From 36a7ab84dff2fe844eeeb07678704c128f215662 Mon Sep 17 00:00:00 2001
From: Yaacov Rydzinski <yaacovCR@gmail.com>
Date: Sun, 26 Jul 2026 17:40:18 +0300
Subject: [PATCH] polish(OverlappingFieldsCanMerge: add tests documenting
 existing behavior

subfield conflict detection is short-circuited by parent conflicts
---
 .../OverlappingFieldsCanBeMergedRule-test.ts  | 110 ++++++++++++++++++
 1 file changed, 110 insertions(+)

diff --git a/src/validation/__tests__/OverlappingFieldsCanBeMergedRule-test.ts b/src/validation/__tests__/OverlappingFieldsCanBeMergedRule-test.ts
index ac7cf7991e..7fed134458 100644
--- a/src/validation/__tests__/OverlappingFieldsCanBeMergedRule-test.ts
+++ b/src/validation/__tests__/OverlappingFieldsCanBeMergedRule-test.ts
@@ -570,6 +570,87 @@ describe('Validate: Overlapping fields can be merged', () => {
     ]);
   });
 
+  it('does not compare subfields of incompatible parent calls', () => {
+    expectErrors(`
+      fragment incompatibleParents on Dog {
+        parent: mother {
+          value: name
+        }
+        parent: father {
+          value: mother { name }
+        }
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "parent" conflict because "mother" and "father" are different fields. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 6, column: 9 },
+        ],
+      },
+    ]);
+  });
+
+  it('still compares subfields of each compatible parent-call group', () => {
+    expectErrors(`
+      fragment mixedParents on Dog {
+        parent: mother {
+          value: name
+        }
+        parent: mother {
+          value: mother { name }
+        }
+        parent: father { name }
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "parent" conflict because subfields "value" conflict because "name" and "mother" are different fields. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 4, column: 11 },
+          { line: 6, column: 9 },
+          { line: 7, column: 11 },
+        ],
+      },
+      {
+        message:
+          'Fields "parent" conflict because "mother" and "father" are different fields. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 9, column: 9 },
+        ],
+      },
+      {
+        message:
+          'Fields "parent" conflict because "mother" and "father" are different fields. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 6, column: 9 },
+          { line: 9, column: 9 },
+        ],
+      },
+    ]);
+  });
+
+  it('does not compare subfields after a stream conflict', () => {
+    expectErrors(`
+      fragment streamBarrier on Dog {
+        parent: mother @stream { value: name }
+        parent: mother { value: father }
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "parent" conflict because they have overlapping stream directives. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 4, column: 9 },
+        ],
+      },
+    ]);
+  });
+
   it('very deep conflict', () => {
     expectErrors(`
       {
@@ -763,6 +844,7 @@ describe('Validate: Overlapping fields can be merged', () => {
         scalar: String
         deepBox: StringBox
         unrelatedField: String
+        listNode: [Node]
         listStringBox: [StringBox]
         stringBox: StringBox
         intBox: IntBox
@@ -772,6 +854,7 @@ describe('Validate: Overlapping fields can be merged', () => {
         scalar: Int
         deepBox: IntBox
         unrelatedField: String
+        node: Node
         listStringBox: [StringBox]
         stringBox: StringBox
         intBox: IntBox
@@ -899,6 +982,33 @@ describe('Validate: Overlapping fields can be merged', () => {
       ]);
     });
 
+    it('does not compare subfields after a response-type conflict', () => {
+      expectErrorsWithSchema(
+        schema,
+        `
+          {
+            someBox {
+              ... on StringBox {
+                parent: listNode { value: name }
+              }
+              ... on IntBox {
+                parent: node { value: id }
+              }
+            }
+          }
+        `,
+      ).toDeepEqual([
+        {
+          message:
+            'Fields "parent" conflict because they return conflicting types "[Node]" and "Node". Use different aliases on the fields to fetch both if this was intentional.',
+          locations: [
+            { line: 5, column: 17 },
+            { line: 8, column: 17 },
+          ],
+        },
+      ]);
+    });
+
     it('reports correctly when a non-exclusive follows an exclusive', () => {
       expectErrorsWithSchema(
         schema,