feat(@angular/cli): autodetect default package manager

packages/angular/cli/commands/add-impl.ts

@@ -12,7 +12,7 @@ import { NodePackageDoesNotSupportSchematics } from '@angular-devkit/schematics/
 import { Arguments } from '../models/interface';
 import { SchematicCommand } from '../models/schematic-command';
 import { NpmInstall } from '../tasks/npm-install';
-import { getPackageManager } from '../utilities/config';
+import { getPackageManager } from '../utilities/package-manager';
 import { Schema as AddCommandSchema } from './add';
 
 export class AddCommand extends SchematicCommand<AddCommandSchema> {
@@ -28,7 +28,7 @@ export class AddCommand extends SchematicCommand<AddCommandSchema> {
       return 1;
     }
 
-    const packageManager = getPackageManager();
+    const packageManager = getPackageManager(this.workspace.root);
 
     const npmInstall: NpmInstall = require('../tasks/npm-install').default;
 

packages/angular/cli/models/schematic-command.ts

@@ -38,13 +38,13 @@ import * as inquirer from 'inquirer';
 import * as systemPath from 'path';
 import { WorkspaceLoader } from '../models/workspace-loader';
 import {
-  getPackageManager,
   getProjectByCwd,
   getSchematicDefaults,
   getWorkspace,
   getWorkspaceRaw,
 } from '../utilities/config';
 import { parseJsonSchemaToOptions } from '../utilities/json-schema';
+import { getPackageManager } from '../utilities/package-manager';
 import { BaseCommandOptions, Command } from './command';
 import { Arguments, CommandContext, CommandDescription, Option } from './interface';
 import { parseArguments, parseFreeFormArguments } from './parser';
@@ -255,7 +255,7 @@ export abstract class SchematicCommand<
         {
           force,
           dryRun,
-          packageManager: getPackageManager(),
+          packageManager: getPackageManager(this.workspace.root),
           root: normalize(this.workspace.root),
         },
     );

packages/angular/cli/utilities/config.ts

@@ -151,7 +151,7 @@ export function getProjectByCwd(workspace: experimental.workspace.Workspace): st
   }
 }
 
-export function getPackageManager(): string {
+export function getConfiguredPackageManager(): string | null {
   let workspace = getWorkspace('local');
 
   if (workspace) {
@@ -186,7 +186,7 @@ export function getPackageManager(): string {
     }
   }
 
-  return 'npm';
+  return null;
 }
 
 export function migrateLegacyGlobalConfig(): boolean {

packages/angular/cli/utilities/package-manager.ts

@@ -0,0 +1,58 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import { execSync } from 'child_process';
+import { existsSync } from 'fs';
+import { join } from 'path';
+import { getConfiguredPackageManager } from './config';
+
+
+export function supportsYarn(): boolean {
+  try {
+    execSync('yarn --version');
+
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export function supportsNpm(): boolean {
+  try {
+    execSync('npm --version');
+
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export function getPackageManager(root: string): string {
+  let packageManager = getConfiguredPackageManager();
+  if (packageManager) {
+    return packageManager;
+  }
+
+  const hasYarn = supportsYarn();
+  const hasYarnLock = existsSync(join(root, 'yarn.lock'));
+  const hasNpm = supportsNpm();
+  const hasNpmLock = existsSync(join(root, 'package-lock.json'));
+
+  if (hasYarn && hasYarnLock && !hasNpmLock) {
+    packageManager = 'yarn';
+  } else if (hasNpm && hasNpmLock && !hasYarnLock) {
+    packageManager = 'npm';
+  } else if (hasYarn && !hasNpm) {
+    packageManager = 'yarn';
+  } else if (hasNpm && !hasYarn) {
+    packageManager = 'npm';
+  }
+
+  // TODO: This should eventually inform the user of ambiguous package manager usage.
+  //       Potentially with a prompt to choose and optionally set as the default.
+  return packageManager || 'npm';
+}