Updates tsp init to generate .gitignore file (#3751)

Fixes https://github.com/microsoft/typespec/issues/3262

This adds a new confirmation prompt to `tsp init` to generate a
.gitignore file. Defaults to yes (true).

---------

Co-authored-by: Christopher Radek <Christopher.Radek@microsoft.com>

.chronus/changes/init-git-ignore-2024-6-3-16-23-13.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/compiler"
+---
+
+Adds option to `tsp init` to generate .gitignore file

packages/compiler/src/init/init.ts

@@ -49,13 +49,19 @@ export async function initTypeSpecProject(
     // eslint-disable-next-line no-console
     console.log(template.description);
   }
-  const { name } = await prompts([
+  const { name, includeGitignore } = await prompts([
     {
       type: "text",
       name: "name",
       message: `Project name`,
       initial: folderName,
     },
+    {
+      type: "confirm",
+      name: "includeGitignore",
+      message: "Do you want to generate a .gitignore file?",
+      initial: true,
+    },
   ]);
 
   const libraries = await selectLibraries(template);
@@ -67,6 +73,7 @@ export async function initTypeSpecProject(
     directory,
     folderName,
     parameters,
+    includeGitignore,
   });
 
   await scaffoldNewProject(host, scaffoldingConfig);

packages/compiler/src/init/scaffold.ts

@@ -42,6 +42,11 @@ export interface ScaffoldingConfig {
    */
   libraries: InitTemplateLibrarySpec[];
 
+  /**
+   * Whether to generate a .gitignore file.
+   */
+  includeGitignore: boolean;
+
   /**
    * Custom parameters provided in the tempalates.
    */
@@ -67,6 +72,7 @@ export function makeScaffoldingConfig(
     directory: config.directory ?? "",
     folderName: config.folderName ?? "",
     parameters: config.parameters ?? {},
+    includeGitignore: config.includeGitignore ?? true,
     ...config,
   };
 }
@@ -81,6 +87,7 @@ export async function scaffoldNewProject(host: CompilerHost, config: Scaffolding
   await writePackageJson(host, config);
   await writeConfig(host, config);
   await writeMain(host, config);
+  await writeGitignore(host, config);
   await writeFiles(host, config);
 }
 
@@ -163,6 +170,25 @@ async function writeMain(host: CompilerHost, config: ScaffoldingConfig) {
   return host.writeFile(joinPaths(config.directory, "main.tsp"), await formatTypeSpec(content));
 }
 
+const defaultGitignore = `
+# MacOS
+.DS_Store
+
+# Default TypeSpec output
+tsp-output/
+dist/
+
+# Dependency directories
+node_modules/
+`.trim();
+async function writeGitignore(host: CompilerHost, config: ScaffoldingConfig) {
+  if (!config.includeGitignore || isFileSkipGeneration(".gitignore", config.template.files ?? [])) {
+    return;
+  }
+
+  return host.writeFile(joinPaths(config.directory, ".gitignore"), defaultGitignore);
+}
+
 async function writeFiles(host: CompilerHost, config: ScaffoldingConfig) {
   const templateContext = createFileTemplatingContext(config);
   if (!config.template.files) {

packages/compiler/test/init/init-template.test.ts

@@ -1,8 +1,12 @@
 import { deepStrictEqual, strictEqual } from "assert";
 import { beforeEach, describe, it } from "vitest";
 import { InitTemplate } from "../../src/init/init-template.js";
-import { makeScaffoldingConfig, scaffoldNewProject } from "../../src/init/scaffold.js";
-import { TestHost, createTestHost, resolveVirtualPath } from "../../src/testing/index.js";
+import {
+  makeScaffoldingConfig,
+  ScaffoldingConfig,
+  scaffoldNewProject,
+} from "../../src/init/scaffold.js";
+import { createTestHost, resolveVirtualPath, TestHost } from "../../src/testing/index.js";
 
 describe("compiler: init: templates", () => {
   let testHost: TestHost;
@@ -14,7 +18,10 @@ describe("compiler: init: templates", () => {
     return testHost.fs.get(resolveVirtualPath(path));
   }
 
-  async function runTemplate(overrides: Partial<InitTemplate>): Promise<void> {
+  async function runTemplate(
+    overrides: Partial<InitTemplate>,
+    configOverrides?: Partial<ScaffoldingConfig>
+  ): Promise<void> {
     const template: InitTemplate = {
       title: "Test Template",
       description: "This is only a test.",
@@ -26,6 +33,7 @@ describe("compiler: init: templates", () => {
         name: "test-template",
         folderName: "test-template",
         template,
+        ...configOverrides,
       })
     );
   }
@@ -45,4 +53,14 @@ describe("compiler: init: templates", () => {
       strictEqual(getOutputFile("main.tsp")!, 'import "foo";\nimport "bar";\n');
     });
   });
+
+  it("can generate .gitignore file by default", async () => {
+    await runTemplate({});
+    strictEqual(typeof getOutputFile(".gitignore"), "string");
+  });
+
+  it("can exclude .gitignore file", async () => {
+    await runTemplate({}, { includeGitignore: false });
+    strictEqual(typeof getOutputFile(".gitignore"), "undefined");
+  });
 });