fix(@angular/build): validate V8 coverage support for browsers in Vitest

This change introduces a validation check in the Vitest runner to ensure that code coverage is only enabled when using supported Chromium-based browsers. Since the Angular CLI integration currently relies exclusively on the V8 coverage provider, running tests in non-Chromium browsers like Firefox or Safari with coverage enabled would result in incomplete data or missing reports. By adding this check, developers will receive a clear, actionable error message early in the process, preventing confusion and ensuring reliable coverage reports.

Author: clydin

packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts

@@ -154,6 +154,22 @@ export async function createVitestConfigPlugin(
         (browser || testConfig?.browser?.enabled) &&
         (options.coverage.enabled || testConfig?.coverage?.enabled)
       ) {
+        // Validate that enabled browsers support V8 coverage
+        if (browser?.instances) {
+          const unsupportedBrowsers = browser.instances.filter(
+            (instance) => !['chrome', 'chromium', 'edge'].includes(instance.browser),
+          );
+
+          if (unsupportedBrowsers.length > 0) {
+            throw new Error(
+              `Code coverage is enabled, but the following configured browsers do not support the V8 coverage provider: ` +
+                `${unsupportedBrowsers.map((i) => i.browser).join(', ')}. ` +
+                `V8 coverage is only supported on Chromium-based browsers (e.g., Chrome, Chromium, Edge). ` +
+                `Please disable coverage or remove the unsupported browsers.`,
+            );
+          }
+        }
+
         projectPlugins.unshift(createSourcemapSupportPlugin());
         setupFiles.unshift('virtual:source-map-support');
       }

tests/e2e/tests/vitest/browser-coverage-validation.ts

@@ -0,0 +1,30 @@
+import assert from 'node:assert/strict';
+import { applyVitestBuilder } from '../../utils/vitest';
+import { execAndCaptureError } from '../../utils/process';
+import { installPackage } from '../../utils/packages';
+import { stripVTControlCharacters } from 'node:util';
+
+export default async function (): Promise<void> {
+  await applyVitestBuilder();
+
+  // Install necessary packages to pass the provider check
+  await installPackage('playwright@1');
+  await installPackage('@vitest/browser-playwright@4');
+
+  // Run test with coverage and an unsupported browser
+  const error = await execAndCaptureError('ng', [
+    'test',
+    '--no-watch',
+    '--coverage',
+    '--browsers',
+    'firefox',
+  ]);
+  const output = stripVTControlCharacters(error.message);
+
+  // Verify that the expected error message is present
+  assert.match(
+    output,
+    /Code coverage is enabled, but the following configured browsers do not support the V8 coverage provider: firefox/,
+    'Expected validation error for unsupported browser with coverage.',
+  );
+}