[compiler] Option to infer names for anonymous functions

Adds a `@enableNameAnonymousFunctions` feature to infer helpful names for anonymous functions within components and hooks. The logic is inspired by a custom Next.js transform, flagged to us by @eps1lon, that does something similar. Implementing this transform within React Compiler means that all React (Compiler) users can benefit from more helpful names when debugging.

The idea builds on the fact that JS engines try to infer helpful names for anonymous functions (in stack traces) when those functions are accessed through an object property lookup:

```js
({'a[xyz]': () => {
  throw new Error('hello!')
} }['a[xyz]'])()

// Stack trace:
Uncaught Error: hello!
    at a[xyz] (<anonymous>:1:26) // <-- note the name here
    at <anonymous>:1:60
```

The new NameAnonymousFunctions transform is gated by the above flag, which is off by default. It attemps to infer names for functions as follows:

First, determine a "local" name:
* Assigning a function to a named variable uses the variable name. `const f = () => {}` gets the name "f".
* Passing the function as an argument to a function gets the name of the function, ie `foo(() => ...)` get the name "foo()", `foo.bar(() => ...)` gets the name "foo.bar()". Note the parenthesis to help understand that it was part of a call.
* Passing the function to a known hook uses the name of the hook, `useEffect(() => ...)` uses "useEffect()".
* Passing the function as a JSX prop uses the element and attr name, eg `<div onClick={() => ...}` uses "<div>.onClick".

Second, the local name is combined with the name of the outer component/hook, so the final names will be strings like `Component[f]` or `useMyHook[useEffect()]`.

Author: josephsavona

compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Pipeline.ts

@@ -103,6 +103,7 @@ import {validateNoFreezingKnownMutableFunctions} from '../Validation/ValidateNoF
 import {inferMutationAliasingEffects} from '../Inference/InferMutationAliasingEffects';
 import {inferMutationAliasingRanges} from '../Inference/InferMutationAliasingRanges';
 import {validateNoDerivedComputationsInEffects} from '../Validation/ValidateNoDerivedComputationsInEffects';
+import {nameAnonymousFunctions} from '../Transform/NameAnonymousFunctions';
 
 export type CompilerPipelineValue =
   | {kind: 'ast'; name: string; value: CodegenFunction}
@@ -414,6 +415,15 @@ function runWithEnvironment(
     });
   }
 
+  if (env.config.enableNameAnonymousFunctions) {
+    nameAnonymousFunctions(hir);
+    log({
+      kind: 'hir',
+      name: 'NameAnonymougFunctions',
+      value: hir,
+    });
+  }
+
   const reactiveFunction = buildReactiveFunction(hir);
   log({
     kind: 'reactive',

compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts

@@ -3566,6 +3566,8 @@ function lowerFunctionToValue(
   let name: string | null = null;
   if (expr.isFunctionExpression()) {
     name = expr.get('id')?.node?.name ?? null;
+  } else if (expr.isFunctionDeclaration()) {
+    name = expr.get('id')?.node?.name ?? null;
   }
   const loweredFunc = lowerFunction(builder, expr);
   if (!loweredFunc) {

compiler/packages/babel-plugin-react-compiler/src/HIR/Environment.ts

@@ -261,6 +261,8 @@ export const EnvironmentConfigSchema = z.object({
 
   enableFire: z.boolean().default(false),
 
+  enableNameAnonymousFunctions: z.boolean().default(false),
+
   /**
    * Enables inference and auto-insertion of effect dependencies. Takes in an array of
    * configurable module and import pairs to allow for user-land experimentation. For example,

compiler/packages/babel-plugin-react-compiler/src/HIR/HIR.ts

@@ -15,6 +15,7 @@ import {Type, makeType} from './Types';
 import {z} from 'zod';
 import type {AliasingEffect} from '../Inference/AliasingEffects';
 import {isReservedWord} from '../Utils/Keyword';
+import {Err, Ok, Result} from '../Utils/Result';
 
 /*
  * *******************************************************************************************
@@ -1298,6 +1299,15 @@ export function forkTemporaryIdentifier(
   };
 }
 
+export function validateIdentifierName(
+  name: string,
+): Result<ValidIdentifierName, null> {
+  if (isReservedWord(name) || !t.isValidIdentifier(name)) {
+    return Err(null);
+  }
+  return Ok(makeIdentifierName(name).value);
+}
+
 /**
  * Creates a valid identifier name. This should *not* be used for synthesizing
  * identifier names: only call this method for identifier names that appear in the

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

@@ -43,6 +43,7 @@ import {
   ValidIdentifierName,
   getHookKind,
   makeIdentifierName,
+  validateIdentifierName,
 } from '../HIR/HIR';
 import {printIdentifier, printInstruction, printPlace} from '../HIR/PrintHIR';
 import {eachPatternOperand} from '../HIR/visitors';
@@ -2326,6 +2327,11 @@ function codegenInstructionValue(
         ),
         reactiveFunction,
       ).unwrap();
+
+      const validatedName =
+        instrValue.name != null
+          ? validateIdentifierName(instrValue.name)
+          : Err(null);
       if (instrValue.type === 'ArrowFunctionExpression') {
         let body: t.BlockStatement | t.Expression = fn.body;
         if (body.body.length === 1 && loweredFunc.directives.length == 0) {
@@ -2337,14 +2343,28 @@ function codegenInstructionValue(
         value = t.arrowFunctionExpression(fn.params, body, fn.async);
       } else {
         value = t.functionExpression(
-          fn.id ??
-            (instrValue.name != null ? t.identifier(instrValue.name) : null),
+          validatedName
+            .map<t.Identifier | null>(name => t.identifier(name))
+            .unwrapOr(null),
           fn.params,
           fn.body,
           fn.generator,
           fn.async,
         );
       }
+      if (
+        cx.env.config.enableNameAnonymousFunctions &&
+        validatedName.isErr() &&
+        instrValue.name != null
+      ) {
+        const name = instrValue.name;
+        value = t.memberExpression(
+          t.objectExpression([t.objectProperty(t.stringLiteral(name), value)]),
+          t.stringLiteral(name),
+          true,
+          false,
+        );
+      }
       break;
     }
     case 'TaggedTemplateExpression': {

compiler/packages/babel-plugin-react-compiler/src/Transform/NameAnonymousFunctions.ts

@@ -0,0 +1,116 @@
+/**
+ * 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 {
+  FunctionExpression,
+  getHookKind,
+  HIRFunction,
+  IdentifierId,
+} from '../HIR';
+
+export function nameAnonymousFunctions(fn: HIRFunction): void {
+  if (fn.id == null) {
+    return;
+  }
+  const parentName = fn.id;
+  const functions: Map<IdentifierId, FunctionExpression> = new Map();
+  const names: Map<IdentifierId, string> = new Map();
+  for (const block of fn.body.blocks.values()) {
+    for (const instr of block.instructions) {
+      const {lvalue, value} = instr;
+      switch (value.kind) {
+        case 'LoadGlobal': {
+          names.set(lvalue.identifier.id, value.binding.name);
+          break;
+        }
+        case 'LoadContext':
+        case 'LoadLocal': {
+          const name = value.place.identifier.name;
+          if (name != null && name.kind === 'named') {
+            names.set(lvalue.identifier.id, name.value);
+          }
+          break;
+        }
+        case 'PropertyLoad': {
+          const objectName = names.get(value.object.identifier.id);
+          if (objectName != null) {
+            names.set(
+              lvalue.identifier.id,
+              `${objectName}.${String(value.property)}`,
+            );
+          }
+          break;
+        }
+        case 'FunctionExpression': {
+          if (value.name == null) {
+            // only track anonymous functions
+            functions.set(lvalue.identifier.id, value);
+          }
+          break;
+        }
+        case 'StoreContext':
+        case 'StoreLocal': {
+          const fn = functions.get(value.value.identifier.id);
+          const variableName = value.lvalue.place.identifier.name;
+          if (
+            fn != null &&
+            variableName != null &&
+            variableName.kind === 'named'
+          ) {
+            fn.name = `${parentName}[${variableName.value}]`;
+            functions.delete(value.value.identifier.id);
+          }
+          break;
+        }
+        case 'CallExpression':
+        case 'MethodCall': {
+          const callee =
+            value.kind === 'MethodCall' ? value.property : value.callee;
+          const hookKind = getHookKind(fn.env, callee.identifier);
+          let calleeName: string | null = null;
+          if (hookKind != null && hookKind !== 'Custom') {
+            calleeName = hookKind;
+          } else {
+            calleeName = names.get(callee.identifier.id) ?? '(anonymous)';
+          }
+          for (const arg of value.args) {
+            if (arg.kind === 'Spread') {
+              continue;
+            }
+            const fn = functions.get(arg.identifier.id);
+            if (fn != null) {
+              fn.name = `${parentName}[${calleeName}()]`;
+              functions.delete(arg.identifier.id);
+            }
+          }
+          break;
+        }
+        case 'JsxExpression': {
+          for (const attr of value.props) {
+            if (attr.kind === 'JsxSpreadAttribute') {
+              continue;
+            }
+            const fn = functions.get(attr.place.identifier.id);
+            if (fn != null) {
+              const elementName =
+                value.tag.kind === 'BuiltinTag'
+                  ? value.tag.name
+                  : (names.get(value.tag.identifier.id) ?? null);
+              const propName =
+                elementName == null
+                  ? attr.name
+                  : `<${elementName}>.${attr.name}`;
+              fn.name = `${parentName}[${propName}]`;
+              functions.delete(attr.place.identifier.id);
+            }
+          }
+          break;
+        }
+      }
+    }
+  }
+}