fix(ng-add): do not throw if custom builder is used for "test" (#14203)

* No longer throws an exception if someone runs `ng-add` but uses a custom builder for the `test` target. Since theme files are not necessarily mandatory for running tests, we should just show a warning instead of exiting the whole `ng-add` process.

Fixes #14176

src/lib/schematics/ng-add/index.spec.ts

@@ -207,6 +207,36 @@ describe('ng-add schematic', () => {
     });
   });
 
+  describe('custom project builders', () => {
+
+    /** Overwrites a target builder for the workspace in the given tree */
+    function overwriteTargetBuilder(tree: Tree, targetName: string, newBuilder: string) {
+      const workspace = getWorkspace(tree);
+      const project = getProjectFromWorkspace(workspace);
+      const targetConfig = project.architect && project.architect[targetName] ||
+                           project.targets && project.targets[targetName];
+      targetConfig['builder'] = newBuilder;
+      tree.overwrite('/angular.json', JSON.stringify(workspace, null, 2));
+    }
+
+    it('should throw an error if the "build" target has been changed', () => {
+      overwriteTargetBuilder(appTree, 'build', 'thirdparty-builder');
+
+      expect(() => runner.runSchematic('ng-add-setup-project', {}, appTree))
+        .toThrowError(/not using the default builders.*build/);
+    });
+
+    it('should warn if the "test" target has been changed', () => {
+      overwriteTargetBuilder(appTree, 'test', 'thirdparty-test-builder');
+
+      spyOn(console, 'warn');
+      runner.runSchematic('ng-add-setup-project', {}, appTree);
+
+      expect(console.warn).toHaveBeenCalledWith(
+        jasmine.stringMatching(/not using the default builders.*cannot add the configured theme/));
+    });
+  });
+
   describe('theme files', () => {
 
     /** Path to the default prebuilt theme file that will be added when running ng-add. */

src/lib/schematics/ng-add/theming/theming.ts

@@ -8,36 +8,38 @@
 
 import {normalize} from '@angular-devkit/core';
 import {WorkspaceProject, WorkspaceSchema} from '@angular-devkit/core/src/workspace';
-import {SchematicsException, Tree} from '@angular-devkit/schematics';
+import {Tree} from '@angular-devkit/schematics';
 import {
   getProjectFromWorkspace,
   getProjectStyleFile,
   getProjectTargetOptions,
 } from '@angular/cdk/schematics';
 import {InsertChange} from '@schematics/angular/utility/change';
 import {getWorkspace} from '@schematics/angular/utility/config';
+import {bold, red, yellow} from 'chalk';
 import {join} from 'path';
 import {Schema} from '../schema';
-import {createCustomTheme} from './custom-theme';
-import {red, bold, yellow} from 'chalk';
+import {createCustomTheme} from './create-custom-theme';
 
 /** Path segment that can be found in paths that refer to a prebuilt theme. */
 const prebuiltThemePathSegment = '@angular/material/prebuilt-themes';
 
 /** Default file name of the custom theme that can be generated. */
 const defaultCustomThemeFilename = 'custom-theme.scss';
 
+/** Object that maps a CLI target to its default builder name. */
+const defaultTargetBuilders = {
+  build: '@angular-devkit/build-angular:browser',
+  test: '@angular-devkit/build-angular:karma',
+};
+
 /** Add pre-built styles to the main project style file. */
 export function addThemeToAppStyles(options: Schema): (host: Tree) => Tree {
   return function(host: Tree): Tree {
     const workspace = getWorkspace(host);
     const project = getProjectFromWorkspace(workspace, options.project);
     const themeName = options.theme || 'indigo-pink';
 
-    // Because the build setup for the Angular CLI can be changed so dramatically, we can't know
-    // where to generate anything if the project is not using the default config for build and test.
-    assertDefaultBuildersConfigured(project);
-
     if (themeName === 'custom') {
       insertCustomTheme(project, options.project, host, workspace);
     } else {
@@ -98,8 +100,12 @@ function insertPrebuiltTheme(project: WorkspaceProject, host: Tree, theme: strin
 }
 
 /** Adds a theming style entry to the given project target options. */
-function addThemeStyleToTarget(project: WorkspaceProject, targetName: string, host: Tree,
-                          assetPath: string, workspace: WorkspaceSchema) {
+function addThemeStyleToTarget(project: WorkspaceProject, targetName: 'test' | 'build', host: Tree,
+                               assetPath: string, workspace: WorkspaceSchema) {
+  // Do not update the builder options in case the target does not use the default CLI builder.
+  if (!validateDefaultTargetBuilder(project, targetName)) {
+    return;
+  }
 
   const targetOptions = getProjectTargetOptions(project, targetName);
 
@@ -135,25 +141,31 @@ function addThemeStyleToTarget(project: WorkspaceProject, targetName: string, ho
   host.overwrite('angular.json', JSON.stringify(workspace, null, 2));
 }
 
-/** Throws if the project is not using the default Angular devkit builders. */
-function assertDefaultBuildersConfigured(project: WorkspaceProject) {
-  checkProjectTargetBuilder(project, 'build', '@angular-devkit/build-angular:browser');
-  checkProjectTargetBuilder(project, 'test', '@angular-devkit/build-angular:karma');
-}
-
 /**
- * Checks if the specified project target is configured with the default builders which are
- * provided by the Angular CLI.
+ * Validates that the specified project target is configured with the default builders which are
+ * provided by the Angular CLI. If the configured builder does not match the default builder,
+ * this function can either throw or just show a warning.
  */
-function checkProjectTargetBuilder(project: WorkspaceProject, targetName: string,
-                            defaultBuilder: string) {
-
+function validateDefaultTargetBuilder(project: WorkspaceProject, targetName: 'build' | 'test') {
+  const defaultBuilder = defaultTargetBuilders[targetName];
   const targetConfig = project.architect && project.architect[targetName] ||
                        project.targets && project.targets[targetName];
-
-  if (!targetConfig || targetConfig['builder'] !== defaultBuilder) {
-    throw new SchematicsException(
-      `Your project is not using the default builders for "${targetName}". The Angular Material ` +
-      'schematics can only be used if the original builders from the Angular CLI are configured.');
+  const isDefaultBuilder = targetConfig && targetConfig['builder'] === defaultBuilder;
+
+  // Because the build setup for the Angular CLI can be customized by developers, we can't know
+  // where to put the theme file in the workspace configuration if custom builders are being
+  // used. In case the builder has been changed for the "build" target, we throw an error and
+  // exit because setting up a theme is a primary goal of `ng-add`. Otherwise if just the "test"
+  // builder has been changed, we warn because a theme is not mandatory for running tests
+  // with Material. See: https://github.com/angular/material2/issues/14176
+  if (!isDefaultBuilder && targetName === 'build') {
+    throw new Error(`Your project is not using the default builders for "${targetName}". The ` +
+      `Angular Material schematics cannot add a theme to the workspace configuration if the ` +
+      `builder has been changed. Exiting..`);
+  } else if (!isDefaultBuilder) {
+    console.warn(`Your project is not using the default builders for "${targetName}". This ` +
+      `means that we cannot add the configured theme to the "${targetName}" target.`);
   }
+
+  return isDefaultBuilder;
 }