tsp init to automatically run tsp install (#5824)

Close #5766.

Per discussion from #5796 and
Teams, this PR:

- automatically runs `tsp install` as part of `tsp init` if the template
created a `package.json` file
- skips running or mentioning `tsp install` if `package.json` is not
created
- does NOT provide a flag for opt in/out
- does NOT provide a confirmation dialogue


![image](https://github.com/user-attachments/assets/53a656d8-c795-419b-92a2-034883a94bcc)

.chronus/changes/tspInitUpdate-2025-0-31-9-41-10.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/compiler"
+---
+
+`tsp init` will not automatically run `tsp install` if a `package.json` file is created.

packages/compiler/src/init/init.ts

@@ -2,6 +2,8 @@ import { readdir } from "fs/promises";
 import pc from "picocolors";
 import prompts from "prompts";
 import * as semver from "semver";
+import { CliCompilerHost } from "../core/cli/types.js";
+import { installTypeSpecDependencies } from "../core/install.js";
 import { createDiagnostic } from "../core/messages.js";
 import { getBaseFileName, getDirectoryPath } from "../core/path-utils.js";
 import { CompilerHost, Diagnostic, NoTarget, SourceFile } from "../core/types.js";
@@ -10,15 +12,20 @@ import { readUrlOrPath } from "../utils/misc.js";
 import { getTypeSpecCoreTemplates } from "./core-templates.js";
 import { validateTemplateDefinitions, ValidationResult } from "./init-template-validate.js";
 import { EmitterTemplate, InitTemplate, InitTemplateLibrarySpec } from "./init-template.js";
-import { makeScaffoldingConfig, normalizeLibrary, scaffoldNewProject } from "./scaffold.js";
+import {
+  isFileSkipGeneration,
+  makeScaffoldingConfig,
+  normalizeLibrary,
+  scaffoldNewProject,
+} from "./scaffold.js";
 
 export interface InitTypeSpecProjectOptions {
   templatesUrl?: string;
   template?: string;
 }
 
 export async function initTypeSpecProject(
-  host: CompilerHost,
+  host: CliCompilerHost,
   directory: string,
   options: InitTypeSpecProjectOptions = {},
 ) {
@@ -80,15 +87,23 @@ export async function initTypeSpecProject(
   });
 
   await scaffoldNewProject(host, scaffoldingConfig);
+  const projectJsonCreated = !isFileSkipGeneration(
+    "package.json",
+    scaffoldingConfig.template.files ?? [],
+  );
 
   // eslint-disable-next-line no-console
   console.log("");
-  // eslint-disable-next-line no-console
-  console.log("TypeSpec init completed. You can run `tsp install` now to install dependencies.");
 
   // eslint-disable-next-line no-console
   console.log(pc.green("Project created successfully."));
 
+  if (projectJsonCreated) {
+    // eslint-disable-next-line no-console
+    console.log(pc.green("Installing dependencies..."));
+    await installTypeSpecDependencies(host, directory);
+  }
+
   if (Object.values(emitters).some((emitter) => emitter.message !== undefined)) {
     // eslint-disable-next-line no-console
     console.log(pc.yellow("\nPlease review the following messages from emitters:"));

packages/compiler/src/init/scaffold.ts

@@ -97,7 +97,7 @@ export async function scaffoldNewProject(host: CompilerHost, config: Scaffolding
   await writeFiles(host, config);
 }
 
-function isFileSkipGeneration(fileName: string, files: InitTemplateFile[]): boolean {
+export function isFileSkipGeneration(fileName: string, files: InitTemplateFile[]): boolean {
   for (const file of files) {
     if (file.destination === fileName) {
       return file.skipGeneration ?? false;