cannot get pointer to nested generic proc due to "unspecified generic parameters" even though they are specified

[alaviss]

This bug concerns future development of CPS regarding the transformation of generic procedures.

Example

type
  C = ref object of RootObj
    fn: ContProc
    ex: ref Exception
  
  ContProc = proc(c: C): C {.nimcall.}

proc noop(c: C): C = c

when false:
  # original proc
  proc foo[T](x: T) {.cps.} =
    noop()
    echo x

type
  Env[T] = ref object of C
    x: T

proc foo_cont[U](c: C): C =
  proc afterCall[V](c: C): C =
    echo Env[V](c).x

  c.fn = afterCall[U]
  return noop(c)
  
proc foo[T](x: T): C =
  return Env[T](fn: foo_cont[T], x: x)

proc tramp(c: sink C) =
  while c != nil and c.fn != nil:
    c = c.fn(c)

tramp foo(10)
tramp foo("string")

Current Output

in.nim(34, 10) template/generic instantiation of `foo` from here
in.nim(28, 29) template/generic instantiation of `foo_cont` from here
in.nim(24, 10) Error: 'afterCall' doesn't have a concrete type, due to unspecified generic parameters.

Expected Output

This should compile correctly.

In fact, if you move afterCall to outside foo_cont, this compiles and functions perfectly.

In CPS these nested procs will be moved out at the end of the transformation, however during IR passes we keep them there, and this bug would prevent immediate code like this from successfully sem.

Additional Information

$ nim -v
Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2021-05-01
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 13b57524d35a18df57bec2a7d6a2faa7ce712e9f
active boot switches: -d:release -d:nimUseLinenoise

[alaviss]

This is blocking try-finally transforms in CPS.