feat(coverage): support --experimental-strip-types via acorn-typescript

[sohil-kshirsagar]

Add TypeScript coverage support for Node.js --experimental-strip-types (and the stable --experimental-transform-types in Node 23+).

Problem

When a project runs .ts files directly via node --experimental-strip-types server.ts, V8 reports coverage against the .ts files. Our coverage processor uses acorn to parse the source AST, but acorn can't handle TypeScript syntax (type annotations, import type, etc.), causing the file to be silently skipped. This resulted in coverage showing only tuskDriftInit.ts (2/2 lines, 100%) while the actual server code was completely missing.

Fix

Added acorn-typescript as a dependency. When processing a .ts/.tsx/.mts/.cts file, the parser uses acorn.Parser.extend(tsPlugin()) to handle TypeScript syntax. Falls back to plain acorn if the plugin isn't available.

The TypeScript detection is based on file extension — only .ts/.tsx files use the plugin. Regular .js files continue using plain acorn with no overhead.

Testing

Tested against drift-node-demo which uses --experimental-strip-types:

• Before: 100.0% lines (2/2) across 1 file (only tuskDriftInit.ts)
• After: 85.5% lines (59/69) across 2 files (server.ts at 85.1% + tuskDriftInit.ts at 100%)

Also verified no regression on CJS/ESM repos (example-express-server, example-express-ts-server).

[cubic-dev-ai]

1 issue found across 3 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="src/core/coverageProcessor.ts">

<violation number="1" location="src/core/coverageProcessor.ts:244">
P2: CJS TypeScript files that use `import type` (a very common pattern) will be misidentified as ESM here. `import type` is TypeScript-only syntax that Node.js strips before execution, but acorn-typescript still rejects `import` declarations in `sourceType: "script"` mode. This causes the script parse to throw, falling through to the module parse with `isCJS` remaining `false`.

Since Node.js `--experimental-strip-types` determines CJS vs ESM from `package.json`/file extension (not from syntax), it still wraps CJS files with the ~62-byte wrapper. With `isCJS = false`, the `wrapperLength` offset won't be applied, silently misaligning all V8 byte offsets and producing incorrect line-level coverage data.

Consider detecting CJS via file extension (`.cts`) or `package.json` type field rather than relying solely on parse success for TypeScript files.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review, or fix all with cubic.}

[tusk-dev]

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View check history

Commit	Status	Output	Created (UTC)
1633799	Generated 1 test - 1 passed	Tests	Apr 8, 2026 4:55AM
217bfdc	No tests generated	Output	Apr 8, 2026 5:14AM

[cubic-dev-ai]

1 issue found across 1 file (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="src/core/coverageProcessor.ts">

<violation number="1" location="src/core/coverageProcessor.ts:252">
P2: For `.ts` files, parsing `script` first can misclassify ESM-with-type-only-imports as CJS, causing an incorrect CommonJS `wrapperLength` offset.

(Based on your team's feedback about treating `import type` TypeScript files as ESM for wrapper offset handling.) [FEEDBACK_USED]</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review, or fix all with cubic.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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