ScopeBlockTraversal Class — react Architecture

Source Code

compiler/packages/babel-plugin-react-compiler/src/HIR/visitors.ts lines 1238–1310

export class ScopeBlockTraversal {
  // Live stack of active scopes
  #activeScopes: Array<ScopeId> = [];
  blockInfos: Map<
    BlockId,
    | {
        kind: 'end';
        scope: ReactiveScope;
        pruned: boolean;
      }
    | {
        kind: 'begin';
        scope: ReactiveScope;
        pruned: boolean;
        fallthrough: BlockId;
      }
  > = new Map();

  recordScopes(block: BasicBlock): void {
    const blockInfo = this.blockInfos.get(block.id);
    if (blockInfo?.kind === 'begin') {
      this.#activeScopes.push(blockInfo.scope.id);
    } else if (blockInfo?.kind === 'end') {
      const top = this.#activeScopes.at(-1);
      CompilerError.invariant(blockInfo.scope.id === top, {
        reason:
          'Expected traversed block fallthrough to match top-most active scope',
        loc: block.instructions[0]?.loc ?? block.terminal.loc,
      });
      this.#activeScopes.pop();
    }

    if (
      block.terminal.kind === 'scope' ||
      block.terminal.kind === 'pruned-scope'
    ) {
      CompilerError.invariant(
        !this.blockInfos.has(block.terminal.block) &&
          !this.blockInfos.has(block.terminal.fallthrough),
        {
          reason: 'Expected unique scope blocks and fallthroughs',
          loc: block.terminal.loc,
        },
      );
      this.blockInfos.set(block.terminal.block, {
        kind: 'begin',
        scope: block.terminal.scope,
        pruned: block.terminal.kind === 'pruned-scope',
        fallthrough: block.terminal.fallthrough,
      });
      this.blockInfos.set(block.terminal.fallthrough, {
        kind: 'end',
        scope: block.terminal.scope,
        pruned: block.terminal.kind === 'pruned-scope',
      });
    }
  }

  /**
   * @returns if the given scope is currently 'active', i.e. if the scope start
   * block but not the scope fallthrough has been recorded.
   */
  isScopeActive(scopeId: ScopeId): boolean {
    return this.#activeScopes.indexOf(scopeId) !== -1;
  }

  /**
   * The current, innermost active scope.
   */
  get currentScope(): ScopeId | null {
    return this.#activeScopes.at(-1) ?? null;
  }
}