From 11001777d0073141f0e642f004f7ed21c9b6819a Mon Sep 17 00:00:00 2001
From: Benjie Gillam <benjie@jemjie.com>
Date: Thu, 9 Nov 2023 12:22:03 +0000
Subject: [PATCH] Reject deprecated fields when interface field is not
 deprecated

---
 src/type/__tests__/validation-test.ts | 27 +++++++++++++++++++++++++++
 src/type/validate.ts                  | 15 +++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/src/type/__tests__/validation-test.ts b/src/type/__tests__/validation-test.ts
index 7d215361f9..cd50be0425 100644
--- a/src/type/__tests__/validation-test.ts
+++ b/src/type/__tests__/validation-test.ts
@@ -2734,6 +2734,33 @@ describe('Interfaces must adhere to Interface they implement', () => {
       },
     ]);
   });
+
+  it('rejects deprecated implementation field when interface field is not deprecated', () => {
+    const schema = buildSchema(`
+      interface Node {
+        id: ID!
+      }
+
+      type Foo implements Node {
+        id: ID! @deprecated
+      }
+
+      type Query {
+        foo: Foo
+      }
+    `);
+
+    expectJSON(validateSchema(schema)).toDeepEqual([
+      {
+        message:
+          'Interface field Node.id is not deprecated, so implementation field Foo.id must not be deprecated.',
+        locations: [
+          { line: 7, column: 17 },
+          { line: 7, column: 13 },
+        ],
+      },
+    ]);
+  });
 });
 
 describe('assertValidSchema', () => {
diff --git a/src/type/validate.ts b/src/type/validate.ts
index deee23a372..8c29a9fe4f 100644
--- a/src/type/validate.ts
+++ b/src/type/validate.ts
@@ -433,6 +433,21 @@ function validateTypeImplementsInterface(
         );
       }
     }
+
+    // Asserts that field is not deprecated unless interface field is
+    if (
+      ifaceField.deprecationReason == null &&
+      typeField.deprecationReason != null
+    ) {
+      context.reportError(
+        `Interface field ${iface.name}.${fieldName} is not deprecated, so ` +
+          `implementation field ${type.name}.${fieldName} must not be deprecated.`,
+        [
+          getDeprecatedDirectiveNode(typeField.astNode),
+          typeField.astNode?.type,
+        ],
+      );
+    }
   }
 }