Earlier quoted context omitted.
I maintain a standalone web layout engine[0] (currently implementing Flexbox and CSS Grid) which has no scripting support. WPT layout tests using is a major blocker to us running WPT tests against our library. Yoga (used by React Native) is in a similar position. Do you think the WPT would accept pull requests replacing such tests with equivalent tests that don't use (perhaps using a build script to generate multiple…
I don't decide WPT policies (and I honestly don't know who does), but I'm pretty sure using a build script would be right out, as WPT is deeply embedded in a lot of other projects. E.g., if you made a build script, you would need to add support for running that script in Blink and in Gecko and in WebKit, and their multiple different runners, and probably also various CI systems. As for the second option, I don't actu…
A build script used by significant swaths of the test suite is almost certainly out; it turns out people like being able to edit the tests they're actually running. (We _do_ have some build scripts — but they're mostly just mechanically generating lots of similar tests.
A lot of the goal of WPT (and the HTML Test Suite, which it effectively grew out of) has been to have a test suite that browsers are actually running in CI: historically, most standards test suites haven't been particularly amenable to automation (often a lot of, or exclusively, manual tests, little concern for flakiness, etc.), and with a lot of policy choices that effectively made browser vendors choose to write tests for themselves and not add new tests to the shared test suite: if you make it notably harder to write tests for the shared test suite, most engineers at a given vendor are simply going to not bother.
As such, there's a lot of hesitancy towards anything that regresses the developer experience for browser engineers (and realistically, browser engineers, by virtue of sheer number, are the ones who are writing the most tests for web technologies).
That said, there are probably ways we could make things better: a decent number of tests for things like Grid use check-layout-th.js (e.g., https://github.com/web-platform-tests/wpt/blob/f763dd7d7b7ed...).
One could definitely imagine a world in which these are a test type of their own, and the test logic (in check-layout-th.js) can be rewritten in a custom test harness to do the same comparisons in an implementation without any JS support.
The other challenge for things like Taffy only targeting flexbox and grid is we're unlikely to add any easy way to distinguish tests which are testing interactions with other layout features (`position: absolute` comes to mind!).
My suggestion would probably be to start with an issue at https://github.com/web-platform-tests/rfcs/issues, describing the rough constraints, and potentially with one or two possible solutions.