fix(@angular/cli): update NPM 7 guidance

Update NPM 7 behavior based on #19957 (comment)

Author: clydin

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

@@ -22,8 +22,6 @@ export class NewCommand extends SchematicCommand<NewCommandSchema> {
   }
 
   public async run(options: NewCommandSchema & Arguments) {
-    await ensureCompatibleNpm(this.context.root);
-
     // Register the version of the CLI in the registry.
     const packageJson = require('../package.json');
     const version = packageJson.version;

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

@@ -30,7 +30,7 @@ import * as systemPath from 'path';
 import { colors } from '../utilities/color';
 import { getProjectByCwd, getSchematicDefaults, getWorkspace } from '../utilities/config';
 import { parseJsonSchemaToOptions } from '../utilities/json-schema';
-import { getPackageManager } from '../utilities/package-manager';
+import { ensureCompatibleNpm, getPackageManager } from '../utilities/package-manager';
 import { isTTY } from '../utilities/tty';
 import { isPackageNameSafeForAnalytics } from './analytics';
 import { BaseCommandOptions, Command } from './command';
@@ -503,6 +503,16 @@ export abstract class SchematicCommand<
       }
     });
 
+    // Temporary compatibility check for NPM 7
+    if (collectionName === '@schematics/angular' && schematicName === 'ng-new') {
+      if (
+        !input.skipInstall &&
+        (input.packageManager === undefined || input.packageManager === 'npm')
+      ) {
+        await ensureCompatibleNpm(this.context.root);
+      }
+    }
+
     return new Promise<number | void>(resolve => {
       workflow
         .execute({

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

@@ -66,16 +66,18 @@ export async function ensureCompatibleNpm(root: string): Promise<void> {
   try {
     const version = execSync('npm --version', {encoding: 'utf8', stdio: 'pipe'}).trim();
     const major = Number(version.match(/^(\d+)\./)?.[1]);
-    if (major === 6) {
+    if (major <= 6) {
       return;
     }
 
     // tslint:disable-next-line: no-console
     console.error(
-      `npm version ${version} detected.\n` +
-      'The Angular CLI currently requires npm version 6.\n\n' +
-      'Please install a compatible version to proceed (`npm install --global npm@6`).\n',
+      `npm version ${version} detected. The Angular CLI temporarily requires npm version 6 while upstream issues are addressed.\n\n` +
+      'Please install a compatible version to proceed (`npm install --global npm@6`).\n' +
+      'For additional information and alternative workarounds, please see ' +
+      'https://github.com/angular/angular-cli/issues/19957#issuecomment-775407654',
     );
+
     process.exit(3);
   } catch {
     // npm is not installed

tests/legacy-cli/e2e/tests/misc/npm-7.ts

@@ -1,8 +1,9 @@
+import { rimraf } from '../../utils/fs';
 import { getActivePackageManager } from '../../utils/packages';
 import { ng, npm } from '../../utils/process';
 import { expectToFail } from '../../utils/utils';
 
-const errorText = 'The Angular CLI currently requires npm version 6.';
+const errorText = 'The Angular CLI temporarily requires npm version 6';
 
 export default async function() {
   // Only relevant with npm as a package manager
@@ -32,14 +33,42 @@ export default async function() {
       throw new Error('ng update expected to show npm version error.');
     }
 
+    // Ensure `ng build` executes successfully
+    const { stderr: stderrBuild } = await ng('build');
+    if (stderrBuild.includes(errorText)) {
+      throw new Error('ng build expected to not show npm version error.');
+    }
+
     // Ensure `ng new` exits and shows npm error
     // Must be outside the project for `ng new`
     process.chdir('..');
     const { message: stderrNew } = await expectToFail(() => ng('new'));
     if (!stderrNew.includes(errorText)) {
       throw new Error('ng new expected to show npm version error.');
     }
+
+    // Ensure `ng new --package-manager=npm` exits and shows npm error
+    const { message: stderrNewNpm } = await expectToFail(() => ng('new', '--package-manager=npm'));
+    if (!stderrNewNpm.includes(errorText)) {
+      throw new Error('ng new expected to show npm version error.');
+    }
+
+    // Ensure `ng new --skip-install` executes successfully
+    const { stderr: stderrNewSkipInstall } = await ng('new', 'npm-seven-skip', '--skip-install');
+    if (stderrNewSkipInstall.includes(errorText)) {
+      throw new Error('ng new --skip-install expected to not show npm version error.');
+    }
+
+    // Ensure `ng new --package-manager=yarn` executes successfully
+    const { stderr: stderrNewYarn } = await ng('new', 'npm-seven-yarn', '--package-manager=yarn');
+    if (stderrNewYarn.includes(errorText)) {
+      throw new Error('ng new --package-manager=yarn expected to not show npm version error.');
+    }
   } finally {
+    // Cleanup extra test projects
+    await rimraf('npm-seven-skip');
+    await rimraf('npm-seven-yarn');
+
     // Change directory back
     process.chdir(currentDirectory);