[compiler] Avoid failing builds when import specifiers conflict or shadow vars

Avoid failing builds when imported function specifiers conflict by using babel's `generateUid`. Failing a build is very disruptive, as it usually presents to developers similar to a javascript parse error.
```js
import {logRender as _logRender} from 'instrument-runtime';

const logRender = () => { /* local conflicting implementation */ }

function Component_optimized() {
  _logRender(); // inserted by compiler
}
```

Currently, we fail builds (even in `panicThreshold:none` cases) when import specifiers are detected to conflict with existing local variables. The reason we destructively throw (instead of bailing out) is because (1) we first generate identifier references to the conflicting name in compiled functions, (2) replaced original functions with compiled functions, and then (3) finally check for conflicts.

When we finally check for conflicts, it's too late to bail out.
```js
// import {logRender} from 'instrument-runtime';

const logRender = () => { /* local conflicting implementation */ }

function Component_optimized() {
  logRender(); // inserted by compiler
}
```

Author: mofeiZ

compiler/packages/babel-plugin-react-compiler/scripts/jest/makeTransform.ts

@@ -182,7 +182,15 @@ function ReactForgetFunctionTransform() {
         forgetOptions,
         'Other',
         'all_features',
-        '_c',
+        {
+          useMemoCacheIdentifier: '_c',
+          gating: null,
+          lowerContextAccess: null,
+          enableEmitInstrumentForget: null,
+          enableEmitFreeze: false,
+          enableEmitDebugInfo: false,
+          enableEmitSourceMaps: false,
+        },
         null,
         null,
         null,

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

@@ -7,7 +7,6 @@
 
 import {NodePath} from '@babel/core';
 import * as t from '@babel/types';
-import {PluginOptions} from './Options';
 import {CompilerError} from '../CompilerError';
 
 /**
@@ -34,7 +33,7 @@ import {CompilerError} from '../CompilerError';
 function insertAdditionalFunctionDeclaration(
   fnPath: NodePath<t.FunctionDeclaration>,
   compiled: t.FunctionDeclaration,
-  gating: NonNullable<PluginOptions['gating']>,
+  gatingImportedName: string,
 ): void {
   const originalFnName = fnPath.node.id;
   const originalFnParams = fnPath.node.params;
@@ -58,7 +57,7 @@ function insertAdditionalFunctionDeclaration(
   });
 
   const gatingCondition = fnPath.scope.generateUidIdentifier(
-    `${gating.importSpecifierName}_result`,
+    `${gatingImportedName}_result`,
   );
   const unoptimizedFnName = fnPath.scope.generateUidIdentifier(
     `${originalFnName.name}_unoptimized`,
@@ -115,7 +114,7 @@ function insertAdditionalFunctionDeclaration(
     t.variableDeclaration('const', [
       t.variableDeclarator(
         gatingCondition,
-        t.callExpression(t.identifier(gating.importSpecifierName), []),
+        t.callExpression(t.identifier(gatingImportedName), []),
       ),
     ]),
   );
@@ -129,7 +128,7 @@ export function insertGatedFunctionDeclaration(
     | t.FunctionDeclaration
     | t.ArrowFunctionExpression
     | t.FunctionExpression,
-  gating: NonNullable<PluginOptions['gating']>,
+  gatingImportedName: string,
   referencedBeforeDeclaration: boolean,
 ): void {
   if (referencedBeforeDeclaration && fnPath.isFunctionDeclaration()) {
@@ -138,10 +137,10 @@ export function insertGatedFunctionDeclaration(
       description: `Got ${compiled.type} but expected FunctionDeclaration`,
       loc: fnPath.node.loc ?? null,
     });
-    insertAdditionalFunctionDeclaration(fnPath, compiled, gating);
+    insertAdditionalFunctionDeclaration(fnPath, compiled, gatingImportedName);
   } else {
     const gatingExpression = t.conditionalExpression(
-      t.callExpression(t.identifier(gating.importSpecifierName), []),
+      t.callExpression(t.identifier(gatingImportedName), []),
       buildFunctionExpression(compiled),
       buildFunctionExpression(fnPath.node),
     );

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

@@ -8,8 +8,9 @@
 import {NodePath} from '@babel/core';
 import * as t from '@babel/types';
 import {CompilerError, ErrorSeverity} from '../CompilerError';
-import {EnvironmentConfig, ExternalFunction, GeneratedSource} from '../HIR';
+import {EnvironmentConfig, GeneratedSource} from '../HIR';
 import {getOrInsertDefault} from '../Utils/utils';
+import {ImportedExternalFunction} from '../HIR/Environment';
 
 export function validateRestrictedImports(
   path: NodePath<t.Program>,
@@ -44,45 +45,36 @@ export function validateRestrictedImports(
 
 export function addImportsToProgram(
   path: NodePath<t.Program>,
-  importList: Array<ExternalFunction>,
+  importList: Array<ImportedExternalFunction>,
 ): void {
-  const identifiers: Set<string> = new Set();
-  const sortedImports: Map<string, Array<string>> = new Map();
-  for (const {importSpecifierName, source} of importList) {
-    /*
-     * Codegen currently does not rename import specifiers, so we do additional
-     * validation here
+  const sortedImports: Map<string, Array<ImportedExternalFunction>> = new Map();
+  for (const import_ of importList) {
+    /**
+     * Assert that the import identifier hasn't already be declared in the program.
+     * Note: we use getBinding here since `Scope.hasBinding` pessimistically returns true
+     * for all allocated uids (from `Scope.getUid`)
      */
-    CompilerError.invariant(identifiers.has(importSpecifierName) === false, {
-      reason: `Encountered conflicting import specifier for ${importSpecifierName} in Forget config.`,
-      description: null,
+    CompilerError.invariant(path.scope.getBinding(import_.local) == null, {
+      reason: 'Encountered conflicting import specifiers in generated program',
+      description: `Conflict from import ${import_.source}:(${import_.importSpecifierName} as ${import_.local}).`,
       loc: GeneratedSource,
       suggestions: null,
     });
-    CompilerError.invariant(
-      path.scope.hasBinding(importSpecifierName) === false,
-      {
-        reason: `Encountered conflicting import specifiers for ${importSpecifierName} in generated program.`,
-        description: null,
-        loc: GeneratedSource,
-        suggestions: null,
-      },
-    );
-    identifiers.add(importSpecifierName);
-
     const importSpecifierNameList = getOrInsertDefault(
       sortedImports,
-      source,
+      import_.source,
       [],
     );
-    importSpecifierNameList.push(importSpecifierName);
+    importSpecifierNameList.push(import_);
   }
 
   const stmts: Array<t.ImportDeclaration> = [];
-  for (const [source, importSpecifierNameList] of sortedImports) {
-    const importSpecifiers = importSpecifierNameList.map(name => {
-      const id = t.identifier(name);
-      return t.importSpecifier(id, id);
+  for (const [source, import_] of sortedImports) {
+    const importSpecifiers = import_.map(specifier => {
+      return t.importSpecifier(
+        t.identifier(specifier.local),
+        t.identifier(specifier.importSpecifierName),
+      );
     });
 
     stmts.push(t.importDeclaration(importSpecifiers, t.stringLiteral(source)));

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

@@ -28,6 +28,7 @@ import {
   Environment,
   EnvironmentConfig,
   ReactFunctionType,
+  ImportedUids,
 } from '../HIR/Environment';
 import {findContextIdentifiers} from '../HIR/FindContextIdentifiers';
 import {
@@ -116,7 +117,7 @@ function run(
   config: EnvironmentConfig,
   fnType: ReactFunctionType,
   mode: CompilerMode,
-  useMemoCacheIdentifier: string,
+  uniquedImports: ImportedUids,
   logger: Logger | null,
   filename: string | null,
   code: string | null,
@@ -131,7 +132,7 @@ function run(
     logger,
     filename,
     code,
-    useMemoCacheIdentifier,
+    uniquedImports,
   );
   env.logger?.debugLogIRs?.({
     kind: 'debug',
@@ -547,7 +548,7 @@ export function compileFn(
   config: EnvironmentConfig,
   fnType: ReactFunctionType,
   mode: CompilerMode,
-  useMemoCacheIdentifier: string,
+  uniquedImports: ImportedUids,
   logger: Logger | null,
   filename: string | null,
   code: string | null,
@@ -557,7 +558,7 @@ export function compileFn(
     config,
     fnType,
     mode,
-    useMemoCacheIdentifier,
+    uniquedImports,
     logger,
     filename,
     code,