From 3a71c65e569f5bb43b2e0781ae83db6c524254f2 Mon Sep 17 00:00:00 2001
From: vrazuvaev <vrazuvaev@microsoft.com_msteamsmdb>
Date: Mon, 13 Jul 2026 13:22:18 +0200
Subject: [PATCH] test(apollo-forest-run): cover null list-difference invariant

Add an intentionally failing update-layer regression for the ring0 CompositeNull plus CompositeListDifference signature.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: d1f3dcb1-ea24-47fc-a789-5723d1bf5a5f
---
 .../src/forest/__tests__/updateObject.test.ts | 56 ++++++++++++++++++-
 1 file changed, 55 insertions(+), 1 deletion(-)

diff --git a/packages/apollo-forest-run/src/forest/__tests__/updateObject.test.ts b/packages/apollo-forest-run/src/forest/__tests__/updateObject.test.ts
index 5f8d28170..aeda98cfc 100644
--- a/packages/apollo-forest-run/src/forest/__tests__/updateObject.test.ts
+++ b/packages/apollo-forest-run/src/forest/__tests__/updateObject.test.ts
@@ -1,10 +1,11 @@
-import { replaceValue } from "../updateObject";
+import { replaceValue, updateObject } from "../updateObject";
 import { UpdateTreeContext } from "../types";
 import { ForestRun } from "../../ForestRun";
 import { gql, createTestOperation } from "../../__tests__/helpers/descriptor";
 import { generateChunk } from "../../__tests__/helpers/values";
 import { resolveFieldValue } from "../../values/resolve";
 import { ObjectChunk } from "../../values/types";
+import * as Difference from "../../diff/difference";
 
 describe("replaceValue invariant", () => {
   it("reports the operation when a scalar is replaced with an object", () => {
@@ -132,3 +133,56 @@ describe("incompatible object difference invariant", () => {
     );
   });
 });
+
+describe("divergent composite chunks", () => {
+  it("keeps a null field when a composite list difference reaches it", () => {
+    const base = generateChunk(`
+      query Ring0CompositeList {
+        emailsInfo @mock(value: null) {
+          address
+        }
+      }
+    `).value;
+    const listDifference = Difference.createCompositeListDifference();
+    listDifference.layout = [];
+    const difference = Difference.createObjectDifference();
+    Difference.addFieldDifference(difference, "emailsInfo", listDifference);
+    Difference.addDirtyField(difference, "emailsInfo");
+
+    const warn = jest.fn();
+    const context = {
+      operation: base.operation,
+      drafts: new Map(),
+      missingFields: new Map(),
+      changes: new Map(),
+      findParent: () => undefined,
+      env: {
+        objectKey: () => false,
+        logger: {
+          debug: jest.fn(),
+          log: jest.fn(),
+          warn,
+          error: jest.fn(),
+        },
+      },
+    } as unknown as UpdateTreeContext;
+
+    let result: ReturnType<typeof updateObject>;
+    expect(() => {
+      result = updateObject(context, base, difference);
+    }).not.toThrow();
+
+    expect(result).toBeUndefined();
+    expect(base.data.emailsInfo).toBeNull();
+    expect(warn).toHaveBeenCalledWith(
+      'Skipping update for "query Ring0CompositeList" at path emailsInfo: ' +
+        "field is an explicit null (CompositeNull) in this chunk, but the incoming " +
+        "CompositeListDifference expects a composite list; the node has divergent " +
+        "chunks for this field (null in one, list in another). Leaving the null value " +
+        "unchanged. This usually means the same node was written with conflicting " +
+        "values in a single operation (e.g. aliased selections or a repeated node id) " +
+        "or via a partial/errored write; ensure such selections resolve this field " +
+        "consistently.",
+    );
+  });
+});