Block parameters prefixed with underscore are incorrectly highlighted

[vinistock]

Our grammar file is not properly handling block parameters that are prefixed with underscore. For example:

# `a` looks ok
# `b` doesn't
[].each do |a, _b|
end

We might be missing _ as a valid character in the regex.

[pepetorres1998]

Can I work on this issue?

[vinistock]

Sure!

[andyw8]

(I don't mind if we do this, but I wonder if this was originally an intentional decision due to the _prefix indicating an unused variable.).

[vinistock]

It cannot have been intentional, because it currently assigns the constant token to them. Additionally, the leading underscore it's just a convention. From Ruby's perspective, it's still a parameter and even referring to it still works.