Gating.ts — react Source File

Source Code

/**
 * 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 {NodePath} from '@babel/core';
import * as t from '@babel/types';
import {CompilerError} from '../CompilerError';
import {GeneratedSource} from '../HIR';
import {ProgramContext} from './Imports';
import {ExternalFunction} from '..';

/**
 * Gating rewrite for function declarations which are referenced before their
 * declaration site.
 *
 * ```js
 * // original
 * export default React.memo(Foo);
 * function Foo() { ... }
 *
 * // React compiler optimized + gated
 * import {gating} from 'myGating';
 * export default React.memo(Foo);
 * const gating_result = gating();  <- inserted
 * function Foo_optimized() {}      <- inserted
 * function Foo_unoptimized() {}    <- renamed from Foo
 * function Foo() {                 <- inserted function, which can be hoisted by JS engines
 *   if (gating_result) return Foo_optimized();
 *   else return Foo_unoptimized();
 * }
 * ```
 */
function insertAdditionalFunctionDeclaration(
  fnPath: NodePath<t.FunctionDeclaration>,
  compiled: t.FunctionDeclaration,
  programContext: ProgramContext,
  gatingFunctionIdentifierName: string,
): void {
  const originalFnName = fnPath.node.id;
  const originalFnParams = fnPath.node.params;
  const compiledParams = fnPath.node.params;
  /**
   * Note that other than `export default function() {}`, all other function
   * declarations must have a binding identifier. Since default exports cannot
   * be referenced, it's safe to assume that all function declarations passed
   * here will have an identifier.
   * https://tc39.es/ecma262/multipage/ecmascript-language-functions-and-classes.html#sec-function-definitions
   */
  CompilerError.invariant(originalFnName != null && compiled.id != null, {
    reason:
      'Expected function declarations that are referenced elsewhere to have a named identifier',
    loc: fnPath.node.loc ?? GeneratedSource,
  });
  CompilerError.invariant(originalFnParams.length === compiledParams.length, {
    reason:
      'Expected React Compiler optimized function declarations to have the same number of parameters as source',
    loc: fnPath.node.loc ?? GeneratedSource,
// ... (161 more lines)