reserved keywords error messages

[c1tt1]

A similar issue was raised in #4121

It would be good to produce proper error messages for using reserved keywords in the language.
The below example shows I am using the out keyword.

def foo(up : String, down : String, out : String)
  bar = JSON.build do |json|
    json.object do
      json.field "up", up
      json.field "down", down
      json.field "out", out
    end
  end

  bar
end

The compiler throw the following error at compile time. Same with crystal tool format.

Syntax Error: can't use variable name 'bar' inside assignment to variable 'bar'

The above message gives no idea about out been a reserved keyword and suggests bar is.
Displaying proper errors for builtin types would be good.

• Crystal compiler version Crystal 0.24.2 (2018-03-10) LLVM: 5.0.1
• OS x86_64-apple-macosx

[straight-shoota]

Reduced example:

def foo(out : String)
  bar = begin
    puts out
  end
  bar # can't use variable name 'bar' inside assignment to variable 'bar'
end

I initially expected this to be resolved by #5930, but out was not considered to be in the list of disallowed argument names.

Still, there seems to be some issue with it. It would be easy to simply restrict the use of out as argument name, but it is usually not an issue because it doesn't have any special meaning outside of argument definitions and there it's usage should be unambiguous.
This seems really odd, as if local var out was confused with bar when used as a method argument, but the syntax error happens in a seemingly unconnected line.

[c1tt1]

#5930 was merged 18 days ago which means it will be available on next release correct?

[Sija]

@stern0 it's correct (unless core team decides to release half-baked version like 0.24.2 was).

[straight-shoota]

@stern0 #5930 doesn't fix this.