applySignature() — react Function Reference

Source Code

compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingEffects.ts lines 572–671

function applySignature(
  context: Context,
  state: InferenceState,
  signature: InstructionSignature,
  instruction: Instruction,
): Array<AliasingEffect> | null {
  const effects: Array<AliasingEffect> = [];
  /**
   * For function instructions, eagerly validate that they aren't mutating
   * a known-frozen value.
   *
   * TODO: make sure we're also validating against global mutations somewhere, but
   * account for this being allowed in effects/event handlers.
   */
  if (
    instruction.value.kind === 'FunctionExpression' ||
    instruction.value.kind === 'ObjectMethod'
  ) {
    const aliasingEffects =
      instruction.value.loweredFunc.func.aliasingEffects ?? [];
    const context = new Set(
      instruction.value.loweredFunc.func.context.map(p => p.identifier.id),
    );
    for (const effect of aliasingEffects) {
      if (effect.kind === 'Mutate' || effect.kind === 'MutateTransitive') {
        if (!context.has(effect.value.identifier.id)) {
          continue;
        }
        const value = state.kind(effect.value);
        switch (value.kind) {
          case ValueKind.Frozen: {
            const reason = getWriteErrorReason({
              kind: value.kind,
              reason: value.reason,
            });
            const variable =
              effect.value.identifier.name !== null &&
              effect.value.identifier.name.kind === 'named'
                ? `\`${effect.value.identifier.name.value}\``
                : 'value';
            const diagnostic = CompilerDiagnostic.create({
              category: ErrorCategory.Immutability,
              reason: 'This value cannot be modified',
              description: reason,
            }).withDetails({
              kind: 'error',
              loc: effect.value.loc,
              message: `${variable} cannot be modified`,
            });
            if (
              effect.kind === 'Mutate' &&
              effect.reason?.kind === 'AssignCurrentProperty'
            ) {
              diagnostic.withDetails({
                kind: 'hint',
                message: `Hint: If this value is a Ref (value returned by \`useRef()\`), rename the variable to end in "Ref".`,
              });
            }
            effects.push({
              kind: 'MutateFrozen',
              place: effect.value,
              error: diagnostic,
            });
          }
        }
      }
    }
  }

  /*
   * Track which values we've already aliased once, so that we can switch to
   * appendAlias() for subsequent aliases into the same value
   */
  const initialized = new Set<IdentifierId>();

  if (DEBUG) {
    console.log(printInstruction(instruction));
  }

  for (const effect of signature.effects) {
    applyEffect(context, state, effect, initialized, effects);