From 511160911415b7c8eaddfdb3972ad879a57a9f3b Mon Sep 17 00:00:00 2001
From: Charles Lyding <19598772+clydin@users.noreply.github.com>
Date: Wed, 22 Jul 2026 11:48:56 -0400
Subject: [PATCH] fix(@angular/build): favor istanbul coverage provider when
 browser testing is enabled

When browser testing is enabled (`browsers` option configured), using V8 coverage in Chromium requires fetching and remapping source maps over CDP/HTTP for every script loaded in the browser window, causing multi-minute delays during report generation on large projects.

This change updates `determineCoverageProvider` to favor `@vitest/coverage-istanbul` when browser mode is active and `@vitest/coverage-istanbul` is installed in `node_modules`. Istanbul instruments code at build time, allowing instant coverage extraction from `window.__coverage__` without CDP sourcemap resolution overhead. Explicit `coverage.provider` settings in user configuration remain fully respected.

Relates to #31724
---
 .../build/src/builders/unit-test/runners/vitest/plugins.ts    | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts b/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts
index a63e95b1d8b3..29455b50cc7c 100644
--- a/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts
+++ b/packages/angular/build/src/builders/unit-test/runners/vitest/plugins.ts
@@ -102,7 +102,9 @@ function determineCoverageProvider(
       const hasIstanbul = checkInstalled('@vitest/coverage-istanbul');
       const hasV8 = checkInstalled('@vitest/coverage-v8');
 
-      if (hasIstanbul && !hasV8) {
+      // Favor istanbul when browser testing is enabled (to avoid slow CDP V8 HTTP sourcemap remapping)
+      // or when only istanbul is installed.
+      if (hasIstanbul && (browsersToCheck.length > 0 || !hasV8)) {
         determinedProvider = 'istanbul';
       } else {
         determinedProvider = 'v8';