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Invalid coverage with --experimental-monocart when using ts-node #561
Description
All metrics of coverage report are incorrectly set to 100% when using --experimental-monocart with ts-node.
Repro, make sure you download the project locally as WebContainers do not support V8 coverage/CDP: https://stackblitz.com/~/edit/c8-ts-node-invalid-monocart
$ pnpm test
------------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
------------|---------|----------|---------|---------|-------------------
All files | 76.47 | 25 | 100 | 76.47 |
example.ts | 76.47 | 25 | 100 | 76.47 | 3-4,13-14
------------|---------|----------|---------|---------|-------------------
$ pnpm test:monocart
------------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
------------|---------|----------|---------|---------|-------------------
All files | 100 | 100 | 100 | 100 |
example.ts | 100 | 100 | 100 | 100 |
------------|---------|----------|---------|---------|-------------------
Activity
AriPerkkio commentedon May 21, 2025
I guess this is because runtime JS files are transformed on the fly, and Monocart does not have access to those?
c8would require a loader or require hook in order to capture all files that user executed? cc. @cenfuncenfun commentedon May 21, 2025
I thought it should be the issue with the sourcemap.
I used your example and it works with
mcrCLI, see here (branch is example)But I haven't figured out why c8 isn't working. The differences:
1, tsconfig.json: https://github.com/cenfun/mcr-ts-node/blob/example/tsconfig.json
2, cross-env NODE_OPTIONS="--loader ts-node/esm --no-warnings"
3, package.json
{ "type": "module" }4, CLI:
mcrAriPerkkio commentedon May 21, 2025
That example is not using
c8at all?cenfun commentedon May 21, 2025
yes, I haven't figured out why c8 isn't working
cenfun commentedon May 22, 2025
I have found that the issue is related to the generated source code.
when using
c8+ts-node, we can not get the generated source code, but there is only a fake code withlineLengthsofsource-map-cache, see https://nodejs.org/docs/latest/api/cli.html#source-map-cache and nodejs/node#48460It said, the sourcemap contains the original code, but it does not have the generated code, instead, it has
lineLengthsonly.So Monocart cannot get the precise location by parsing the AST of the generated code.
In order to get the generated code,
mcrCLI uses Node.js customization-hooks to save the generated code in some cases. (It doesn't always succeed, for example, it fails when using tsx)see https://github.com/cenfun/monocart-coverage-reports/blob/main/lib/register/hooks.js
AriPerkkio commentedon May 22, 2025
Yep, that's exactly what I meant by #561 (comment).