Migrate init templates to createTester API and update ESLint to latest standard

.chronus/changes/copilot-update-init-templates-testing-framework-2026-1-5-20-11-37.md

@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/compiler"
+---
+
+Update init templates to use createTester API and modern ESLint configuration

packages/compiler/templates/__snapshots__/emitter-ts/eslint.config.js

@@ -1,11 +1,20 @@
 // @ts-check
 import eslint from "@eslint/js";
+import { defineConfig } from "eslint/config";
 import tsEslint from "typescript-eslint";
 
-export default tsEslint.config(
+export default defineConfig(
   {
     ignores: ["**/dist/**/*", "**/.temp/**/*"],
   },
   eslint.configs.recommended,
   ...tsEslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-unused-vars": [
+        "warn",
+        { varsIgnorePattern: "^_", argsIgnorePattern: "^_" },
+      ],
+    },
+  },
 );

packages/compiler/templates/__snapshots__/emitter-ts/package.json

@@ -18,8 +18,7 @@
   },
   "devDependencies": {
     "@types/node": "latest",
-    "@typescript-eslint/eslint-plugin": "^8.15.0",
-    "@typescript-eslint/parser": "^8.15.0",
+    "typescript-eslint": "^8.49.0",
     "eslint": "^9.15.0",
     "@typespec/compiler": "latest",
     "typescript": "^5.3.3",

packages/compiler/templates/__snapshots__/emitter-ts/test/test-host.ts

@@ -1,43 +1,16 @@
 import { Diagnostic, resolvePath } from "@typespec/compiler";
-import {
-  createTestHost,
-  createTestWrapper,
-  expectDiagnosticEmpty,
-} from "@typespec/compiler/testing";
-import { EmitterTsTestLibrary } from "../src/testing/index.js";
+import { expectDiagnosticEmpty } from "@typespec/compiler/testing";
+import { createTester } from "@typespec/compiler/testing";
 
-export async function createEmitterTsTestHost() {
-  return createTestHost({
-    libraries: [EmitterTsTestLibrary],
-  });
-}
-
-export async function createEmitterTsTestRunner() {
-  const host = await createEmitterTsTestHost();
-
-  return createTestWrapper(host, {
-    compilerOptions: {
-      noEmit: false,
-      emit: ["emitter-ts"],
-    },
-  });
-}
+export const Tester = createTester(resolvePath(import.meta.dirname, "../.."), {
+  libraries: ["emitter-ts"],
+}).emit("emitter-ts");
 
 export async function emitWithDiagnostics(
   code: string
 ): Promise<[Record<string, string>, readonly Diagnostic[]]> {
-  const runner = await createEmitterTsTestRunner();
-  await runner.compileAndDiagnose(code, {
-    outputDir: "tsp-output",
-  });
-  const emitterOutputDir = "./tsp-output/emitter-ts";
-  const files = await runner.program.host.readDir(emitterOutputDir);
-
-  const result: Record<string, string> = {};
-  for (const file of files) {
-    result[file] = (await runner.program.host.readFile(resolvePath(emitterOutputDir, file))).text;
-  }
-  return [result, runner.program.diagnostics];
+  const [{ outputs }, diagnostics] = await Tester.compileAndDiagnose(code);
+  return [outputs, diagnostics];
 }
 
 export async function emit(code: string): Promise<Record<string, string>> {

packages/compiler/templates/__snapshots__/library-ts/eslint.config.js

@@ -1,11 +1,20 @@
 // @ts-check
 import eslint from "@eslint/js";
+import { defineConfig } from "eslint/config";
 import tsEslint from "typescript-eslint";
 
-export default tsEslint.config(
+export default defineConfig(
   {
     ignores: ["**/dist/**/*", "**/.temp/**/*"],
   },
   eslint.configs.recommended,
   ...tsEslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-unused-vars": [
+        "warn",
+        { varsIgnorePattern: "^_", argsIgnorePattern: "^_" },
+      ],
+    },
+  },
 );

packages/compiler/templates/__snapshots__/library-ts/package.json

@@ -19,8 +19,7 @@
   },
   "devDependencies": {
     "@types/node": "latest",
-    "@typescript-eslint/eslint-plugin": "^8.15.0",
-    "@typescript-eslint/parser": "^8.15.0",
+    "typescript-eslint": "^8.49.0",
     "@typespec/compiler": "latest",
     "@typespec/library-linter": "latest",
     "eslint": "^9.15.0",

packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts

@@ -1,29 +1,25 @@
 import { strictEqual } from "node:assert";
-import { describe, it, beforeEach } from "node:test";
-import type { Operation } from "@typespec/compiler";
-import { BasicTestRunner, expectDiagnostics, extractCursor } from "@typespec/compiler/testing";
+import { describe, it } from "node:test";
+import type { Operation, Program } from "@typespec/compiler";
+import { expectDiagnostics } from "@typespec/compiler/testing";
 import { getAlternateName } from "../src/decorators.js";
-import { createLibraryTsTestRunner } from "./test-host.js";
+import { Tester } from "./test-host.js";
 
 describe("decorators", () => {
-  let runner: BasicTestRunner;
-
-  beforeEach(async () => {
-    runner = await createLibraryTsTestRunner();
-  })
-
   describe("@alternateName", () => {
     it("set alternate name on operation", async () => {
-      const { test } = (await runner.compile(
-        `@alternateName("bar") @test op test(): void;`
-      )) as { test: Operation };
-      strictEqual(getAlternateName(runner.program, test), "bar");
+      const { test, program } = (await Tester.compile(`
+        using LibraryTs;
+        @alternateName("bar") @test op test(): void;
+      `)) as unknown as { test: Operation; program: Program };
+      strictEqual(getAlternateName(program, test), "bar");
     });
 
     it("emit diagnostic if not used on an operation", async () => {
-      const diagnostics = await runner.diagnose(
-        `@alternateName("bar") model Test {}`
-      );
+      const diagnostics = await Tester.diagnose(`
+        using LibraryTs;
+        @alternateName("bar") model Test {}
+      `);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "decorator-wrong-target",
@@ -33,15 +29,14 @@ describe("decorators", () => {
 
 
     it("emit diagnostic if using banned name", async () => {
-      const {pos, source} = extractCursor(`@alternateName(┆"banned") op test(): void;`)
-      const diagnostics = await runner.diagnose(
-        source
-      );
+      const diagnostics = await Tester.diagnose(`
+        using LibraryTs;
+        @alternateName("banned") op test(): void;
+      `);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "library-ts/banned-alternate-name",
-        message: `Banned alternate name "banned".`,
-        pos: pos + runner.autoCodeOffset
+        message: `Banned alternate name "banned".`
       })
     });
   });

packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts

@@ -1,17 +1,7 @@
-import { createTestHost, createTestWrapper } from "@typespec/compiler/testing";
-import { LibraryTsTestLibrary } from "../src/testing/index.js";
+import { resolvePath } from "@typespec/compiler";
+import { createTester } from "@typespec/compiler/testing";
 
-export async function createLibraryTsTestHost() {
-  return createTestHost({
-    libraries: [LibraryTsTestLibrary],
-  });
-}
-
-export async function createLibraryTsTestRunner() {
-  const host = await createLibraryTsTestHost();
-
-  return createTestWrapper(host, {
-    autoUsings: ["LibraryTs"]
-  });
-}
+export const Tester = createTester(resolvePath(import.meta.dirname, "../.."), {
+  libraries: ["library-ts"],
+}).import("library-ts");
 

packages/compiler/templates/emitter-ts/eslint.config.js

@@ -1,11 +1,20 @@
 // @ts-check
 import eslint from "@eslint/js";
+import { defineConfig } from "eslint/config";
 import tsEslint from "typescript-eslint";
 
-export default tsEslint.config(
+export default defineConfig(
   {
     ignores: ["**/dist/**/*", "**/.temp/**/*"],
   },
   eslint.configs.recommended,
   ...tsEslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-unused-vars": [
+        "warn",
+        { varsIgnorePattern: "^_", argsIgnorePattern: "^_" },
+      ],
+    },
+  },
 );

packages/compiler/templates/emitter-ts/package.json

@@ -18,8 +18,7 @@
   },
   "devDependencies": {
     "@types/node": "latest",
-    "@typescript-eslint/eslint-plugin": "^8.15.0",
-    "@typescript-eslint/parser": "^8.15.0",
+    "typescript-eslint": "^8.49.0",
     "eslint": "^9.15.0",
     "@typespec/compiler": "latest",
     "typescript": "^5.3.3",

packages/compiler/templates/emitter-ts/test/test-host.ts.mu

@@ -1,43 +1,16 @@
 import { Diagnostic, resolvePath } from "@typespec/compiler";
-import {
-  createTestHost,
-  createTestWrapper,
-  expectDiagnosticEmpty,
-} from "@typespec/compiler/testing";
-import { {{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestLibrary } from "../src/testing/index.js";
+import { expectDiagnosticEmpty } from "@typespec/compiler/testing";
+import { createTester } from "@typespec/compiler/testing";
 
-export async function create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestHost() {
-  return createTestHost({
-    libraries: [{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestLibrary],
-  });
-}
-
-export async function create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestRunner() {
-  const host = await create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestHost();
-
-  return createTestWrapper(host, {
-    compilerOptions: {
-      noEmit: false,
-      emit: ["{{name}}"],
-    },
-  });
-}
+export const Tester = createTester(resolvePath(import.meta.dirname, "../.."), {
+  libraries: ["{{name}}"],
+}).emit("{{name}}");
 
 export async function emitWithDiagnostics(
   code: string
 ): Promise<[Record<string, string>, readonly Diagnostic[]]> {
-  const runner = await create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestRunner();
-  await runner.compileAndDiagnose(code, {
-    outputDir: "tsp-output",
-  });
-  const emitterOutputDir = "./tsp-output/{{name}}";
-  const files = await runner.program.host.readDir(emitterOutputDir);
-
-  const result: Record<string, string> = {};
-  for (const file of files) {
-    result[file] = (await runner.program.host.readFile(resolvePath(emitterOutputDir, file))).text;
-  }
-  return [result, runner.program.diagnostics];
+  const [{ outputs }, diagnostics] = await Tester.compileAndDiagnose(code);
+  return [outputs, diagnostics];
 }
 
 export async function emit(code: string): Promise<Record<string, string>> {

packages/compiler/templates/library-ts/eslint.config.js

@@ -1,11 +1,20 @@
 // @ts-check
 import eslint from "@eslint/js";
+import { defineConfig } from "eslint/config";
 import tsEslint from "typescript-eslint";
 
-export default tsEslint.config(
+export default defineConfig(
   {
     ignores: ["**/dist/**/*", "**/.temp/**/*"],
   },
   eslint.configs.recommended,
   ...tsEslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-unused-vars": [
+        "warn",
+        { varsIgnorePattern: "^_", argsIgnorePattern: "^_" },
+      ],
+    },
+  },
 );

packages/compiler/templates/library-ts/package.json

@@ -19,8 +19,7 @@
   },
   "devDependencies": {
     "@types/node": "latest",
-    "@typescript-eslint/eslint-plugin": "^8.15.0",
-    "@typescript-eslint/parser": "^8.15.0",
+    "typescript-eslint": "^8.49.0",
     "@typespec/compiler": "latest",
     "@typespec/library-linter": "latest",
     "eslint": "^9.15.0",

packages/compiler/templates/library-ts/test/decorators.test.ts.mu

@@ -1,29 +1,25 @@
 import { strictEqual } from "node:assert";
-import { describe, it, beforeEach } from "node:test";
-import type { Operation } from "@typespec/compiler";
-import { BasicTestRunner, expectDiagnostics, extractCursor } from "@typespec/compiler/testing";
+import { describe, it } from "node:test";
+import type { Operation, Program } from "@typespec/compiler";
+import { expectDiagnostics } from "@typespec/compiler/testing";
 import { getAlternateName } from "../src/decorators.js";
-import { create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestRunner } from "./test-host.js";
+import { Tester } from "./test-host.js";
 
 describe("decorators", () => {
-  let runner: BasicTestRunner;
-
-  beforeEach(async () => {
-    runner = await create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestRunner();
-  })
-
   describe("@alternateName", () => {
     it("set alternate name on operation", async () => {
-      const { test } = (await runner.compile(
-        `@alternateName("bar") @test op test(): void;`
-      )) as { test: Operation };
-      strictEqual(getAlternateName(runner.program, test), "bar");
+      const { test, program } = (await Tester.compile(`
+        using {{#casing.pascalCase}}{{name}}{{/casing.pascalCase}};
+        @alternateName("bar") @test op test(): void;
+      `)) as unknown as { test: Operation; program: Program };
+      strictEqual(getAlternateName(program, test), "bar");
     });
 
     it("emit diagnostic if not used on an operation", async () => {
-      const diagnostics = await runner.diagnose(
-        `@alternateName("bar") model Test {}`
-      );
+      const diagnostics = await Tester.diagnose(`
+        using {{#casing.pascalCase}}{{name}}{{/casing.pascalCase}};
+        @alternateName("bar") model Test {}
+      `);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "decorator-wrong-target",
@@ -33,15 +29,14 @@ describe("decorators", () => {
 
 
     it("emit diagnostic if using banned name", async () => {
-      const {pos, source} = extractCursor(`@alternateName(┆"banned") op test(): void;`)
-      const diagnostics = await runner.diagnose(
-        source
-      );
+      const diagnostics = await Tester.diagnose(`
+        using {{#casing.pascalCase}}{{name}}{{/casing.pascalCase}};
+        @alternateName("banned") op test(): void;
+      `);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "{{name}}/banned-alternate-name",
-        message: `Banned alternate name "banned".`,
-        pos: pos + runner.autoCodeOffset
+        message: `Banned alternate name "banned".`
       })
     });
   });