fix(@angular-devkit/build-angular): transform remapped sourcemap into a plain object

packages/angular_devkit/build_angular/src/babel/webpack-loader.ts

@@ -240,10 +240,16 @@ export default custom<AngularCustomOptions>(() => {
         // `@ampproject/remapping` source map objects but both are compatible with Webpack.
         // This method for merging is used because it provides more accurate output
         // and is faster while using less memory.
-        result.map = remapping(
-          [result.map as SourceMapInput, inputSourceMap as SourceMapInput],
-          () => null,
-        ) as typeof result.map;
+        result.map = {
+          // Convert the SourceMap back to simple plain object.
+          // This is needed because otherwise code-coverage will fail with `don't know how to turn this value into a node`
+          // Which is throw by Babel when it is invoked again from `istanbul-lib-instrument`.
+          // https://github.com/babel/babel/blob/780aa48d2a34dc55f556843074b6aed45e7eabeb/packages/babel-types/src/converters/valueToNode.ts#L115-L130
+          ...(remapping(
+            [result.map as SourceMapInput, inputSourceMap as SourceMapInput],
+            () => null,
+          ) as typeof result.map),
+        };
       }
 
       return result;

packages/angular_devkit/build_angular/src/builders/karma/tests/behavior/code-coverage_spec.ts

@@ -0,0 +1,89 @@
+/**
+ * @license
+ * Copyright Google LLC 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 { last, tap } from 'rxjs/operators';
+import { promisify } from 'util';
+import { execute } from '../../index';
+import { BASE_OPTIONS, KARMA_BUILDER_INFO, describeBuilder } from '../setup';
+
+// In each of the test below we'll have to call setTimeout to wait for the coverage
+// analysis to be done. This is because karma-coverage performs the analysis
+// asynchronously but the promise that it returns is not awaited by Karma.
+// Coverage analysis begins when onRunComplete() is invoked, and output files
+// are subsequently written to disk. For more information, see
+// https://github.com/karma-runner/karma-coverage/blob/32acafa90ed621abd1df730edb44ae55a4009c2c/lib/reporter.js#L221
+
+const setTimeoutPromise = promisify(setTimeout);
+const coveragePath = 'coverage/lcov.info';
+
+describeBuilder(execute, KARMA_BUILDER_INFO, (harness) => {
+  describe('Behavior: "codeCoverage"', () => {
+    it('should generate coverage report when file was previously processed by Babel', async () => {
+      // Force Babel transformation.
+      await harness.appendToFile('src/app/app.component.ts', '// async');
+
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+        codeCoverage: true,
+      });
+
+      const { result } = await harness.executeOnce();
+      expect(result?.success).toBeTrue();
+
+      await setTimeoutPromise(1000);
+      harness.expectFile(coveragePath).toExist();
+    });
+
+    it('should exit with non-zero code when coverage is below threshold', async () => {
+      await harness.modifyFile('karma.conf.js', (content) =>
+        content.replace(
+          'coverageReporter: {',
+          `coverageReporter: {
+             check: {
+               global: {
+                 statements: 100,
+                 lines: 100,
+                 branches: 100,
+                 functions: 100
+               }
+             },
+            `,
+        ),
+      );
+
+      await harness.appendToFile(
+        'src/app/app.component.ts',
+        `
+           export function nonCovered(): boolean {
+             return true;
+           }
+         `,
+      );
+
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+        codeCoverage: true,
+      });
+
+      await harness
+        .execute()
+        .pipe(
+          // In incremental mode, karma-coverage does not have the ability to mark a
+          // run as failed if code coverage does not pass. This is because it does
+          // the coverage asynchoronously and Karma does not await the promise
+          // returned by the plugin.
+
+          // However the program must exit with non-zero exit code.
+          // This is a more common use case of coverage testing and must be supported.
+          last(),
+          tap((buildEvent) => expect(buildEvent.result?.success).toBeFalse()),
+        )
+        .toPromise();
+    });
+  });
+});

packages/angular_devkit/build_angular/src/builders/karma/tests/options/code-coverage_spec.ts

@@ -109,52 +109,5 @@ describeBuilder(execute, KARMA_BUILDER_INFO, (harness) => {
       await setTimeoutPromise(1000);
       harness.expectFile(coveragePath).content.not.toContain('my-lib');
     });
-
-    it('should exit with non-zero code when coverage is below threshold', async () => {
-      await harness.modifyFile('karma.conf.js', (content) =>
-        content.replace(
-          'coverageReporter: {',
-          `coverageReporter: {
-            check: {
-              global: {
-                statements: 100,
-                lines: 100,
-                branches: 100,
-                functions: 100
-              }
-            },
-           `,
-        ),
-      );
-
-      await harness.appendToFile(
-        'src/app/app.component.ts',
-        `
-          export function nonCovered(): boolean {
-            return true;
-          }
-        `,
-      );
-
-      harness.useTarget('test', {
-        ...BASE_OPTIONS,
-        codeCoverage: true,
-      });
-
-      await harness
-        .execute()
-        .pipe(
-          // In incremental mode, karma-coverage does not have the ability to mark a
-          // run as failed if code coverage does not pass. This is because it does
-          // the coverage asynchoronously and Karma does not await the promise
-          // returned by the plugin.
-
-          // However the program must exit with non-zero exit code.
-          // This is a more common use case of coverage testing and must be supported.
-          last(),
-          tap((buildEvent) => expect(buildEvent.result?.success).toBeFalse()),
-        )
-        .toPromise();
-    });
   });
 });