fix(@angular-devkit/build-angular): identify plugin provided as string

Karma plugins could be provided either a string or object, but our detection
logic for code coverage plugin only covers the string case.

Fix #19571

(cherry picked from commit 48a278e)

Author: kyliau

packages/angular_devkit/build_angular/src/karma/code-coverage_spec.ts

@@ -169,4 +169,19 @@ describe('Karma Builder code coverage', () => {
     await run.stop();
 
   }, 120000);
+
+  it('is able to process coverage plugin provided as string', async () => {
+    host.replaceInFile('karma.conf.js', /plugins: \[.+?\]/s, `plugins: [
+      require('karma-jasmine'),
+      require('karma-chrome-launcher'),
+      require('karma-jasmine-html-reporter'),
+      require('@angular-devkit/build-angular/plugins/karma'),
+      'karma-coverage', // instead of require('karma-coverage')
+    ]`);
+    const run = await architect.scheduleTarget(karmaTargetSpec, { codeCoverage: true });
+
+    const {success} = await run.result;
+    expect(success).toBe(true);
+    await run.stop();
+  }, 120000);
 });

packages/angular_devkit/build_angular/src/webpack/plugins/karma.ts

@@ -93,8 +93,8 @@ const init: any = (config: any, emitter: any, customFileHandlers: any) => {
     config.plugins = config.plugins || [];
     config.reporters = config.reporters || [];
     const {plugins, reporters} = config;
-    const hasCoveragePlugin = plugins.some((p: {}) => 'reporter:coverage' in p);
-    const hasIstanbulPlugin = plugins.some((p: {}) => 'reporter:coverage-istanbul' in p);
+    const hasCoveragePlugin = plugins.some(isPlugin('karma-coverage', 'reporter:coverage'));
+    const hasIstanbulPlugin = plugins.some(isPlugin('karma-coverage-istanbul-reporter', 'reporter:coverage-istanbul'));
     const hasCoverageReporter = reporters.includes('coverage');
     const hasIstanbulReporter = reporters.includes('coverage-istanbul');
     if (hasCoveragePlugin && !hasCoverageReporter) {
@@ -336,6 +336,22 @@ function fallbackMiddleware() {
   };
 }
 
+/**
+ * Returns a function that returns true if the plugin identifier matches the
+ * `moduleId` or `pluginName`. A plugin identifier can be either a string or
+ * an object according to https://karma-runner.github.io/5.2/config/plugins.html
+ * @param moduleId name of the node module (e.g. karma-coverage)
+ * @param pluginName name of the karma plugin (e.g. reporter:coverage)
+ */
+function isPlugin(moduleId: string, pluginName: string) {
+  return (plugin: string|{}): boolean => {
+    if (typeof plugin === 'string') {
+      return plugin === moduleId;
+    }
+    return pluginName in plugin;
+  }
+}
+
 module.exports = {
   'framework:@angular-devkit/build-angular': ['factory', init],
   'reporter:@angular-devkit/build-angular--sourcemap-reporter': ['type', sourceMapReporter],