fix: link merging

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

@@ -84,6 +84,14 @@ const matchValues = (a: ValueNode, b: ValueNode): boolean => {
   return false;
 };
 
+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;
+};
+
 const matchArguments = (a: ArgumentNode, b: ArgumentNode): boolean =>
   a.name.value === b.name.value && a.value.kind === b.value.kind && matchValues(a.value, b.value);
 
@@ -124,6 +132,15 @@ export function mergeDirectives(
         // if did not find a directive with this name on the result set already
         result.push(directive);
       } else {
+        if (isLinkDirective(directive) && isLinkDirective(result[firstAt])) {
+          const url1 = getLinkDirectiveURL(directive);
+          const url2 = getLinkDirectiveURL(result[firstAt]);
+          // if both are link directives but with different urls, do not merge them
+          if (url1 && url2 && url1 !== url2) {
+            result.push(directive);
+            continue;
+          }
+        }
         // if not repeatable and found directive with the same name already in the result set,
         // then merge the arguments of the existing directive and the new directive
         const mergedArguments = mergeArguments(

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

@@ -1749,6 +1749,39 @@ describe('Merge TypeDefs', () => {
     expect(reformulatedGraphQL).toBeSimilarString(schemaWithDescription);
   });
 
+  it('merges the directives with the same name and same arguments (@link)', () => {
+    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 = [schema1, schema2];
+    const merged = mergeTypeDefs(typeDefs);
+    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);
+  });
+
   it('merges the directives with the same name and same arguments', () => {
     const directive = parse(/* GraphQL */ `
       directive @link(
@@ -1762,7 +1795,6 @@ describe('Merge TypeDefs', () => {
     const merged = mergeTypeDefs(typeDefs);
     expect(print(merged)).toBeSimilarString(print(directive));
   });
-
   it('does not merge repeatable Federation directives without the same arguments', () => {
     const ast = parse(/* GraphQL */ `
       extend schema