Accept coverage info, collected from the browser

I’m developing a cross-platform testing tool, which can run tests in browsers, Node and Deno: https://siesta.works

I’m trying to promote c8 as a recommended code coverage tool for it. It seems to work well for the Node.js tests.

However, if I collect coverage objects from the Chromium web pages, c8 does not recognize them as such. This is because Chromium’s coverage object seems to have different format from Node’s.

Node’s format:

{
    "result": [{
        "scriptId": "7",
        "url": "file:///home/nickolay/workspace/siesta-workspace/siesta-monorepo/packages/siesta/bin/siesta.js",
        ...
    }],
    "source-map-cache": {
        "file:///home/nickolay/workspace/siesta-workspace/siesta-monorepo/node_modules/.pnpm/@web+dev-server@0.1.24_rollup@2.58.0/node_modules/@web/dev-server/dist/index.js": {
            "lineLengths": [13, 62, 137, 51, 133, 54, 127, 61, 148, 57, 130, 65, 142, 33],
        },

Chromium’s format:

[
    {
        "scriptId": "32",
        "url": "http://localhost:8000/browser.js",
        ...
        "source": "..."
    }
]

So browser’s format includes “raw” sources and does not contain the results property. Data from browser is collected with Playwright: https://playwright.dev/docs/api/class-coverage

I’m willing to contribute a PR normalizing this format difference when generating a report, would you accept it and may be provide some guidance?

[bcoe]

@canonic-epicure this seems like a great feature request.

I think the logic might end up complicated enough for resolving URLs, and making it fit into the assumptions made by c8, that we should probably add a new helper, something like ./lib/util/chrome-to-v8.js, which would spit out a file that then works with v8-to-istanbul?

[canonic-epicure]

So, by changing all urls to file:// with el.url = el.url.replace(/^https?:\/\//, 'file:///'), wrapping the results from browser with { result : ... }, using --allowExternal and applying this small patch to lib/report.js: https://github.com/canonic-epicure/c8/commit/0ed7994cec03ab10052f9c974971a789a256e064

I was able to receive decently looking report:

Sources are not shown of course:

This makes me positive its overall doable.