upgrade executor to non-duplicating incremental delivery format

.changeset/fifty-bobcats-jog.md

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+---
+'@graphql-tools/executor': major
+'@graphql-tools/utils': minor
+---
+
+Upgrade to non-duplicating Incremental Delivery format
+
+## Description
+
+GraphQL Incremental Delivery is moving to a [new response format without duplication](https://github.com/graphql/defer-stream-wg/discussions/69).
+
+This PR updates the executor within graphql-tools to follow the new format, a BREAKING CHANGE.
+
+Incremental Delivery has now been disabled for subscriptions, also a BREAKING CHANGE. The GraphQL Working Group has decided to disable incremental delivery support for subscriptions (1) to gather more information about use cases and (2) explore how to interleaving the incremental response streams generated from different source events into one overall subscription response stream.

packages/executor/src/execution/AccumulatorMap.ts

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+/**
+ * ES6 Map with additional `add` method to accumulate items.
+ */
+export class AccumulatorMap<K, T> extends Map<K, Array<T>> {
+  get [Symbol.toStringTag]() {
+    return 'AccumulatorMap';
+  }
+
+  add(key: K, item: T): void {
+    const group = this.get(key);
+    if (group === undefined) {
+      this.set(key, [item]);
+    } else {
+      group.push(item);
+    }
+  }
+}

packages/executor/src/execution/BoxedPromiseOrValue.ts

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+import { isPromise } from '@graphql-tools/utils';
+import type { MaybePromise } from '@graphql-tools/utils';
+
+/**
+ * A BoxedPromiseOrValue is a container for a value or promise where the value
+ * will be updated when the promise resolves.
+ *
+ * A BoxedPromiseOrValue may only be used with promises whose possible
+ * rejection has already been handled, otherwise this will lead to unhandled
+ * promise rejections.
+ *
+ * @internal
+ * */
+export class BoxedPromiseOrValue<T> {
+  value: MaybePromise<T>;
+
+  constructor(value: MaybePromise<T>) {
+    this.value = value;
+    if (isPromise(value)) {
+      value.then(resolved => {
+        this.value = resolved;
+      });
+    }
+  }
+}

packages/executor/src/execution/IncrementalGraph.ts

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+import type { GraphQLError } from 'graphql';
+import { isPromise } from '@graphql-tools/utils';
+import { BoxedPromiseOrValue } from './BoxedPromiseOrValue.js';
+import { invariant } from './invariant.js';
+import { promiseWithResolvers } from './promiseWithResolvers.js';
+import type {
+  DeferredFragmentRecord,
+  DeferredGroupedFieldSetRecord,
+  DeferredGroupedFieldSetResult,
+  IncrementalDataRecord,
+  IncrementalDataRecordResult,
+  ReconcilableDeferredGroupedFieldSetResult,
+  StreamItemRecord,
+  StreamRecord,
+  SubsequentResultRecord,
+} from './types.js';
+import { isDeferredFragmentRecord, isDeferredGroupedFieldSetRecord } from './types.js';
+
+/**
+ * @internal
+ */
+export class IncrementalGraph {
+  private _rootNodes: Set<SubsequentResultRecord>;
+
+  private _completedQueue: Array<IncrementalDataRecordResult>;
+  private _nextQueue: Array<
+    (iterable: IteratorResult<Iterable<IncrementalDataRecordResult>>) => void
+  >;
+
+  constructor() {
+    this._rootNodes = new Set();
+    this._completedQueue = [];
+    this._nextQueue = [];
+  }
+
+  getNewPending(
+    incrementalDataRecords: ReadonlyArray<IncrementalDataRecord>,
+  ): ReadonlyArray<SubsequentResultRecord> {
+    const initialResultChildren = new Set<SubsequentResultRecord>();
+    this._addIncrementalDataRecords(incrementalDataRecords, undefined, initialResultChildren);
+    return this._promoteNonEmptyToRoot(initialResultChildren);
+  }
+
+  addCompletedReconcilableDeferredGroupedFieldSet(
+    reconcilableResult: ReconcilableDeferredGroupedFieldSetResult,
+  ): void {
+    for (const deferredFragmentRecord of reconcilableResult.deferredGroupedFieldSetRecord
+      .deferredFragmentRecords) {
+      deferredFragmentRecord.deferredGroupedFieldSetRecords.delete(
+        reconcilableResult.deferredGroupedFieldSetRecord,
+      );
+      deferredFragmentRecord.reconcilableResults.add(reconcilableResult);
+    }
+
+    const incrementalDataRecords = reconcilableResult.incrementalDataRecords;
+    if (incrementalDataRecords !== undefined) {
+      this._addIncrementalDataRecords(
+        incrementalDataRecords,
+        reconcilableResult.deferredGroupedFieldSetRecord.deferredFragmentRecords,
+      );
+    }
+  }
+
+  completedIncrementalData() {
+    return {
+      [Symbol.asyncIterator]() {
+        return this;
+      },
+      next: (): Promise<IteratorResult<Iterable<IncrementalDataRecordResult>>> => {
+        const firstResult = this._completedQueue.shift();
+        if (firstResult !== undefined) {
+          return Promise.resolve({
+            value: this._yieldCurrentCompletedIncrementalData(firstResult),
+            done: false,
+          });
+        }
+        const { promise, resolve } =
+          promiseWithResolvers<IteratorResult<Iterable<IncrementalDataRecordResult>>>();
+        this._nextQueue.push(resolve);
+        return promise;
+      },
+      return: (): Promise<IteratorResult<Iterable<IncrementalDataRecordResult>>> => {
+        for (const resolve of this._nextQueue) {
+          resolve({ value: undefined, done: true });
+        }
+        return Promise.resolve({ value: undefined, done: true });
+      },
+    };
+  }
+
+  hasNext(): boolean {
+    return this._rootNodes.size > 0;
+  }
+
+  completeDeferredFragment(deferredFragmentRecord: DeferredFragmentRecord):
+    | {
+        newPending: ReadonlyArray<SubsequentResultRecord>;
+        reconcilableResults: ReadonlyArray<ReconcilableDeferredGroupedFieldSetResult>;
+      }
+    | undefined {
+    if (
+      !this._rootNodes.has(deferredFragmentRecord) ||
+      deferredFragmentRecord.deferredGroupedFieldSetRecords.size > 0
+    ) {
+      return;
+    }
+    const reconcilableResults = Array.from(deferredFragmentRecord.reconcilableResults);
+    this._removePending(deferredFragmentRecord);
+    for (const reconcilableResult of reconcilableResults) {
+      for (const otherDeferredFragmentRecord of reconcilableResult.deferredGroupedFieldSetRecord
+        .deferredFragmentRecords) {
+        otherDeferredFragmentRecord.reconcilableResults.delete(reconcilableResult);
+      }
+    }
+    const newPending = this._promoteNonEmptyToRoot(deferredFragmentRecord.children);
+    return { newPending, reconcilableResults };
+  }
+
+  removeDeferredFragment(deferredFragmentRecord: DeferredFragmentRecord): boolean {
+    if (!this._rootNodes.has(deferredFragmentRecord)) {
+      return false;
+    }
+    this._removePending(deferredFragmentRecord);
+    return true;
+  }
+
+  removeStream(streamRecord: StreamRecord): void {
+    this._removePending(streamRecord);
+  }
+
+  private _removePending(subsequentResultRecord: SubsequentResultRecord): void {
+    this._rootNodes.delete(subsequentResultRecord);
+    if (this._rootNodes.size === 0) {
+      for (const resolve of this._nextQueue) {
+        resolve({ value: undefined, done: true });
+      }
+    }
+  }
+
+  private _addIncrementalDataRecords(
+    incrementalDataRecords: ReadonlyArray<IncrementalDataRecord>,
+    parents: ReadonlyArray<DeferredFragmentRecord> | undefined,
+    initialResultChildren?: Set<SubsequentResultRecord> | undefined,
+  ): void {
+    for (const incrementalDataRecord of incrementalDataRecords) {
+      if (isDeferredGroupedFieldSetRecord(incrementalDataRecord)) {
+        for (const deferredFragmentRecord of incrementalDataRecord.deferredFragmentRecords) {
+          this._addDeferredFragment(deferredFragmentRecord, initialResultChildren);
+          deferredFragmentRecord.deferredGroupedFieldSetRecords.add(incrementalDataRecord);
+        }
+        if (this._hasPendingFragment(incrementalDataRecord)) {
+          this._onDeferredGroupedFieldSet(incrementalDataRecord);
+        }
+      } else if (parents === undefined) {
+        invariant(initialResultChildren !== undefined);
+        initialResultChildren.add(incrementalDataRecord);
+      } else {
+        for (const parent of parents) {
+          this._addDeferredFragment(parent, initialResultChildren);
+          parent.children.add(incrementalDataRecord);
+        }
+      }
+    }
+  }
+
+  private _promoteNonEmptyToRoot(
+    maybeEmptyNewPending: Set<SubsequentResultRecord>,
+  ): ReadonlyArray<SubsequentResultRecord> {
+    const newPending: Array<SubsequentResultRecord> = [];
+    for (const subsequentResultRecord of maybeEmptyNewPending) {
+      if (isDeferredFragmentRecord(subsequentResultRecord)) {
+        if (subsequentResultRecord.deferredGroupedFieldSetRecords.size > 0) {
+          subsequentResultRecord.setAsPending();
+          for (const deferredGroupedFieldSetRecord of subsequentResultRecord.deferredGroupedFieldSetRecords) {
+            if (!this._hasPendingFragment(deferredGroupedFieldSetRecord)) {
+              this._onDeferredGroupedFieldSet(deferredGroupedFieldSetRecord);
+            }
+          }
+          this._rootNodes.add(subsequentResultRecord);
+          newPending.push(subsequentResultRecord);
+          continue;
+        }
+        for (const child of subsequentResultRecord.children) {
+          maybeEmptyNewPending.add(child);
+        }
+      } else {
+        this._rootNodes.add(subsequentResultRecord);
+        newPending.push(subsequentResultRecord);
+
+        this._onStreamItems(subsequentResultRecord);
+      }
+    }
+    return newPending;
+  }
+
+  private _hasPendingFragment(
+    deferredGroupedFieldSetRecord: DeferredGroupedFieldSetRecord,
+  ): boolean {
+    return deferredGroupedFieldSetRecord.deferredFragmentRecords.some(deferredFragmentRecord =>
+      this._rootNodes.has(deferredFragmentRecord),
+    );
+  }
+
+  private _addDeferredFragment(
+    deferredFragmentRecord: DeferredFragmentRecord,
+    subsequentResultRecords: Set<SubsequentResultRecord> | undefined,
+  ): void {
+    if (this._rootNodes.has(deferredFragmentRecord)) {
+      return;
+    }
+    const parent = deferredFragmentRecord.parent;
+    if (parent === undefined) {
+      invariant(subsequentResultRecords !== undefined);
+      subsequentResultRecords.add(deferredFragmentRecord);
+      return;
+    }
+    parent.children.add(deferredFragmentRecord);
+    this._addDeferredFragment(parent, subsequentResultRecords);
+  }
+
+  private _onDeferredGroupedFieldSet(
+    deferredGroupedFieldSetRecord: DeferredGroupedFieldSetRecord,
+  ): void {
+    const result = (
+      deferredGroupedFieldSetRecord.result as BoxedPromiseOrValue<DeferredGroupedFieldSetResult>
+    ).value;
+    if (isPromise(result)) {
+      result.then(resolved => this._enqueue(resolved));
+    } else {
+      this._enqueue(result);
+    }
+  }
+
+  private async _onStreamItems(streamRecord: StreamRecord): Promise<void> {
+    let items: Array<unknown> = [];
+    let errors: Array<GraphQLError> = [];
+    let incrementalDataRecords: Array<IncrementalDataRecord> = [];
+    const streamItemQueue = streamRecord.streamItemQueue;
+    let streamItemRecord: StreamItemRecord | undefined;
+    while ((streamItemRecord = streamItemQueue.shift()) !== undefined) {
+      let result =
+        streamItemRecord instanceof BoxedPromiseOrValue
+          ? streamItemRecord.value
+          : streamItemRecord().value;
+      if (isPromise(result)) {
+        if (items.length > 0) {
+          this._enqueue({
+            streamRecord,
+            result:
+              // TODO add additional test case or rework for coverage
+              errors.length > 0 /* c8 ignore start */
+                ? { items, errors } /* c8 ignore stop */
+                : { items },
+            incrementalDataRecords,
+          });
+          items = [];
+          errors = [];
+          incrementalDataRecords = [];
+        }
+        result = await result;
+        // wait an additional tick to coalesce resolving additional promises
+        // within the queue
+        await Promise.resolve();
+      }
+      if (result.item === undefined) {
+        if (items.length > 0) {
+          this._enqueue({
+            streamRecord,
+            result: errors.length > 0 ? { items, errors } : { items },
+            incrementalDataRecords,
+          });
+        }
+        this._enqueue(
+          result.errors === undefined
+            ? { streamRecord }
+            : {
+                streamRecord,
+                errors: result.errors,
+              },
+        );
+        return;
+      }
+      items.push(result.item);
+      if (result.errors !== undefined) {
+        errors.push(...result.errors);
+      }
+      if (result.incrementalDataRecords !== undefined) {
+        incrementalDataRecords.push(...result.incrementalDataRecords);
+      }
+    }
+  }
+
+  private *_yieldCurrentCompletedIncrementalData(
+    first: IncrementalDataRecordResult,
+  ): Generator<IncrementalDataRecordResult> {
+    yield first;
+    let completed;
+    while ((completed = this._completedQueue.shift()) !== undefined) {
+      yield completed;
+    }
+  }
+
+  private _enqueue(completed: IncrementalDataRecordResult): void {
+    const next = this._nextQueue.shift();
+    if (next !== undefined) {
+      next({
+        value: this._yieldCurrentCompletedIncrementalData(completed),
+        done: false,
+      });
+      return;
+    }
+    this._completedQueue.push(completed);
+  }
+}