fix: link merging

packages/merge/src/typedefs-mergers/directives.ts

@@ -8,11 +8,35 @@ import {
 import { isSome } from '@graphql-tools/utils';
 import { Config } from './merge-typedefs.js';
 
+const isLinkDirective = (directive: DirectiveNode): boolean => directive.name.value === 'link';
+
+const getLinkDirectiveURL = (directive: DirectiveNode): string | undefined => {
+  const stringValue = isLinkDirective(directive)
+    ? directive.arguments?.find(arg => arg.name.value === 'url')?.value
+    : undefined;
+  return stringValue?.kind === 'StringValue' ? stringValue.value : undefined;
+};
+
+/**
+ * Directives by default do not carry distinctual metadata, thus are not
+ * considered distinct by default by this function. However @link directives are
+ * only considered distinct if they have different URLs.
+ */
+const isDirectiveMetadataDistinct = (directiveA: DirectiveNode, directiveB: DirectiveNode) => {
+  const isLinkPair = isLinkDirective(directiveA) && isLinkDirective(directiveB);
+  return isLinkPair ? getLinkDirectiveURL(directiveA) !== getLinkDirectiveURL(directiveB) : false;
+};
+
+const isMatchingDirective = (a: DirectiveNode, b: DirectiveNode) => a.name.value === b.name.value;
+
 function directiveAlreadyExists(
   directivesArr: ReadonlyArray<DirectiveNode>,
   otherDirective: DirectiveNode,
 ): boolean {
-  return !!directivesArr.find(directive => directive.name.value === otherDirective.name.value);
+  return !!directivesArr.find(directive => {
+    const isDirectiveNameMatching = directive.name.value === otherDirective.name.value;
+    return isDirectiveNameMatching && !isDirectiveMetadataDistinct(directive, otherDirective);
+  });
 }
 
 function isRepeatableDirective(
@@ -98,7 +122,7 @@ export function mergeDirectives(
       directiveAlreadyExists(result, directive) &&
       !isRepeatableDirective(directive, directives)
     ) {
-      const existingDirectiveIndex = result.findIndex(d => d.name.value === directive.name.value);
+      const existingDirectiveIndex = result.findIndex(it => isMatchingDirective(it, directive));
       const existingDirective = result[existingDirectiveIndex];
       (result[existingDirectiveIndex] as any).arguments = mergeArguments(
         directive.arguments || [],

packages/merge/tests/merge-typedefs.spec.ts

@@ -1704,17 +1704,37 @@ describe('Merge TypeDefs', () => {
     });
     expect(reformulatedGraphQL).toBeSimilarString(schemaWithDescription);
   });
+
   it('merges the directives with the same name and same arguments', () => {
-    const directive = parse(/* GraphQL */ `
-      directive @link(
-        url: String!
-        as: String
-        import: [link__Import]
-        for: link__Purpose
-      ) on SCHEMA
+    const schema1 = parse(/* GraphQL */ `
+      extend schema
+        @link(
+          url: "https://specs.apollo.dev/federation/v2.3"
+          import: ["@composeDirective", "@external", "@foo"]
+        )
+    `);
+
+    const schema2 = parse(/* GraphQL */ `
+      extend schema
+        @link(
+          url: "https://specs.apollo.dev/federation/v2.3"
+          import: ["@composeDirective", "@external"]
+        )
+        @link(url: "file://foo.org/trackable/v2.3", import: ["@trackable"])
     `);
-    const typeDefs = [directive, directive];
+    const typeDefs = [schema1, schema2];
     const merged = mergeTypeDefs(typeDefs);
-    expect(print(merged)).toBeSimilarString(print(directive));
+    const prettyOutput = print(merged);
+    const prettyExpected = print(
+      parse(/* GraphQL */ `
+        extend schema
+          @link(
+            url: "https://specs.apollo.dev/federation/v2.3"
+            import: ["@composeDirective", "@external", "@foo"]
+          )
+          @link(url: "file://foo.org/trackable/v2.3", import: ["@trackable"]) # unique to schema 2
+      `),
+    );
+    expect(prettyOutput).toBeSimilarString(prettyExpected);
   });
 });