RequestTracker.js

// @flow strict-local

import type {AbortSignal} from 'abortcontroller-polyfill/dist/cjs-ponyfill';
import type {Async, EnvMap} from '@parcel/types';
import type {EventType, Options as WatcherOptions} from '@parcel/watcher';
import type WorkerFarm from '@parcel/workers';
import type {ContentKey, NodeId, SerializedContentGraph} from '@parcel/graph';
import type {
  ParcelOptions,
  RequestInvalidation,
  InternalFile,
  InternalFileCreateInvalidation,
  InternalGlob,
} from './types';
import type {Deferred} from '@parcel/utils';

import invariant from 'assert';
import nullthrows from 'nullthrows';
import path from 'path';
import {
  isGlobMatch,
  isDirectoryInside,
  makeDeferredWithPromise,
} from '@parcel/utils';
import {hashString} from '@parcel/hash';
import {ContentGraph} from '@parcel/graph';
import {deserialize, serialize} from './serializer';
import {assertSignalNotAborted, hashFromOption} from './utils';
import {
  type ProjectPath,
  fromProjectPathRelative,
  toProjectPathUnsafe,
  toProjectPath,
} from './projectPath';

import {
  PARCEL_VERSION,
  VALID,
  INITIAL_BUILD,
  FILE_CREATE,
  FILE_UPDATE,
  FILE_DELETE,
  ENV_CHANGE,
  OPTION_CHANGE,
  STARTUP,
  ERROR,
} from './constants';

export const requestGraphEdgeTypes = {
  subrequest: 2,
  invalidated_by_update: 3,
  invalidated_by_delete: 4,
  invalidated_by_create: 5,
  invalidated_by_create_above: 6,
  dirname: 7,
};

export type RequestGraphEdgeType = $Values<typeof requestGraphEdgeTypes>;
type SerializedRequestGraph = {|
  ...SerializedContentGraph<RequestGraphNode, RequestGraphEdgeType>,
  invalidNodeIds: Set<NodeId>,
  incompleteNodeIds: Set<NodeId>,
  globNodeIds: Set<NodeId>,
  envNodeIds: Set<NodeId>,
  optionNodeIds: Set<NodeId>,
  unpredicatableNodeIds: Set<NodeId>,
|};

type FileNode = {|id: ContentKey, +type: 'file', value: InternalFile|};
type GlobNode = {|id: ContentKey, +type: 'glob', value: InternalGlob|};
type FileNameNode = {|
  id: ContentKey,
  +type: 'file_name',
  value: string,
|};
type EnvNode = {|
  id: ContentKey,
  +type: 'env',
  value: {|key: string, value: string | void|},
|};

type OptionNode = {|
  id: ContentKey,
  +type: 'option',
  value: {|key: string, hash: string|},
|};

type Request<TInput, TResult> = {|
  id: string,
  +type: string,
  input: TInput,
  run: ({|input: TInput, ...StaticRunOpts|}) => Async<TResult>,
|};

type StoredRequest = {|
  id: string,
  +type: string,
  result?: mixed,
  resultCacheKey?: ?string,
|};

type InvalidateReason = number;
type RequestNode = {|
  id: ContentKey,
  +type: 'request',
  value: StoredRequest,
  invalidateReason: InvalidateReason,
|};
type RequestGraphNode =
  | RequestNode
  | FileNode
  | GlobNode
  | FileNameNode
  | EnvNode
  | OptionNode;

export type RunAPI = {|
  invalidateOnFileCreate: InternalFileCreateInvalidation => void,
  invalidateOnFileDelete: ProjectPath => void,
  invalidateOnFileUpdate: ProjectPath => void,
  invalidateOnStartup: () => void,
  invalidateOnEnvChange: string => void,
  invalidateOnOptionChange: string => void,
  getInvalidations(): Array<RequestInvalidation>,
  storeResult: (result: mixed, cacheKey?: string) => void,
  getRequestResult<T>(contentKey: ContentKey): Async<?T>,
  getPreviousResult<T>(ifMatch?: string): Async<?T>,
  getSubRequests(): Array<StoredRequest>,
  canSkipSubrequest(ContentKey): boolean,
  runRequest: <TInput, TResult>(
    subRequest: Request<TInput, TResult>,
    opts?: RunRequestOpts,
  ) => Async<TResult>,
|};

type RunRequestOpts = {|
  force: boolean,
|};

export type StaticRunOpts = {|
  farm: WorkerFarm,
  options: ParcelOptions,
  api: RunAPI,
  invalidateReason: InvalidateReason,
|};

const nodeFromFilePath = (filePath: ProjectPath): RequestGraphNode => ({
  id: fromProjectPathRelative(filePath),
  type: 'file',
  value: {filePath},
});

const nodeFromGlob = (glob: InternalGlob): RequestGraphNode => ({
  id: fromProjectPathRelative(glob),
  type: 'glob',
  value: glob,
});

const nodeFromFileName = (fileName: string): RequestGraphNode => ({
  id: 'file_name:' + fileName,
  type: 'file_name',
  value: fileName,
});

const nodeFromRequest = (request: StoredRequest): RequestGraphNode => ({
  id: request.id,
  type: 'request',
  value: request,
  invalidateReason: INITIAL_BUILD,
});

const nodeFromEnv = (env: string, value: string | void): RequestGraphNode => ({
  id: 'env:' + env,
  type: 'env',
  value: {
    key: env,
    value,
  },
});

const nodeFromOption = (option: string, value: mixed): RequestGraphNode => ({
  id: 'option:' + option,
  type: 'option',
  value: {
    key: option,
    hash: hashFromOption(value),
  },
});

export class RequestGraph extends ContentGraph<
  RequestGraphNode,
  RequestGraphEdgeType,
> {
  invalidNodeIds: Set<NodeId> = new Set();
  incompleteNodeIds: Set<NodeId> = new Set();
  incompleteNodePromises: Map<NodeId, Promise<boolean>> = new Map();
  globNodeIds: Set<NodeId> = new Set();
  envNodeIds: Set<NodeId> = new Set();
  optionNodeIds: Set<NodeId> = new Set();
  // Unpredictable nodes are requests that cannot be predicted whether they should rerun based on
  // filesystem changes alone. They should rerun on each startup of Parcel.
  unpredicatableNodeIds: Set<NodeId> = new Set();

  // $FlowFixMe[prop-missing]
  static deserialize(opts: SerializedRequestGraph): RequestGraph {
    // $FlowFixMe[prop-missing]
    let deserialized = new RequestGraph(opts);
    deserialized.invalidNodeIds = opts.invalidNodeIds;
    deserialized.incompleteNodeIds = opts.incompleteNodeIds;
    deserialized.globNodeIds = opts.globNodeIds;
    deserialized.envNodeIds = opts.envNodeIds;
    deserialized.optionNodeIds = opts.optionNodeIds;
    deserialized.unpredicatableNodeIds = opts.unpredicatableNodeIds;
    return deserialized;
  }

  // $FlowFixMe[prop-missing]
  serialize(): SerializedRequestGraph {
    return {
      ...super.serialize(),
      invalidNodeIds: this.invalidNodeIds,
      incompleteNodeIds: this.incompleteNodeIds,
      globNodeIds: this.globNodeIds,
      envNodeIds: this.envNodeIds,
      optionNodeIds: this.optionNodeIds,
      unpredicatableNodeIds: this.unpredicatableNodeIds,
    };
  }

  // addNode for RequestGraph should not override the value if added multiple times
  addNode(node: RequestGraphNode): NodeId {
    let nodeId = this._contentKeyToNodeId.get(node.id);
    if (nodeId != null) {
      return nodeId;
    }

    nodeId = super.addNodeByContentKey(node.id, node);
    if (node.type === 'glob') {
      this.globNodeIds.add(nodeId);
    } else if (node.type === 'env') {
      this.envNodeIds.add(nodeId);
    } else if (node.type === 'option') {
      this.optionNodeIds.add(nodeId);
    }

    return nodeId;
  }

  removeNode(nodeId: NodeId): void {
    this.invalidNodeIds.delete(nodeId);
    this.incompleteNodeIds.delete(nodeId);
    this.incompleteNodePromises.delete(nodeId);
    this.unpredicatableNodeIds.delete(nodeId);
    let node = nullthrows(this.getNode(nodeId));
    if (node.type === 'glob') {
      this.globNodeIds.delete(nodeId);
    } else if (node.type === 'env') {
      this.envNodeIds.delete(nodeId);
    } else if (node.type === 'option') {
      this.optionNodeIds.delete(nodeId);
    }
    return super.removeNode(nodeId);
  }

  getRequestNode(nodeId: NodeId): RequestNode {
    let node = nullthrows(this.getNode(nodeId));
    invariant(node.type === 'request');
    return node;
  }

  replaceSubrequests(
    requestNodeId: NodeId,
    subrequestContentKeys: Array<ContentKey>,
  ) {
    let subrequestNodeIds = [];
    for (let key of subrequestContentKeys) {
      if (this.hasContentKey(key)) {
        subrequestNodeIds.push(this.getNodeIdByContentKey(key));
      }
    }

    this.replaceNodeIdsConnectedTo(
      requestNodeId,
      subrequestNodeIds,
      null,
      requestGraphEdgeTypes.subrequest,
    );
  }

  invalidateNode(nodeId: NodeId, reason: InvalidateReason) {
    let node = nullthrows(this.getNode(nodeId));
    invariant(node.type === 'request');
    node.invalidateReason |= reason;
    this.invalidNodeIds.add(nodeId);

    let parentNodes = this.getNodeIdsConnectedTo(
      nodeId,
      requestGraphEdgeTypes.subrequest,
    );
    for (let parentNode of parentNodes) {
      this.invalidateNode(parentNode, reason);
    }
  }

  invalidateUnpredictableNodes() {
    for (let nodeId of this.unpredicatableNodeIds) {
      let node = nullthrows(this.getNode(nodeId));
      invariant(node.type !== 'file' && node.type !== 'glob');
      this.invalidateNode(nodeId, STARTUP);
    }
  }

  invalidateEnvNodes(env: EnvMap) {
    for (let nodeId of this.envNodeIds) {
      let node = nullthrows(this.getNode(nodeId));
      invariant(node.type === 'env');
      if (env[node.value.key] !== node.value.value) {
        let parentNodes = this.getNodeIdsConnectedTo(
          nodeId,
          requestGraphEdgeTypes.invalidated_by_update,
        );
        for (let parentNode of parentNodes) {
          this.invalidateNode(parentNode, ENV_CHANGE);
        }
      }
    }
  }

  invalidateOptionNodes(options: ParcelOptions) {
    for (let nodeId of this.optionNodeIds) {
      let node = nullthrows(this.getNode(nodeId));
      invariant(node.type === 'option');
      if (hashFromOption(options[node.value.key]) !== node.value.hash) {
        let parentNodes = this.getNodeIdsConnectedTo(
          nodeId,
          requestGraphEdgeTypes.invalidated_by_update,
        );
        for (let parentNode of parentNodes) {
          this.invalidateNode(parentNode, OPTION_CHANGE);
        }
      }
    }
  }

  invalidateOnFileUpdate(requestNodeId: NodeId, filePath: ProjectPath) {
    let fileNodeId = this.addNode(nodeFromFilePath(filePath));

    if (
      !this.hasEdge(
        requestNodeId,
        fileNodeId,
        requestGraphEdgeTypes.invalidated_by_update,
      )
    ) {
      this.addEdge(
        requestNodeId,
        fileNodeId,
        requestGraphEdgeTypes.invalidated_by_update,
      );
    }
  }

  invalidateOnFileDelete(requestNodeId: NodeId, filePath: ProjectPath) {
    let fileNodeId = this.addNode(nodeFromFilePath(filePath));

    if (
      !this.hasEdge(
        requestNodeId,
        fileNodeId,
        requestGraphEdgeTypes.invalidated_by_delete,
      )
    ) {
      this.addEdge(
        requestNodeId,
        fileNodeId,
        requestGraphEdgeTypes.invalidated_by_delete,
      );
    }
  }

  invalidateOnFileCreate(
    requestNodeId: NodeId,
    input: InternalFileCreateInvalidation,
  ) {
    let node;
    if (input.glob != null) {
      node = nodeFromGlob(input.glob);
    } else if (input.fileName != null && input.aboveFilePath != null) {
      let aboveFilePath = input.aboveFilePath;

      // Create nodes and edges for each part of the filename pattern.
      // For example, 'node_modules/foo' would create two nodes and one edge.
      // This creates a sort of trie structure within the graph that can be
      // quickly matched by following the edges. This is also memory efficient
      // since common sub-paths (e.g. 'node_modules') are deduplicated.
      let parts = input.fileName.split('/').reverse();
      let lastNodeId;
      for (let part of parts) {
        let fileNameNode = nodeFromFileName(part);

        let fileNameNodeId = this.addNode(fileNameNode);
        if (
          lastNodeId != null &&
          !this.hasEdge(
            lastNodeId,
            fileNameNodeId,
            requestGraphEdgeTypes.dirname,
          )
        ) {
          this.addEdge(
            lastNodeId,
            fileNameNodeId,
            requestGraphEdgeTypes.dirname,
          );
        }

        lastNodeId = fileNameNodeId;
      }

      // The `aboveFilePath` condition asserts that requests are only invalidated
      // if the file being created is "above" it in the filesystem (e.g. the file
      // is created in a parent directory). There is likely to already be a node
      // for this file in the graph (e.g. the source file) that we can reuse for this.
      node = nodeFromFilePath(aboveFilePath);
      let nodeId = this.addNode(node);

      // Now create an edge from the `aboveFilePath` node to the first file_name node
      // in the chain created above, and an edge from the last node in the chain back to
      // the `aboveFilePath` node. When matching, we will start from the first node in
      // the chain, and continue following it to parent directories until there is an
      // edge pointing an `aboveFilePath` node that also points to the start of the chain.
      // This indicates a complete match, and any requests attached to the `aboveFilePath`
      // node will be invalidated.
      let firstId = 'file_name:' + parts[0];
      let firstNodeId = this.getNodeIdByContentKey(firstId);
      if (
        !this.hasEdge(
          nodeId,
          firstNodeId,
          requestGraphEdgeTypes.invalidated_by_create_above,
        )
      ) {
        this.addEdge(
          nodeId,
          firstNodeId,
          requestGraphEdgeTypes.invalidated_by_create_above,
        );
      }

      invariant(lastNodeId != null);
      if (
        !this.hasEdge(
          lastNodeId,
          nodeId,
          requestGraphEdgeTypes.invalidated_by_create_above,
        )
      ) {
        this.addEdge(
          lastNodeId,
          nodeId,
          requestGraphEdgeTypes.invalidated_by_create_above,
        );
      }
    } else if (input.filePath != null) {
      node = nodeFromFilePath(input.filePath);
    } else {
      throw new Error('Invalid invalidation');
    }

    let nodeId = this.addNode(node);
    if (
      !this.hasEdge(
        requestNodeId,
        nodeId,
        requestGraphEdgeTypes.invalidated_by_create,
      )
    ) {
      this.addEdge(
        requestNodeId,
        nodeId,
        requestGraphEdgeTypes.invalidated_by_create,
      );
    }
  }

  invalidateOnStartup(requestNodeId: NodeId) {
    this.getRequestNode(requestNodeId);
    this.unpredicatableNodeIds.add(requestNodeId);
  }

  invalidateOnEnvChange(
    requestNodeId: NodeId,
    env: string,
    value: string | void,
  ) {
    let envNode = nodeFromEnv(env, value);
    let envNodeId = this.addNode(envNode);

    if (
      !this.hasEdge(
        requestNodeId,
        envNodeId,
        requestGraphEdgeTypes.invalidated_by_update,
      )
    ) {
      this.addEdge(
        requestNodeId,
        envNodeId,
        requestGraphEdgeTypes.invalidated_by_update,
      );
    }
  }

  invalidateOnOptionChange(
    requestNodeId: NodeId,
    option: string,
    value: mixed,
  ) {
    let optionNode = nodeFromOption(option, value);
    let optionNodeId = this.addNode(optionNode);

    if (
      !this.hasEdge(
        requestNodeId,
        optionNodeId,
        requestGraphEdgeTypes.invalidated_by_update,
      )
    ) {
      this.addEdge(
        requestNodeId,
        optionNodeId,
        requestGraphEdgeTypes.invalidated_by_update,
      );
    }
  }

  clearInvalidations(nodeId: NodeId) {
    this.unpredicatableNodeIds.delete(nodeId);
    this.replaceNodeIdsConnectedTo(
      nodeId,
      [],
      null,
      requestGraphEdgeTypes.invalidated_by_update,
    );
    this.replaceNodeIdsConnectedTo(
      nodeId,
      [],
      null,
      requestGraphEdgeTypes.invalidated_by_delete,
    );
    this.replaceNodeIdsConnectedTo(
      nodeId,
      [],
      null,
      requestGraphEdgeTypes.invalidated_by_create,
    );
  }

  getInvalidations(requestNodeId: NodeId): Array<RequestInvalidation> {
    if (!this.hasNode(requestNodeId)) {
      return [];
    }

    // For now just handling updates. Could add creates/deletes later if needed.
    let invalidations = this.getNodeIdsConnectedFrom(
      requestNodeId,
      requestGraphEdgeTypes.invalidated_by_update,
    );
    return invalidations
      .map(nodeId => {
        let node = nullthrows(this.getNode(nodeId));
        switch (node.type) {
          case 'file':
            return {type: 'file', filePath: node.value.filePath};
          case 'env':
            return {type: 'env', key: node.value.key};
          case 'option':
            return {type: 'option', key: node.value.key};
        }
      })
      .filter(Boolean);
  }

  getSubRequests(requestNodeId: NodeId): Array<StoredRequest> {
    if (!this.hasNode(requestNodeId)) {
      return [];
    }

    let subRequests = this.getNodeIdsConnectedFrom(
      requestNodeId,
      requestGraphEdgeTypes.subrequest,
    );

    return subRequests.map(nodeId => {
      let node = nullthrows(this.getNode(nodeId));
      invariant(node.type === 'request');
      return node.value;
    });
  }

  invalidateFileNameNode(
    node: FileNameNode,
    filePath: ProjectPath,
    matchNodes: Array<FileNode>,
  ) {
    // If there is an edge between this file_name node and one of the original file nodes pointed to
    // by the original file_name node, and the matched node is inside the current directory, invalidate
    // all connected requests pointed to by the file node.
    let dirname = path.dirname(fromProjectPathRelative(filePath));

    let nodeId = this.getNodeIdByContentKey(node.id);
    for (let matchNode of matchNodes) {
      let matchNodeId = this.getNodeIdByContentKey(matchNode.id);
      if (
        this.hasEdge(
          nodeId,
          matchNodeId,
          requestGraphEdgeTypes.invalidated_by_create_above,
        ) &&
        isDirectoryInside(
          path.dirname(fromProjectPathRelative(matchNode.value.filePath)),
          dirname,
        )
      ) {
        let connectedNodes = this.getNodeIdsConnectedTo(
          matchNodeId,
          requestGraphEdgeTypes.invalidated_by_create,
        );
        for (let connectedNode of connectedNodes) {
          this.invalidateNode(connectedNode, FILE_CREATE);
        }
      }
    }

    // Find the `file_name` node for the parent directory and
    // recursively invalidate connected requests as described above.
    let basename = path.basename(dirname);
    let contentKey = 'file_name:' + basename;
    if (this.hasContentKey(contentKey)) {
      if (
        this.hasEdge(
          nodeId,
          this.getNodeIdByContentKey(contentKey),
          requestGraphEdgeTypes.dirname,
        )
      ) {
        let parent = nullthrows(this.getNodeByContentKey(contentKey));
        invariant(parent.type === 'file_name');
        this.invalidateFileNameNode(
          parent,
          toProjectPathUnsafe(dirname),
          matchNodes,
        );
      }
    }
  }

  respondToFSEvents(
    events: Array<{|path: ProjectPath, type: EventType|}>,
  ): boolean {
    let didInvalidate = false;
    for (let {path: _filePath, type} of events) {
      let filePath = fromProjectPathRelative(_filePath);
      let hasFileRequest = this.hasContentKey(filePath);

      // If we see a 'create' event for the project root itself,
      // this means the project root was moved and we need to
      // re-run all requests.
      if (type === 'create' && filePath === '') {
        for (let [id, node] of this.nodes) {
          if (node.type === 'request') {
            this.invalidNodeIds.add(id);
          }
        }
        return true;
      }

      // sometimes mac os reports update events as create events.
      // if it was a create event, but the file already exists in the graph,
      // then also invalidate nodes connected by invalidated_by_update edges.
      if (hasFileRequest && (type === 'create' || type === 'update')) {
        let nodeId = this.getNodeIdByContentKey(filePath);
        let nodes = this.getNodeIdsConnectedTo(
          nodeId,
          requestGraphEdgeTypes.invalidated_by_update,
        );

        for (let connectedNode of nodes) {
          didInvalidate = true;
          this.invalidateNode(connectedNode, FILE_UPDATE);
        }

        if (type === 'create') {
          let nodes = this.getNodeIdsConnectedTo(
            nodeId,
            requestGraphEdgeTypes.invalidated_by_create,
          );
          for (let connectedNode of nodes) {
            didInvalidate = true;
            this.invalidateNode(connectedNode, FILE_CREATE);
          }
        }
      } else if (type === 'create') {
        let basename = path.basename(filePath);
        let fileNameNode = this.getNodeByContentKey('file_name:' + basename);
        if (fileNameNode != null && fileNameNode?.type === 'file_name') {
          let fileNameNodeId = this.getNodeIdByContentKey(
            'file_name:' + basename,
          );
          // Find potential file nodes to be invalidated if this file name pattern matches
          let above = this.getNodeIdsConnectedTo(
            fileNameNodeId,
            requestGraphEdgeTypes.invalidated_by_create_above,
          ).map(nodeId => {
            let node = nullthrows(this.getNode(nodeId));
            invariant(node.type === 'file');
            return node;
          });

          if (above.length > 0) {
            didInvalidate = true;
            this.invalidateFileNameNode(fileNameNode, _filePath, above);
          }
        }

        for (let globeNodeId of this.globNodeIds) {
          let globNode = this.getNode(globeNodeId);
          invariant(globNode && globNode.type === 'glob');

          if (isGlobMatch(filePath, fromProjectPathRelative(globNode.value))) {
            let connectedNodes = this.getNodeIdsConnectedTo(
              globeNodeId,
              requestGraphEdgeTypes.invalidated_by_create,
            );
            for (let connectedNode of connectedNodes) {
              didInvalidate = true;
              this.invalidateNode(connectedNode, FILE_CREATE);
            }
          }
        }
      } else if (hasFileRequest && type === 'delete') {
        let nodeId = this.getNodeIdByContentKey(filePath);
        for (let connectedNode of this.getNodeIdsConnectedTo(
          nodeId,
          requestGraphEdgeTypes.invalidated_by_delete,
        )) {
          didInvalidate = true;
          this.invalidateNode(connectedNode, FILE_DELETE);
        }

        // Delete the file node since it doesn't exist anymore.
        // This ensures that files that don't exist aren't sent
        // to requests as invalidations for future requests.
        this.removeNode(nodeId);
      }
    }

    return didInvalidate && this.invalidNodeIds.size > 0;
  }
}

export default class RequestTracker {
  graph: RequestGraph;
  farm: WorkerFarm;
  options: ParcelOptions;
  signal: ?AbortSignal;

  constructor({
    graph,
    farm,
    options,
  }: {|
    graph?: RequestGraph,
    farm: WorkerFarm,
    options: ParcelOptions,
  |}) {
    this.graph = graph || new RequestGraph();
    this.farm = farm;
    this.options = options;
  }

  // TODO: refactor (abortcontroller should be created by RequestTracker)
  setSignal(signal?: AbortSignal) {
    this.signal = signal;
  }

  startRequest(
    request: StoredRequest,
  ): {|requestNodeId: NodeId, deferred: Deferred<boolean>|} {
    let didPreviouslyExist = this.graph.hasContentKey(request.id);
    let requestNodeId;
    if (didPreviouslyExist) {
      requestNodeId = this.graph.getNodeIdByContentKey(request.id);
      // Clear existing invalidations for the request so that the new
      // invalidations created during the request replace the existing ones.
      this.graph.clearInvalidations(requestNodeId);
    } else {
      requestNodeId = this.graph.addNode(nodeFromRequest(request));
    }

    this.graph.incompleteNodeIds.add(requestNodeId);
    this.graph.invalidNodeIds.delete(requestNodeId);

    let {promise, deferred} = makeDeferredWithPromise();
    this.graph.incompleteNodePromises.set(requestNodeId, promise);

    return {requestNodeId, deferred};
  }

  // If a cache key is provided, the result will be removed from the node and stored in a separate cache entry
  storeResult(nodeId: NodeId, result: mixed, cacheKey: ?string) {
    let node = this.graph.getNode(nodeId);
    if (node && node.type === 'request') {
      node.value.result = result;
      node.value.resultCacheKey = cacheKey;
    }
  }

  hasValidResult(nodeId: NodeId): boolean {
    return (
      this.graph.hasNode(nodeId) &&
      !this.graph.invalidNodeIds.has(nodeId) &&
      !this.graph.incompleteNodeIds.has(nodeId)
    );
  }

  async getRequestResult<T>(
    contentKey: ContentKey,
    ifMatch?: string,
  ): Async<?T> {
    let node = nullthrows(this.graph.getNodeByContentKey(contentKey));
    invariant(node.type === 'request');

    if (ifMatch != null && node.value.resultCacheKey !== ifMatch) {
      return null;
    }

    if (node.value.result != undefined) {
      // $FlowFixMe
      let result: T = (node.value.result: any);
      return result;
    } else if (node.value.resultCacheKey != null && ifMatch == null) {
      let cachedResult: T = (nullthrows(
        await this.options.cache.get(node.value.resultCacheKey),
        // $FlowFixMe
      ): any);
      node.value.result = cachedResult;
      return cachedResult;
    }
  }

  completeRequest(nodeId: NodeId) {
    this.graph.invalidNodeIds.delete(nodeId);
    this.graph.incompleteNodeIds.delete(nodeId);
    this.graph.incompleteNodePromises.delete(nodeId);
    let node = this.graph.getNode(nodeId);
    if (node?.type === 'request') {
      node.invalidateReason = VALID;
    }
  }

  rejectRequest(nodeId: NodeId) {
    this.graph.incompleteNodeIds.delete(nodeId);
    this.graph.incompleteNodePromises.delete(nodeId);

    let node = this.graph.getNode(nodeId);
    if (node?.type === 'request') {
      this.graph.invalidateNode(nodeId, ERROR);
    }
  }

  respondToFSEvents(
    events: Array<{|path: ProjectPath, type: EventType|}>,
  ): boolean {
    return this.graph.respondToFSEvents(events);
  }

  hasInvalidRequests(): boolean {
    return this.graph.invalidNodeIds.size > 0;
  }

  getInvalidRequests(): Array<StoredRequest> {
    let invalidRequests = [];
    for (let id of this.graph.invalidNodeIds) {
      let node = nullthrows(this.graph.getNode(id));
      invariant(node.type === 'request');
      invalidRequests.push(node.value);
    }
    return invalidRequests;
  }

  replaceSubrequests(
    requestNodeId: NodeId,
    subrequestContextKeys: Array<ContentKey>,
  ) {
    this.graph.replaceSubrequests(requestNodeId, subrequestContextKeys);
  }

  async runRequest<TInput, TResult>(
    request: Request<TInput, TResult>,
    opts?: ?RunRequestOpts,
  ): Async<TResult> {
    let requestId = this.graph.hasContentKey(request.id)
      ? this.graph.getNodeIdByContentKey(request.id)
      : undefined;
    let hasValidResult = requestId != null && this.hasValidResult(requestId);

    if (!opts?.force && hasValidResult) {
      // $FlowFixMe[incompatible-type]
      return this.getRequestResult<TResult>(request.id);
    }

    if (requestId != null) {
      let incompletePromise = this.graph.incompleteNodePromises.get(requestId);
      if (incompletePromise != null) {
        // There is a another instance of this request already running, wait for its completion and reuse its result
        try {
          if (await incompletePromise) {
            // $FlowFixMe[incompatible-type]
            return this.getRequestResult<TResult>(request.id);
          }
        } catch (e) {
          // Rerun this request
        }
      }
    }

    let previousInvalidations =
      requestId != null ? this.graph.getInvalidations(requestId) : [];
    let {requestNodeId, deferred} = this.startRequest({
      id: request.id,
      type: request.type,
    });

    let {api, subRequestContentKeys} = this.createAPI(
      requestNodeId,
      previousInvalidations,
    );

    try {
      let node = this.graph.getRequestNode(requestNodeId);

      let result = await request.run({
        input: request.input,
        api,
        farm: this.farm,
        options: this.options,
        invalidateReason: node.invalidateReason,
      });

      assertSignalNotAborted(this.signal);
      this.completeRequest(requestNodeId);

      deferred.resolve(true);
      return result;
    } catch (err) {
      this.rejectRequest(requestNodeId);
      deferred.resolve(false);
      throw err;
    } finally {
      this.graph.replaceSubrequests(requestNodeId, [...subRequestContentKeys]);
    }
  }

  createAPI(
    requestId: NodeId,
    previousInvalidations: Array<RequestInvalidation>,
  ): {|api: RunAPI, subRequestContentKeys: Set<ContentKey>|} {
    let subRequestContentKeys = new Set<ContentKey>();
    let api: RunAPI = {
      invalidateOnFileCreate: input =>
        this.graph.invalidateOnFileCreate(requestId, input),
      invalidateOnFileDelete: filePath =>
        this.graph.invalidateOnFileDelete(requestId, filePath),
      invalidateOnFileUpdate: filePath =>
        this.graph.invalidateOnFileUpdate(requestId, filePath),
      invalidateOnStartup: () => this.graph.invalidateOnStartup(requestId),
      invalidateOnEnvChange: env =>
        this.graph.invalidateOnEnvChange(requestId, env, this.options.env[env]),
      invalidateOnOptionChange: option =>
        this.graph.invalidateOnOptionChange(
          requestId,
          option,
          this.options[option],
        ),
      getInvalidations: () => previousInvalidations,
      storeResult: (result, cacheKey) => {
        this.storeResult(requestId, result, cacheKey);
      },
      getSubRequests: () => this.graph.getSubRequests(requestId),
      getPreviousResult: <T>(ifMatch?: string): Async<?T> => {
        let contentKey = nullthrows(this.graph.getNode(requestId)?.id);
        return this.getRequestResult<T>(contentKey, ifMatch);
      },
      getRequestResult: <T>(id): Async<?T> => this.getRequestResult<T>(id),
      canSkipSubrequest: contentKey => {
        if (
          this.graph.hasContentKey(contentKey) &&
          this.hasValidResult(this.graph.getNodeIdByContentKey(contentKey))
        ) {
          subRequestContentKeys.add(contentKey);
          return true;
        }

        return false;
      },
      runRequest: <TInput, TResult>(
        subRequest: Request<TInput, TResult>,
        opts?: RunRequestOpts,
      ): Async<TResult> => {
        subRequestContentKeys.add(subRequest.id);
        return this.runRequest<TInput, TResult>(subRequest, opts);
      },
    };

    return {api, subRequestContentKeys};
  }

  async writeToCache() {
    let cacheKey = getCacheKey(this.options);
    let requestGraphKey = hashString(`${cacheKey}:requestGraph`);
    let snapshotKey = hashString(`${cacheKey}:snapshot`);

    if (this.options.shouldDisableCache) {
      return;
    }

    let promises = [];
    for (let [, node] of this.graph.nodes) {
      if (node.type !== 'request') {
        continue;
      }

      let resultCacheKey = node.value.resultCacheKey;
      if (resultCacheKey != null && node.value.result != null) {
        promises.push(
          this.options.cache.set(resultCacheKey, node.value.result),
        );
        delete node.value.result;
      }
    }

    promises.push(
      this.options.cache.setLargeBlob(requestGraphKey, serialize(this.graph)),
    );

    let opts = getWatcherOptions(this.options);
    let snapshotPath = path.join(this.options.cacheDir, snapshotKey + '.txt');
    promises.push(
      this.options.inputFS.writeSnapshot(
        this.options.projectRoot,
        snapshotPath,
        opts,
      ),
    );

    await Promise.all(promises);
  }

  static async init({
    farm,
    options,
  }: {|
    farm: WorkerFarm,
    options: ParcelOptions,
  |}): Async<RequestTracker> {
    let graph = await loadRequestGraph(options);
    return new RequestTracker({farm, options, graph});
  }
}

export function getWatcherOptions(options: ParcelOptions): WatcherOptions {
  let vcsDirs = ['.git', '.hg'].map(dir => path.join(options.projectRoot, dir));
  let ignore = [options.cacheDir, ...vcsDirs];
  return {ignore};
}

function getCacheKey(options) {
  return `${PARCEL_VERSION}:${JSON.stringify(options.entries)}:${options.mode}`;
}

async function loadRequestGraph(options): Async<RequestGraph> {
  if (options.shouldDisableCache) {
    return new RequestGraph();
  }

  let cacheKey = getCacheKey(options);
  let requestGraphKey = hashString(`${cacheKey}:requestGraph`);
  if (await options.cache.hasLargeBlob(requestGraphKey)) {
    let requestGraph: RequestGraph = deserialize(
      await options.cache.getLargeBlob(requestGraphKey),
    );
    let opts = getWatcherOptions(options);
    let snapshotKey = hashString(`${cacheKey}:snapshot`);
    let snapshotPath = path.join(options.cacheDir, snapshotKey + '.txt');
    let events = await options.inputFS.getEventsSince(
      options.projectRoot,
      snapshotPath,
      opts,
    );
    requestGraph.invalidateUnpredictableNodes();
    requestGraph.invalidateEnvNodes(options.env);
    requestGraph.invalidateOptionNodes(options);
    requestGraph.respondToFSEvents(
      events.map(e => ({
        type: e.type,
        path: toProjectPath(options.projectRoot, e.path),
      })),
    );

    return requestGraph;
  }

  return new RequestGraph();
}