feat(coverage): v8 experimental AST-aware remapping

Author: AriPerkkio

docs/guide/coverage.md

@@ -190,24 +190,21 @@ Both coverage providers have their own ways how to ignore code from coverage rep
 
 - [`v8`](https://github.com/istanbuljs/v8-to-istanbul#ignoring-uncovered-lines)
 - [`ìstanbul`](https://github.com/istanbuljs/nyc#parsing-hints-ignoring-lines)
+- `v8` with `experimentalAstAwareRemapping` - TODO
 
 When using TypeScript the source codes are transpiled using `esbuild`, which strips all comments from the source codes ([esbuild#516](https://github.com/evanw/esbuild/issues/516)).
 Comments which are considered as [legal comments](https://esbuild.github.io/api/#legal-comments) are preserved.
 
-For `istanbul` provider you can include a `@preserve` keyword in the ignore hint.
+You can include a `@preserve` keyword in the ignore hint.
 Beware that these ignore hints may now be included in final production build as well.
 
 ```diff
 -/* istanbul ignore if */
 +/* istanbul ignore if -- @preserve */
 if (condition) {
-```
-
-For `v8` this does not cause any issues. You can use `v8 ignore` comments with Typescript as usual:
 
-<!-- eslint-skip -->
-```ts
-/* v8 ignore next 3 */
+-/* v8 ignore if */
++/* v8 ignore if -- @preserve */
 if (condition) {
 ```
 

packages/coverage-v8/package.json

@@ -56,6 +56,7 @@
   "dependencies": {
     "@ampproject/remapping": "catalog:",
     "@bcoe/v8-coverage": "^1.0.2",
+    "ast-v8-to-istanbul": "https://pkg.pr.new/AriPerkkio/ast-v8-to-istanbul@81965c4",
     "debug": "catalog:",
     "istanbul-lib-coverage": "catalog:",
     "istanbul-lib-report": "catalog:",

packages/coverage-v8/src/provider.ts

@@ -9,6 +9,7 @@ import { fileURLToPath, pathToFileURL } from 'node:url'
 import remapping from '@ampproject/remapping'
 // @ts-expect-error -- untyped
 import { mergeProcessCovs } from '@bcoe/v8-coverage'
+import astV8ToIstanbul from 'ast-v8-to-istanbul'
 import createDebug from 'debug'
 import libCoverage from 'istanbul-lib-coverage'
 import libReport from 'istanbul-lib-report'
@@ -24,6 +25,7 @@ import v8ToIstanbul from 'v8-to-istanbul'
 import { cleanUrl } from 'vite-node/utils'
 
 import { BaseCoverageProvider } from 'vitest/coverage'
+import { parseAstAsync } from 'vitest/node'
 import { version } from '../package.json' with { type: 'json' }
 
 export interface ScriptCoverageWithOffset extends Profiler.ScriptCoverage {
@@ -34,10 +36,10 @@ type TransformResults = Map<string, FetchResult>
 interface RawCoverage { result: ScriptCoverageWithOffset[] }
 
 // 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", \[[^\]]*\]\),*/g
+const VITE_EXPORTS_LINE_PATTERN = /Object\.defineProperty\(__vite_ssr_exports__.*\n/g
+const VITE_EXPORTS_LINE_PATTERN_2 = /^__vite_ssr_exports__\..*/gm
+const VITE_IMPORTS_LINE_PATTERN = /^const __vite_ssr_import_.*$/gm
+const DECORATOR_METADATA_PATTERN = /_ts_metadata\("design:paramtypes", \[[^\]]*\]\),*/g
 const FILE_PROTOCOL = 'file://'
 
 const debug = createDebug('vitest:coverage')
@@ -219,6 +221,25 @@ export class V8CoverageProvider extends BaseCoverageProvider<ResolvedCoverageOpt
   }
 
   private async v8ToIstanbul(filename: string, wrapperLength: number, sources: Awaited<ReturnType<typeof this.getSources>>, functions: Profiler.FunctionCoverage[]) {
+    if (this.options.experimentalAstAwareRemapping) {
+      const sourceMap = sources.sourceMap?.sourcemap as any || {
+        mappings: '',
+        version: 3,
+        names: [],
+        sources: [],
+      } satisfies FetchResult['map']
+
+      return await astV8ToIstanbul({
+        code: sources.source,
+        sourceMap,
+        ast: parseAstAsync(sources.source) as any,
+        coverage: { functions, url: filename },
+        ignoreClassMethods: this.options.ignoreClassMethods,
+        wrapperLength,
+      },
+      )
+    }
+
     const converter = v8ToIstanbul(
       filename,
       wrapperLength,
@@ -265,7 +286,7 @@ export class V8CoverageProvider extends BaseCoverageProvider<ResolvedCoverageOpt
         // 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)
       })
     }
 
@@ -392,13 +413,17 @@ function excludeGeneratedCode(
 
   if (
     !source.match(VITE_EXPORTS_LINE_PATTERN)
+    && !source.match(VITE_EXPORTS_LINE_PATTERN_2)
+    && !source.match(VITE_IMPORTS_LINE_PATTERN)
     && !source.match(DECORATOR_METADATA_PATTERN)
   ) {
     return map
   }
 
   const trimmed = new MagicString(source)
   trimmed.replaceAll(VITE_EXPORTS_LINE_PATTERN, '\n')
+  trimmed.replaceAll(VITE_IMPORTS_LINE_PATTERN, '')
+  trimmed.replaceAll(VITE_EXPORTS_LINE_PATTERN_2, '')
   trimmed.replaceAll(DECORATOR_METADATA_PATTERN, match =>
     '\n'.repeat(match.split('\n').length - 1))
 

packages/vitest/src/node/types/coverage.ts

@@ -270,13 +270,29 @@ export interface CoverageIstanbulOptions extends BaseCoverageOptions {
    * @default []
    */
   ignoreClassMethods?: string[]
+
 }
 
 export interface CoverageV8Options extends BaseCoverageOptions {
   /**
    * Ignore empty lines, comments and other non-runtime code, e.g. Typescript types
+   * - Requires `experimentalAstAwareRemapping: false`
    */
   ignoreEmptyLines?: boolean
+
+  /**
+   * Remap coverage with experimental AST based analysis
+   * - Provides more accurate results compared to default mode
+   */
+  experimentalAstAwareRemapping?: boolean
+
+  /**
+   * Set to array of class method names to ignore for coverage.
+   * - Requires `experimentalAstAwareRemapping: true`
+   *
+   * @default []
+   */
+  ignoreClassMethods?: string[]
 }
 
 export interface CustomProviderOptions

pnpm-lock.yaml

@@ -11,7 +11,7 @@ export function second() {
 // Covered line
 second()
 
-/* v8 ignore next -- Uncovered line v8 */
+/* v8 ignore next -- @preserve, Uncovered line v8 */
 second()
 
 /* istanbul ignore next -- @preserve, Uncovered line istanbul */