potential optimization - bail out of executeSubSelectedArray calls

.changeset/mean-singers-cheer.md

@@ -0,0 +1,5 @@
+---
+"@apollo/client": patch
+---
+
+Bail out of `executeSubSelectedArray` calls if the array has 0 elements.

.size-limits.json

@@ -1,4 +1,4 @@
 {
-  "dist/apollo-client.min.cjs": 39319,
-  "import { ApolloClient, InMemoryCache, HttpLink } from \"dist/index.js\" (production)": 32630
+  "dist/apollo-client.min.cjs": 39325,
+  "import { ApolloClient, InMemoryCache, HttpLink } from \"dist/index.js\" (production)": 32634
 }

src/cache/inmemory/__tests__/readFromStore.ts

@@ -560,6 +560,69 @@ describe("reading from the store", () => {
     });
   });
 
+  it("runs a nested query - skips iterating into an empty array", () => {
+    const reader = new StoreReader({
+      cache: new InMemoryCache(),
+    });
+
+    const result = {
+      id: "abcd",
+      stringField: "This is a string!",
+      numberField: 5,
+      nullField: null,
+      nestedArray: [
+        {
+          id: "abcde",
+          stringField: "This is a string also!",
+          numberField: 7,
+          nullField: null,
+        },
+      ],
+      emptyArray: [],
+    } satisfies StoreObject;
+
+    const store = defaultNormalizedCacheFactory({
+      ROOT_QUERY: { ...result, nestedArray: [makeReference("abcde")] },
+      abcde: result.nestedArray[0],
+    });
+
+    expect(reader["executeSubSelectedArray"].size).toBe(0);
+
+    // assumption: cache size does not increase for empty array
+    readQueryFromStore(reader, {
+      store,
+      query: gql`
+        {
+          stringField
+          numberField
+          emptyArray {
+            id
+            stringField
+            numberField
+          }
+        }
+      `,
+    });
+    expect(reader["executeSubSelectedArray"].size).toBe(0);
+
+    // assumption: cache size increases for array with content
+    readQueryFromStore(reader, {
+      store,
+      query: gql`
+        {
+          stringField
+          numberField
+          nestedArray {
+            id
+            stringField
+            numberField
+          }
+        }
+      `,
+    });
+    expect(reader["executeSubSelectedArray"].size).toBe(1);
+  });
+
   it("throws on a missing field", () => {
     const result = {
       id: "abcd",

src/cache/inmemory/readFromStore.ts

@@ -403,15 +403,17 @@ export class StoreReader {
             });
           }
         } else if (isArray(fieldValue)) {
-          fieldValue = handleMissing(
-            this.executeSubSelectedArray({
-              field: selection,
-              array: fieldValue,
-              enclosingRef,
-              context,
-            }),
-            resultName
-          );
+          if (fieldValue.length > 0) {
+            fieldValue = handleMissing(
+              this.executeSubSelectedArray({
+                field: selection,
+                array: fieldValue,
+                enclosingRef,
+                context,
+              }),
+              resultName
+            );
+          }
         } else if (!selection.selectionSet) {
           // If the field does not have a selection set, then we handle it
           // as a scalar value. To keep this.canon from canonicalizing