fix(coverage): apply patch from istanbuljs/istanbuljs#838

[AriPerkkio]

Description

• Fixes coverage-v8: Duplicate statements when merging coverage from multiple projects with different environments #9366
• Applies patch from fix: use lenient matching for coverage merge when end.column differs istanbuljs/istanbuljs#838

Patching istanbul-lib-coverage is tricky as it's still installed by multiple packages that depend on it. I'm a bit concerned users might run into this error due to multiple istanbul-lib-coverage instances on runtime:

https://github.com/istanbuljs/istanbuljs/blob/28ffdbc314596bdcb3007e85d30a62372602b262/packages/istanbul-lib-coverage/lib/file-coverage.js#L37-L42

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commit: f2cd51a

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[AriPerkkio]

@stevez could you verify if these preview version fix the issue in your project?

#9480 (comment)

[stevez]

Hi @AriPerkkio, I can verify that #9366 is getting fixed in this preview build,
repo: https://github.com/stevez/vitest-coverage-merge-bug
branch: test/verify-pr-9480-fix
in src/constants.ts: before total statements was 6 in main branch, now it is 3 in branch test/verify-pr-9480-fix

[AriPerkkio]

We still need test case for this to pick up regressions. I've been trying to come up with one but haven't figured out good way without relying on third party plugins.

Maybe we need to manually construct incompatible transform results and feed those via custom plugin.

[AriPerkkio]

@stevez looks like merging is still wrong. Functions of this file are shown twice due to different end.column mappings.

This is the file tests are loading:

vitest/test/coverage-test/fixtures/src/math.ts

Lines 1 to 15 in c8d2c41

	export function sum(a: number, b: number) {
	return a + b
	}
	export function subtract(a: number, b: number) {
	return a - b
	}
	export function multiply(a: number, b: number) {
	return a * b
	}
	export function remainder(a: number, b:number) {
	return a % b
	}

[stevez]

Let me take a look tonight

[stevez]

@AriPerkkio, I want to confirm the test case, the test failed due to trying to merge 2 different transforms coverage result, now both have different start column as well, I want to confirm do we need to support this scenario, or I feel it is a kind of expanding the scope