feat(reporter): add support for function type to classname option in the junit reporter

[jpleclerc]

Description

This PR adds support for a function for the classname option for the junit reporter.
It is currently possible to specify a static string as the classname of the junit reporter but it is not flexible enough in some case.

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[hi-ogawa]

Hey, thanks for the PR. Can you explain your specific use case? While exposing Task gives flexibility, that comes with increased API surface and potential breaking change in the future, so we might need to discuss a bit.

As an alternative, would it work for you if we support classNameTemplate like jest's reporter? https://github.com/jest-community/jest-junit?tab=readme-ov-file#configuration They have functions too https://github.com/jest-community/jest-junit?tab=readme-ov-file#example-5, but it looks like the argument is normalized first, so internal is not exposed.

Btw, what we support right now for options.classname is probably weird/useless #3808 as it looks like OP introduced to just hide classname #3691

[jpleclerc]

We ended up having test cases with duplicated class names in our project and our CI/CD reporting UI couldn't handle duplicates. For that reason we need a more flexible way to generate classnames in order to make them more unique.

Exposing Task definitly felt a bit wrong. I just looked at jest's classNameTemplate and definitly feels cleaner. I'll make the change to mimic that behavior.

Current classname option feels useless indeed, can't see a use for that.

[AriPerkkio]

@jpleclerc what properties of Task would you like to use here to create those unique names? Instead of exposing whole Task, we could expose some specific parts that are easier to maintain.

[jpleclerc]

@AriPerkkio In our case the file name and path is enough. I think the jest-junit project got it right. I'm thinking of supporting at least the following:

• suitename
• filepath
• filename

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[hi-ogawa]

Looks good!
I think we can deprecate (and remove later) classname as it's useless and easy to move to classnameTemplate as a constant.

[AriPerkkio]

Looks good! We should also update documentation. Maybe something about classnameTemplate after this section:

vitest/docs/guide/reporters.md

Lines 252 to 262 in 5d4b382

	The outputted XML contains nested `testsuites` and `testcase` tags. You can use the reporter options to configure these attributes:
	```ts
	export default defineConfig({
	test: {
	reporters: [
	['junit', { suiteName: 'custom suite name', classname: 'custom-classname' }]
	]
	},
	})
	```