fix(coverage): ignore generated TS decorators (#5206)

Co-authored-by: Vladimir <sleuths.slews0s@icloud.com>

Author: AriPerkkio

Diff for: packages/coverage-istanbul/src/provider.ts

@@ -114,6 +114,9 @@ export class IstanbulCoverageProvider extends BaseCoverageProvider implements Co
     const sourceMap = pluginCtx.getCombinedSourcemap()
     sourceMap.sources = sourceMap.sources.map(removeQueryParameters)
 
+    // Exclude SWC's decorators that are left in source maps
+    sourceCode = sourceCode.replaceAll('_ts_decorate', '/* istanbul ignore next */_ts_decorate')
+
     const code = this.instrumenter.instrumentSync(sourceCode, id, sourceMap as any)
     const map = this.instrumenter.lastSourceMap() as any
 

Diff for: packages/coverage-v8/src/provider.ts

@@ -51,6 +51,7 @@ const WRAPPER_LENGTH = 185
 
 // Note that this needs to match the line ending as well
 const VITE_EXPORTS_LINE_PATTERN = /Object\.defineProperty\(__vite_ssr_exports__.*\n/g
+const DECORATOR_METADATA_PATTERN = /_ts_metadata\("design:paramtypes"(\s|.)+?]\),/g
 const DEFAULT_PROJECT = Symbol.for('default-project')
 
 const debug = createDebug('vitest:coverage')
@@ -312,7 +313,7 @@ export class V8CoverageProvider extends BaseCoverageProvider implements Coverage
       originalSource: sourcesContent,
       source: code || sourcesContent,
       sourceMap: {
-        sourcemap: removeViteHelpersFromSourceMaps(code, {
+        sourcemap: excludeGeneratedCode(code, {
           ...map,
           version: 3,
           sources: [url],
@@ -363,21 +364,24 @@ async function transformCoverage(coverageMap: CoverageMap) {
 /**
  * Remove generated code from the source maps:
  * - Vite's export helpers: e.g. `Object.defineProperty(__vite_ssr_exports__, "sum", { enumerable: true, configurable: true, get(){ return sum }});`
+ * - SWC's decorator metadata: e.g. `_ts_metadata("design:paramtypes", [\ntypeof Request === "undefined" ? Object : Request\n]),`
  */
-function removeViteHelpersFromSourceMaps(source: string | undefined, map: EncodedSourceMap) {
-  if (!source || !source.match(VITE_EXPORTS_LINE_PATTERN))
+function excludeGeneratedCode(source: string | undefined, map: EncodedSourceMap) {
+  if (!source)
     return map
 
-  const sourceWithoutHelpers = new MagicString(source)
-  sourceWithoutHelpers.replaceAll(VITE_EXPORTS_LINE_PATTERN, '\n')
+  if (!source.match(VITE_EXPORTS_LINE_PATTERN) && !source.match(DECORATOR_METADATA_PATTERN))
+    return map
+
+  const trimmed = new MagicString(source)
+  trimmed.replaceAll(VITE_EXPORTS_LINE_PATTERN, '\n')
+  trimmed.replaceAll(DECORATOR_METADATA_PATTERN, match => '\n'.repeat(match.split('\n').length - 1))
 
-  const mapWithoutHelpers = sourceWithoutHelpers.generateMap({
-    hires: 'boundary',
-  })
+  const trimmedMap = trimmed.generateMap({ hires: 'boundary' })
 
-  // A merged source map where the first one excludes helpers
+  // A merged source map where the first one excludes generated parts
   const combinedMap = remapping(
-    [{ ...mapWithoutHelpers, version: 3 }, map],
+    [{ ...trimmedMap, version: 3 }, map],
     () => null,
   )
 

Diff for: pnpm-lock.yaml

@@ -20,6 +20,7 @@ exports[`custom json report 1`] = `
     "<process-cwd>/src/Defined.vue",
     "<process-cwd>/src/Hello.vue",
     "<process-cwd>/src/another-setup.ts",
+    "<process-cwd>/src/decorators.ts",
     "<process-cwd>/src/dynamic-file-esm.ignore.js",
     "<process-cwd>/src/dynamic-files.ts",
     "<process-cwd>/src/function-count.ts",