Ouch, this regressed all tests depending on html.idl. You can see it in https://github.com/web-platform-tests/wpt/runs/207949624 right on this PR but I didn't check that when reviewing. You can also see all the broken tests live on wpt.fyi.

@web-platform-tests/wpt-core-team can someone quickly revert this? I don't have access to a computer with a command line this weekend, but can follow up with "stop this from happening again" types of bugs next week.

@lukebjerring a case for regression detection here :)

What the failure saya::

FAIL message: promise_test: Unhandled rejection with value: object "WebIDLParseError: Syntax error at line 1471, since `interface CustomElementRegistry`:
 define(DOMString name, CustomElementConstructor constructor, optional ElementDefinitionOptions
                        ^ Trailing comma in arguments list"

This looks like a webidl2.js regression to me.

For anyone who also didn't know, @jgraham pointed out that it is possible to revert from the GitHub UI. It shows up next to the "Ms2ger merged commit 41a1425 into master 21 hours ago" event.

I've filed w3c/webidl2.js#402.