Regression with mixin and generics from 2.0.8 to version-2-0/version-2-2, fixed in devel

[tersec]

Description

type
  K = distinct int
  M = object

proc p(e: auto, T: type): T =
  mixin p
  p(e, result)

proc p[T](r: M, g: T) =
  when g is object:
    mixin p
    discard p(r, K)
  else:
    {.error: "u".}

proc p(_: M, _: K | K) = discard

Nim Version

Builds:
v2.0.8:

Nim Compiler Version 2.0.8 [Linux: amd64]
Compiled at 2024-09-23
Copyright (c) 2006-2023 by Andreas Rumpf

git hash: 5935c3bfa9fec6505394867b23510eb5cbab3dbf
active boot switches: -d:release

devel:

Nim Compiler Version 2.1.99 [Linux: amd64]
Compiled at 2024-09-23
Copyright (c) 2006-2024 by Andreas Rumpf

git hash: a55c15c651b805c5eca4475f9845a57adf6cddef
active boot switches: -d:release

Does not build:
version-2-0:

Nim Compiler Version 2.0.9 [Linux: amd64]
Compiled at 2024-09-23
Copyright (c) 2006-2023 by Andreas Rumpf

git hash: 27381cc60213e19aa34664176bd358ca5e45bd5a
active boot switches: -d:release

version-2-2:

Nim Compiler Version 2.1.99 [Linux: amd64]
Compiled at 2024-09-23
Copyright (c) 2006-2024 by Andreas Rumpf

git hash: 755307be61e4ee7b32c8354b2c303d04bdfc3a3e
active boot switches: -d:release

Current Output

/tmp/v.nim(17, 10) template/generic instantiation of `p` from here
/tmp/v.nim(7, 4) template/generic instantiation of `p` from here
/tmp/v.nim(14, 12) Error: u

Expected Output

No response

Known Workarounds

No response

Additional Information

Fixed in devel, so presumably there's something to backport from devel to version 2-0/version-2-2.

[metagn]

Was caused by #23870 and fixed by #24144 @narimiran

[narimiran]

Was caused by #23870 and fixed by #24144 @narimiran

Thanks for the ping. Backported now. @tersec, it should be ok now (the example now works on my machine).

[tersec]

Was caused by #23870 and fixed by #24144 @narimiran

Thanks for the ping. Backported now. @tersec, it should be ok now (the example now works on my machine).

Well, I realized the repro I posted above somehow omitted the last line, so it always compiles. For reference, one example of how to complete it:

type
  K = distinct int
  M = object

proc p(e: auto, T: type): T =
  mixin p
  p(e, result)

proc p[T](r: M, g: T) =
  when g is object:
    mixin p
    discard p(r, K)
  else:
    {.error: "u".}

proc p(_: M, _: K | K) = discard
p(default(M), default(K))

and, obviously, that first p overload isn't used anymore, and

type
  K = distinct int
  M = object

proc p[T](r: M, g: T) =
  when g is object:
    mixin p
    discard p(r, K)
  else:
    {.error: "u".}

proc p(_: M, _: K | K) = discard
p(default(M), default(K))

exhibits the same pattern.

But haven't verified yet with new version-2-0.

[metagn]

I noticed and forgot to mention it, that's what I used to check the issue

[narimiran]

The fix is backported, I think this can be closed. (If not, please reopen)