Coverage ignore hints (/* istanbul ignore next */, /* v8 ignore next */) are broken with Vite 8

[marzelc]

Describe the bug

Coverage ignore hints no longer have any effect when running on Vite 8.
Annotated branches are still reported as uncovered, causing coverage threshold failures.

Vite 8 dropped esbuild entirely in favor of Oxc. Oxc seems to strips all comments during transformation and I found no option to preserve them. So, by the time the coverage plugin receives the code, the ignore hints are gone.

Reproduction

With or without @preserve the if is still considered as uncovered by istanbul despite the ignre

/* istanbul ignore if -- @preserve */
if (condition) {
  return false;
}

System Info

Environment                                                                                                                                                                                                                                                                                                                                                     
  - vitest: 4.1.0                                                                                                                                                                                                                                                                                                                                                 
  - @vitest/coverage-istanbul: 4.1.0                                         
  - vite: 8.0.1

Used Package Manager

yarn

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[github-actions]

Hello @marzelc. Please provide a minimal reproduction using a GitHub repository or StackBlitz (you can also use examples). Issues marked with needs reproduction will be closed if they have no activity within 3 days.

[AriPerkkio]

Unable to reproduce this with

{
  "dependencies": {
    "@vitest/coverage-istanbul": "4.1.0",
    "vite": "^8.0.1",
    "vitest": "^4.1.0"
  }
}

Note that now with Vite 8 you don't even need the @preserve - it works without it too:

[marzelc]

@AriPerkkio thanks you for your time, sorry the reproduction is a little bit more tricky finally, it's finally only in certains cases like when ignoring a default of switch (note that the ignore of return b works but i still have the default part that is not ignored) or the else part of a ternary expression:

or without @preserve

[AriPerkkio]

Created upstream issue:

• codegen: preserve coverage comments before ConditionalExpression's alternate and between SwitchStatement's cases oxc-project/oxc#20549

[marzelc]

Thanks for your reactivity!
I found another case where it doesn't work, I don't know if I should put it in the oxc bug report

[AriPerkkio]

Yes, please mention it in the upstream issue.

This kind of bugs (or rather lack of supported functionality) will come up in the early days of Vite 8 + Vitest. This is new feature of oxc that was built by the request of Vitest team. I would expect us to run into couple of similar issues in future.