feat(cli): allow disabling legacy federation injection for FederationV2 schemas (#10788)

* feat(cli): allow disabling legacy federation injection for Federation v2 schemas

* Add changeset

---------

Co-authored-by: Eddy Nguyen <ch@eddeee888.me>
Co-authored-by: Eddy Nguyen <github@eddeee888.me>

Author: robertobadalamenti

.changeset/strong-eagles-obey.md

@@ -0,0 +1,5 @@
+---
+'@graphql-codegen/core': minor
+---
+
+Add disableFederationDirectiveAndScalarInjection config to better support Federation v2

packages/graphql-codegen-cli/tests/codegen.spec.ts

@@ -1505,4 +1505,86 @@ describe('Codegen Executor', () => {
     expect(result.length).toBe(1);
     expect(result[0].content).toContain('export type WpCoreImageBlockForGalleryFragment = ');
   });
+
+  describe('Federation', () => {
+    it('should include federation directives and scalar when federation: true ', async () => {
+      const { result } = await executeCodegen({
+        schema: [SIMPLE_TEST_SCHEMA],
+        generates: {
+          'out1.graphql': {
+            plugins: ['schema-ast'],
+          },
+        },
+        config: {
+          federation: true,
+        },
+      });
+
+      expect(result[0].content).toContain('directive @external on FIELD_DEFINITION');
+      expect(result[0].content).toContain(
+        'directive @requires(fields: _FieldSet!) on FIELD_DEFINITION',
+      );
+      expect(result[0].content).toContain(
+        'directive @provides(fields: _FieldSet!) on FIELD_DEFINITION',
+      );
+      expect(result[0].content).toContain(
+        'directive @key(fields: _FieldSet!) on OBJECT | INTERFACE',
+      );
+      expect(result[0].content).toContain('scalar _FieldSet');
+    });
+    it('should not include federation directives and scalar when federation: true and disableFederationDirectiveAndScalarInjection: true', async () => {
+      const { result } = await executeCodegen({
+        schema: [SIMPLE_TEST_SCHEMA],
+        generates: {
+          'out1.graphql': {
+            plugins: ['schema-ast'],
+          },
+        },
+        config: {
+          federation: true,
+          disableFederationDirectiveAndScalarInjection: true,
+        },
+      });
+
+      expect(result[0].content).not.toContain('directive @external on FIELD_DEFINITION');
+      expect(result[0].content).not.toContain(
+        'directive @requires(fields: _FieldSet!) on FIELD_DEFINITION',
+      );
+      expect(result[0].content).not.toContain(
+        'directive @provides(fields: _FieldSet!) on FIELD_DEFINITION',
+      );
+      expect(result[0].content).not.toContain(
+        'directive @key(fields: _FieldSet!) on OBJECT | INTERFACE',
+      );
+      expect(result[0].content).not.toContain('scalar _FieldSet');
+      expect(result[0].content).toContain('type MyType');
+    });
+    it('should not include federation directives and scalar when federation: false and disableFederationDirectiveAndScalarInjection: true', async () => {
+      const { result } = await executeCodegen({
+        schema: [SIMPLE_TEST_SCHEMA],
+        generates: {
+          'out1.graphql': {
+            plugins: ['schema-ast'],
+          },
+        },
+        config: {
+          federation: false,
+          disableFederationDirectiveAndScalarInjection: true,
+        },
+      });
+
+      expect(result[0].content).not.toContain('directive @external on FIELD_DEFINITION');
+      expect(result[0].content).not.toContain(
+        'directive @requires(fields: _FieldSet!) on FIELD_DEFINITION',
+      );
+      expect(result[0].content).not.toContain(
+        'directive @provides(fields: _FieldSet!) on FIELD_DEFINITION',
+      );
+      expect(result[0].content).not.toContain(
+        'directive @key(fields: _FieldSet!) on OBJECT | INTERFACE',
+      );
+      expect(result[0].content).not.toContain('scalar _FieldSet');
+      expect(result[0].content).toContain('type MyType');
+    });
+  });
 });

packages/graphql-codegen-core/src/codegen.ts

@@ -58,9 +58,20 @@ export async function codegen(options: Types.GenerateOptions): Promise<string> {
   }
 
   const federationInConfig: boolean = pickFlag('federation', options.config);
+  /**
+   * @description When set to `true`, it disables the automatic injection of legacy Federation v1 directives and scalars (such as `@key`, `@external`, and `_FieldSet`).
+   */
+  const disableFederationDirectiveAndScalarInjection: boolean = pickFlag(
+    'disableFederationDirectiveAndScalarInjection',
+    options.config,
+  );
   const isFederation = prioritize(federationInConfig, false);
 
-  if (isFederation && !hasFederationSpec(options.schemaAst || options.schema)) {
+  if (
+    isFederation &&
+    !disableFederationDirectiveAndScalarInjection &&
+    !hasFederationSpec(options.schemaAst || options.schema)
+  ) {
     additionalTypeDefs.push(federationSpec);
   }
 

website/src/pages/docs/integrations/federation.mdx

@@ -26,3 +26,27 @@ export default config
 
 It will add the required GraphQL directives to your codegen schema and generate a compatible
 resolvers signature for [Apollo Federation](https://the-guild.dev/graphql/hive/federation).
+
+For schemas using Apollo Federation v2, the automatic injection of legacy Federation v1 definitions
+(such as `scalar _FieldSet`) can cause duplicate definition errors during validation.
+
+To resolve this, set `disableFederationDirectiveAndScalarInjection` to true in your configuration.
+This suppresses the automatic injection of legacy directives and scalars, ensuring full
+compatibility with Federation v2 schemas and preventing validation failures.
+
+```ts
+import { CodegenConfig } from '@graphql-codegen/cli'
+
+const config: CodegenConfig = {
+  schema: '<path_to_your_schema>',
+  config: {
+    federation: true,
+    disableFederationDirectiveAndScalarInjection: true
+  },
+  generates: {
+    // ...
+  }
+}
+
+export default config
+```