[compiler] Always error on async reassignments

Summary: Addresses the issue in #30109: any mutation of a local in an async function may occur after rendering has finished.

[ghstack-poisoned]

Author: mvitousek

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateLocalsNotReassignedAfterRender.ts

@@ -19,7 +19,7 @@ import {
  */
 export function validateLocalsNotReassignedAfterRender(fn: HIRFunction): void {
   const contextVariables = new Set<IdentifierId>();
-  const reassignment = getContextReassignment(fn, contextVariables, false);
+  const reassignment = getContextReassignment(fn, contextVariables, false, false);
   if (reassignment !== null) {
     CompilerError.throwInvalidReact({
       reason:
@@ -37,7 +37,8 @@ export function validateLocalsNotReassignedAfterRender(fn: HIRFunction): void {
 function getContextReassignment(
   fn: HIRFunction,
   contextVariables: Set<IdentifierId>,
-  isFunctionExpression: boolean
+  isFunctionExpression: boolean,
+  isAsync: boolean,
 ): Place | null {
   const reassigningFunctions = new Map<IdentifierId, Place>();
   for (const [, block] of fn.body.blocks) {
@@ -49,7 +50,8 @@ function getContextReassignment(
           let reassignment = getContextReassignment(
             value.loweredFunc.func,
             contextVariables,
-            true
+            true,
+            isAsync || value.loweredFunc.func.async,
           );
           if (reassignment === null) {
             // If the function itself doesn't reassign, does one of its dependencies?
@@ -65,6 +67,18 @@ function getContextReassignment(
           }
           // if the function or its depends reassign, propagate that fact on the lvalue
           if (reassignment !== null) {
+            if (isAsync || value.loweredFunc.func.async) {
+              CompilerError.throwInvalidReact({
+                reason:
+                  "Reassigning a variable in an async function can cause inconsistent behavior on subsequent renders. Consider using state instead",
+                description:
+                  reassignment.identifier.name !== null &&
+                  reassignment.identifier.name.kind === "named"
+                    ? `Variable \`${reassignment.identifier.name.value}\` cannot be reassigned after render`
+                    : "",
+                loc: reassignment.loc,
+              });
+            }
             reassigningFunctions.set(lvalue.identifier.id, reassignment);
           }
           break;

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-reassign-local-variable-in-async-callback.expect.md

@@ -0,0 +1,37 @@
+
+## Input
+
+```javascript
+function Component() {
+  let value = null;
+  const reassign = async () => {
+    await foo().then((result) => {
+      // Reassigning a local variable in an async function is *always* mutating
+      // after render, so this should error regardless of where this ends up
+      // getting called
+      value = result;
+    });
+  };
+
+  const onClick = async () => {
+    await reassign();
+  };
+  return <div onClick={onClick}>Click</div>;
+}
+
+```
+
+
+## Error
+
+```
+   6 |       // after render, so this should error regardless of where this ends up
+   7 |       // getting called
+>  8 |       value = result;
+     |       ^^^^^ InvalidReact: Reassigning a variable in an async function can cause inconsistent behavior on subsequent renders. Consider using state instead. Variable `value` cannot be reassigned after render (8:8)
+   9 |     });
+  10 |   };
+  11 |
+```
+          
+      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/todo.invalid-reassign-local-variable-in-async-callback.js compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-reassign-local-variable-in-async-callback.js

@@ -483,12 +483,6 @@ const skipFilter = new Set([
   "rules-of-hooks/rules-of-hooks-93dc5d5e538a",
   "rules-of-hooks/rules-of-hooks-69521d94fa03",
 
-  // should error
-  "todo.invalid-reassign-local-variable-in-jsx-callback",
-  "todo.invalid-reassign-local-variable-in-hook-argument",
-  "todo.invalid-reassign-local-variable-in-effect",
-  "todo.invalid-reassign-local-variable-in-async-callback",
-
   // bugs
   "bug-invalid-hoisting-functionexpr",
   "original-reactive-scopes-fork/bug-nonmutating-capture-in-unsplittable-memo-block",