ok I know the problem and I will describe it as the actual fix might take a little thought. We allocate lvars and kwargs using the same StaticScope storage. We depend on strings which represent the variable name. So we do not complain about 'a:' since opt arg 'a=' exists. This seemed safe since you cannot actually have a method like:

def foo(a=1, a:)
end

The parser realizes that you are trying to use the same name in two different ways which is ambiguous. What the current solution did not consider is that we need to know if a particular name is a kwarg or an ordinary arg. So there are many ways to skin this cat but it means some extra state somewhere. Most obvious thought would be a kwargs start at offset x field. Then if we find 'a' exists before that we know it is not a kwarg?

Wow, blazing fast fix! Thanks! 😄

@ivoanjo I thought I had fixed all keyword argument bugs relating to methods (we have some other issues still with blocks) in our last point release so I was determined!