Bez: Generating a browser engine from specs and tests
4 hours ago
- Bez generates a web rendering engine from specifications and tests, avoiding manual implementation by hundreds of engineers.
- Goals include complete or tree-shaken builds, fast performance on any device, easy embedding, and fastest updates via regeneration.
- The engine works by modeling specs into candidates, running them, and checking against Chrome, Firefox, and WebKit for consistency.
- Current status shows 93% unreached functionality; CSS leads with 2.5% generated, while HTML, JavaScript, and others remain at 0%.
- Findings reveal that the three browsers mostly agree, Firefox is an outlier in certain cases, and conformance suites like WPT are usable oracles.
- Logic programming (Datalog) accurately replicated margin collapsing across 1195 offsets and caught bugs missed by geometry checks.
- About 55–60% of engine-relevant features have usable automated oracles and generatable spec prose, while 8–18% lack both.
- Open questions remain about cost, feature scope, WPT reachability without JavaScript, and boundaries of IDL-generated code.