Regression from 1.6 to 2.0 and devel with generics across modules

[tersec]

Description

Current approach requires three modules to reproduce -- it seems to relate to the import structure (A imports C, then A imports B which imports C). This probably isn't 100% required, but there are no other external imports required, stdlib or otherwise.

# Order matters to reproduce this; switch these and it builds
import ./altair
import ./forks_light_client

template lazy_header(name: untyped): untyped {.dirty.} =
  var `name _ ptr`: ptr[data_fork.LightClientHeader]  # this data_fork.Foo part seems required to reproduce

proc createLightClientUpdates(data_fork: static LightClientDataFork) =
  lazy_header(attested_header)

createLightClientUpdates(LightClientDataFork.Altair)

Where altair.nim:

type
  LightClientHeader* = object

and forks_light_client.nim:

import ./altair

type
  LightClientDataFork* {.pure.} = enum
    None = 0,
    Altair = 1

template LightClientHeader*(kind: static LightClientDataFork): auto =
  when kind == LightClientDataFork.Altair:
    typedesc[altair.LightClientHeader]
  else:
    static: raiseAssert "Unreachable"

A number of interesting quirks here, e.g., without the `{.dirty.} it fails with

a.nim(6, 35) Error: ambiguous identifier: 'LightClientHeader' -- use one of the following:
  altair.LightClientHeader: LightClientHeader
  forks_light_client.LightClientHeader: template (kind: static[LightClientDataFork]): auto

regardless of Nim 1.6/2.0/devel

Nim Version

Nim Compiler Version 1.6.14 [Linux: amd64]
Compiled at 2023-06-29
Copyright (c) 2006-2023 by Andreas Rumpf

active boot switches: -d:release

Nim Compiler Version 2.0.0 [Linux: amd64]
Compiled at 2023-08-03
Copyright (c) 2006-2023 by Andreas Rumpf

git hash: a488067a4130f029000be4550a0fb1b39e0e9e7c
active boot switches: -d:release

Nim Compiler Version 2.1.1 [Linux: amd64]
Compiled at 2023-08-03
Copyright (c) 2006-2023 by Andreas Rumpf

git hash: b40da812f7aa590ed16df54a492684c228320549
active boot switches: -d:release

Current Output

Nim 1.6 builds successfully.

Nim 2.0/devel:
a.nim(11, 25) template/generic instantiation of `createLightClientUpdates` from here
a.nim(6, 34) Error: type mismatch: got 'LightClientDataFork' for 'LightClientDataFork.Altair' but expected 'LightClientHeader = object'

Expected Output

No response

Possible Solution

No response

Additional Information

No response

[metagn]

Simplified (generics bug, not related to templates or interpolating symbol names):

# a.nim
type TypeOrTemplate* = object

# b.nim
import a

template TypeOrTemplate*(num: int): untyped =
  # module a only exists so we can pick the type version of TypeOrTemplate here
  typedesc[a.TypeOrTemplate]

# c.nim
import a, b

proc generic[T](abc: T) =
  var x: abc.TypeOrTemplate

generic(123)

Caused by #21837