Raise syntax error when using out as an arg

[esse]

That commit fixes issue #6042.

[bew]

Can you add a spec somehow?

[Sija]

@bew it's there, see the diff.

[straight-shoota]

I'm not sure this is right. There should not really be an issue with accessing out as local variable. #6042 could be fixed differently.

[straight-shoota]

I'm pretty sure @makenowjust didn't just forget to add a restriction to out in #5930.

[asterite]

out as a local variable should be forbidden. out is a keyword and it can be confused with the out var syntax.

[asterite]

That said, out taken as a keyword just for interacting with C seems like a bad design choice.

[asterite]

Basically...

out = 1
foo(out) # Error: expecting variable or instance variable after out

That's why out should not work for local variables, because you can't pass them to other methods.

[straight-shoota]

Then all keywords should be forbidden?

out var could be confused with a method call, but not really with a local variable called out.

[straight-shoota]

If out is not followed by a variable name, it's not a keyword.

[asterite]

@straight-shoota That's just confusing, but if someone wants to implement that, please go ahead (and revert this PR).

[makenowjust]

@straight-shoota Yes, I did't forget to add out. However, @asterite's opinion makes a sense to me. I have no disagreement with this PR.