fix(forest-run): eliminate unnecessary array allocations in list diffing when history is disabled

packages/apollo-forest-run/src/ForestRun.ts

@@ -417,7 +417,7 @@ export class ForestRun extends ApolloCache<SerializedCache> {
 
     const output: SerializedCache = {};
     for (const [_, tree] of dataForest.trees.entries()) {
-      const historyLength = tree.history.getAll()?.length ?? 0;
+      const historyLength = tree.history?.getAll()?.length ?? 0;
       output[key(tree.operation)] = stableConvert(
         tree.operation,
         tree.result.data,
@@ -429,7 +429,7 @@ export class ForestRun extends ApolloCache<SerializedCache> {
       for (const layer of this.store.optimisticLayers) {
         for (const [id, optimisticTree] of layer.trees.entries()) {
           const tree = dataForest.trees.get(id);
-          const historyLength = tree?.history.getAll()?.length ?? 0;
+          const historyLength = tree?.history?.getAll()?.length ?? 0;
           output[key(optimisticTree.operation)] = stableConvert(
             optimisticTree.operation,
             tree?.result.data ?? null,

packages/apollo-forest-run/src/__tests__/extract.test.ts

@@ -19,13 +19,15 @@ describe("ForestRun.extract()", () => {
           "data": {
             "foo": 0,
           },
+          "hasHistory": false,
           "optimisticData": null,
           "variables": {},
         },
         "query Foo:2": {
           "data": {
             "foo": 1,
           },
+          "hasHistory": false,
           "optimisticData": null,
           "variables": {
             "i": 1,
@@ -54,6 +56,7 @@ describe("ForestRun.extract()", () => {
           "data": {
             "foo": 0,
           },
+          "hasHistory": false,
           "optimisticData": {
             "foo": 2,
           },
@@ -63,6 +66,7 @@ describe("ForestRun.extract()", () => {
           "data": {
             "foo": 1,
           },
+          "hasHistory": false,
           "optimisticData": null,
           "variables": {
             "i": 1,
@@ -87,6 +91,7 @@ describe("ForestRun.extract()", () => {
       {
         "query Foo:1": {
           "data": null,
+          "hasHistory": false,
           "optimisticData": {
             "foo": 1,
           },

packages/apollo-forest-run/src/diff/__tests__/diffObject.test.ts

@@ -1660,7 +1660,7 @@ describe("diff against base with missing fields", () => {
     const forestEnv = {
       objectKey: (obj: any) => obj.id,
     };
-    const diffEnv = {};
+    const diffEnv = { enableHistory: false, enableDataHistory: false };
     const doc = gql`
       query ($arg: String) {
         foo(arg: $arg)
@@ -1724,6 +1724,8 @@ function diff(
 ) {
   const env = {
     objectKey: (obj: any) => obj.id,
+    enableHistory: false,
+    enableDataHistory: false,
     ...testEnv,
   };
   const baseOperation = createTestOperation(completeObjectDoc, baseVariables);

packages/apollo-forest-run/src/diff/diffObject.ts

@@ -423,7 +423,10 @@ function diffCompositeListValue(
     return undefined;
   }
 
-  const itemsChanges: CompositeListLayoutChange[] = [];
+  const itemsChanges: CompositeListLayoutChange[] | undefined = context.env
+    .enableHistory
+    ? []
+    : undefined;
   const layoutDiffResult =
     diff?.layout ?? diffCompositeListLayout(context, base, model, itemsChanges);
 
@@ -483,7 +486,7 @@ function diffCompositeListLayout(
   context: DiffContext,
   base: CompositeListValue,
   model: CompositeListValue,
-  listContext: CompositeListLayoutChange[],
+  listContext?: CompositeListLayoutChange[],
 ): CompositeListLayoutDifference | undefined | "BREAK" {
   // What constitutes layout change?
   // - Change of "keyed object" position in the list
@@ -496,7 +499,6 @@ function diffCompositeListLayout(
   const baseChunk = Value.isAggregate(base) ? base.chunks[0] : base;
   const modelChunk = Value.isAggregate(model) ? model.chunks[0] : model;
   const unusedBaseIndixes = new Set<number>();
-  const itemChanges: CompositeListLayoutChange[] = [];
   for (let i = 0; i < baseLen; i++) {
     unusedBaseIndixes.add(i);
   }
@@ -524,7 +526,7 @@ function diffCompositeListLayout(
   // Fast-path: no layout difference found
   if (firstDirtyIndex === -1) {
     for (const index of unusedBaseIndixes) {
-      listContext.push(
+      listContext?.push(
         LayoutChange.createItemRemoved(index, baseChunk.data[index], env),
       );
     }
@@ -548,7 +550,7 @@ function diffCompositeListLayout(
     if (modelChunk.data[i] === null) {
       layout.push(null);
       if (baseChunk.data[i] !== null) {
-        itemChanges.push(LayoutChange.createItemAdded(i, null, env));
+        listContext?.push(LayoutChange.createItemAdded(i, null, env));
       }
       continue;
     }
@@ -567,7 +569,7 @@ function diffCompositeListLayout(
       layout.push(baseIndex);
       unusedBaseIndixes.delete(baseIndex);
       if (i !== baseIndex) {
-        listContext.push(
+        listContext?.push(
           LayoutChange.createIndexChange(
             i,
             baseIndex,
@@ -595,7 +597,7 @@ function diffCompositeListLayout(
   }
 
   for (const oldIndex of unusedBaseIndixes) {
-    listContext.push(
+    listContext?.push(
       LayoutChange.createItemRemoved(oldIndex, baseChunk.data[oldIndex], env),
     );
   }

packages/apollo-forest-run/src/diff/difference.ts

@@ -77,7 +77,7 @@ export function createCompositeListDifference(): CompositeListDifference {
     itemQueue: new Set(),
     dirtyItems: undefined,
     layout: undefined,
-    itemsChanges: [],
+    itemsChanges: undefined,
     errors: undefined,
   };
 }

packages/apollo-forest-run/src/diff/types.ts

@@ -129,7 +129,7 @@ export type CompositeListDifference = {
   itemState: Map<number, ValueDifference>;
   dirtyItems?: Set<number>;
   layout?: CompositeListLayoutDifference;
-  itemsChanges: CompositeListLayoutChange[];
+  itemsChanges: CompositeListLayoutChange[] | undefined;
   errors?: DiffError[];
 };
 

packages/apollo-forest-run/src/forest/__tests__/updateTree.test.ts

@@ -1662,12 +1662,12 @@ describe("change reporting", () => {
 
     const [[first, firstFields], [second, secondFields]] = changes.entries();
     expect(firstFields?.length).toEqual(1);
-    expect(firstFields?.[0]?.name).toEqual("foo");
-    expect(first.data).toBe(base.plainObject);
+    expect(firstFields?.[0]?.fieldInfo.name).toEqual("scalar");
+    expect(first.data).toBe(base);
 
     expect(secondFields?.length).toEqual(1);
-    expect(secondFields?.[0]?.name).toEqual("scalar");
-    expect(second.data).toBe(base);
+    expect(secondFields?.[0]?.fieldInfo.name).toEqual("foo");
+    expect(second.data).toBe(base.plainObject);
   });
 
   test("does not report parent as changed on nested chunk change", () => {
@@ -1683,7 +1683,7 @@ describe("change reporting", () => {
 
     const [[first, firstFields]] = changes.entries();
     expect(firstFields?.length).toEqual(1);
-    expect(firstFields?.[0]?.name).toEqual("foo");
+    expect(firstFields?.[0]?.fieldInfo.name).toEqual("foo");
     expect(first.data).toBe(base.plainObject);
   });
 
@@ -1710,7 +1710,7 @@ describe("change reporting", () => {
       // Expected to report as a change in parent object field
       const [[first, firstFields]] = changes.entries();
       expect(firstFields?.length).toEqual(1);
-      expect(firstFields?.[0]?.name).toEqual("scalarList");
+      expect(firstFields?.[0]?.fieldInfo.name).toEqual("scalarList");
       expect(first.data).toBe(base);
     });
   });
@@ -1998,6 +1998,8 @@ function prepareDiffTrees(
   const env: DiffEnv & ForestEnv = {
     objectKey: (obj) => obj.id as string,
     logUpdateStats: false,
+    enableHistory: false,
+    enableDataHistory: false,
     ...(testEnv ?? {}),
   };
   const baseTree = isTree(base)

packages/apollo-forest-run/src/forest/updateObject.ts

@@ -47,9 +47,6 @@ export function recordFieldChange(
   updated: SourceValue | undefined,
 ): void {
   const { enableHistory, enableDataHistory } = context.env;
-  if (!enableHistory) {
-    return;
-  }
 
   let changes = context.changes.get(base);
   if (!changes) {
@@ -276,7 +273,7 @@ function updateCompositeListValue(
       assert(newValue.data);
       accumulateMissingFields(context, newValue);
       result[i] = newValue.data;
-      arrayChanges.push(
+      arrayChanges?.push(
         LayoutChange.createItemAdded(
           i,
           newValue.data,
@@ -307,7 +304,7 @@ function updateCompositeListValue(
   if (copy.length !== base.data.length) {
     dirty = true;
   }
-  context.childChanges = arrayChanges;
+  context.childChanges = arrayChanges ?? [];
 
   return copy ?? base.data;
 }