Supports browser mode for custom provider module

[cenfun]

Clear and concise description of the problem

It doesn't automatically switch to browser mode for custom provider module. for example:

export default defineConfig({
    test: {
        include: ['test/*.test.js'],
        coverage: {
            enabled: true,
            include: ['src/**'],
            
            provider: 'custom',
            customProviderModule: 'vitest-monocart-coverage'

        },

        browser: {
            enabled: true,
            headless: true,
            instances: [{
                browser: 'chromium'
            }],
            provider: 'playwright'
        }
    }
});

It works if the browser mode is manually used

...
customProviderModule: 'vitest-monocart-coverage/browser'
...

Related issue: cenfun/vitest-monocart-coverage#8

Suggested solution

For build-in modules 'v8' and 'istanbul', the solution is below

const provider = options.provider

  if (provider === 'v8' || provider === 'istanbul') {
    let builtInModule = CoverageProviderMap[provider]

    if (provider === 'v8' && loader.isBrowser) {
      builtInModule += '/browser'
    }

    const { default: coverageModule } = await loader.executeId(builtInModule)
...

see source

So can we do something similar for custom module?

  let customProviderModule
  
  // do something here?
  let customModule = options.customProviderModule;
  if (loader.isBrowser) {
      customModule += '/browser'
  }

  try {
    customProviderModule = await loader.executeId(customModule)
  }
  catch (error) {
    throw new Error(
      `Failed to load custom CoverageProviderModule from ${options.customProviderModule}`,
      { cause: error },
    )
  }

Possible questions:
1, What if customProviderModule is a file path like ./path-to/my-file.js?
2, What if customProviderModule does not support browser mode?

Alternative

No response

Additional context

If it cannot be supported, should we consider restructuring the custom module architecture, since vitest@3 has just been released and we still have the opportunity?
I personally think we should separate the code for browser mode and Node.js mode. Otherwise, it will lead to very high complexity and is prone to errors.

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[chapmanio]

I'm interested in this, without the switching we can't (automatically) gather coverage from both sources - and Vitest doesn't allow us to set up separate coverage providers for each workspace project.

[AriPerkkio]

without the switching we can't (automatically) gather coverage from both sources - and Vitest doesn't allow us to set up separate coverage providers for each workspace project.

Sure you can. Vitest's built-in coverage providers work out-of-the-box - you can have multiple Node and browser projects in you workspace and get coverage report with merged results automatically.

The issue is just about 3rd party coverage provider packages being able to define additional entrypoint for browsers. I'm not yet sure how this could be solved. At the moment they could probably work-around this by having separate bundles for Node and browser, and using dynamic import when loading those.