fix(coverage): v8 to ignore type-only files

packages/coverage-v8/rollup.config.js

@@ -19,6 +19,7 @@ const external = [
   ...Object.keys(pkg.dependencies || {}),
   ...Object.keys(pkg.peerDependencies || {}),
   'node:inspector',
+  'vite',
   /^@?vitest(\/|$)/,
 ]
 

packages/coverage-v8/src/provider.ts

@@ -1,6 +1,7 @@
 import { existsSync, promises as fs, writeFileSync } from 'node:fs'
 import type { Profiler } from 'node:inspector'
 import { fileURLToPath, pathToFileURL } from 'node:url'
+import { parseAstAsync } from 'vite'
 import v8ToIstanbul from 'v8-to-istanbul'
 import { mergeProcessCovs } from '@bcoe/v8-coverage'
 import libReport from 'istanbul-lib-report'
@@ -260,7 +261,13 @@ export class V8CoverageProvider extends BaseCoverageProvider implements Coverage
       }
 
       const coverages = await Promise.all(chunk.map(async (filename) => {
-        const { source } = await this.getSources(filename.href, transformResults)
+        const transformResult = await this.ctx.vitenode.transformRequest(filename.pathname)
+
+        // Ignore empty files, e.g. files that contain only typescript types and no runtime code
+        if (transformResult && await isFileEmpty(transformResult.code))
+          return null
+
+        const { originalSource } = await this.getSources(filename.href, transformResults)
 
         const coverage = {
           url: filename.href,
@@ -269,7 +276,7 @@ export class V8CoverageProvider extends BaseCoverageProvider implements Coverage
           functions: [{
             ranges: [{
               startOffset: 0,
-              endOffset: source.length,
+              endOffset: originalSource.length,
               count: 0,
             }],
             isBlockCoverage: true,
@@ -281,15 +288,18 @@ export class V8CoverageProvider extends BaseCoverageProvider implements Coverage
         return { result: [coverage] }
       }))
 
-      merged = mergeProcessCovs([merged, ...coverages])
+      merged = mergeProcessCovs([
+        merged,
+        ...coverages.filter((cov): cov is NonNullable<typeof cov> => cov != null),
+      ])
     }
 
     return merged
   }
 
   private async getSources(url: string, transformResults: TransformResults, functions: Profiler.FunctionCoverage[] = []): Promise<{
     source: string
-    originalSource?: string
+    originalSource: string
     sourceMap?: { sourcemap: EncodedSourceMap }
   }> {
     const filePath = normalize(fileURLToPath(url))
@@ -302,12 +312,16 @@ export class V8CoverageProvider extends BaseCoverageProvider implements Coverage
       // If file does not exist construct a dummy source for it.
       // These can be files that were generated dynamically during the test run and were removed after it.
       const length = findLongestFunctionLength(functions)
-      return '.'.repeat(length)
+      return '/'.repeat(length)
     })
 
     // These can be uncovered files included by "all: true" or files that are loaded outside vite-node
-    if (!map)
-      return { source: code || sourcesContent }
+    if (!map) {
+      return {
+        source: code || sourcesContent,
+        originalSource: sourcesContent,
+      }
+    }
 
     return {
       originalSource: sourcesContent,
@@ -411,3 +425,15 @@ function normalizeTransformResults(fetchCache: Map<string, { result: FetchResult
 
   return normalized
 }
+
+async function isFileEmpty(code: string) {
+  try {
+    const ast = await parseAstAsync(code, { allowReturnOutsideFunction: true })
+    return ast.body.length === 0
+  }
+  catch (_) {
+    // Ignore possible parsing errors
+  }
+
+  return false
+}

test/coverage-test/src/types.ts

@@ -0,0 +1,3 @@
+export type First = 'This' | 'file' | 'should'
+
+export type Second = 'be' | 'excluded' | 'from' | 'report'