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Contributing to Grida | Web Platform Tests

This guide covers how to run the upstream web-platform-tests suite against Grida's grida::htmlcss renderer. It is relevant only if you are working on the htmlcss renderer and want to validate against the CSS spec; for day-to-day Chromium-parity work use the in-tree refbrowser pipeline (see render-reftest skill).

Status: PoC. Reftest pair-matching works end-to-end. Testharness and crashtest executors are not yet wired. Most tests fail — the goal right now is to make the plumbing reliable, not to ship a pass rate.

One-time setup​

1. Clone the Grida WPT fork as a sibling​

The WPT tree with Grida's product plugin lives at gridaco/wpt. Clone it as a sibling of the grida repo:

cd /path/to/grida/..  # parent of the grida/ checkout
git clone --depth=1 https://github.com/gridaco/wpt.git wpt

Layout after cloning:

Apps/grida/
├── grida/         # this repo
└── wpt/           # the fork

Do not use a random upstream WPT checkout — it lacks the grida product registration.

That's it — just wpt handles build + binary path + report output.

Run​

From this repo:

just wpt css/css-transforms/2d-rotate-001.html  # one file (pilot test)
just wpt css/css-transforms/                    # one subsuite
just wpt                                        # all of css/ (default)

Expected output on the pilot: SUITE_START → TEST_START → TEST_END: FAIL, expected PASS. The FAIL is not a setup error — it means the pipeline ran end-to-end and grida's rendering of the pair did not match within fuzzy tolerance. See the [primitives inventory][inventory] for what feature gaps cause most of the fails.

[inventory]: https://github.com/gridaco/grida/issues

Wide runs write a structured report to target/wpt-report.json. Mine it with jq:

jq '.results | group_by(.status) | map({status: .[0].status, count: length})' \
   target/wpt-report.json

The plugin is reftest-only; testharness, crashtest, wdspec, and print-reftest types warn "Unsupported test type" and are skipped.

Under the hood​

just wpt runs:

cargo build -p grida_wpt --release
cd ../wpt && ./wpt run \
    --binary=<repo>/target/release/grida_wpt \
    --log-wptreport=<repo>/target/wpt-report.json \
    --log-mach-level=info \
    grida <target>

Skip the recipe and call ./wpt run directly if you need custom flags (--include-file, --repeat, etc.).

What the plugin does​

Pipeline: wptrunner invokes grida_wpt render --url <test_url> --out <tmp> once per reftest screenshot. Both test.html and ref.html render through grida::htmlcss. Wptrunner's built-in RefTestImplementation compares the two PNGs, honoring <meta name="fuzzy"> tolerances.

Source:

  • Rust side: crates/grida_wpt/ in this repo. The render subcommand handles --url mode.
  • Python side: tools/wptrunner/wptrunner/browsers/grida.py and executors/executorgrida.py in the fork. See README-GRIDA.md at the fork root for the exact list of changed files.

Known gotchas​

  • No /etc/hosts edits needed. Our plugin's env_options hardcodes server_host: 127.0.0.1 and the Python executor rewrites web-platform.test:<port> URLs to 127.0.0.1:<port> before invoking grida_wpt. Do not pass --enable-dns; wptrunner has an unrelated bug where its TCP readiness probe cannot detect a UDP-only DNS server.
  • No auto-install of the binary. Always pass --binary=<path> explicitly. Grida does not implement the install_webdriver hooks.
  • External stylesheets / images are not resolved. grida_wpt fetches the test HTML but does not follow <link rel="stylesheet"> or <img src>. Tests that depend on external support files will mismatch until the adoption plan's P4 lands.

Troubleshooting​

Unknown product 'grida' → You are pointing at the wrong WPT checkout. Confirm git remote get-url origin in ../wpt is https://github.com/gridaco/wpt (or a fork thereof).

Missing hosts file configuration → Same cause; the fork's tools/wpt/run.py adds grida to the skip-list. If this error fires, the fork is stale or the wrong clone.

Tests CRASH with network error in stderr → wptserve did not start. Check for port conflicts on 8000–8003 / 8443–8446 / 9000. pkill -f "wpt serve" and retry.

Keeping the fork current​

When upstream WPT drifts, rebase the Grida commit onto latest master inside the fork:

cd ../wpt
git fetch upstream master   # add upstream remote first if needed
git rebase upstream/master
git push --force-with-lease origin master

Three patches to carry: tools/wpt/run.py, tools/wpt/browser.py, tools/wptrunner/wptrunner/products.py. The two plugin files (grida.py, executorgrida.py) are new, so rebase-clean.

See also​