Overloading resolution chooses a generic template instead of a method for an inherited type

[ghost]

This code is expected to call the dispose method but it calls a template instead.

Found in the 4th NiGui example.
It crashes with ARC/ORC because Nim calls ARC's dispose from here instead of NiGui's dispose defined here (it's exported in the forward declaration at the top of the file).

Example

type
  Window* = ref object of RootObj
  WindowImpl* = ref object of Window

# Without that template the method will be called
template dispose[T](x: ref T) = 
  echo "called the template dispose"

method dispose(t: Window) {.base.} = 
  echo "called the method dispose"

var t = WindowImpl()
t.dispose()

Current Output

called the template dispose

Expected Output

called the method dispose

$ nim -v
Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2021-02-10
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 216be4060a853b3425501318537d598c4842eefc
active boot switches: -d:release

[Araq]

From the spec:

Every arg in args needs to match. There are multiple different categories how an
argument can match. Let f be the formal parameter's type and a the type
of the argument.

3. Generic match: f is a generic type and a matches, for
   instance a is int and f is a generic (constrained) parameter
   type (like in [T] or [T: int|char].
4. Subrange or subtype match: a is a range[T] and T
   matches f exactly. Or: a is a subtype of f.

These matching categories have a priority: An exact match is better than a
literal match and that is better than a generic match etc.

The compiler is correct.