-call.ts:6:14
+  4 |
+  5 | function Component() {
+> 6 |   const now = Date.now();
+    |               ^^^^^^^^^^ `Date.now` is an impure function.
+  7 |   const f = () => {
+  8 |     const array = makeArray(now);
+  9 |     const hasDate = identity(array);
+```
+          
+      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-function-call.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-function-call.js
@@ -0,0 +1,14 @@
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const now = Date.now();
+  const f = () => {
+    const array = makeArray(now);
+    const hasDate = identity(array);
+    return hasDate;
+  };
+  const hasDate = f();
+  return <Foo hasDate={hasDate} />;
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper-typed.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper-typed.expect.md
@@ -0,0 +1,50 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+
+import {typedArrayPush, typedIdentity} from 'shared-runtime';
+
+function Component() {
+  const now = Date.now();
+  const renderItem = () => {
+    const array = [];
+    typedArrayPush(array, now());
+    const hasDate = typedIdentity(array);
+    return <Bar hasDate={hasDate} />;
+  };
+  return <Foo renderItem={renderItem} />;
+}
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: Cannot access impure value during render
+
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render-via-render-helper-typed.ts:13:26
+  11 |     return <Bar hasDate={hasDate} />;
+  12 |   };
+> 13 |   return <Foo renderItem={renderItem} />;
+     |                           ^^^^^^^^^^ Cannot access impure value during render
+  14 | }
+  15 |
+
+error.invalid-impure-functions-in-render-via-render-helper-typed.ts:6:14
+  4 |
+  5 | function Component() {
+> 6 |   const now = Date.now();
+    |               ^^^^^^^^^^ `Date.now` is an impure function.
+  7 |   const renderItem = () => {
+  8 |     const array = [];
+  9 |     typedArrayPush(array, now());
+```
+          
+      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper-typed.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper-typed.js
@@ -0,0 +1,14 @@
+// @validateNoImpureFunctionsInRender
+
+import {typedArrayPush, typedIdentity} from 'shared-runtime';
+
+function Component() {
+  const now = Date.now();
+  const renderItem = () => {
+    const array = [];
+    typedArrayPush(array, now());
+    const hasDate = typedIdentity(array);
+    return <Bar hasDate={hasDate} />;
+  };
+  return <Foo renderItem={renderItem} />;
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper.expect.md
@@ -0,0 +1,49 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const now = Date.now();
+  const renderItem = () => {
+    const array = makeArray(now);
+    const hasDate = identity(array);
+    return <Bar hasDate={hasDate} />;
+  };
+  return <Foo renderItem={renderItem} />;
+}
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: Cannot access impure value during render
+
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render-via-render-helper.ts:12:26
+  10 |     return <Bar hasDate={hasDate} />;
+  11 |   };
+> 12 |   return <Foo renderItem={renderItem} />;
+     |                           ^^^^^^^^^^ Cannot access impure value during render
+  13 | }
+  14 |
+
+error.invalid-impure-functions-in-render-via-render-helper.ts:6:14
+  4 |
+  5 | function Component() {
+> 6 |   const now = Date.now();
+    |               ^^^^^^^^^^ `Date.now` is an impure function.
+  7 |   const renderItem = () => {
+  8 |     const array = makeArray(now);
+  9 |     const hasDate = identity(array);
+```
+          
+      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper.js
@@ -0,0 +1,13 @@
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const now = Date.now();
+  const renderItem = () => {
+    const array = makeArray(now);
+    const hasDate = identity(array);
+    return <Bar hasDate={hasDate} />;
+  };
+  return <Foo renderItem={renderItem} />;
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-functions-in-render.expect.md
@@ -19,41 +19,65 @@ function Component() {
 ```
 Found 3 errors:

-Error: Cannot call impure function during render
+Error: Cannot access impure value during render

-`Date.now` is an impure function. Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render.ts:7:20
+  5 |   const now = performance.now();
+  6 |   const rand = Math.random();
+> 7 |   return <Foo date={date} now={now} rand={rand} />;
+    |                     ^^^^ Cannot access impure value during render
+  8 | }
+  9 |

 error.invalid-impure-functions-in-render.ts:4:15
  2 |
  3 | function Component() {
 > 4 |   const date = Date.now();
-    |                ^^^^^^^^^^ Cannot call impure function
+    |                ^^^^^^^^^^ `Date.now` is an impure function.
  5 |   const now = performance.now();
  6 |   const rand = Math.random();
  7 |   return <Foo date={date} now={now} rand={rand} />;

-Error: Cannot call impure function during render
+Error: Cannot access impure value during render

-`performance.now` is an impure function. Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render.ts:7:31
+  5 |   const now = performance.now();
+  6 |   const rand = Math.random();
+> 7 |   return <Foo date={date} now={now} rand={rand} />;
+    |                                ^^^ Cannot access impure value during render
+  8 | }
+  9 |

 error.invalid-impure-functions-in-render.ts:5:14
  3 | function Component() {
  4 |   const date = Date.now();
 > 5 |   const now = performance.now();
-    |               ^^^^^^^^^^^^^^^^^ Cannot call impure function
+    |               ^^^^^^^^^^^^^^^^^ `performance.now` is an impure function.
  6 |   const rand = Math.random();
  7 |   return <Foo date={date} now={now} rand={rand} />;
  8 | }

-Error: Cannot call impure function during render
+Error: Cannot access impure value during render

-`Math.random` is an impure function. Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render.ts:7:42
+  5 |   const now = performance.now();
+  6 |   const rand = Math.random();
+> 7 |   return <Foo date={date} now={now} rand={rand} />;
+    |                                           ^^^^ Cannot access impure value during render
+  8 | }
+  9 |

 error.invalid-impure-functions-in-render.ts:6:15
  4 |   const date = Date.now();
  5 |   const now = performance.now();
 > 6 |   const rand = Math.random();
-    |                ^^^^^^^^^^^^^ Cannot call impure function
+    |                ^^^^^^^^^^^^^ `Math.random` is an impure function.
  7 |   return <Foo date={date} now={now} rand={rand} />;
  8 | }
  9 |
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-value-in-render-helper.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-value-in-render-helper.expect.md
@@ -0,0 +1,45 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+function Component() {
+  const now = () => Date.now();
+  const render = () => {
+    return <div>{now()}</div>;
+  };
+  return <div>{render()}</div>;
+}
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: Cannot access impure value during render
+
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-value-in-render-helper.ts:5:17
+  3 |   const now = () => Date.now();
+  4 |   const render = () => {
+> 5 |     return <div>{now()}</div>;
+    |                  ^^^^^ Cannot access impure value during render
+  6 |   };
+  7 |   return <div>{render()}</div>;
+  8 | }
+
+error.invalid-impure-value-in-render-helper.ts:3:20
+  1 | // @validateNoImpureFunctionsInRender
+  2 | function Component() {
+> 3 |   const now = () => Date.now();
+    |                     ^^^^^^^^^^ `Date.now` is an impure function.
+  4 |   const render = () => {
+  5 |     return <div>{now()}</div>;
+  6 |   };
+```
+          
+      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-value-in-render-helper.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-impure-value-in-render-helper.js
@@ -0,0 +1,8 @@
+// @validateNoImpureFunctionsInRender
+function Component() {
+  const now = () => Date.now();
+  const render = () => {
+    return <div>{now()}</div>;
+  };
+  return <div>{render()}</div>;
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-read-ref-prop-in-render-destructure.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-read-ref-prop-in-render-destructure.expect.md
@@ -16,15 +16,23 @@ function Component({ref}) {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

+error.invalid-read-ref-prop-in-render-destructure.ts:4:15
+  2 | function Component({ref}) {
+  3 |   const value = ref.current;
+> 4 |   return <div>{value}</div>;
+    |                ^^^^^ Ref value is used during render
+  5 | }
+  6 |
+
 error.invalid-read-ref-prop-in-render-destructure.ts:3:16
  1 | // @validateRefAccessDuringRender @compilationMode:"infer"
  2 | function Component({ref}) {
 > 3 |   const value = ref.current;
-    |                 ^^^^^^^^^^^ Cannot access ref value during render
+    |                 ^^^^^^^^^^^ Ref is initially accessed
  4 |   return <div>{value}</div>;
  5 | }
  6 |
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-read-ref-prop-in-render-property-load.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-read-ref-prop-in-render-property-load.expect.md
@@ -16,15 +16,23 @@ function Component(props) {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

+error.invalid-read-ref-prop-in-render-property-load.ts:4:15
+  2 | function Component(props) {
+  3 |   const value = props.ref.current;
+> 4 |   return <div>{value}</div>;
+    |                ^^^^^ Ref value is used during render
+  5 | }
+  6 |
+
 error.invalid-read-ref-prop-in-render-property-load.ts:3:16
  1 | // @validateRefAccessDuringRender @compilationMode:"infer"
  2 | function Component(props) {
 > 3 |   const value = props.ref.current;
-    |                 ^^^^^^^^^^^^^^^^^ Cannot access ref value during render
+    |                 ^^^^^^^^^^^^^^^^^ Ref is initially accessed
  4 |   return <div>{value}</div>;
  5 | }
  6 |
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-ref-access-render-unary.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-ref-access-render-unary.expect.md
@@ -22,57 +22,27 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error

 ```
-Found 4 errors:
+Found 1 error:

-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-  4 | component C() {
-  5 |   const r = useRef(null);
-> 6 |   const current = !r.current;
-    |                    ^^^^^^^^^ Cannot access ref value during render
-  7 |   return <div>{current}</div>;
-  8 | }
-  9 |
-
-To initialize a ref only once, check that the ref is null with the pattern `if (ref.current == null) { ref.current = ... }`
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-  4 | component C() {
-  5 |   const r = useRef(null);
-> 6 |   const current = !r.current;
-    |                   ^^^^^^^^^^ Cannot access ref value during render
-  7 |   return <div>{current}</div>;
-  8 | }
-  9 |
-
-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

   5 |   const r = useRef(null);
   6 |   const current = !r.current;
 >  7 |   return <div>{current}</div>;
-     |                ^^^^^^^ Cannot access ref value during render
+     |                ^^^^^^^ Ref value is used during render
   8 | }
   9 |
  10 | export const FIXTURE_ENTRYPOINT = {

-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-   5 |   const r = useRef(null);
-   6 |   const current = !r.current;
->  7 |   return <div>{current}</div>;
-     |                ^^^^^^^ Cannot access ref value during render
-   8 | }
-   9 |
-  10 | export const FIXTURE_ENTRYPOINT = {
+  4 | component C() {
+  5 |   const r = useRef(null);
+> 6 |   const current = !r.current;
+    |                    ^^^^^^^^^ Ref is initially accessed
+  7 |   return <div>{current}</div>;
+  8 | }
+  9 |
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-ref-in-callback-invoked-during-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-ref-in-callback-invoked-during-render.expect.md
@@ -20,17 +20,27 @@ function Component(props) {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

-error.invalid-ref-in-callback-invoked-during-render.ts:8:33
-   6 |     return <Foo item={item} current={current} />;
-   7 |   };
->  8 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
-     |                                  ^^^^^^^^^^^^^^^^^^^^^^^^ Cannot access ref value during render
-   9 | }
-  10 |
+error.invalid-ref-in-callback-invoked-during-render.ts:6:37
+  4 |   const renderItem = item => {
+  5 |     const current = ref.current;
+> 6 |     return <Foo item={item} current={current} />;
+    |                                      ^^^^^^^ Ref value is used during render
+  7 |   };
+  8 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
+  9 | }
+
+error.invalid-ref-in-callback-invoked-during-render.ts:5:20
+  3 |   const ref = useRef(null);
+  4 |   const renderItem = item => {
+> 5 |     const current = ref.current;
+    |                     ^^^^^^^^^^^ Ref is initially accessed
+  6 |     return <Foo item={item} current={current} />;
+  7 |   };
+  8 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-ref-initialization-unary-not.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-ref-initialization-unary-not.expect.md
@@ -29,15 +29,13 @@ Error: Cannot access refs during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

-  4 | component C() {
-  5 |   const r = useRef(null);
-> 6 |   if (!r.current) {
-    |        ^^^^^^^^^ Cannot access ref value during render
-  7 |     r.current = 1;
-  8 |   }
-  9 | }
-
-To initialize a ref only once, check that the ref is null with the pattern `if (ref.current == null) { ref.current = ... }`
+   5 |   const r = useRef(null);
+   6 |   if (!r.current) {
+>  7 |     r.current = 1;
+     |     ^ Cannot update ref during render
+   8 |   }
+   9 | }
+  10 |
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-ref-value-as-props.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-ref-value-as-props.expect.md
@@ -16,7 +16,7 @@ function Component(props) {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

@@ -24,7 +24,7 @@ error.invalid-ref-value-as-props.ts:4:19
  2 | function Component(props) {
  3 |   const ref = useRef(null);
 > 4 |   return <Foo ref={ref.current} />;
-    |                    ^^^^^^^^^^^ Cannot access ref value during render
+    |                    ^^^^^^^^^^^ Ref value is used during render
  5 | }
  6 |
 ```
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-set-and-read-ref-during-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-set-and-read-ref-during-render.expect.md
@@ -15,22 +15,9 @@ function Component(props) {
 ## Error

 ```
-Found 2 errors:
+Found 1 error:

-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.invalid-set-and-read-ref-during-render.ts:4:2
-  2 | function Component(props) {
-  3 |   const ref = useRef(null);
-> 4 |   ref.current = props.value;
-    |   ^^^^^^^^^^^ Cannot update ref during render
-  5 |   return ref.current;
-  6 | }
-  7 |
-
-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

@@ -38,7 +25,7 @@ error.invalid-set-and-read-ref-during-render.ts:5:9
  3 |   const ref = useRef(null);
  4 |   ref.current = props.value;
 > 5 |   return ref.current;
-    |          ^^^^^^^^^^^ Cannot access ref value during render
+    |          ^^^^^^^^^^^ Ref value is used during render
  6 | }
  7 |
 ```
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-set-and-read-ref-nested-property-during-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-set-and-read-ref-nested-property-during-render.expect.md
@@ -15,22 +15,9 @@ function Component(props) {
 ## Error

 ```
-Found 2 errors:
+Found 1 error:

-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.invalid-set-and-read-ref-nested-property-during-render.ts:4:2
-  2 | function Component(props) {
-  3 |   const ref = useRef({inner: null});
-> 4 |   ref.current.inner = props.value;
-    |   ^^^^^^^^^^^ Cannot update ref during render
-  5 |   return ref.current.inner;
-  6 | }
-  7 |
-
-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

@@ -38,7 +25,15 @@ error.invalid-set-and-read-ref-nested-property-during-render.ts:5:9
  3 |   const ref = useRef({inner: null});
  4 |   ref.current.inner = props.value;
 > 5 |   return ref.current.inner;
-    |          ^^^^^^^^^^^^^^^^^ Cannot access ref value during render
+    |          ^^^^^^^^^^^^^^^^^ Ref value is used during render
+  6 | }
+  7 |
+
+error.invalid-set-and-read-ref-nested-property-during-render.ts:5:9
+  3 |   const ref = useRef({inner: null});
+  4 |   ref.current.inner = props.value;
+> 5 |   return ref.current.inner;
+    |          ^^^^^^^^^^^ Ref is initially accessed
  6 | }
  7 |
 ```
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-write-but-dont-read-ref-in-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-write-but-dont-read-ref-in-render.expect.md
@@ -27,7 +27,7 @@ error.invalid-write-but-dont-read-ref-in-render.ts:5:2
  3 |   const ref = useRef(null);
  4 |   // Writing to a ref in render is against the rules:
 > 5 |   ref.current = value;
-    |   ^^^^^^^^^^^ Cannot update ref during render
+    |   ^^^ Cannot update ref during render
  6 |   // returning a ref is allowed, so this alone doesn't trigger an error:
  7 |   return ref;
  8 | }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-write-ref-prop-in-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.invalid-write-ref-prop-in-render.expect.md
@@ -25,7 +25,7 @@ error.invalid-write-ref-prop-in-render.ts:4:2
  2 | function Component(props) {
  3 |   const ref = props.ref;
 > 4 |   ref.current = true;
-    |   ^^^^^^^^^^^ Cannot update ref during render
+    |   ^^^ Cannot update ref during render
  5 |   return <div>{value}</div>;
  6 | }
  7 |
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-arbitrary.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-arbitrary.expect.md
@@ -25,19 +25,7 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error

 ```
-Found 2 errors:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-   6 | component C() {
-   7 |   const r = useRef(DEFAULT_VALUE);
->  8 |   if (r.current == DEFAULT_VALUE) {
-     |       ^^^^^^^^^ Cannot access ref value during render
-   9 |     r.current = 1;
-  10 |   }
-  11 | }
+Found 1 error:

 Error: Cannot access refs during render

@@ -46,7 +34,7 @@ React refs are values that are not needed for rendering. Refs should only be acc
   7 |   const r = useRef(DEFAULT_VALUE);
   8 |   if (r.current == DEFAULT_VALUE) {
 >  9 |     r.current = 1;
-     |     ^^^^^^^^^ Cannot update ref during render
+     |     ^ Cannot update ref during render
  10 |   }
  11 | }
  12 |
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-linear.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-linear.expect.md
@@ -24,19 +24,35 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error

 ```
-Found 1 error:
+Found 2 errors:

-Error: Cannot access refs during render
+Error: Mutating refs during render is not allowed

-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
+React refs are mutable containers that should only be mutated outside of render, such as in event handlers or effects. Mutating a ref during render can cause bugs because the mutation may not be associated with a particular render. See https://react.dev/reference/react/useRef.
+
+   5 |   const r = useRef(null);
+   6 |   if (r.current == null) {
+>  7 |     r.current = 42;
+     |     ^ Cannot mutate ref during render
+   8 |     r.current = 42;
+   9 |   }
+  10 | }
+
+Refs may be mutated during render if initialized with `if (ref.current == null)`
+
+Error: Mutating refs during render is not allowed
+
+React refs are mutable containers that should only be mutated outside of render, such as in event handlers or effects. Mutating a ref during render can cause bugs because the mutation may not be associated with a particular render. See https://react.dev/reference/react/useRef.

   6 |   if (r.current == null) {
   7 |     r.current = 42;
 >  8 |     r.current = 42;
-     |     ^^^^^^^^^ Cannot update ref during render
+     |     ^ Cannot mutate ref during render
   9 |   }
  10 | }
  11 |
+
+Refs may be mutated during render if initialized with `if (ref.current == null)`
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-nonif.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-nonif.expect.md
@@ -24,31 +24,19 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error

 ```
-Found 2 errors:
+Found 1 error:

 Error: Cannot access refs during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

-  4 | component C() {
-  5 |   const r = useRef(null);
-> 6 |   const guard = r.current == null;
-    |                 ^^^^^^^^^^^^^^^^^ Cannot access ref value during render
-  7 |   if (guard) {
-  8 |     r.current = 1;
-  9 |   }
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-   5 |   const r = useRef(null);
   6 |   const guard = r.current == null;
->  7 |   if (guard) {
-     |       ^^^^^ Cannot access ref value during render
-   8 |     r.current = 1;
+   7 |   if (guard) {
+>  8 |     r.current = 1;
+     |     ^ Cannot update ref during render
   9 |   }
  10 | }
+  11 |
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-other.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-other.expect.md
@@ -33,7 +33,7 @@ React refs are values that are not needed for rendering. Refs should only be acc
   6 |   const r2 = useRef(null);
   7 |   if (r.current == null) {
 >  8 |     r2.current = 1;
-     |     ^^^^^^^^^^ Cannot update ref during render
+     |     ^^ Cannot update ref during render
   9 |   }
  10 | }
  11 |
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-post-access-2.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-post-access-2.expect.md
@@ -26,17 +26,19 @@ export const FIXTURE_ENTRYPOINT = {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Mutating refs during render is not allowed

-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
+React refs are mutable containers that should only be mutated outside of render, such as in event handlers or effects. Mutating a ref during render can cause bugs because the mutation may not be associated with a particular render. See https://react.dev/reference/react/useRef.

-   7 |     r.current = 1;
+   5 |   const r = useRef(null);
+   6 |   if (r.current == null) {
+>  7 |     r.current = 1;
+     |     ^ Cannot mutate ref during render
   8 |   }
->  9 |   f(r.current);
-     |     ^^^^^^^^^ Passing a ref to a function may read its value during render
+   9 |   f(r.current);
  10 | }
-  11 |
-  12 | export const FIXTURE_ENTRYPOINT = {
+
+Refs may be mutated during render if initialized with `if (ref.current == null)`
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-post-access.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-initialization-post-access.expect.md
@@ -33,7 +33,7 @@ React refs are values that are not needed for rendering. Refs should only be acc
   7 |     r.current = 1;
   8 |   }
 >  9 |   r.current = 1;
-     |   ^^^^^^^^^ Cannot update ref during render
+     |   ^ Cannot update ref during render
  10 | }
  11 |
  12 | export const FIXTURE_ENTRYPOINT = {
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-optional.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-optional.expect.md
@@ -22,7 +22,7 @@ export const FIXTURE_ENTRYPOINT = {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

@@ -30,7 +30,7 @@ error.ref-optional.ts:5:9
  3 | function Component(props) {
  4 |   const ref = useRef();
 > 5 |   return ref?.current;
-    |          ^^^^^^^^^^^^ Cannot access ref value during render
+    |          ^^^^^^^^^^^^ Ref value is used during render
  6 | }
  7 |
  8 | export const FIXTURE_ENTRYPOINT = {
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-value-in-event-handler-wrapper.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.ref-value-in-event-handler-wrapper.expect.md
@@ -38,15 +38,24 @@ export const FIXTURE_ENTRYPOINT = {
 ```
 Found 1 error:

-Error: Cannot access refs during render
+Error: Cannot access ref value during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

+error.ref-value-in-event-handler-wrapper.ts:19:6
+  17 |     <>
+  18 |       <input ref={ref} />
+> 19 |       <button onClick={handleClick(ref.current)}>Click</button>
+     |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ref value is used during render
+  20 |     </>
+  21 |   );
+  22 | }
+
 error.ref-value-in-event-handler-wrapper.ts:19:35
  17 |     <>
  18 |       <input ref={ref} />
 > 19 |       <button onClick={handleClick(ref.current)}>Click</button>
-     |                                    ^^^^^^^^^^^ Cannot access ref value during render
+     |                                    ^^^^^^^^^^^ Ref is initially accessed
  20 |     </>
  21 |   );
  22 | }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.useCallback-accesses-ref-mutated-later-via-function-preserve-memoization.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.useCallback-accesses-ref-mutated-later-via-function-preserve-memoization.expect.md
@@ -40,14 +40,14 @@ Error: Cannot access refs during render

 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).

-error.useCallback-accesses-ref-mutated-later-via-function-preserve-memoization.ts:17:2
-  15 |     ref.current.inner = null;
+error.useCallback-accesses-ref-mutated-later-via-function-preserve-memoization.ts:15:4
+  13 |   // The ref is modified later, extending its range and preventing memoization of onChange
+  14 |   const reset = () => {
+> 15 |     ref.current.inner = null;
+     |     ^^^^^^^^^^^ Cannot update ref during render
  16 |   };
-> 17 |   reset();
-     |   ^^^^^ This function accesses a ref value
+  17 |   reset();
  18 |
-  19 |   return <input onChange={onChange} />;
-  20 | }
 ```
          
      
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/exhaustive-deps/error.invalid-exhaustive-deps.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/exhaustive-deps/error.invalid-exhaustive-deps.expect.md
@@ -2,7 +2,7 @@
 ## Input

 ```javascript
-// @validateExhaustiveMemoizationDependencies
+// @validateExhaustiveMemoizationDependencies @validateRefAccessDuringRender:false
 import {useMemo} from 'react';
 import {Stringify} from 'shared-runtime';

--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/exhaustive-deps/error.invalid-exhaustive-deps.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/exhaustive-deps/error.invalid-exhaustive-deps.js
@@ -1,4 +1,4 @@
-// @validateExhaustiveMemoizationDependencies
+// @validateExhaustiveMemoizationDependencies @validateRefAccessDuringRender:false
 import {useMemo} from 'react';
 import {Stringify} from 'shared-runtime';

--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/new-mutability/error.invalid-impure-functions-in-render.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/new-mutability/error.invalid-impure-functions-in-render.expect.md
@@ -19,41 +19,65 @@ function Component() {
 ```
 Found 3 errors:

-Error: Cannot call impure function during render
+Error: Cannot access impure value during render

-`Date.now` is an impure function. Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render.ts:7:20
+  5 |   const now = performance.now();
+  6 |   const rand = Math.random();
+> 7 |   return <Foo date={date} now={now} rand={rand} />;
+    |                     ^^^^ Cannot access impure value during render
+  8 | }
+  9 |

 error.invalid-impure-functions-in-render.ts:4:15
  2 |
  3 | function Component() {
 > 4 |   const date = Date.now();
-    |                ^^^^^^^^^^ Cannot call impure function
+    |                ^^^^^^^^^^ `Date.now` is an impure function.
  5 |   const now = performance.now();
  6 |   const rand = Math.random();
  7 |   return <Foo date={date} now={now} rand={rand} />;

-Error: Cannot call impure function during render
+Error: Cannot access impure value during render

-`performance.now` is an impure function. Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render.ts:7:31
+  5 |   const now = performance.now();
+  6 |   const rand = Math.random();
+> 7 |   return <Foo date={date} now={now} rand={rand} />;
+    |                                ^^^ Cannot access impure value during render
+  8 | }
+  9 |

 error.invalid-impure-functions-in-render.ts:5:14
  3 | function Component() {
  4 |   const date = Date.now();
 > 5 |   const now = performance.now();
-    |               ^^^^^^^^^^^^^^^^^ Cannot call impure function
+    |               ^^^^^^^^^^^^^^^^^ `performance.now` is an impure function.
  6 |   const rand = Math.random();
  7 |   return <Foo date={date} now={now} rand={rand} />;
  8 | }

-Error: Cannot call impure function during render
+Error: Cannot access impure value during render

-`Math.random` is an impure function. Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-functions-in-render.ts:7:42
+  5 |   const now = performance.now();
+  6 |   const rand = Math.random();
+> 7 |   return <Foo date={date} now={now} rand={rand} />;
+    |                                           ^^^^ Cannot access impure value during render
+  8 | }
+  9 |

 error.invalid-impure-functions-in-render.ts:6:15
  4 |   const date = Date.now();
  5 |   const now = performance.now();
 > 6 |   const rand = Math.random();
-    |                ^^^^^^^^^^^^^ Cannot call impure function
+    |                ^^^^^^^^^^^^^ `Math.random` is an impure function.
  7 |   return <Foo date={date} now={now} rand={rand} />;
  8 | }
  9 |
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/return-ref-callback.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/return-ref-callback.expect.md
@@ -6,7 +6,7 @@

 import {useRef} from 'react';

-component Foo() {
+hook useFoo() {
  const ref = useRef();

  const s = () => {
@@ -16,6 +16,10 @@ component Foo() {
  return s;
 }

+component Foo() {
+  useFoo();
+}
+
 export const FIXTURE_ENTRYPOINT = {
  fn: Foo,
  params: [],
@@ -30,7 +34,7 @@ import { c as _c } from "react/compiler-runtime";

 import { useRef } from "react";

-function Foo() {
+function useFoo() {
  const $ = _c(1);
  const ref = useRef();
  let t0;
@@ -44,6 +48,10 @@ function Foo() {
  return s;
 }

+function Foo() {
+  useFoo();
+}
+
 export const FIXTURE_ENTRYPOINT = {
  fn: Foo,
  params: [],
@@ -52,4 +60,4 @@ export const FIXTURE_ENTRYPOINT = {
 ```
      
 ### Eval output
-(kind: ok) "[[ function params=0 ]]"
+(kind: ok) 
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/return-ref-callback.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/return-ref-callback.js
@@ -2,7 +2,7 @@

 import {useRef} from 'react';

-component Foo() {
+hook useFoo() {
  const ref = useRef();

  const s = () => {
@@ -12,6 +12,10 @@ component Foo() {
  return s;
 }

+component Foo() {
+  useFoo();
+}
+
 export const FIXTURE_ENTRYPOINT = {
  fn: Foo,
  params: [],
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/transform-fire/bailout-retry/bailout-validate-ref-current-access.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/transform-fire/bailout-retry/bailout-validate-ref-current-access.expect.md
@@ -25,22 +25,40 @@ component Component(prop1, ref) {
 ## Code

 ```javascript
-import { useFire } from "react/compiler-runtime";
+import { c as _c, useFire } from "react/compiler-runtime";
 import { fire } from "react";
 import { print } from "shared-runtime";

 const Component = React.forwardRef(Component_withRef);
 function Component_withRef(t0, ref) {
+  const $ = _c(5);
  const { prop1 } = t0;
-  const foo = () => {
-    console.log(prop1);
-  };
-  const t1 = useFire(foo);
-  useEffect(() => {
-    t1(prop1);
-    bar();
-    t1();
-  });
+  let t1;
+  if ($[0] !== prop1) {
+    t1 = () => {
+      console.log(prop1);
+    };
+    $[0] = prop1;
+    $[1] = t1;
+  } else {
+    t1 = $[1];
+  }
+  const foo = t1;
+  const t2 = useFire(foo);
+  let t3;
+  if ($[2] !== prop1 || $[3] !== t2) {
+    t3 = () => {
+      t2(prop1);
+      bar();
+      t2();
+    };
+    $[2] = prop1;
+    $[3] = t2;
+    $[4] = t3;
+  } else {
+    t3 = $[4];
+  }
+  useEffect(t3);
  print(ref.current);
  return null;
 }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/valid-use-impure-value-in-ref.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/valid-use-impure-value-in-ref.expect.md
@@ -0,0 +1,49 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+import {useIdentity} from 'shared-runtime';
+
+function Component() {
+  const f = () => Math.random();
+  const ref = useRef(f());
+  return <div ref={ref} />;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validateNoImpureFunctionsInRender
+import { useIdentity } from "shared-runtime";
+
+function Component() {
+  const $ = _c(2);
+  const f = _temp;
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = f();
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  const ref = useRef(t0);
+  let t1;
+  if ($[1] === Symbol.for("react.memo_cache_sentinel")) {
+    t1 = <div ref={ref} />;
+    $[1] = t1;
+  } else {
+    t1 = $[1];
+  }
+  return t1;
+}
+function _temp() {
+  return Math.random();
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/valid-use-impure-value-in-ref.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/valid-use-impure-value-in-ref.js
@@ -0,0 +1,8 @@
+// @validateNoImpureFunctionsInRender
+import {useIdentity} from 'shared-runtime';
+
+function Component() {
+  const f = () => Math.random();
+  const ref = useRef(f());
+  return <div ref={ref} />;
+}
--- a/compiler/packages/eslint-plugin-react-compiler/tests/ImpureFunctionCallsRule-test.ts
+++ b/compiler/packages/eslint-plugin-react-compiler/tests/ImpureFunctionCallsRule-test.ts
@@ -29,9 +29,9 @@ testRule(
      }
    `,
        errors: [
-          makeTestCaseError('Cannot call impure function during render'),
-          makeTestCaseError('Cannot call impure function during render'),
-          makeTestCaseError('Cannot call impure function during render'),
+          makeTestCaseError('Cannot access impure value during render'),
+          makeTestCaseError('Cannot access impure value during render'),
+          makeTestCaseError('Cannot access impure value during render'),
        ],
      },
    ],
--- a/compiler/packages/snap/src/constants.ts
+++ b/compiler/packages/snap/src/constants.ts
@@ -26,3 +26,5 @@ export const FIXTURES_PATH = path.join(
  'compiler',
 );
 export const SNAPSHOT_EXTENSION = '.expect.md';
+export const FILTER_FILENAME = 'testfilter.txt';
+export const FILTER_PATH = path.join(PROJECT_ROOT, FILTER_FILENAME);
--- a/compiler/packages/snap/src/fixture-utils.ts
+++ b/compiler/packages/snap/src/fixture-utils.ts
@@ -8,7 +8,7 @@
 import fs from 'fs/promises';
 import * as glob from 'glob';
 import path from 'path';
-import {FIXTURES_PATH, SNAPSHOT_EXTENSION} from './constants';
+import {FILTER_PATH, FIXTURES_PATH, SNAPSHOT_EXTENSION} from './constants';

 const INPUT_EXTENSIONS = [
  '.js',
@@ -22,9 +22,19 @@ const INPUT_EXTENSIONS = [
 ];

 export type TestFilter = {
+  debug: boolean;
  paths: Array<string>;
 };

+async function exists(file: string): Promise<boolean> {
+  try {
+    await fs.access(file);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
 function stripExtension(filename: string, extensions: Array<string>): string {
  for (const ext of extensions) {
    if (filename.endsWith(ext)) {
@@ -34,6 +44,37 @@ function stripExtension(filename: string, extensions: Array<string>): string {
  return filename;
 }

+export async function readTestFilter(): Promise<TestFilter | null> {
+  if (!(await exists(FILTER_PATH))) {
+    throw new Error(`testfilter file not found at \`${FILTER_PATH}\``);
+  }
+
+  const input = await fs.readFile(FILTER_PATH, 'utf8');
+  const lines = input.trim().split('\n');
+
+  let debug: boolean = false;
+  const line0 = lines[0];
+  if (line0 != null) {
+    // Try to parse pragmas
+    let consumedLine0 = false;
+    if (line0.indexOf('@only') !== -1) {
+      consumedLine0 = true;
+    }
+    if (line0.indexOf('@debug') !== -1) {
+      debug = true;
+      consumedLine0 = true;
+    }
+
+    if (consumedLine0) {
+      lines.shift();
+    }
+  }
+  return {
+    debug,
+    paths: lines.filter(line => !line.trimStart().startsWith('//')),
+  };
+}
+
 export function getBasename(fixture: TestFixture): string {
  return stripExtension(path.basename(fixture.inputPath), INPUT_EXTENSIONS);
 }
--- a/compiler/packages/snap/src/runner-watch.ts
+++ b/compiler/packages/snap/src/runner-watch.ts
@@ -8,8 +8,8 @@
 import watcher from '@parcel/watcher';
 import path from 'path';
 import ts from 'typescript';
-import {FIXTURES_PATH, PROJECT_ROOT} from './constants';
-import {TestFilter} from './fixture-utils';
+import {FILTER_FILENAME, FIXTURES_PATH, PROJECT_ROOT} from './constants';
+import {TestFilter, readTestFilter} from './fixture-utils';
 import {execSync} from 'child_process';

 export function watchSrc(
@@ -117,10 +117,6 @@ export type RunnerState = {
  lastUpdate: number;
  mode: RunnerMode;
  filter: TestFilter | null;
-  debug: boolean;
-  // Input mode for interactive pattern entry
-  inputMode: 'none' | 'pattern';
-  inputBuffer: string;
 };

 function subscribeFixtures(
@@ -146,6 +142,26 @@ function subscribeFixtures(
  });
 }

+function subscribeFilterFile(
+  state: RunnerState,
+  onChange: (state: RunnerState) => void,
+) {
+  watcher.subscribe(PROJECT_ROOT, async (err, events) => {
+    if (err) {
+      console.error(err);
+      process.exit(1);
+    } else if (
+      events.findIndex(event => event.path.includes(FILTER_FILENAME)) !== -1
+    ) {
+      if (state.mode.filter) {
+        state.filter = await readTestFilter();
+        state.mode.action = RunnerAction.Test;
+        onChange(state);
+      }
+    }
+  });
+}
+
 function subscribeTsc(
  state: RunnerState,
  onChange: (state: RunnerState) => void,
@@ -184,67 +200,15 @@ function subscribeKeyEvents(
  onChange: (state: RunnerState) => void,
 ) {
  process.stdin.on('keypress', async (str, key) => {
-    // Handle input mode (pattern entry)
-    if (state.inputMode !== 'none') {
-      if (key.name === 'return') {
-        // Enter pressed - process input
-        const pattern = state.inputBuffer.trim();
-        state.inputMode = 'none';
-        state.inputBuffer = '';
-        process.stdout.write('\n');
-
-        if (pattern !== '') {
-          // Set the pattern as filter
-          state.filter = {paths: [pattern]};
-          state.mode.filter = true;
-          state.mode.action = RunnerAction.Test;
-          onChange(state);
-        }
-        // If empty, just exit input mode without changes
-        return;
-      } else if (key.name === 'escape') {
-        // Cancel input mode
-        state.inputMode = 'none';
-        state.inputBuffer = '';
-        process.stdout.write(' (cancelled)\n');
-        return;
-      } else if (key.name === 'backspace') {
-        if (state.inputBuffer.length > 0) {
-          state.inputBuffer = state.inputBuffer.slice(0, -1);
-          // Erase character: backspace, space, backspace
-          process.stdout.write('\b \b');
-        }
-        return;
-      } else if (str && !key.ctrl && !key.meta) {
-        // Regular character - accumulate and echo
-        state.inputBuffer += str;
-        process.stdout.write(str);
-        return;
-      }
-      return; // Ignore other keys in input mode
-    }
-
-    // Normal mode keypress handling
    if (key.name === 'u') {
      // u => update fixtures
      state.mode.action = RunnerAction.Update;
    } else if (key.name === 'q') {
      process.exit(0);
-    } else if (key.name === 'a') {
-      // a => exit filter mode and run all tests
-      state.mode.filter = false;
-      state.filter = null;
+    } else if (key.name === 'f') {
+      state.mode.filter = !state.mode.filter;
+      state.filter = state.mode.filter ? await readTestFilter() : null;
      state.mode.action = RunnerAction.Test;
-    } else if (key.name === 'd') {
-      // d => toggle debug logging
-      state.debug = !state.debug;
-      state.mode.action = RunnerAction.Test;
-    } else if (key.name === 'p') {
-      // p => enter pattern input mode
-      state.inputMode = 'pattern';
-      state.inputBuffer = '';
-      process.stdout.write('Pattern: ');
-      return; // Don't trigger onChange yet
    } else {
      // any other key re-runs tests
      state.mode.action = RunnerAction.Test;
@@ -255,33 +219,21 @@ function subscribeKeyEvents(

 export async function makeWatchRunner(
  onChange: (state: RunnerState) => void,
-  debugMode: boolean,
-  initialPattern?: string,
+  filterMode: boolean,
 ): Promise<void> {
-  // Determine initial filter state
-  let filter: TestFilter | null = null;
-  let filterEnabled = false;
-
-  if (initialPattern) {
-    filter = {paths: [initialPattern]};
-    filterEnabled = true;
-  }
-
-  const state: RunnerState = {
+  const state = {
    compilerVersion: 0,
    isCompilerBuildValid: false,
    lastUpdate: -1,
    mode: {
      action: RunnerAction.Test,
-      filter: filterEnabled,
+      filter: filterMode,
    },
-    filter,
-    debug: debugMode,
-    inputMode: 'none',
-    inputBuffer: '',
+    filter: filterMode ? await readTestFilter() : null,
  };

  subscribeTsc(state, onChange);
  subscribeFixtures(state, onChange);
  subscribeKeyEvents(state, onChange);
+  subscribeFilterFile(state, onChange);
 }
--- a/compiler/packages/snap/src/runner.ts
+++ b/compiler/packages/snap/src/runner.ts
@@ -12,8 +12,8 @@ import * as readline from 'readline';
 import ts from 'typescript';
 import yargs from 'yargs';
 import {hideBin} from 'yargs/helpers';
-import {PROJECT_ROOT} from './constants';
-import {TestFilter, getFixtures} from './fixture-utils';
+import {FILTER_PATH, PROJECT_ROOT} from './constants';
+import {TestFilter, getFixtures, readTestFilter} from './fixture-utils';
 import {TestResult, TestResults, report, update} from './reporter';
 import {
  RunnerAction,
@@ -33,9 +33,9 @@ type RunnerOptions = {
  sync: boolean;
  workerThreads: boolean;
  watch: boolean;
+  filter: boolean;
  update: boolean;
  pattern?: string;
-  debug: boolean;
 };

 const opts: RunnerOptions = yargs
@@ -59,16 +59,18 @@ const opts: RunnerOptions = yargs
  .alias('u', 'update')
  .describe('update', 'Update fixtures')
  .default('update', false)
+  .boolean('filter')
+  .describe(
+    'filter',
+    'Only run fixtures which match the contents of testfilter.txt',
+  )
+  .default('filter', false)
  .string('pattern')
  .alias('p', 'pattern')
  .describe(
    'pattern',
    'Optional glob pattern to filter fixtures (e.g., "error.*", "use-memo")',
  )
-  .boolean('debug')
-  .alias('d', 'debug')
-  .describe('debug', 'Enable debug logging to print HIR for each pass')
-  .default('debug', false)
  .help('help')
  .strict()
  .parseSync(hideBin(process.argv)) as RunnerOptions;
@@ -80,15 +82,12 @@ async function runFixtures(
  worker: Worker & typeof runnerWorker,
  filter: TestFilter | null,
  compilerVersion: number,
-  debug: boolean,
-  requireSingleFixture: boolean,
 ): Promise<TestResults> {
  // We could in theory be fancy about tracking the contents of the fixtures
  // directory via our file subscription, but it's simpler to just re-read
  // the directory each time.
  const fixtures = await getFixtures(filter);
  const isOnlyFixture = filter !== null && fixtures.size === 1;
-  const shouldLog = debug && (!requireSingleFixture || isOnlyFixture);

  let entries: Array<[string, TestResult]>;
  if (!opts.sync) {
@@ -97,7 +96,12 @@ async function runFixtures(
    for (const [fixtureName, fixture] of fixtures) {
      work.push(
        worker
-          .transformFixture(fixture, compilerVersion, shouldLog, true)
+          .transformFixture(
+            fixture,
+            compilerVersion,
+            (filter?.debug ?? false) && isOnlyFixture,
+            true,
+          )
          .then(result => [fixtureName, result]),
      );
    }
@@ -109,7 +113,7 @@ async function runFixtures(
      let output = await runnerWorker.transformFixture(
        fixture,
        compilerVersion,
-        shouldLog,
+        (filter?.debug ?? false) && isOnlyFixture,
        true,
      );
      entries.push([fixtureName, output]);
@@ -124,7 +128,7 @@ async function onChange(
  worker: Worker & typeof runnerWorker,
  state: RunnerState,
 ) {
-  const {compilerVersion, isCompilerBuildValid, mode, filter, debug} = state;
+  const {compilerVersion, isCompilerBuildValid, mode, filter} = state;
  if (isCompilerBuildValid) {
    const start = performance.now();

@@ -138,8 +142,6 @@ async function onChange(
      worker,
      mode.filter ? filter : null,
      compilerVersion,
-      debug,
-      true, // requireSingleFixture in watch mode
    );
    const end = performance.now();
    if (mode.action === RunnerAction.Update) {
@@ -157,13 +159,11 @@ async function onChange(
  console.log(
    '\n' +
      (mode.filter
-        ? `Current mode = FILTER, pattern = "${filter?.paths[0] ?? ''}".`
+        ? `Current mode = FILTER, filter test fixtures by "${FILTER_PATH}".`
        : 'Current mode = NORMAL, run all test fixtures.') +
      '\nWaiting for input or file changes...\n' +
      'u     - update all fixtures\n' +
-      `d     - toggle (turn ${debug ? 'off' : 'on'}) debug logging\n` +
-      'p     - enter pattern to filter fixtures\n' +
-      (mode.filter ? 'a     - run all tests (exit filter mode)\n' : '') +
+      `f     - toggle (turn ${mode.filter ? 'off' : 'on'}) filter mode\n` +
      'q     - quit\n' +
      '[any] - rerun tests\n',
  );
@@ -180,12 +180,15 @@ export async function main(opts: RunnerOptions): Promise<void> {
  worker.getStderr().pipe(process.stderr);
  worker.getStdout().pipe(process.stdout);

-  // Check if watch mode should be enabled
-  const shouldWatch = opts.watch;
+  // If pattern is provided, force watch mode off and use pattern filter
+  const shouldWatch = opts.watch && opts.pattern == null;
+  if (opts.watch && opts.pattern != null) {
+    console.warn('NOTE: --watch is ignored when a --pattern is supplied');
+  }

  if (shouldWatch) {
-    makeWatchRunner(state => onChange(worker, state), opts.debug, opts.pattern);
-    if (opts.pattern) {
+    makeWatchRunner(state => onChange(worker, state), opts.filter);
+    if (opts.filter) {
      /**
       * Warm up wormers when in watch mode. Loading the Forget babel plugin
       * and all of its transitive dependencies takes 1-3s (per worker) on a M1.
@@ -233,17 +236,14 @@ export async function main(opts: RunnerOptions): Promise<void> {
              let testFilter: TestFilter | null = null;
              if (opts.pattern) {
                testFilter = {
+                  debug: true,
                  paths: [opts.pattern],
                };
+              } else if (opts.filter) {
+                testFilter = await readTestFilter();
              }

-              const results = await runFixtures(
-                worker,
-                testFilter,
-                0,
-                opts.debug,
-                false, // no requireSingleFixture in non-watch mode
-              );
+              const results = await runFixtures(worker, testFilter, 0);
              if (opts.update) {
                update(results);
                isSuccess = true;
Author	SHA1	Message	Date
Joe Savona	ae3c5a707f	[compiler] Revert error description	2026-01-14 13:18:15 -08:00
Joe Savona	cb021861a5	[compiler] Simplify ref mutation validation to single forward pass Rewrites ValidateNoRefAccessInRender to use a simpler single-pass algorithm that only validates ref mutations (reads are now handled separately by ValidateNoImpureValuesInRender). The new approach: - Tracks refs and ref values through the function - Identifies functions that mutate refs (directly or transitively) - Only errors when ref-mutating functions are called at the top level - Supports null-guard exception: mutations inside `if (ref.current == null)` are allowed for the initialization pattern This reduces ~700 lines of complex fixpoint iteration to ~400 lines of straightforward forward data-flow analysis.	2026-01-14 13:11:17 -08:00
Joe Savona	7505808cd4	[compiler] Claude file/settings	2026-01-13 18:57:40 -08:00
Joe Savona	a974753ddf	[compiler] Use aliasing effects for impurity inference	2026-01-13 18:56:35 -08:00
Joe Savona	2c4a3b9587	[compiler] Validate ref reads in render via improved impure value validation Updates to guard against reading refs during render via the improved validateNoImpureValuesInRender() pass. InferMutationAliasingEffects generates `Impure` effects for ref reads, and then this pass validates that those accesses don't flow into `Render` effects. We now call the impure value validation first so that it takes priority over validateNoRefAccessInRender - the latter still has all the existing logic for now, but we can dramatically simplify it in a follow-up PR so that it only has to validate against ref writes.	2026-01-12 16:38:51 -08:00
Joe Savona	8428a7ec5f	[compiler] Improve impurity/ref tracking note: This implements the idea discussed in https://github.com/reactwg/react/discussions/389#discussioncomment-14252280 Currently we create `Impure` effects for impure functions like `Date.now()` or `Math.random()`, and then throw if the effect is reachable during render. However, impurity is a property of the resulting value: if the value isn't accessed during render then it's okay: maybe you're console-logging the time while debugging (fine), or storing the impure value into a ref and only accessing it in an effect or event handler (totally ok). This PR updates to validate that impure values are not transitively consumed during render, building on the `Render` effect. The validation currently uses an algorithm very similar to that of InferReactivePlaces - building a set of known impure values, starting with `Impure` effects as the sources and then flowing outward via data flow and mutations. If a transitively impure value reaches a `Render` effect, it's an error. We record both the source of the impure value and where it gets rendered to make it easier to understand and fix errors: ``` Error: Cannot access impure value during render Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent). error.invalid-impure-functions-in-render-via-render-helper.ts:10:25 8 \| const array = makeArray(now); 9 \| const hasDate = identity(array); > 10 \| return <Bar hasDate={hasDate} />; \| ^^^^^^^ Cannot access impure value during render 11 \| }; 12 \| return <Foo renderItem={renderItem} />; 13 \| } error.invalid-impure-functions-in-render-via-render-helper.ts:6:14 4 \| 5 \| function Component() { > 6 \| const now = Date.now(); \| ^^^^^^^^^^ `Date.now` is an impure function. 7 \| const renderItem = () => { 8 \| const array = makeArray(now); 9 \| const hasDate = identity(array); ``` Impure values are allowed to flow into refs, meaning that we now allow `useRef(Date.now())` or `useRef(localFunctionThatReturnsMathDotRandom())` which would have errored previously. The next PR reuses this improved impurity tracking to validate ref access in render as well.	2026-01-12 16:38:51 -08:00