[compiler] Null out source locations where not explicitly preserved

Inspired by #32950. Specifically from https://github.com/facebook/react/issues/32950#issuecomment-2837887871, it sounds like Babel by default emits source map information for all nodes, even when they don't have a `loc` property set. Code coverage tools then pick up the synthesized source location information for this, leading to the issue described.

A few google searches didn't turn up any documented way to opt-out of generating source span information, but AI tools answer that explicitly setting `node.loc = null` omits the node from source maps. This PR is a quick hack to confirm that.

[ghstack-poisoned]

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/CodegenReactiveFunction.ts

@@ -48,7 +48,7 @@ import {printIdentifier, printPlace} from '../HIR/PrintHIR';
 import {eachPatternOperand} from '../HIR/visitors';
 import {Err, Ok, Result} from '../Utils/Result';
 import {GuardKind} from '../Utils/RuntimeDiagnosticConstants';
-import {assertExhaustive} from '../Utils/utils';
+import {assertExhaustive, hasOwnProperty} from '../Utils/utils';
 import {buildReactiveFunction} from './BuildReactiveFunction';
 import {SINGLE_CHILD_FBT_TAGS} from './MemoizeFbtAndMacroOperandsInSameScope';
 import {ReactiveFunctionVisitor, visitReactiveFunction} from './visitors';
@@ -374,6 +374,8 @@ function codegenReactiveFunction(
   const countMemoBlockVisitor = new CountMemoBlockVisitor(fn.env);
   visitReactiveFunction(fn, countMemoBlockVisitor, undefined);
 
+  setMissingLocationsToNull(body);
+
   return Ok({
     type: 'CodegenFunction',
     loc: fn.loc,
@@ -2665,3 +2667,33 @@ function compareScopeDeclaration(
   else if (aName > bName) return 1;
   else return 0;
 }
+
+function setMissingLocationsToNull(ast: any): void {
+  if (Array.isArray(ast)) {
+    ast.forEach(item => setMissingLocationsToNull(item));
+    return;
+  } else if (
+    ast == null ||
+    typeof ast !== 'object' ||
+    typeof ast['type'] !== 'string'
+  ) {
+    return;
+  }
+  if (ast['loc'] == null) {
+    ast['loc'] = null;
+  }
+  for (const key in ast) {
+    if (!hasOwnProperty(ast, key)) {
+      continue;
+    }
+    const value = ast[key];
+    if (typeof value !== 'object') {
+      /*
+       * We handle this above too, but avoid extra function calls in the majority of
+       * cases where we're traversing an AST node's properties
+       */
+      continue;
+    }
+    setMissingLocationsToNull(ast[key]);
+  }
+}