fix(bazel): Respect existing angular installation (#27495)

If user has already installed Angular, Bazel should fetch the same
version. Otherwise, user will see an error in the post-install step
that performs version check.

PR Close #27495

packages/bazel/src/schematics/bazel-workspace/index.ts

@@ -15,6 +15,31 @@ import {validateProjectName} from '@schematics/angular/utility/validation';
 
 import {Schema as BazelWorkspaceOptions} from './schema';
 
+/**
+ * Look for package.json file for @angular/core in node_modules and extract its
+ * version.
+ */
+function findAngularVersion(options: BazelWorkspaceOptions, host: Tree): string|null {
+  // Need to look in multiple locations because we could be working in a subtree.
+  const candidates = [
+    'node_modules/@angular/core/package.json',
+    `${options.name}/node_modules/@angular/core/package.json`,
+  ];
+  for (const candidate of candidates) {
+    if (host.exists(candidate)) {
+      try {
+        const packageJson = JSON.parse(host.read(candidate).toString());
+        if (packageJson.name === '@angular/core' && packageJson.version) {
+          return packageJson.version;
+        }
+      } catch {
+      }
+    }
+  }
+  return null;
+}
+
+
 export default function(options: BazelWorkspaceOptions): Rule {
   return (host: Tree, context: SchematicContext) => {
     if (!options.name) {
@@ -29,8 +54,11 @@ export default function(options: BazelWorkspaceOptions): Rule {
     }
     const appDir = `${newProjectRoot}/${options.name}`;
 
+    // If user already has angular installed, Bazel should use that version
+    const existingAngularVersion = findAngularVersion(options, host);
+
     const workspaceVersions = {
-      'ANGULAR_VERSION': '7.1.0',
+      'ANGULAR_VERSION': existingAngularVersion || '7.1.1',
       'RULES_SASS_VERSION': '1.14.1',
       'RXJS_VERSION': '6.3.3',
     };

packages/bazel/src/schematics/bazel-workspace/index_spec.ts

@@ -6,7 +6,8 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {SchematicTestRunner} from '@angular-devkit/schematics/testing';
+import {HostTree} from '@angular-devkit/schematics';
+import {SchematicTestRunner, UnitTestTree} from '@angular-devkit/schematics/testing';
 
 describe('Bazel-workspace Schematic', () => {
   const schematicRunner =
@@ -27,6 +28,19 @@ describe('Bazel-workspace Schematic', () => {
     expect(files).toContain('/demo/yarn.lock');
   });
 
+  it('should find existing Angular version', () => {
+    let host = new UnitTestTree(new HostTree);
+    host.create('/demo/node_modules/@angular/core/package.json', JSON.stringify({
+      name: '@angular/core',
+      version: '6.6.6',
+    }));
+    const options = {...defaultOptions};
+    host = schematicRunner.runSchematic('bazel-workspace', options, host);
+    expect(host.files).toContain('/demo/WORKSPACE');
+    const workspace = host.readContent('/demo/WORKSPACE');
+    expect(workspace).toMatch('ANGULAR_VERSION = "6.6.6"');
+  });
+
   describe('WORKSPACE', () => {
     it('should contain project name', () => {
       const options = {...defaultOptions};