Trailing comma in tuple after rest #35375

Search Terms: Trailing comma tuple

Code

var [...x]: [...string[]] = [];
var [...x,]: [...string[]] = [];
var [...x]: [...string[],] = [];

Actual/Expected behavior:

Currently, the first line is valid, the second line is invalid because a rest element can't be followed by a trailing comma, and the third line is considered as valid by TypeScript.

I think that for symmetry with array and object rest elements, also rest elements in tuples shouldn't be allowed to have a trailing comma.
This behavior was likely introduced in #28919, but since that PR doesn't mention rest types, probably it was an oversight.

Playground Link: Playground Link

Related Issues:

babel/babel#10769 - If this is the expected behavior, we'll fix it in Babel. If instead, you think that this should be fixed in TypeScript, let me know because this should first be fixed in prettier to avoid a broken development workflow.