From 372e86fdef381038a2c4999fc9007dd7292a0628 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ari=20Perkki=C3=B6?= <ari.perkkio@gmail.com>
Date: Mon, 8 Dec 2025 16:31:42 +0200
Subject: [PATCH] fix(coverage): istanbul untested files source maps are off
 (#9208)

---
 packages/coverage-istanbul/src/provider.ts    | 40 ++++++++++---------
 test/coverage-test/setup.ts                   |  4 +-
 .../test/results-snapshot.test.ts             | 30 ++++++++++++++
 3 files changed, 53 insertions(+), 21 deletions(-)

diff --git a/packages/coverage-istanbul/src/provider.ts b/packages/coverage-istanbul/src/provider.ts
index 5851c5589..4fdef9629 100644
--- a/packages/coverage-istanbul/src/provider.ts
+++ b/packages/coverage-istanbul/src/provider.ts
@@ -88,28 +88,30 @@ export class IstanbulCoverageProvider extends BaseCoverageProvider<ResolvedCover
       sourceMap as any,
     )
 
-    const transformMap = new GenMapping(sourceMap)
+    if (!id.includes('vitest-uncovered-coverage=true')) {
+      const transformMap = new GenMapping(sourceMap)
 
-    eachMapping(new TraceMap(sourceMap as any), (mapping) => {
-      addMapping(transformMap, {
-        generated: { line: mapping.generatedLine, column: mapping.generatedColumn },
-        original: { line: mapping.generatedLine, column: mapping.generatedColumn },
-        content: sourceCode,
-        name: mapping.name || '',
-        source: mapping.source || '',
+      eachMapping(new TraceMap(sourceMap as any), (mapping) => {
+        addMapping(transformMap, {
+          generated: { line: mapping.generatedLine, column: mapping.generatedColumn },
+          original: { line: mapping.generatedLine, column: mapping.generatedColumn },
+          content: sourceCode,
+          name: mapping.name || '',
+          source: mapping.source || '',
+        })
       })
-    })
 
-    const encodedMap = toEncodedMap(transformMap)
-    delete encodedMap.file
-    delete encodedMap.ignoreList
-    delete encodedMap.sourceRoot
+      const encodedMap = toEncodedMap(transformMap)
+      delete encodedMap.file
+      delete encodedMap.ignoreList
+      delete encodedMap.sourceRoot
 
-    this.instrumenter.instrumentSync(
-      sourceCode,
-      id,
-      encodedMap as any,
-    )
+      this.instrumenter.instrumentSync(
+        sourceCode,
+        id,
+        encodedMap as any,
+      )
+    }
 
     const map = this.instrumenter.lastSourceMap() as any
     this.transformedModuleIds.add(id)
@@ -225,7 +227,7 @@ export class IstanbulCoverageProvider extends BaseCoverageProvider<ResolvedCover
       }
 
       // Make sure file is not served from cache so that instrumenter loads up requested file coverage
-      await transform(`${filename}?cache=${cacheKey}`)
+      await transform(`${filename}?cache=${cacheKey}&vitest-uncovered-coverage=true`)
       const lastCoverage = this.instrumenter.lastFileCoverage()
       coverageMap.addFileCoverage(lastCoverage)
 
diff --git a/test/coverage-test/setup.ts b/test/coverage-test/setup.ts
index 473f409af..a763a153b 100644
--- a/test/coverage-test/setup.ts
+++ b/test/coverage-test/setup.ts
@@ -3,14 +3,14 @@ import { expect } from 'vitest'
 import { formatSummary } from './utils'
 
 expect.addSnapshotSerializer({
-  test: val => val.constructor.name === 'CoverageMap',
+  test: val => val.constructor?.name === 'CoverageMap',
   serialize: (val: CoverageMap, config, indentation, depth, refs, printer) => {
     return printer(formatSummary(val.getCoverageSummary()), config, indentation, depth, refs)
   },
 })
 
 expect.addSnapshotSerializer({
-  test: val => val.constructor.name === 'FileCoverage',
+  test: val => val.constructor?.name === 'FileCoverage',
   serialize: (val: FileCoverage, config, indentation, depth, refs, printer) => {
     return printer(formatSummary(val.toSummary()), config, indentation, depth, refs)
   },
diff --git a/test/coverage-test/test/results-snapshot.test.ts b/test/coverage-test/test/results-snapshot.test.ts
index e5f32f3c6..63ea4aeb1 100644
--- a/test/coverage-test/test/results-snapshot.test.ts
+++ b/test/coverage-test/test/results-snapshot.test.ts
@@ -39,4 +39,34 @@ test('coverage results matches snapshot', async () => {
       },
     }
   `)
+
+  const lineCoverages = coverageMap.files().reduce((all, file) => ({
+    [file]: coverageMap.fileCoverageFor(file).getLineCoverage(),
+    ...all,
+  }), {})
+
+  expect(lineCoverages).toMatchInlineSnapshot(`
+    {
+      "<process-cwd>/fixtures/src/even.ts": {
+        "2": 1,
+        "6": 0,
+      },
+      "<process-cwd>/fixtures/src/math.ts": {
+        "10": 0,
+        "14": 0,
+        "2": 1,
+        "6": 0,
+      },
+      "<process-cwd>/fixtures/src/untested-file.ts": {
+        "14": 0,
+        "21": 0,
+        "33": 0,
+        "35": 0,
+        "39": 0,
+        "41": 0,
+        "46": 0,
+        "9": 0,
+      },
+    }
+  `)
 })