fix(coverage): c8 aliased paths

[AriPerkkio]

• Fixes Tests report does not cover exported function from typescript. #3268

vitenode.fetchCache contains file path without extension when module is imported using alias. This does not end up in coverage report due to missing extension.

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[AriPerkkio]

When an aliased modules is loaded the fsPath doesn't contain extension at all. @sheremet-va
should I make this change to fsPath instead so that everywhere it's used would be affected, e.g. stacktraces I think?

With alias, without PR changes:

import { addThreeNumbers } from "src/logic/utils";

{
  __filename: '/x/y/repro/src/logic/utils',
  id: 'src/logic/utils',
  fsPath: 'src/logic/utils'
}

Without alias, without PR changes, works OK:

import { addThreeNumbers } from "../../logic/utils";

{
  __filename: '/x/y/repro/src/logic/utils.ts',
  id: '/src/logic/utils.ts',
  fsPath: '/x/y/repro/src/logic/utils.ts'
}

With alias, with PR changes:

import { addThreeNumbers } from "src/logic/utils";

{
  __filename: '/x/y/repro/src/logic/utils.ts',
  id: 'src/logic/utils',
  fsPath: 'src/logic/utils'
}

[sheremet-va]

This should not even be allowed. Vitest should fail if the module is not resolved. I am coming up with a fix for this. Some people rely on tsconfig resolution when in practice we don't support it.

[AriPerkkio]

I see, the reproduction case is not using alias in vitest.config.ts. By adding following the coverage works OK:

    alias: {
      src: fileURLToPath(new URL("./src", import.meta.url)),
    },

So I guess in your fix Vitest will fail to load module (or warn?) if only tsconfig.json has alias but vitest.config.ts does not?

[sheremet-va]

We can finally stop supporting this weird edge case: #3307

[sheremet-va]

So I guess in your fix Vitest will fail to load module (or warn?) if only tsconfig.json has alias but vitest.config.ts does not?

People rely on the fact that their modules are relative to the baseDir which is never true in Vite. Because of this, we have a lot of issues when the file is not resolved correctly, but it can still fetch module code.