feat(coverage): v8 experimental AST-aware remapping

Author: AriPerkkio

docs/config/index.md

@@ -1638,7 +1638,7 @@ Sets thresholds to 100 for files matching the glob pattern.
 - **Available for providers:** `'v8'`
 - **CLI:** `--coverage.ignoreEmptyLines=<boolean>`
 
-Ignore empty lines, comments and other non-runtime code, e.g. Typescript types.
+Ignore empty lines, comments and other non-runtime code, e.g. Typescript types. Requires `experimentalAstAwareRemapping: false`.
 
 This option works only if the used compiler removes comments and other non-runtime code from the transpiled code.
 By default Vite uses ESBuild which removes comments and Typescript types from `.ts`, `.tsx` and `.jsx` files.
@@ -1662,6 +1662,14 @@ export default defineConfig({
   },
 })
 ```
+#### coverage.experimentalAstAwareRemapping
+
+- **Type:** `boolean`
+- **Default:** `false`
+- **Available for providers:** `'v8'`
+- **CLI:** `--coverage.experimentalAstAwareRemapping=<boolean>`
+
+Remap coverage with experimental AST based analysis. Provides more accurate results compared to default mode.
 
 #### coverage.ignoreClassMethods
 

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: true`](https://vitest.dev/config/#coverage-experimentalAstAwareRemapping) see [ast-v8-to-istanbul | Ignoring code](https://github.com/AriPerkkio/ast-v8-to-istanbul?tab=readme-ov-file#ignoring-code)
 
 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": "^0.1.0",
     "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 {
@@ -219,6 +221,51 @@ 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) {
+      let ast
+      try {
+        ast = parseAstAsync(sources.source)
+      }
+      catch (error) {
+        this.ctx.logger.error(`Failed to parse ${filename}. Excluding it from coverage.\n`, error)
+        return {}
+      }
+
+      return await astV8ToIstanbul({
+        code: sources.source,
+        sourceMap: sources.sourceMap?.sourcemap,
+        ast,
+        coverage: { functions, url: filename },
+        ignoreClassMethods: this.options.ignoreClassMethods,
+        wrapperLength,
+        ignoreNode: (node, type) => {
+          // SSR transformed imports
+          if (
+            type === 'statement'
+            && node.type === 'AwaitExpression'
+            && node.argument.type === 'CallExpression'
+            && node.argument.callee.type === 'Identifier'
+            && node.argument.callee.name === '__vite_ssr_import__'
+          ) {
+            return true
+          }
+
+          // SSR transformed exports
+          if (
+            type === 'statement'
+            && node.type === 'ExpressionStatement'
+            && node.expression.type === 'AssignmentExpression'
+            && node.expression.left.type === 'MemberExpression'
+            && node.expression.left.object.type === 'Identifier'
+            && node.expression.left.object.name === '__vite_ssr_exports__'
+          ) {
+            return true
+          }
+        },
+      },
+      )
+    }
+
     const converter = v8ToIstanbul(
       filename,
       wrapperLength,
@@ -265,7 +312,7 @@ 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)
       })
     }
 

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

@@ -275,8 +275,23 @@ export interface CoverageIstanbulOptions extends BaseCoverageOptions {
 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 */

test/coverage-test/fixtures/src/ignore-hints.ts

@@ -75,15 +75,17 @@ test('provider options, generic', () => {
 test('provider specific options, v8', () => {
   assertType<Coverage>({
     provider: 'v8',
-    // @ts-expect-error -- Istanbul-only option is not allowed
-    ignoreClassMethods: ['string'],
+    experimentalAstAwareRemapping: true,
   })
 })
 
 test('provider specific options, istanbul', () => {
   assertType<Coverage>({
     provider: 'istanbul',
     ignoreClassMethods: ['string'],
+
+    // @ts-expect-error -- v8 specific error
+    experimentalAstAwareRemapping: true,
   })
 })
 

test/coverage-test/test/configuration-options.test-d.ts

@@ -1,6 +1,6 @@
 import { createRequire } from 'node:module'
 import { expect } from 'vitest'
-import { coverageTest, isV8Provider, normalizeURL, readCoverageMap, runVitest, test } from '../utils'
+import { coverageTest, isExperimentalV8Provider, isV8Provider, normalizeURL, readCoverageMap, runVitest, test } from '../utils'
 
 test('does not crash when file outside Vite is loaded (#5639)', async () => {
   await runVitest({
@@ -11,7 +11,7 @@ test('does not crash when file outside Vite is loaded (#5639)', async () => {
   const coverageMap = await readCoverageMap()
   const fileCoverage = coverageMap.fileCoverageFor('<process-cwd>/fixtures/src/load-outside-vite.cjs')
 
-  if (isV8Provider()) {
+  if (isV8Provider() || isExperimentalV8Provider()) {
     expect(fileCoverage).toMatchInlineSnapshot(`
       {
         "branches": "0/0 (100%)",
@@ -22,6 +22,8 @@ test('does not crash when file outside Vite is loaded (#5639)', async () => {
     `)
   }
   else {
+    // On istanbul the instrumentation happens on Vite plugin, so files
+    // loaded outsite Vite should have 0% coverage
     expect(fileCoverage).toMatchInlineSnapshot(`
       {
         "branches": "0/0 (100%)",

test/coverage-test/test/file-outside-vite.test.ts

@@ -4,7 +4,7 @@
 */
 
 import { expect } from 'vitest'
-import { isV8Provider, readCoverageMap, runVitest, test } from '../utils'
+import { isExperimentalV8Provider, isV8Provider, readCoverageMap, runVitest, test } from '../utils'
 
 test('ignore hints work', async () => {
   await runVitest({
@@ -23,6 +23,10 @@ test('ignore hints work', async () => {
     expect(lines[15]).toBeUndefined()
     expect(lines[18]).toBeGreaterThanOrEqual(1)
   }
+  else if (isExperimentalV8Provider()) {
+    expect(lines[15]).toBeUndefined()
+    expect(lines[18]).toBeUndefined()
+  }
   else {
     expect(lines[15]).toBeGreaterThanOrEqual(1)
     expect(lines[18]).toBeUndefined()