simplify CollectFields for @defer and @stream (#3994)

minimizes the changes to `CollectFields` required for incremental delivery (inspired by #3982) -- but retains a single memoized incremental field plan per list item.

Author: yaacovCR

src/execution/IncrementalPublisher.ts

@@ -8,7 +8,7 @@ import type {
   GraphQLFormattedError,
 } from '../error/GraphQLError.js';
 
-import type { GroupedFieldSet } from './collectFields.js';
+import type { GroupedFieldSet } from './buildFieldPlan.js';
 
 interface IncrementalUpdate<TData = unknown, TExtensions = ObjMap<unknown>> {
   pending: ReadonlyArray<PendingResult>;

src/execution/buildFieldPlan.ts

@@ -0,0 +1,165 @@
+import { getBySet } from '../jsutils/getBySet.js';
+import { isSameSet } from '../jsutils/isSameSet.js';
+
+import type { DeferUsage, FieldDetails } from './collectFields.js';
+
+export type DeferUsageSet = ReadonlySet<DeferUsage>;
+
+export interface FieldGroup {
+  fields: ReadonlyArray<FieldDetails>;
+  deferUsages?: DeferUsageSet | undefined;
+  knownDeferUsages?: DeferUsageSet | undefined;
+}
+
+export type GroupedFieldSet = Map<string, FieldGroup>;
+
+export interface NewGroupedFieldSetDetails {
+  groupedFieldSet: GroupedFieldSet;
+  shouldInitiateDefer: boolean;
+}
+
+export function buildFieldPlan(
+  fields: Map<string, ReadonlyArray<FieldDetails>>,
+  parentDeferUsages: DeferUsageSet = new Set<DeferUsage>(),
+  knownDeferUsages: DeferUsageSet = new Set<DeferUsage>(),
+): {
+  groupedFieldSet: GroupedFieldSet;
+  newGroupedFieldSetDetailsMap: Map<DeferUsageSet, NewGroupedFieldSetDetails>;
+  newDeferUsages: ReadonlyArray<DeferUsage>;
+} {
+  const newDeferUsages: Set<DeferUsage> = new Set<DeferUsage>();
+  const newKnownDeferUsages = new Set<DeferUsage>(knownDeferUsages);
+
+  const groupedFieldSet = new Map<
+    string,
+    {
+      fields: Array<FieldDetails>;
+      deferUsages: DeferUsageSet;
+      knownDeferUsages: DeferUsageSet;
+    }
+  >();
+
+  const newGroupedFieldSetDetailsMap = new Map<
+    DeferUsageSet,
+    {
+      groupedFieldSet: Map<
+        string,
+        {
+          fields: Array<FieldDetails>;
+          deferUsages: DeferUsageSet;
+          knownDeferUsages: DeferUsageSet;
+        }
+      >;
+      shouldInitiateDefer: boolean;
+    }
+  >();
+
+  const map = new Map<
+    string,
+    {
+      deferUsageSet: DeferUsageSet;
+      fieldDetailsList: ReadonlyArray<FieldDetails>;
+    }
+  >();
+
+  for (const [responseKey, fieldDetailsList] of fields) {
+    const deferUsageSet = new Set<DeferUsage>();
+    let inOriginalResult = false;
+    for (const fieldDetails of fieldDetailsList) {
+      const deferUsage = fieldDetails.deferUsage;
+      if (deferUsage === undefined) {
+        inOriginalResult = true;
+        continue;
+      }
+      deferUsageSet.add(deferUsage);
+      if (!knownDeferUsages.has(deferUsage)) {
+        newDeferUsages.add(deferUsage);
+        newKnownDeferUsages.add(deferUsage);
+      }
+    }
+    if (inOriginalResult) {
+      deferUsageSet.clear();
+    } else {
+      deferUsageSet.forEach((deferUsage) => {
+        const ancestors = getAncestors(deferUsage);
+        for (const ancestor of ancestors) {
+          if (deferUsageSet.has(ancestor)) {
+            deferUsageSet.delete(deferUsage);
+          }
+        }
+      });
+    }
+    map.set(responseKey, { deferUsageSet, fieldDetailsList });
+  }
+
+  for (const [responseKey, { deferUsageSet, fieldDetailsList }] of map) {
+    if (isSameSet(deferUsageSet, parentDeferUsages)) {
+      let fieldGroup = groupedFieldSet.get(responseKey);
+      if (fieldGroup === undefined) {
+        fieldGroup = {
+          fields: [],
+          deferUsages: deferUsageSet,
+          knownDeferUsages: newKnownDeferUsages,
+        };
+        groupedFieldSet.set(responseKey, fieldGroup);
+      }
+      fieldGroup.fields.push(...fieldDetailsList);
+      continue;
+    }
+
+    let newGroupedFieldSetDetails = getBySet(
+      newGroupedFieldSetDetailsMap,
+      deferUsageSet,
+    );
+    let newGroupedFieldSet;
+    if (newGroupedFieldSetDetails === undefined) {
+      newGroupedFieldSet = new Map<
+        string,
+        {
+          fields: Array<FieldDetails>;
+          deferUsages: DeferUsageSet;
+          knownDeferUsages: DeferUsageSet;
+        }
+      >();
+
+      newGroupedFieldSetDetails = {
+        groupedFieldSet: newGroupedFieldSet,
+        shouldInitiateDefer: Array.from(deferUsageSet).some(
+          (deferUsage) => !parentDeferUsages.has(deferUsage),
+        ),
+      };
+      newGroupedFieldSetDetailsMap.set(
+        deferUsageSet,
+        newGroupedFieldSetDetails,
+      );
+    } else {
+      newGroupedFieldSet = newGroupedFieldSetDetails.groupedFieldSet;
+    }
+    let fieldGroup = newGroupedFieldSet.get(responseKey);
+    if (fieldGroup === undefined) {
+      fieldGroup = {
+        fields: [],
+        deferUsages: deferUsageSet,
+        knownDeferUsages: newKnownDeferUsages,
+      };
+      newGroupedFieldSet.set(responseKey, fieldGroup);
+    }
+    fieldGroup.fields.push(...fieldDetailsList);
+  }
+
+  return {
+    groupedFieldSet,
+    newGroupedFieldSetDetailsMap,
+    newDeferUsages: Array.from(newDeferUsages),
+  };
+}
+
+function getAncestors(deferUsage: DeferUsage): ReadonlyArray<DeferUsage> {
+  const ancestors: Array<DeferUsage> = [];
+  let parentDeferUsage: DeferUsage | undefined = deferUsage.parentDeferUsage;
+  while (parentDeferUsage !== undefined) {
+    ancestors.unshift(parentDeferUsage);
+    parentDeferUsage = parentDeferUsage.parentDeferUsage;
+  }
+  return ancestors;
+}