fix(coverage): v8 to ignore type-only files (vitest-dev#5328)

packages/coverage-v8/package.json

@@ -55,6 +55,7 @@
     "magicast": "^0.3.3",
     "picocolors": "^1.0.0",
     "std-env": "^3.5.0",
+    "strip-literal": "^2.0.0",
     "test-exclude": "^6.0.0",
     "v8-to-istanbul": "^9.2.0"
   },

packages/coverage-v8/src/provider.ts

@@ -14,6 +14,7 @@ import remapping from '@ampproject/remapping'
 import { normalize, resolve } from 'pathe'
 import c from 'picocolors'
 import { provider } from 'std-env'
+import { stripLiteral } from 'strip-literal'
 import createDebug from 'debug'
 import { cleanUrl } from 'vite-node/utils'
 import type { EncodedSourceMap, FetchResult } from 'vite-node'
@@ -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).catch(() => {})
+
+        // Ignore empty files, e.g. files that contain only typescript types and no runtime code
+        if (transformResult && stripLiteral(transformResult.code).trim() === '')
+          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))
@@ -306,8 +316,12 @@ export class V8CoverageProvider extends BaseCoverageProvider implements Coverage
     })
 
     // 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,

test/coverage-test/src/types.ts

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