All code that is not present on source maps should already be excluded from final coverage report. Bundlers tend to inject plenty of helpers, generators and polyfills that are not present on source maps - these should be automatically be excluded.

All code that is not present on source maps should already be excluded from final coverage report.

Was it the case even before having this patch #5457? I agree that should be the expected behavior of v8-to-istanbul in any cases, but there's still an edge case even after the patch when the injected code's line overlaps with original code as in the reproduction #7130 (comment):

// source
console.log("x");

// generated  ("prepended" doesn't get excluded from coverage)
function prepended(){};console.log("x");
function appended(){};

Also it turned out this is also the case for istanbul provider too as seen in the new snapshot test/coverage-test/test/injected-functions.test.ts, which is not fixed in this PR and haven't investigated yet.

This looks to me a bug, which is fixable either Vitest side or v8-to-istanbul eventually. I'm wondering how you see this issue in general. We want to land ssr transform fix vitejs/vite#18983, which can cause this edge case more often, so I would like to know your opinions on whether it's fine to land or wait until we get a better understanding of the issue.

I did some manual testing with this and see now why this work-around is required. To me this looks like a bug in v8-to-istanbul. Ideally we should file a bug report there with minimal repro and PR later on. Or even better, not use v8-to-istanbul at all and roll our own V8 coverage processing.

The #5457 is only about line coverage and does not affect function coverage at all. The v8-to-istanbul has some special handing for line coverage that is not done for function coverage.

I see that VITE_EXPORTS_LINE_PATTERN is now conflicting when using Vite version from the PR. Can we remove that and be backwards compatible?