In generator-aspnetcore-spa, use 'yarn' (if available) instead of 'npm' to restore dependencies because it's > 10x faster

Author: SteveSandersonMS

templates/package-builder/src/yeoman/app/index.ts

@@ -2,6 +2,7 @@ import * as path from 'path';
 import * as yeoman from 'yeoman-generator';
 import * as uuid from 'node-uuid';
 import * as glob from 'glob';
+import npmWhich = require('npm-which');
 const yosay = require('yosay');
 const toPascalCase = require('to-pascal-case');
 
@@ -80,6 +81,15 @@ class MyGenerator extends yeoman.Base {
     }
 
     installingDeps() {
+        // If available, restore dependencies using Yarn instead of NPM
+        const yarnPath = getPathToExecutable('yarn');
+        if (!!yarnPath) {
+            this.log('Will restore NPM dependencies using \'yarn\' installed at ' + yarnPath);
+            this.npmInstall = (pkgs, options, cb) => {
+                return (this as any).runInstall(yarnPath, pkgs, options, cb);
+            };
+        }
+
         this.installDependencies({
             npm: true,
             bower: false,
@@ -92,5 +102,13 @@ class MyGenerator extends yeoman.Base {
     }
 }
 
+function getPathToExecutable(executableName: string) {
+    try {
+        return npmWhich(__dirname).sync(executableName);
+    } catch(ex) {
+        return null;
+    }
+}
+
 declare var module: any;
 (module).exports = MyGenerator;

templates/package-builder/src/yeoman/package.json

@@ -1,6 +1,6 @@
 {
   "name": "generator-aspnetcore-spa",
-  "version": "0.4.0",
+  "version": "0.4.1",
   "description": "Single-Page App templates for ASP.NET Core",
   "author": "Microsoft",
   "license": "Apache-2.0",
@@ -20,6 +20,7 @@
   "dependencies": {
     "glob": "^7.0.3",
     "node-uuid": "^1.4.7",
+    "npm-which": "^3.0.1",
     "to-pascal-case": "^1.0.0",
     "yeoman-generator": "^0.20.2",
     "yeoman-option-or-prompt": "^1.0.2",

templates/package-builder/typings/npm-which/npm-which.d.ts

@@ -0,0 +1,8 @@
+declare module 'npm-which' {
+    interface NpmWhichContext {
+        sync(executableName: string): string;
+    }
+
+    function defaultFunction(rootDir: string) : NpmWhichContext;
+    export = defaultFunction;
+}