ValidateLocalsNotReassignedAfterRender.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 {CompilerDiagnostic, CompilerError, Effect} from '..';
import {ErrorCategory} from '../CompilerError';
import {HIRFunction, IdentifierId, Place} from '../HIR';
import {
  eachInstructionLValue,
  eachInstructionValueOperand,
  eachTerminalOperand,
} from '../HIR/visitors';
import {getFunctionCallSignature} from '../Inference/InferMutationAliasingEffects';

/**
 * Validates that local variables cannot be reassigned after render.
 * This prevents a category of bugs in which a closure captures a
 * binding from one render but does not update
 */
export function validateLocalsNotReassignedAfterRender(fn: HIRFunction): void {
  const contextVariables = new Set<IdentifierId>();
  const reassignment = getContextReassignment(
    fn,
    contextVariables,
    false,
    false,
  );
  if (reassignment !== null) {
    const errors = new CompilerError();
    const variable =
      reassignment.identifier.name != null &&
      reassignment.identifier.name.kind === 'named'
        ? `\`${reassignment.identifier.name.value}\``
        : 'variable';
    errors.pushDiagnostic(
      CompilerDiagnostic.create({
        category: ErrorCategory.Immutability,
        reason: 'Cannot reassign variable after render completes',
        description: `Reassigning ${variable} after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead`,
      }).withDetails({
        kind: 'error',
        loc: reassignment.loc,
        message: `Cannot reassign ${variable} after render completes`,
      }),
    );
    throw errors;
  }
}

function getContextReassignment(
  fn: HIRFunction,
  contextVariables: Set<IdentifierId>,
  isFunctionExpression: boolean,
  isAsync: boolean,
): Place | null {
  const reassigningFunctions = new Map<IdentifierId, Place>();
  for (const [, block] of fn.body.blocks) {
// ... (170 more lines)