Add @schema decorator to mark namespaces as GraphQL schemas

Using the `TypeSpec.GraphQL.@schema` decorator on a namespace indicates that the decorated namespace represents a GraphQL schema that should be generated by the GraphQL emitter.

Because this allows for multiple schemas to be specified in a TypeSpec source, our test host is reworked to provide a `GraphQLSchemaRecord` corresponding to each schema produced.

This commit does not actually implement any emitter functionality, but populates a state map that will be used by the emitter in the future.

packages/graphql/lib/main.tsp

@@ -0,0 +1 @@
+import "./schema.tsp";

packages/graphql/lib/schema.tsp

@@ -0,0 +1,23 @@
+import "../dist/src/lib/schema.js";
+
+using TypeSpec.Reflection;
+
+namespace TypeSpec.GraphQL;
+
+namespace Schema {
+  model SchemaOptions {
+    name?: string;
+  }
+}
+
+/**
+ * Mark this namespace as describing a GraphQL schema and configure schema properties.
+ *
+ * @example
+ *
+ * ```typespec
+ * @schema(#{name: "MySchema"})
+ * namespace MySchema {};
+ * ```
+ */
+extern dec schema(target: Namespace, options?: valueof Schema.SchemaOptions);

packages/graphql/package.json

@@ -20,6 +20,7 @@
   "main": "dist/src/index.js",
   "exports": {
     ".": {
+      "typespec": "./lib/main.tsp",
       "types": "./dist/src/index.d.ts",
       "default": "./dist/src/index.js"
     },
@@ -31,6 +32,12 @@
   "engines": {
     "node": ">=18.0.0"
   },
+  "graphql": {
+    "documents": "test/**/*.{js,ts}"
+  },
+  "dependencies": {
+    "graphql": "^16.9.0"
+  },
   "scripts": {
     "clean": "rimraf ./dist ./temp",
     "build": "tsc",

packages/graphql/src/index.ts

@@ -1,2 +1,3 @@
 export { $onEmit } from "./emitter.js";
 export { $lib } from "./lib.js";
+export { $decorators } from "./tsp-index.js";

packages/graphql/src/lib.ts

@@ -1,5 +1,7 @@
 import { createTypeSpecLibrary, type JSONSchemaType } from "@typespec/compiler";
 
+export const NAMESPACE = "TypeSpec.GraphQL";
+
 export interface GraphQLEmitterOptions {
   /**
    * Name of the output file.
@@ -95,8 +97,11 @@ export const libDef = {
   emitter: {
     options: EmitterOptionsSchema as JSONSchemaType<GraphQLEmitterOptions>,
   },
+  state: {
+    schema: { description: "State for the @schema decorator." },
+  },
 } as const;
 
 export const $lib = createTypeSpecLibrary(libDef);
 
-export const { reportDiagnostic, createDiagnostic } = $lib;
+export const { reportDiagnostic, createDiagnostic, stateKeys: GraphQLKeys } = $lib;

packages/graphql/src/lib/schema.ts

@@ -0,0 +1,77 @@
+import {
+  type DecoratorContext,
+  type DecoratorFunction,
+  type Namespace,
+  type Program,
+  validateDecoratorUniqueOnNode,
+} from "@typespec/compiler";
+
+import { GraphQLKeys, NAMESPACE } from "../lib.js";
+import { useStateMap } from "./state-map.js";
+
+// This will set the namespace for decorators implemented in this file
+export const namespace = NAMESPACE;
+
+export interface SchemaDetails {
+  name?: string;
+}
+
+export interface Schema extends SchemaDetails {
+  type: Namespace;
+}
+
+const [getSchema, setSchema, getSchemaMap] = useStateMap<Namespace, Schema>(GraphQLKeys.schema);
+
+/**
+ * List all the schemas defined in the TypeSpec program
+ * @param program Program
+ * @returns List of schemas.
+ */
+export function listSchemas(program: Program): Schema[] {
+  return [...getSchemaMap(program).values()];
+}
+
+export {
+  /**
+   * Get the schema information for the given namespace.
+   * @param program Program
+   * @param namespace Schema namespace
+   * @returns Schema information or undefined if namespace is not a schema namespace.
+   */
+  getSchema,
+};
+
+/**
+ * Check if the namespace is defined as a schema.
+ * @param program Program
+ * @param namespace Namespace
+ * @returns Boolean
+ */
+export function isSchema(program: Program, namespace: Namespace): boolean {
+  return getSchemaMap(program).has(namespace);
+}
+
+/**
+ * Mark the given namespace as a schema.
+ * @param program Program
+ * @param namespace Namespace
+ * @param details Schema details
+ */
+export function addSchema(
+  program: Program,
+  namespace: Namespace,
+  details: SchemaDetails = {},
+): void {
+  const schemaMap = getSchemaMap(program);
+  const existing = schemaMap.get(namespace) ?? {};
+  setSchema(program, namespace, { ...existing, ...details, type: namespace });
+}
+
+export const $schema: DecoratorFunction = (
+  context: DecoratorContext,
+  target: Namespace,
+  options: SchemaDetails = {},
+) => {
+  validateDecoratorUniqueOnNode(context, target, $schema);
+  addSchema(context.program, target, options);
+};

packages/graphql/src/lib/state-map.ts

@@ -0,0 +1,10 @@
+import type { Type } from "@typespec/compiler";
+import { unsafe_useStateMap, unsafe_useStateSet } from "@typespec/compiler/experimental";
+
+export function useStateMap<K extends Type, V>(key: symbol) {
+  return unsafe_useStateMap<K, V>(key);
+}
+
+export function useStateSet<K extends Type>(key: symbol) {
+  return unsafe_useStateSet<K>(key);
+}

packages/graphql/src/schema-emitter.ts

@@ -18,7 +18,7 @@ export function createGraphQLEmitter(
       const filePath = interpolatePath(options.outputFile, { "schema-name": "schema" });
       await emitFile(program, {
         path: filePath,
-        content: "Hello world",
+        content: "",
         newLine: options.newLine,
       });
     }

packages/graphql/src/tsp-index.ts

@@ -0,0 +1,9 @@
+import type { DecoratorImplementations } from "@typespec/compiler";
+import { NAMESPACE } from "./lib.js";
+import { $schema } from "./lib/schema.js";
+
+export const $decorators: DecoratorImplementations = {
+  [NAMESPACE]: {
+    schema: $schema,
+  },
+};

packages/graphql/src/types.d.ts

@@ -0,0 +1,18 @@
+import type { Diagnostic } from "@typespec/compiler";
+import type { GraphQLSchema } from "graphql";
+import type { Schema } from "./lib/schema.ts";
+
+/**
+ * A record containing the GraphQL schema corresponding to
+ * a particular schema definition.
+ */
+export interface GraphQLSchemaRecord {
+  /** The declared schema that generated this GraphQL schema */
+  readonly schema: Schema;
+
+  /** The GraphQLSchema */
+  readonly graphQLSchema: GraphQLSchema;
+
+  /** The diagnostics created for this schema */
+  readonly diagnostics: readonly Diagnostic[];
+}

packages/graphql/test/schema.test.ts

@@ -0,0 +1,37 @@
+import type { Namespace } from "@typespec/compiler";
+import { expectDiagnosticEmpty } from "@typespec/compiler/testing";
+import { describe, expect, it } from "vitest";
+import { getSchema } from "../src/lib/schema.js";
+import { compileAndDiagnose } from "./test-host.js";
+
+describe("@schema", () => {
+  it("Creates a schema with no name", async () => {
+    const [program, { TestNamespace }, diagnostics] = await compileAndDiagnose<{
+      TestNamespace: Namespace;
+    }>(`
+      @schema
+      @test namespace TestNamespace {}
+    `);
+    expectDiagnosticEmpty(diagnostics);
+
+    const schema = getSchema(program, TestNamespace);
+
+    expect(schema?.type).toBe(TestNamespace);
+    expect(schema?.name).toBeUndefined();
+  });
+
+  it("Creates a schema with a specified name", async () => {
+    const [program, { TestNamespace }, diagnostics] = await compileAndDiagnose<{
+      TestNamespace: Namespace;
+    }>(`
+      @schema(#{name: "MySchema"})
+      @test namespace TestNamespace {}
+    `);
+    expectDiagnosticEmpty(diagnostics);
+
+    const schema = getSchema(program, TestNamespace);
+
+    expect(schema?.type).toBe(TestNamespace);
+    expect(schema?.name).toBe("MySchema");
+  });
+});

packages/graphql/test/test-host.ts

@@ -1,11 +1,14 @@
-import type { Diagnostic } from "@typespec/compiler";
+import type { Diagnostic, Program, Type } from "@typespec/compiler";
 import {
   createTestHost,
   createTestWrapper,
   expectDiagnosticEmpty,
   resolveVirtualPath,
 } from "@typespec/compiler/testing";
 import { ok } from "assert";
+import type { GraphQLSchema } from "graphql";
+import { buildSchema } from "graphql";
+import { expect } from "vitest";
 import type { GraphQLEmitterOptions } from "../src/lib.js";
 import { GraphqlTestLibrary } from "../src/testing/index.js";
 
@@ -15,21 +18,41 @@ export async function createGraphqlTestHost() {
   });
 }
 
+export interface GraphQLTestResult {
+  readonly graphQLSchema?: GraphQLSchema;
+  readonly graphQLOutput?: string;
+  readonly diagnostics: readonly Diagnostic[];
+}
+
 export async function createGraphqlTestRunner() {
   const host = await createGraphqlTestHost();
 
   return createTestWrapper(host, {
+    autoUsings: ["TypeSpec.GraphQL"],
     compilerOptions: {
       noEmit: false,
       emit: ["@typespec/graphql"],
     },
   });
 }
 
+export async function diagnose(code: string): Promise<readonly Diagnostic[]> {
+  const runner = await createGraphqlTestRunner();
+  return runner.diagnose(code);
+}
+
+export async function compileAndDiagnose<T extends Record<string, Type>>(
+  code: string,
+): Promise<[Program, T, readonly Diagnostic[]]> {
+  const runner = await createGraphqlTestRunner();
+  const [testTypes, diagnostics] = await runner.compileAndDiagnose(code);
+  return [runner.program, testTypes as T, diagnostics];
+}
+
 export async function emitWithDiagnostics(
   code: string,
   options: GraphQLEmitterOptions = {},
-): Promise<[string, readonly Diagnostic[]]> {
+): Promise<readonly GraphQLTestResult[]> {
   const runner = await createGraphqlTestRunner();
   const outputFile = resolveVirtualPath("schema.graphql");
   const compilerOptions = { ...options, "output-file": outputFile };
@@ -40,14 +63,47 @@ export async function emitWithDiagnostics(
       "@typespec/graphql": compilerOptions,
     },
   });
+
+  /**
+   * There doesn't appear to be a good way to hook into the emit process and get the GraphQLSchema
+   * that's produced by the emitter. So we're going to read the file that was emitted and parse it.
+   *
+   * This is the same way it's done in @typespec/openapi3:
+   * https://github.com/microsoft/typespec/blame/1cf8601d0f65f707926d58d56566fb0cb4d4f4ff/packages/openapi3/test/test-host.ts#L105
+   */
+
   const content = runner.fs.get(outputFile);
-  ok(content, "Expected to have found graphql output");
-  // Change this to whatever makes sense for the actual GraphQL emitter, probably a GraphQLSchemaRecord
-  return [content, diagnostics];
+  const schema = content
+    ? buildSchema(content, {
+        assumeValidSDL: true,
+        noLocation: true,
+      })
+    : undefined;
+
+  return [
+    {
+      graphQLSchema: schema,
+      graphQLOutput: content,
+      diagnostics,
+    },
+  ];
 }
 
-export async function emit(code: string, options: GraphQLEmitterOptions = {}): Promise<string> {
-  const [result, diagnostics] = await emitWithDiagnostics(code, options);
-  expectDiagnosticEmpty(diagnostics);
-  return result;
+export async function emitSingleSchemaWithDiagnostics(
+  code: string,
+  options: GraphQLEmitterOptions = {},
+): Promise<GraphQLTestResult> {
+  const schemaRecords = await emitWithDiagnostics(code, options);
+  expect(schemaRecords.length).toBe(1);
+  return schemaRecords[0];
+}
+
+export async function emitSingleSchema(
+  code: string,
+  options: GraphQLEmitterOptions = {},
+): Promise<string> {
+  const schemaRecord = await emitSingleSchemaWithDiagnostics(code, options);
+  expectDiagnosticEmpty(schemaRecord.diagnostics);
+  ok(schemaRecord.graphQLOutput, "Expected to have found graphql output");
+  return schemaRecord.graphQLOutput;
 }