incremental: introduce OrderedSets

src/execution/collectFields.ts

@@ -1,8 +1,8 @@
 import { AccumulatorMap } from '../jsutils/AccumulatorMap.js';
-import { getBySet } from '../jsutils/getBySet.js';
 import { invariant } from '../jsutils/invariant.js';
-import { isSameSet } from '../jsutils/isSameSet.js';
 import type { ObjMap } from '../jsutils/ObjMap.js';
+import type { ReadonlyOrderedSet } from '../jsutils/OrderedSet.js';
+import { OrderedSet } from '../jsutils/OrderedSet.js';
 
 import type {
   FieldNode,
@@ -33,11 +33,13 @@ export interface DeferUsage {
   ancestors: ReadonlyArray<Target>;
 }
 
-export const NON_DEFERRED_TARGET_SET: TargetSet = new Set<Target>([undefined]);
+export const NON_DEFERRED_TARGET_SET = new OrderedSet<Target>([
+  undefined,
+]).freeze();
 
 export type Target = DeferUsage | undefined;
-export type TargetSet = ReadonlySet<Target>;
-export type DeferUsageSet = ReadonlySet<DeferUsage>;
+export type TargetSet = ReadonlyOrderedSet<Target>;
+export type DeferUsageSet = ReadonlyOrderedSet<DeferUsage>;
 
 export interface FieldDetails {
   node: FieldNode;
@@ -430,13 +432,13 @@ function getTargetSetDetails(
       }
     }
 
-    const maskingTargets: TargetSet = new Set<Target>(maskingTargetList);
-    if (isSameSet(maskingTargets, parentTargets)) {
+    const maskingTargets = new OrderedSet(maskingTargetList).freeze();
+    if (maskingTargets === parentTargets) {
       parentTargetKeys.add(responseKey);
       continue;
     }
 
-    let targetSetDetails = getBySet(targetSetDetailsMap, maskingTargets);
+    let targetSetDetails = targetSetDetailsMap.get(maskingTargets);
     if (targetSetDetails === undefined) {
       targetSetDetails = {
         keys: new Set(),

src/jsutils/OrderedSet.ts

@@ -0,0 +1,93 @@
+const setContainingUndefined = new Set([undefined]);
+const setsContainingOneItem = new WeakMap<object, Set<object | undefined>>();
+const setsAppendedByUndefined = new WeakMap<
+  ReadonlySet<object | undefined>,
+  Set<object | undefined>
+>();
+const setsAppendedByDefined = new WeakMap<
+  ReadonlySet<object | undefined>,
+  WeakMap<object, Set<object | undefined>>
+>();
+
+function createOrderedSet<T extends object | undefined>(
+  item: T,
+): ReadonlySet<T | undefined> {
+  if (item === undefined) {
+    return setContainingUndefined;
+  }
+
+  let set = setsContainingOneItem.get(item);
+  if (set === undefined) {
+    set = new Set([item]);
+    set.add(item);
+    setsContainingOneItem.set(item, set);
+  }
+  return set as ReadonlyOrderedSet<T | undefined>;
+}
+
+function appendToOrderedSet<T extends object | undefined>(
+  set: ReadonlySet<T | undefined>,
+  item: T | undefined,
+): ReadonlySet<T | undefined> {
+  if (set.has(item)) {
+    return set;
+  }
+
+  if (item === undefined) {
+    let appendedSet = setsAppendedByUndefined.get(set);
+    if (appendedSet === undefined) {
+      appendedSet = new Set(set);
+      appendedSet.add(undefined);
+      setsAppendedByUndefined.set(set, appendedSet);
+    }
+    return appendedSet as ReadonlySet<T | undefined>;
+  }
+
+  let appendedSets = setsAppendedByDefined.get(set);
+  if (appendedSets === undefined) {
+    appendedSets = new WeakMap();
+    setsAppendedByDefined.set(set, appendedSets);
+    const appendedSet = new Set(set);
+    appendedSet.add(item);
+    appendedSets.set(item, appendedSet);
+    return appendedSet as ReadonlySet<T | undefined>;
+  }
+
+  let appendedSet: Set<object | undefined> | undefined = appendedSets.get(item);
+  if (appendedSet === undefined) {
+    appendedSet = new Set<object | undefined>(set);
+    appendedSet.add(item);
+    appendedSets.set(item, appendedSet);
+  }
+
+  return appendedSet as ReadonlySet<T | undefined>;
+}
+
+export type ReadonlyOrderedSet<T> = ReadonlySet<T>;
+
+const emptySet = new Set();
+
+/**
+ * A set that when frozen can be directly compared for equality.
+ *
+ * Sets are limited to JSON serializable values.
+ *
+ * @internal
+ */
+export class OrderedSet<T extends object | undefined> {
+  _set: ReadonlySet<T | undefined> = emptySet as ReadonlySet<T>;
+  constructor(items: Iterable<T>) {
+    for (const item of items) {
+      if (this._set === emptySet) {
+        this._set = createOrderedSet(item);
+        continue;
+      }
+
+      this._set = appendToOrderedSet(this._set, item);
+    }
+  }
+
+  freeze(): ReadonlyOrderedSet<T> {
+    return this._set as ReadonlyOrderedSet<T>;
+  }
+}

src/jsutils/__tests__/OrderedSet-test.ts

@@ -0,0 +1,34 @@
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import { OrderedSet } from '../OrderedSet.js';
+
+describe('OrderedSet', () => {
+  it('empty sets are equal', () => {
+    const orderedSetA = new OrderedSet([]).freeze();
+    const orderedSetB = new OrderedSet([]).freeze();
+
+    expect(orderedSetA).to.equal(orderedSetB);
+  });
+
+  it('sets with members in different orders or numbers are equal', () => {
+    const a = { a: 'a' };
+    const b = { b: 'b' };
+    const c = { c: 'c' };
+    const orderedSetA = new OrderedSet([a, b, c, a, undefined]).freeze();
+    const orderedSetB = new OrderedSet([undefined, b, a, b, c]).freeze();
+
+    expect(orderedSetA).to.not.equal(orderedSetB);
+  });
+
+  it('sets with members in different orders or numbers are equal', () => {
+    const a = { a: 'a' };
+    const b = { b: 'b' };
+    const c = { c: 'c' };
+    const d = { c: 'd' };
+    const orderedSetA = new OrderedSet([a, b, c, a, undefined]).freeze();
+    const orderedSetB = new OrderedSet([undefined, b, a, b, d]).freeze();
+
+    expect(orderedSetA).to.not.equal(orderedSetB);
+  });
+});