ManualMemoBlockState Type — react Architecture

Source Code

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidatePreservedManualMemoization.ts lines 63–113

type ManualMemoBlockState = {
  /**
   * Tracks reassigned temporaries.
   * This is necessary because useMemo calls are usually inlined.
   * Inlining produces a `let` declaration, followed by reassignments
   * to the newly declared variable (one per return statement).
   * Since InferReactiveScopes does not merge scopes across reassigned
   * variables (except in the case of a mutate-after-phi), we need to
   * track reassignments to validate we're retaining manual memo.
   */
  reassignments: Map<DeclarationId, Set<Identifier>>;
  // The source of the original memoization, used when reporting errors
  loc: SourceLocation;

  /**
   * Values produced within manual memoization blocks.
   * We track these to ensure our inferred dependencies are
   * produced before the manual memo block starts
   *
   * As an example:
   * ```js
   * // source
   * const result = useMemo(() => {
   *   return [makeObject(input1), input2],
   * }, [input1, input2]);
   * ```
   * Here, we record inferred dependencies as [input1, input2]
   * but not t0
   * ```js
   * // StartMemoize
   * let t0;
   * if ($[0] != input1) {
   *   t0 = makeObject(input1);
   *   // ...
   * } else { ... }
   *
   * let result;
   * if ($[1] != t0 || $[2] != input2) {
   *   result = [t0, input2];
   * } else { ... }
   * ```
   */
  decls: Set<DeclarationId>;

  /*
   * normalized depslist from useMemo/useCallback
   * callsite in source
   */
  depsFromSource: Array<ManualMemoDependency> | null;
  manualMemoId: number;
};