From 4ef000a938ca3e54eee1c8dd02e2eb9b1afff0c3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ari=20Perkki=C3=B6?= <ari.perkkio@gmail.com>
Date: Wed, 7 Oct 2026 08:10:42 +0300
Subject: [PATCH] fix(coverage): `allowExternal` fails to include uncovered
 files (#11513)

---
 packages/vitest/src/node/coverage.ts          | 21 +++++++++++++------
 .../coverage-test/test/allow-external.test.ts |  9 +++++++-
 .../test-utils/fixtures/external-uncovered.ts |  3 +++
 3 files changed, 26 insertions(+), 7 deletions(-)
 create mode 100644 test/test-utils/fixtures/external-uncovered.ts

diff --git a/packages/vitest/src/node/coverage.ts b/packages/vitest/src/node/coverage.ts
index 8a57bbd17..052e7c613 100644
--- a/packages/vitest/src/node/coverage.ts
+++ b/packages/vitest/src/node/coverage.ts
@@ -170,17 +170,20 @@ export class BaseCoverageProvider {
       return false
     }
 
-    const relativeFilename = matchingRoot ? relative(matchingRoot, filename) : filename
+    // Files outside roots can be matched by absolute or "../" patterns
+    const candidates = matchingRoot
+      ? [relative(matchingRoot, filename)]
+      : [filename, ...roots.map((root) => relative(root, filename))]
 
     const { matchExclude, matchInclude } = this.getGlobMatchers()
 
-    if (matchExclude(relativeFilename)) {
+    if (candidates.some(matchExclude)) {
       this.globCache.set(filename, false)
       return false
     }
 
     // By default `coverage.include` matches all files, except "coverage.exclude"
-    let included = matchInclude(relativeFilename)
+    let included = candidates.some(matchInclude)
 
     if (included && this.changedFiles) {
       included = this.changedFiles.includes(filename)
@@ -779,10 +782,11 @@ export class BaseCoverageProvider {
   }
 
   createUncoveredFileTransformer(ctx: Vitest) {
+    const rootProject = ctx.getRootProject()
     const projects = new Set([
       ...ctx.projects,
       // Check core last as it will match all files anyway
-      ctx.getRootProject(),
+      rootProject,
     ])
 
     return async (filename: string): Promise<TransformResult | null | undefined> => {
@@ -791,8 +795,13 @@ export class BaseCoverageProvider {
       for (const project of projects) {
         const root = project.config.root
 
-        // On Windows root doesn't start with "/" while filenames do
-        if (!filename.startsWith(root) && !filename.startsWith(`/${root}`)) {
+        if (
+          // On Windows root doesn't start with "/" while filenames do
+          !filename.startsWith(root) &&
+          !filename.startsWith(`/${root}`) &&
+          // If it's file outside project (allowExternal), transform it with the root project
+          project !== rootProject
+        ) {
           continue
         }
 
diff --git a/test/coverage-test/test/allow-external.test.ts b/test/coverage-test/test/allow-external.test.ts
index 1307d72a9..e4108653a 100644
--- a/test/coverage-test/test/allow-external.test.ts
+++ b/test/coverage-test/test/allow-external.test.ts
@@ -7,7 +7,11 @@ test('{ allowExternal: true } includes files outside project root', async () =>
     coverage: {
       allowExternal: true,
       reporter: 'json',
-      include: ['**/fixtures/src/math.ts', '**/fixtures/external-math.ts'],
+      include: [
+        '**/fixtures/src/math.ts',
+        '**/fixtures/external-math.ts',
+        '../test-utils/fixtures/**.ts',
+      ],
     },
   })
   const coverageMap = await readCoverageMap()
@@ -16,6 +20,9 @@ test('{ allowExternal: true } includes files outside project root', async () =>
   // File outside project root
   expect(files).toContain('<project-root>/test/test-utils/fixtures/external-math.ts')
 
+  // Uncovered file outside project root
+  expect(files).toContain('<project-root>/test/test-utils/fixtures/external-uncovered.ts')
+
   // Files inside project root should always be included
   expect(files).toContain('<process-cwd>/fixtures/src/math.ts')
 })
diff --git a/test/test-utils/fixtures/external-uncovered.ts b/test/test-utils/fixtures/external-uncovered.ts
new file mode 100644
index 000000000..52568ba2e
--- /dev/null
+++ b/test/test-utils/fixtures/external-uncovered.ts
@@ -0,0 +1,3 @@
+export function subtract(a: number, b: number) {
+  return a - b
+}
-- 
2.51.2