Ruby

It's the same with parse.y:

$ ruby -v --parser=parse.y -e 'def x?(y, z) = y in { x: ^z }' ruby 3.5.0dev (2025-05-28T04:34:40Z master d064fd067b) [x86_64-linux] -e:1: z: no such local variable ruby: compile error (SyntaxError) 

So I think we should assign matz and not prism.

I guess it's a pitfall of the weird precedence of def =, which has already been reported many times in various variants.
def x?(y, z); y in { x: ^z }; end works fine of course.

@yui-knk (Kaneko Yuichiro) Do you think this is possible to implement?