nim-1.4.0 regression: expandMacros compilation error

[slonik-az]

The following code compiles (and runs) perfectly fine under 1.2.6 and 1.2.8 but fails compilation in 1.4.0

MWE code

https://play.nim-lang.org/#ix=2BF4

import std/macros

template mk_discard*(macroName: untyped): untyped =
  macro `macroName`(args: varargs[untyped]): untyped = discard

expandMacros:
  mk_discard(foo)

foo(a,b,c,1, 2, 3)

Produced output (nim-1.4.0)

Compilation fails with the following error message

macro foo(args`gensym0: varargs[untyped]): untyped =
  discard

/usercode/in.nim(6, 1) template/generic instantiation of `expandMacros` from here
/usercode/in.nim(7, 3) Error: illformed AST: macro foo(args`gensym0: varargs[untyped]): untyped =
  discard

Expected Output

The MWE code is expected to compile and produce no output when run. The expected behavior is observed under nim 1.2.8 and 1.2.6.

Additional Information

MacOS Mojave (10.14.6)

$ nim -v
Nim Compiler Version 1.4.0 [MacOSX: amd64]
Compiled at 2020-10-17
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: 1caa193d9367c8da49c22ee3e124e10dda03caf3
active boot switches: -d:release

[timotheecour]

git bisect returns #15158:

commit fb58066b61b14f4a1d6cdb0f4a8f0a9ea4174d82
Author: Clyybber <darkmine956@gmail.com>
Date:   Thu Aug 27 15:50:59 2020 +0200

    Fix #5691 (#15158)

    * Fix #5691
    * Cleanup and thoughts
    * Use scope approach
    * Seperate defined/declared/declaredInScope magics
    * Fix declaredInScope
    * Update spec accordingly

/cc @Clyybber

[andreaferretti]

I did not investigate this thouroughly, but this may be also the reason why tests of https://github.com/andreaferretti/interfaced fail

[demotomohiro]

This bug still exists in recent devel Nim.
This is minimal code to reproduce the bug:

import std/macros

macro simplifiedExpandMacros(body: typed): untyped =
  result = body

simplifiedExpandMacros:
  proc testProc() = discard

simplifiedExpandMacros:
  template testTemplate(): untyped = discard

# Error: illformed AST: macro testMacro(): untyped =
simplifiedExpandMacros:
  macro testMacro(): untyped = discard

expandMacros takes code block as typed and return it.
It cause illformed AST error only when it got macro declaration.

Nim version:

$ nim -v
Nim Compiler Version 1.7.1 [Linux: amd64]
Compiled at 2022-06-30
Copyright (c) 2006-2022 by Andreas Rumpf

git hash: bcff13debcbdd8108237c8033e4dc9c38bb331e0
active boot switches: -d:release