Using sum types with module specifiers typechecks inconsistently

[tersec]

Using sum types with module specifiers typechecks inconsistently.

Example

module z:

type
  A* = object
    discard

  B* = object
    discard

  C* = A | B

module z2 (or any other name, probably):

import z

when true:
  # These work fine.
  discard default(z.A)
  proc f1(x: z.A) = discard
  discard default(z.B)
  proc f2(x: z.B) = discard
  discard default(A)
  proc f3(x: A) = discard
  discard default(B)
  proc f4(x: B) = discard
  proc f5(x: C) = discard
  proc f6(x: z.C | C) = discard

# Doesn't compile.
proc f(x: z.C) = discard

Current Output

z2.nim(17, 7) Error: invalid type: 'typeof(C)' in this context: 'proc (x: typeof(C))' for proc

Tested on 1.2.12, 1.4.2, and current head:

Nim Compiler Version 1.2.12 [Linux: amd64]
Compiled at 2021-05-25
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: 121628357ec7fae91335bd392f03b0e6dd249319
active boot switches: -d:release

Nim Compiler Version 1.4.2 [Linux: amd64]
Compiled at 2021-05-13
Copyright (c) 2006-2020 by Andreas Rumpf

active boot switches: -d:release

Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2021-05-25
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 478f717377c4cd60cfce112b8b21d58031b118b4
active boot switches: -d:release

Expected Output

Successful compilation.

[timotheecour]

reduced with a single module t12311:

type
  A* = object
  B* = object
  C* = A | B
type B2 = t12311.B
type C2 = t12311.C
proc fn1(a: t12311.B) = discard
proc fn2(a: C) = discard
proc f3(a: C2) = discard # Error: invalid type: 'C2' in this context: 'proc (a: C2)' for proc
# proc fn4(a: t12311.C) = discard # ditto