[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.
[compiler] Improve impurity/ref tracking
2026-01-12 16:38:51 -08:00 · 2026-01-12 16:38:51 -08:00
60 changed files with 1560 additions and 678 deletions
--- a/compiler/.claude/settings.local.json
+++ b/compiler/.claude/settings.local.json
@@ -1,8 +1,6 @@
 {
  "permissions": {
    "allow": [
-      "Bash(yarn snap:*)",
-      "Bash(yarn snap:build)",
      "Bash(node scripts/enable-feature-flag.js:*)"
    ],
    "deny": [],
--- 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
@@ -1,221 +0,0 @@
-# React Compiler Knowledge Base
-
-This document contains knowledge about the React Compiler gathered during development sessions. It serves as a reference for understanding the codebase architecture and key concepts.
-
-## Project Structure
-
- `packages/babel-plugin-react-compiler/` - Main compiler package
-  - `src/HIR/` - High-level Intermediate Representation types and utilities
-  - `src/Inference/` - Effect inference passes (aliasing, mutation, etc.)
-  - `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
-    - `*.expect.md` - Expected output for each fixture
-
-## Running Tests
-
-```bash
-# Run all tests
-yarn snap
-
-# Run tests matching a pattern
-# Example: yarn snap -p 'error.*'
-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)
-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.
-
-```bash
-# Check status
-sl status
-
-# Add new files, remove deleted files
-sl addremove
-
-# Commit all changes
-sl commit -m "Your commit message"
-
-# Commit with multi-line message using heredoc
-sl commit -m "$(cat <<'EOF'
-Summary line
-
-Detailed description here
-EOF
-)"
-```
-
-## Key Concepts
-
-### HIR (High-level Intermediate Representation)
-
-The compiler converts source code to HIR for analysis. Key types in `src/HIR/HIR.ts`:
-
- **HIRFunction** - A function being compiled
-  - `body.blocks` - Map of BasicBlocks
-  - `context` - Captured variables from outer scope
-  - `params` - Function parameters
-  - `returns` - The function's return place
-  - `aliasingEffects` - Effects that describe the function's behavior when called
-
- **Instruction** - A single operation
-  - `lvalue` - The place being assigned to
-  - `value` - The instruction kind (CallExpression, FunctionExpression, LoadLocal, etc.)
-  - `effects` - Array of AliasingEffects for this instruction
-
- **Terminal** - Block terminators (return, branch, etc.)
-  - `effects` - Array of AliasingEffects
-
- **Place** - A reference to a value
-  - `identifier.id` - Unique IdentifierId
-
- **Phi nodes** - Join points for values from different control flow paths
-  - Located at `block.phis`
-  - `phi.place` - The result place
-  - `phi.operands` - Map of predecessor block to source place
-
-### AliasingEffects System
-
-Effects describe data flow and operations. Defined in `src/Inference/AliasingEffects.ts`:
-
-**Data Flow Effects:**
- `Impure` - Marks a place as containing an impure value (e.g., Date.now() result, ref.current)
- `Capture a -> b` - Value from `a` is captured into `b` (mutable capture)
- `Alias a -> b` - `b` aliases `a`
- `ImmutableCapture a -> b` - Immutable capture (like Capture but read-only)
- `Assign a -> b` - Direct assignment
- `MaybeAlias a -> b` - Possible aliasing
- `CreateFrom a -> b` - Created from source
-
-**Mutation Effects:**
- `Mutate value` - Value is mutated
- `MutateTransitive value` - Value and transitive captures are mutated
- `MutateConditionally value` - May mutate
- `MutateTransitiveConditionally value` - May mutate transitively
-
-**Other Effects:**
- `Render place` - Place is used in render context (JSX props, component return)
- `Freeze place` - Place is frozen (made immutable)
- `Create place` - New value created
- `CreateFunction` - Function expression created, includes `captures` array
- `Apply` - Function application with receiver, function, args, and result
-
-### Hook Aliasing Signatures
-
-Located in `src/HIR/Globals.ts`, hooks can define custom aliasing signatures to control how data flows through them.
-
-**Structure:**
-```typescript
-aliasing: {
-  receiver: '@receiver',    // The hook function itself
-  params: ['@param0'],      // Named positional parameters
-  rest: '@rest',            // Rest parameters (or null)
-  returns: '@returns',      // Return value
-  temporaries: [],          // Temporary values during execution
-  effects: [                // Array of effects to apply when hook is called
-    {kind: 'Freeze', value: '@param0', reason: ValueReason.HookCaptured},
-    {kind: 'Assign', from: '@param0', into: '@returns'},
-  ],
-}
-```
-
-**Common patterns:**
-
-1. **RenderHookAliasing** (useState, useContext, useMemo, useCallback):
-   - Freezes arguments (`Freeze @rest`)
-   - Marks arguments as render-time (`Render @rest`)
-   - Creates frozen return value
-   - Aliases arguments to return
-
-2. **EffectHookAliasing** (useEffect, useLayoutEffect, useInsertionEffect):
-   - Freezes function and deps
-   - Creates internal effect object
-   - Captures function and deps into effect
-   - Returns undefined
-
-3. **Event handler hooks** (useEffectEvent):
-   - Freezes callback (`Freeze @fn`)
-   - Aliases input to return (`Assign @fn -> @returns`)
-   - NO Render effect (callback not called during render)
-
-**Example: useEffectEvent**
-```typescript
-const UseEffectEventHook = addHook(
-  DEFAULT_SHAPES,
-  {
-    positionalParams: [Effect.Freeze],  // Takes one positional param
-    restParam: null,
-    returnType: {kind: 'Function', ...},
-    calleeEffect: Effect.Read,
-    hookKind: 'useEffectEvent',
-    returnValueKind: ValueKind.Frozen,
-    aliasing: {
-      receiver: '@receiver',
-      params: ['@fn'],              // Name for the callback parameter
-      rest: null,
-      returns: '@returns',
-      temporaries: [],
-      effects: [
-        {kind: 'Freeze', value: '@fn', reason: ValueReason.HookCaptured},
-        {kind: 'Assign', from: '@fn', into: '@returns'},
-        // Note: NO Render effect - callback is not called during render
-      ],
-    },
-  },
-  BuiltInUseEffectEventId,
-);
-
-// Add as both names for compatibility
-['useEffectEvent', UseEffectEventHook],
-['experimental_useEffectEvent', UseEffectEventHook],
-```
-
-**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
-
-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:
-
-```javascript
-// enableJsxOutlining @enableChangeVariableCodegen:false
-
-...code...
-```
-
-Would enable the `enableJsxOutlining` feature and disable the `enableChangeVariableCodegen` feature.
-
-## Debugging Tips
-
-1. Run `yarn snap -p <fixture>` to see full HIR output with effects
-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 '..';
@@ -626,6 +626,78 @@ 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: [],
+  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,
+    },
+  ],
+};
+
 /*
 * TODO(mofeiZ): We currently only store rest param effects for hooks.
 * now that FeatureFlag `enableTreatHooksAsFunctions` is removed we can
@@ -644,6 +716,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        hookKind: 'useContext',
        returnValueKind: ValueKind.Frozen,
        returnValueReason: ValueReason.Context,
+        aliasing: RenderHookAliasing(ValueReason.Context),
      },
      BuiltInUseContextHookId,
    ),
@@ -658,6 +731,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      hookKind: 'useState',
      returnValueKind: ValueKind.Frozen,
      returnValueReason: ValueReason.State,
+      aliasing: RenderHookAliasing(ValueReason.State),
    }),
  ],
  [
@@ -670,6 +744,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      hookKind: 'useActionState',
      returnValueKind: ValueKind.Frozen,
      returnValueReason: ValueReason.State,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -682,6 +757,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      hookKind: 'useReducer',
      returnValueKind: ValueKind.Frozen,
      returnValueReason: ValueReason.ReducerState,
+      aliasing: RenderHookAliasing(ValueReason.ReducerState),
    }),
  ],
  [
@@ -715,6 +791,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      calleeEffect: Effect.Read,
      hookKind: 'useMemo',
      returnValueKind: ValueKind.Frozen,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -726,6 +803,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      calleeEffect: Effect.Read,
      hookKind: 'useCallback',
      returnValueKind: ValueKind.Frozen,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -739,41 +817,7 @@ 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 +833,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        calleeEffect: Effect.Read,
        hookKind: 'useLayoutEffect',
        returnValueKind: ValueKind.Frozen,
+        aliasing: EffectHookAliasing,
      },
      BuiltInUseLayoutEffectHookId,
    ),
@@ -804,6 +849,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        calleeEffect: Effect.Read,
        hookKind: 'useInsertionEffect',
        returnValueKind: ValueKind.Frozen,
+        aliasing: EffectHookAliasing,
      },
      BuiltInUseInsertionEffectHookId,
    ),
@@ -817,6 +863,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      calleeEffect: Effect.Read,
      hookKind: 'useTransition',
      returnValueKind: ValueKind.Frozen,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -829,6 +876,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      hookKind: 'useOptimistic',
      returnValueKind: ValueKind.Frozen,
      returnValueReason: ValueReason.State,
+      aliasing: RenderHookAliasing(ValueReason.HookCaptured),
    }),
  ],
  [
@@ -842,6 +890,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        returnType: {kind: 'Poly'},
        calleeEffect: Effect.Read,
        returnValueKind: ValueKind.Frozen,
+        aliasing: RenderHookAliasing(ValueReason.HookCaptured),
      },
      BuiltInUseOperatorId,
    ),
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/HIR.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/HIR.ts
@@ -1890,6 +1890,13 @@ 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 +2065,23 @@ 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 +27,12 @@ import {
  InstructionKind,
  InstructionValue,
  isArrayType,
-  isJsxType,
+  isJsxOrJsxUnionType,
  isMapType,
  isPrimitiveType,
  isRefOrRefValue,
  isSetType,
+  isUseRefType,
  makeIdentifierId,
  Phi,
  Place,
@@ -70,6 +71,7 @@ import {
  MutationReason,
 } from './AliasingEffects';
 import {ErrorCategory} from '../CompilerError';
+import {REF_ERROR_DESCRIPTION} from '../Validation/ValidateNoRefAccessInRender';

 const DEBUG = false;

@@ -569,14 +571,21 @@ 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,
        }),
-      ];
+      );
    }
  }
 }
@@ -1973,6 +1982,20 @@ 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 +2160,15 @@ 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 +2177,20 @@ 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 (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,
            });
          }
        }
@@ -2423,7 +2446,7 @@ 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 +2459,18 @@ 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 +2769,23 @@ 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') &&
@@ -244,6 +241,11 @@ export function inferMutationAliasingRanges(
  }

  for (const mutation of mutations) {
+    if (DEBUG) {
+      console.log(
+        `[${mutation.index}] mutate ${printIdentifier(mutation.place.identifier)}`,
+      );
+    }
    state.mutate(
      mutation.index,
      mutation.place.identifier,
@@ -255,8 +257,16 @@ export function inferMutationAliasingRanges(
      errors,
    );
  }
+  if (DEBUG) {
+    console.log(state.debug());
+  }
  for (const render of renders) {
-    state.render(render.index, render.place.identifier, errors);
+    if (DEBUG) {
+      console.log(
+        `[${render.index}] render ${printIdentifier(render.place.identifier)}`,
+      );
+    }
+    state.render(render.index, render.place, errors);
  }
  for (const param of [...fn.context, ...fn.params]) {
    const place = param.kind === 'Identifier' ? param : param.place;
@@ -515,6 +525,13 @@ export function inferMutationAliasingRanges(
  const ignoredErrors = new CompilerError();
  for (const param of [...fn.params, ...fn.context, fn.returns]) {
    const place = param.kind === 'Identifier' ? param : param.place;
+    const node = state.nodes.get(place.identifier);
+    if (node != null && node.render != null) {
+      functionEffects.push({
+        kind: 'Render',
+        place: place,
+      });
+    }
    tracked.push(place);
  }
  for (const into of tracked) {
@@ -577,7 +594,6 @@ export function inferMutationAliasingRanges(
 function appendFunctionErrors(errors: CompilerError, fn: HIRFunction): void {
  for (const effect of fn.aliasingEffects ?? []) {
    switch (effect.kind) {
-      case 'Impure':
      case 'MutateFrozen':
      case 'MutateGlobal': {
        errors.pushDiagnostic(effect.error);
@@ -612,10 +628,74 @@ type Node = {
    | {kind: 'Object'}
    | {kind: 'Phi'}
    | {kind: 'Function'; function: HIRFunction};
+  render: Place | null;
 };
+
+function _printNode(node: Node): string {
+  const out: Array<string> = [];
+  debugNode(out, node);
+  return out.join('\n');
+}
+function debugNode(out: Array<string>, node: Node): void {
+  out.push(
+    printIdentifier(node.id) +
+      printType(node.id.type) +
+      ` lastMutated=[${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 +709,7 @@ class AliasingState {
      lastMutated: 0,
      mutationReason: null,
      value,
+      render: null,
    });
  }

@@ -681,9 +762,9 @@ 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 +772,34 @@ 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 +813,12 @@ 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/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 +1,291 @@
+/**
+ * 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, Effect} from '..';
+import {
+  areEqualSourceLocations,
+  HIRFunction,
+  IdentifierId,
+  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} from '../Utils/utils';
+
+type ImpureEffect = Extract<AliasingEffect, {kind: 'Impure'}>;
+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,
+    () => {
+      return inferImpureValues(fn, impure, cache);
+    },
+  );
+}
+
+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) {
+        let impureEffect: ImpureEffect | undefined = instr.effects?.find(
+          (effect: AliasingEffect): effect is ImpureEffect =>
+            effect.kind === 'Impure',
+        );
+
+        if (
+          impureEffect == null &&
+          (instr.value.kind === 'FunctionExpression' ||
+            instr.value.kind === 'ObjectMethod')
+        ) {
+          impureEffect = instr.value.loweredFunc.func.aliasingEffects?.find(
+            (effect: AliasingEffect): effect is ImpureEffect =>
+              effect.kind === 'Impure',
+          );
+          if (impureEffect == null) {
+            const result = inferFunctionExpressionMemo(
+              instr.value.loweredFunc.func,
+              impure,
+              cache,
+            );
+            if (!result.error.hasAnyErrors()) {
+              impureEffect = result.effects[0];
+            }
+          }
+        }
+
+        if (impureEffect == null) {
+          for (const operand of eachInstructionValueOperand(instr.value)) {
+            const operandEffect = impure.get(operand.identifier.id);
+            if (operandEffect != null) {
+              impureEffect = operandEffect;
+              break;
+            }
+          }
+        }
+
+        if (impureEffect != null) {
+          for (const lvalue of eachInstructionLValue(instr)) {
+            if (isUseRefType(lvalue.identifier)) {
+              continue;
+            }
+            if (!impure.has(lvalue.identifier.id)) {
+              impure.set(lvalue.identifier.id, impureEffect);
+              hasChanges = true;
+            }
+          }
+        }
+        if (impureEffect != null || controlImpureEffect != null) {
+          for (const operand of eachInstructionValueOperand(instr.value)) {
+            switch (operand.effect) {
+              case Effect.Capture:
+              case Effect.Store:
+              case Effect.ConditionallyMutate:
+              case Effect.ConditionallyMutateIterator:
+              case Effect.Mutate: {
+                if (
+                  !impure.has(operand.identifier.id) &&
+                  isMutable(instr, operand)
+                ) {
+                  impure.set(
+                    operand.identifier.id,
+                    (impureEffect ?? controlImpureEffect)!,
+                  );
+                  hasChanges = true;
+                }
+                break;
+              }
+              case Effect.Freeze:
+              case Effect.Read: {
+                // no-op
+                break;
+              }
+              case Effect.Unknown: {
+                CompilerError.invariant(false, {
+                  reason: 'Unexpected unknown effect',
+                  description: null,
+                  details: [
+                    {
+                      kind: 'error',
+                      loc: operand.loc,
+                      message: null,
+                    },
+                  ],
+                  suggestions: null,
+                });
+              }
+              default: {
+                assertExhaustive(
+                  operand.effect,
+                  `Unexpected effect kind \`${operand.effect}\``,
+                );
+              }
+            }
+          }
+        }
+        if (impureEffect == null) {
+          const lvalueEffect = impure.get(instr.lvalue.identifier.id)!;
+          if (lvalueEffect != null) {
+            for (const operand of eachInstructionValueOperand(instr.value)) {
+              if (
+                isMutable(instr, operand) &&
+                !impure.has(operand.identifier.id)
+              ) {
+                impure.set(operand.identifier.id, lvalueEffect);
+                hasChanges = true;
+              }
+            }
+          }
+        }
+      }
+
+      if (block.terminal.kind === 'return') {
+        const terminalEffect = impure.get(block.terminal.value.identifier.id);
+        if (terminalEffect != null && !impure.has(fn.returns.identifier.id)) {
+          impure.set(fn.returns.identifier.id, terminalEffect);
+          hasChanges = true;
+        }
+      }
+    }
+  } while (hasChanges);
+
+  const error = new CompilerError();
+  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' ||
+          !impure.has(effect.place.identifier.id)
+        ) {
+          continue;
+        }
+        const impureEffect = impure.get(effect.place.identifier.id)!;
+        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);
+      }
+    }
+  }
+  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: {...place},
+        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
@@ -511,7 +511,7 @@ function validateNoRefAccessInRenderImpl(
                  CompilerDiagnostic.create({
                    category: ErrorCategory.Refs,
                    reason: 'Cannot access refs during render',
-                    description: ERROR_DESCRIPTION,
+                    description: REF_ERROR_DESCRIPTION,
                  }).withDetails({
                    kind: 'error',
                    loc: callee.loc,
@@ -666,7 +666,7 @@ function validateNoRefAccessInRenderImpl(
                  CompilerDiagnostic.create({
                    category: ErrorCategory.Refs,
                    reason: 'Cannot access refs during render',
-                    description: ERROR_DESCRIPTION,
+                    description: REF_ERROR_DESCRIPTION,
                  })
                    .withDetails({
                      kind: 'error',
@@ -814,7 +814,7 @@ function guardCheck(errors: CompilerError, operand: Place, env: Env): void {
      CompilerDiagnostic.create({
        category: ErrorCategory.Refs,
        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
+        description: REF_ERROR_DESCRIPTION,
      }).withDetails({
        kind: 'error',
        loc: operand.loc,
@@ -838,7 +838,7 @@ function validateNoRefValueAccess(
      CompilerDiagnostic.create({
        category: ErrorCategory.Refs,
        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
+        description: REF_ERROR_DESCRIPTION,
      }).withDetails({
        kind: 'error',
        loc: (type.kind === 'RefValue' && type.loc) || operand.loc,
@@ -864,7 +864,7 @@ function validateNoRefPassedToFunction(
      CompilerDiagnostic.create({
        category: ErrorCategory.Refs,
        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
+        description: REF_ERROR_DESCRIPTION,
      }).withDetails({
        kind: 'error',
        loc: (type.kind === 'RefValue' && type.loc) || loc,
@@ -886,7 +886,7 @@ function validateNoRefUpdate(
      CompilerDiagnostic.create({
        category: ErrorCategory.Refs,
        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
+        description: REF_ERROR_DESCRIPTION,
      }).withDetails({
        kind: 'error',
        loc: (type.kind === 'RefValue' && type.loc) || loc,
@@ -907,7 +907,7 @@ function validateNoDirectRefValueAccess(
      CompilerDiagnostic.create({
        category: ErrorCategory.Refs,
        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
+        description: REF_ERROR_DESCRIPTION,
      }).withDetails({
        kind: 'error',
        loc: type.loc ?? operand.loc,
@@ -917,7 +917,7 @@ function validateNoDirectRefValueAccess(
  }
 }

-const ERROR_DESCRIPTION =
+export const REF_ERROR_DESCRIPTION =
  '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 ' +
--- 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.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
@@ -26,9 +26,9 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error

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

-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 +36,29 @@ 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: 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-reducer-init.ts:11:27
+   9 |   );
+  10 |
+> 11 |   return <Stringify state={state} />;
+     |                            ^^^^^ Ref value is used during render
+  12 | }
+  13 |
+  14 | export const FIXTURE_ENTRYPOINT = {
+
+error.invalid-access-ref-in-reducer-init.ts:8:4
+   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
@@ -22,9 +22,9 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error

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

-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 +32,29 @@ 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: 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-reducer.ts:7:27
+   5 |   const [state] = useReducer(() => ref.current, null);
+   6 |
+>  7 |   return <Stringify state={state} />;
+     |                            ^^^^^ Ref value is used during render
+   8 | }
+   9 |
+  10 | export const FIXTURE_ENTRYPOINT = {
+
+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);
+    |                              ^^^^^^^^^^^^^^^^^ 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:6:15
+  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
@@ -22,9 +22,9 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error

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

-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 +32,29 @@ 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: 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-state-initializer.ts:7:27
+   5 |   const [state] = useState(() => ref.current);
+   6 |
+>  7 |   return <Stringify state={state} />;
+     |                            ^^^^^ Ref value is used during render
+   8 | }
+   9 |
+  10 | export const FIXTURE_ENTRYPOINT = {
+
+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);
+    |                            ^^^^^^^^^^^^^^^^^ 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-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:7:15
+   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-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:6:18
+  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:6:18
+  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:10:28
+   8 |     // this should error but we currently lose track of the impurity bc
+   9 |     // the impure value comes from behind a call
+> 10 |     const array = makeArray(now());
+     |                             ^^^ `Date.now` is an impure function.
+  11 |     const hasDate = identity(array);
+  12 |     return hasDate;
+  13 |   };
+```
+          
+      
--- 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:8:28
+   6 |   const now = Date.now();
+   7 |   const f = () => {
+>  8 |     const array = makeArray(now);
+     |                             ^^^ `Date.now` is an impure function.
+   9 |     const hasDate = identity(array);
+  10 |     return hasDate;
+  11 |   };
+```
+          
+      
--- 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.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 +1,71 @@
+
+## 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 2 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);
+
+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 +1,66 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+function Component() {
+  const now = () => Date.now();
+  const render = () => {
+    return <div>{now()}</div>;
+  };
+  return <div>{render()}</div>;
+}
+
+```
+
+
+## Error
+
+```
+Found 2 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-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:3:14
+  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 |   };
+
+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:7:15
+  5 |     return <div>{now()}</div>;
+  6 |   };
+> 7 |   return <div>{render()}</div>;
+    |                ^^^^^^^^ Cannot access impure value during render
+  8 | }
+  9 |
+
+error.invalid-impure-value-in-render-helper.ts:3:14
+  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-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.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/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/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;