Add `excludeAfterRemap` option for c8 coverage

[RebeccaStevens]

Clear and concise description of the problem

The option --exclude-after-remap can't currently be set in vite.config.ts.

Suggested solution

Add excludeAfterRemap as an option to the test.coverage config for provider v8.

Alternative

Use the c8 provider or run vitest as c8 vitest run and a .c8rc.json config file.

Additional context

The c8 provider currently supports excludeAfterRemap but TypeScript complains about it not being a valid option.

Also: #3813

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.

[AriPerkkio]

The @vitest/coverage-c8 package has been removed and won't be receiving any updates from now. See #3614.

[RebeccaStevens]

This issue relates to @vitest/coverage-v8 as well.

[RebeccaStevens]

@AriPerkkio I was going off this quote from #3339

Adds new coverage provider package @vitest/coverage-v8. For end-users it should provide identical coverage results as @vitest/coverage-c8.

My assumption being that the v8 provider also supports source map remappming like c8 does. Is this not the case?

[AriPerkkio]

The @vitest/coverage-v8 and @vitest/coverage-istanbul both remap the coverage results back to source files using istanbul-lib-source-maps. Without source map remapping users who are using Typescript, Vue, React, Svelte, or any compiled language/feature would be unable to see coverage of their source files.

Doesn't coverage.exclude achieve everything that excludeAfterRemap could provide? After reading #3813 I'm not really sure what your use case is.

[RebeccaStevens]

This is the vite.config.ts that works for my currently:

// ...

export default defineConfig({
  plugins: [tsconfigPaths()],

  test: {
    include: [testFilePattern],
    coverage: {
      provider: "c8",
      include: ["src/**/*.ts"],
      exclude: ["src/util/conditional-imports/**/*.ts"],
      // @ts-expect-error -- Untyped option.
      excludeAfterRemap: true,
      clean: true,
      reporter: ["lcov", "text"],
      watermarks: {
        lines: [80, 95],
        functions: [80, 95],
        branches: [80, 95],
        statements: [80, 95],
      },
    },
  },
});

With this config, the coverage result look like this:

If I remove excludeAfterRemap, the remapping doesn't work properly and I get:

If I also remove the include and exclude options so we can see all the coverage is on the compiled files, not the source files:

[RebeccaStevens]

Here's a link to the repo if you want to have a look there: https://github.com/eslint-functional/eslint-plugin-functional/tree/next

[RebeccaStevens]

excludeAfterRemap is also an option for nyc

https://github.com/istanbuljs/nyc/blob/ab7c53b2f340b458789a746dff2abd3e2e4790c3/index.js#L439

[AriPerkkio]

This was accidentally locked by the bot.

Sorry for forgetting this feature request @RebeccaStevens! I didn't understand the issue completely earlier. I've now run into this same issue myself and see what you meant.

Let's add support for this. As the globbing might be slow, and people who don't bundle their source files for tests do not need this feature, let's make this opt-in and disabled by default. Exactly as c8 does.