lint federation subgraphs schemas without parse errors

.changeset/@graphql-eslint_eslint-plugin-2814-dependencies.md

@@ -0,0 +1,6 @@
+---
+"@graphql-eslint/eslint-plugin": patch
+---
+dependencies updates:
+  - Updated dependency [`@graphql-tools/graphql-tag-pluck@^8.3.4` ↗︎](https://www.npmjs.com/package/@graphql-tools/graphql-tag-pluck/v/8.3.4) (from `8.3.4`, in `dependencies`)
+  - Added dependency [`@apollo/subgraph@^2` ↗︎](https://www.npmjs.com/package/@apollo/subgraph/v/2.0.0) (to `peerDependencies`)

.changeset/fluffy-bottles-switch.md

@@ -0,0 +1,5 @@
+---
+'@graphql-eslint/eslint-plugin': minor
+---
+
+lint federation subgraphs schemas without parse errors

packages/plugin/__tests__/federation.spec.ts

@@ -0,0 +1,28 @@
+import { GRAPHQL_JS_VALIDATIONS } from '../src/rules/graphql-js-validation.js';
+import { ruleTester, withSchema } from './test-utils.js';
+
+ruleTester.run('federation', GRAPHQL_JS_VALIDATIONS['known-directives'], {
+  valid: [
+    withSchema({
+      name: 'should parse federation directive without errors',
+      code: /* GraphQL */ `
+        scalar DateTime
+
+        type Post @key(fields: "id") {
+          id: ID!
+          title: String
+          createdAt: DateTime
+          modifiedAt: DateTime
+        }
+
+        type Query {
+          post: Post!
+          posts: [Post!]
+        }
+
+        extend schema @link(url: "https://specs.apollo.dev/federation/v2.3", import: ["@key"])
+      `,
+    }),
+  ],
+  invalid: [],
+});

packages/plugin/package.json

@@ -35,18 +35,22 @@
     "typecheck": "tsc --noEmit"
   },
   "peerDependencies": {
+    "@apollo/subgraph": "^2",
     "eslint": ">=8.44.0",
     "graphql": "^16",
     "json-schema-to-ts": "^3"
   },
   "peerDependenciesMeta": {
+    "@apollo/subgraph": {
+      "optional": true
+    },
     "json-schema-to-ts": {
       "optional": true
     }
   },
   "dependencies": {
     "@graphql-tools/code-file-loader": "^8.0.0",
-    "@graphql-tools/graphql-tag-pluck": "8.3.4",
+    "@graphql-tools/graphql-tag-pluck": "^8.3.4",
     "@graphql-tools/utils": "^10.0.0",
     "debug": "^4.3.4",
     "fast-glob": "^3.2.12",
@@ -55,6 +59,7 @@
     "lodash.lowercase": "^4.3.0"
   },
   "devDependencies": {
+    "@apollo/subgraph": "^2.9.3",
     "@theguild/eslint-rule-tester": "workspace:*",
     "@types/debug": "4.1.12",
     "@types/eslint": "9.6.1",

packages/plugin/src/schema.ts

@@ -1,6 +1,6 @@
 import debugFactory from 'debug';
 import fg from 'fast-glob';
-import { GraphQLSchema } from 'graphql';
+import { BREAK, GraphQLSchema, visit } from 'graphql';
 import { GraphQLProjectConfig } from 'graphql-config';
 import { ModuleCache } from './cache.js';
 import { Pointer, Schema } from './types.js';
@@ -22,9 +22,39 @@ export function getSchema(project: GraphQLProjectConfig): Schema {
   }
 
   debug('Loading schema from %o', project.schema);
-  const schema = project.loadSchemaSync(project.schema, 'GraphQLSchema', {
+
+  const opts = {
     pluckConfig: project.extensions.pluckConfig,
+  };
+
+  const typeDefs = project.loadSchemaSync(project.schema, 'DocumentNode', opts);
+  let isFederation = false;
+
+  visit(typeDefs, {
+    SchemaExtension(node) {
+      const linkDirective = node.directives?.find(d => d.name.value === 'link');
+      if (!linkDirective) return BREAK;
+
+      const urlArgument = linkDirective.arguments?.find(a => a.name.value === 'url');
+      if (!urlArgument) return BREAK;
+
+      if (urlArgument.value.kind !== 'StringValue') return BREAK;
+
+      isFederation = urlArgument.value.value.includes('/federation/');
+    },
   });
+
+  let schema: GraphQLSchema;
+
+  if (isFederation) {
+    // eslint-disable-next-line @typescript-eslint/no-require-imports -- we inject createRequire in `tsup.config.ts`
+    const { buildSubgraphSchema } = require('@apollo/subgraph');
+
+    schema = buildSubgraphSchema({ typeDefs });
+  } else {
+    schema = project.loadSchemaSync(project.schema, 'GraphQLSchema', opts);
+  }
+
   if (debug.enabled) {
     debug('Schema loaded: %o', schema instanceof GraphQLSchema);
     const schemaPaths = fg.sync(project.schema as Pointer, { absolute: true });

packages/plugin/tsup.config.ts

@@ -27,6 +27,31 @@ export default defineConfig([
     ...opts,
     outDir: 'dist/esm',
     target: 'esnext',
+    esbuildPlugins: [
+      {
+        name: 'inject-create-require',
+        setup(build) {
+          build.onLoad({ filter: /schema\.ts$/ }, async args => {
+            const code = await fs.readFile(args.path, 'utf8');
+            const index = code.indexOf('export function getSchema');
+
+            if (index === -1) {
+              throw new Error('Unable to inject `createRequire` for file ' + args.path);
+            }
+
+            return {
+              contents: [
+                'import { createRequire } from "module"',
+                code.slice(0, index),
+                'const require = createRequire(import.meta.url)',
+                code.slice(index),
+              ].join('\n'),
+              loader: 'ts',
+            };
+          });
+        },
+      },
+    ],
   },
   {
     ...opts,