From 76cb9c2a39d477a64824a985ade40507e3bbade1 Mon Sep 17 00:00:00 2001
From: Adam Mathes <adam@adammathes.com>
Date: Fri, 13 Feb 2026 21:34:48 -0800
Subject: feat(vanilla): add testing infrastructure and tests (NK-wjnczv)

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+# `ast-v8-to-istanbul`
+
+[![Version][version-badge]][npm-url]
+[![Downloads][downloads-url]][npm-url]
+
+> - Speed of V8 coverage 🏎
+> - Accuracy of Istanbul coverage 🔍
+
+[Ignoring code](#ignoring-code) | [Source maps](#source-maps) | [Istanbul Compatibility](#istanbul-compatibility) | [Limitations](#limitations)
+
+---
+
+AST-aware [`v8-to-istanbul`](https://www.npmjs.com/package/v8-to-istanbul).
+
+Unopinionated - _bring-your-own_ AST parser and source maps.
+
+Passes all 195 tests<sup>[*](#istanbul-compatibility)</sup> of [`istanbul-lib-instrument`](https://github.com/istanbuljs/istanbuljs/tree/main/packages/istanbul-lib-instrument/test/specs). ✅
+
+Test cases run against:
+- `vite/parseAst` ✅
+- `acorn` ✅
+- `oxc-parser` ✅
+- `@babel/parser` ✅
+
+See example report at https://ariperkkio.github.io/ast-v8-to-istanbul.
+
+```ts
+import { convert } from "ast-v8-to-istanbul";
+import { parseAstAsync } from "vite";
+import type { CoverageMapData } from "istanbul-lib-coverage";
+
+const data: CoverageMapData = await convert({
+  // Bring-your-own AST parser
+  ast: parseAstAsync(<code>),
+
+  // Code of the executed file (not the source file)
+  code: "function sum(a, b) {\n  return a + b ...",
+
+  // Execution wrapper offset
+  wrapperLength: 0,
+
+  // Script coverage of the executed file
+  coverage: {
+    scriptId: "123",
+    url: "file:///absolute/path/to/dist/index.js",
+    functions: [
+      {
+        functionName: "sum",
+        ranges: [{ startOffset: 223, endOffset: 261, count: 0 }],
+        isBlockCoverage: false,
+      },
+      // ... etc
+    ],
+  },
+
+  // Source map of the executed file
+  sourceMap: {
+    version: 3,
+    sources: ["../sources.ts"],
+    sourcesContent: ["export function sum(a: number, b: number) {\n..."],
+    mappings: ";AAAO,SAAS,...",
+    names: [],
+  },
+});
+```
+
+## Ignoring code
+
+### Ignoring source code
+
+#### Ignore hints
+
+See live example at https://ariperkkio.github.io/ast-v8-to-istanbul/ignore-examples.html.
+
+The typical ignore hints from `nyc` are supported: https://github.com/istanbuljs/nyc?tab=readme-ov-file#parsing-hints-ignoring-lines:
+
+> * `/* istanbul ignore if */`: ignore the next if statement.
+> * `/* istanbul ignore else */`: ignore the else portion of an if statement.
+> * `/* istanbul ignore next */`: ignore the next _thing_ in the source-code (functions, if statements, classes, you name it).
+> * `/* istanbul ignore file */`: ignore an entire source-file (this should be placed at the top of the file).
+
+In addition to `istanbul` keyword, you can use `v8`, `c8` and `node:coverage`:
+
+- `/* istanbul ignore if */`
+- `/* v8 ignore else */`
+- `/* c8 ignore file */`
+- `/* node:coverage ignore next */`
+
+Also `start` and `stop` ignore hints from original [`v8-to-istanbul`](https://www.npmjs.com/package/v8-to-istanbul) are supported.
+These ignore hints are checked from the original sources instead of transpiled code.
+
+> * `/* v8 ignore start */`: start ignoring lines
+> * `/* v8 ignore stop */`: stop ignoring lines
+> * `<!-- /* v8 ignore start */ -->`: start ignoring lines
+> * `<!-- /* v8 ignore stop */ -->`: stop ignoring lines
+> * `anything /* v8 ignore start */ anything`: start ignoring lines
+> * `anything /* v8 ignore stop */ anything`: stop ignoring lines
+
+#### Class methods
+
+The `ignore-class-method` from `nyc` is also supported: https://github.com/istanbuljs/nyc?tab=readme-ov-file#ignoring-methods
+
+> You can ignore every instance of a method simply by adding its name to the `ignore-class-method` array in your `nyc` config.
+
+```ts
+import { convert } from "ast-v8-to-istanbul";
+
+await convert({
+  ignoreClassMethods: ['render']
+});
+```
+
+#### Ignore after remapping
+
+You can ignore source code after coverage results have been remapped back to original sources using `ignoreSourceCode`.
+This is a high level API that can be exposed to end-users by tooling developers.
+
+It's mostly intended for excluding code that is incorrectly shown in coverage report when compilers add generated code in the source maps.
+
+Note that as the exclusion happens after remapping, this option is slower than [`ignoreNode`](#ignoring-generated-code) option.
+
+```ts
+function ignoreSourceCode(
+  code: string,
+  type: "function" | "statement" | "branch",
+  location: Record<"start" | "end", { line: number; column: number }>,
+): boolean | void;
+```
+
+```ts
+import { convert } from "ast-v8-to-istanbul";
+
+await convert({
+  ignoreSourceCode: (code, type, location) => {
+    // Ignore all "noop()" calls
+    if(type === "function" && code.includes("noop(")) {
+      return true;
+    }
+
+    // In Vue "<script>" tags generate code that is incorrectly left in source maps - exclude it
+    if(code === '<script>') {
+      return true;
+    }
+
+    // Ignore anything above line 5
+    return location.start.line < 5;
+  },
+});
+```
+
+### Ignoring generated code
+
+This API is mostly for developers integrating `ast-v8-to-istanbul` with other tooling.
+
+If your code transform pipeline is adding generated code that's included in the source maps, it will be included in coverage too.
+You can exclude these known patterns by defining `ignoreNode` for filtering such nodes.
+
+By returning `"ignore-this-and-nested-nodes"` from the handler, you can ignore all nested nodes too.
+This can be useful when you need to ignore everything a certain node wraps, e.g. `IfStatement`.
+
+```ts
+function ignoreNode(
+  node: Node,
+  type: "branch" | "function" | "statement"
+): boolean | "ignore-this-and-nested-nodes" | void;
+```
+
+```ts
+import { convert } from "ast-v8-to-istanbul";
+
+await convert({
+  ignoreNode: (node, type) => {
+    // Ignore all `await __vite_ssr_import__( ... )` calls that Vite SSR transform adds
+    return (
+      type === "statement" &&
+      node.type === "AwaitExpression" &&
+      node.argument.type === "CallExpression" &&
+      node.argument.callee.type === "Identifier" &&
+      node.argument.callee.name === "__vite_ssr_import__"
+    );
+  },
+});
+```
+
+## Source maps
+
+Source maps are optional and supported by various ways:
+
+- Pass directly to `convert` as argument:
+  ```ts
+  import { convert } from "ast-v8-to-istanbul";
+
+  await convert({
+    sourceMap: {
+      version: 3,
+      sources: ["../sources.ts"],
+      sourcesContent: ["export function sum(a: number, b: number) {\n..."],
+      mappings: ";AAAO,SAAS,...",
+      names: [],
+    }
+  });
+  ```
+- Include base64 encoded inline maps in `code`:
+  ```ts
+  await convert({
+    code: `\
+    function hello() {}
+    //# sourceMappingURL=data:application/json;base64,eyJzb3VyY2VzIjpbIi9zb21lL...
+    `
+  });
+  ```
+- Include inline maps with filename in `code`:
+  ```ts
+  await convert({
+    code: `\
+    function hello() {}
+    //# sourceMappingURL=some-file-on-file-system.js.map
+    `
+  });
+  ```
+- Don't use source maps at all, and pass original source code in `code`:
+  ```ts
+  await convert({
+    code: `function hello() {}`,
+    sourceMap: undefined,
+  });
+  ```
+
+## Istanbul Compatibility
+
+This project tests itself against test cases of `istanbul-lib-instrument` and verifies coverage maps are 100% identical. Some cases, like [deprecated `with()` statement](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/with) and edge cases of strict mode are skipped, as all tests are run in strict mode.
+
+100% istanbul compatibility guarantees that coverage reports between V8 and Istanbul can be merged together.
+
+<img src="https://github.com/user-attachments/assets/f74f129c-d63a-403e-8091-aefa53f6f97e" width="400" />
+
+## Limitations
+
+The way how V8 reports runtime coverage has some limitations when compared to pre-instrumented coverage:
+
+- Unable to detect uncovered `AssignmentPattern`'s if line is otherwise covered
+  - https://github.com/nodejs/node/issues/57435
+
+- Unable to detect uncovered parts when block execution stops due to function throwing:
+  - ```js
+    function first() {
+      throws()
+
+      // unreachable, but incorrectly covered
+      return "first";
+    }
+
+    const throws = ()  => { throw new Error() }
+
+    try { first(1) } catch {}
+    ```
+  - ```json
+    [
+      {
+        "ranges": [{ "startOffset": 0, "endOffset": 165, "count": 1 }],
+        "isBlockCoverage": true
+      },
+      {
+        "functionName": "first",
+        "ranges": [{ "startOffset": 0, "endOffset": 92, "count": 1 }],
+        "isBlockCoverage": true
+      },
+      {
+        "functionName": "throws",
+        "ranges": [{ "startOffset": 109, "endOffset": 137, "count": 1 }],
+        "isBlockCoverage": true
+      }
+    ]
+    ```
+
+[version-badge]: https://img.shields.io/npm/v/ast-v8-to-istanbul
+[npm-url]: https://www.npmjs.com/package/ast-v8-to-istanbul
+[downloads-url]: https://img.shields.io/npm/dm/ast-v8-to-istanbul
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