[Concepts] Declarations in concept body are not considered

[konsumlamm]

Defining a concept without any type that matches it, leads to errors when trying to use that concept.

Example

type
  Comparable = concept
    proc compare(a, b: Self): int # so that there are no conflicts with `cmp`

proc test[T: Comparable](x, y: T) =
  echo compare(x, y)

Current Output

Error: undeclared identifier: 'compare'

Expected Output

No error.

Possible Solution

Make name resolution consider concept declarations (compare in this case).

Additional Information

$ nim -v
Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2021-03-18
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: de5a8265384c2f23eca744b4fc9feda9721faefd
active boot switches: -d:release

[Araq]

This wasn't covered by my RFC. I think this requires a different RFC, "name resolution in generics that use new-styled concepts". That said, I agree that we should do it. But notice that symbol lookup is only the first step, we could also type-check generic bodies completely.