Cannot instantiate generic type when a macro reuses a OpenSymChoice

[Menduist]

Example

import macros

type
  Past[Z] = object
  OpenObject = object

macro rewriter(prc: untyped): untyped =
  prc.body.add(nnkCall.newTree(
    prc.params[0]
  ))
  prc
  
macro macroAsync(name, restype: untyped): untyped =
  quote do:
    proc `name`(): Past[seq[`restype`]] {.rewriter.} = discard
    
macroAsync(testMacro, OpenObject)

Current Output

Error: cannot instantiate Past [type declared in /tmp/test.nim(4, 3)]
got: <T>
but expected: <Z>

Expected Output

Compiles correctly

Additional Information

On every nim version I tested. Caused problems in chronos, worked around with: status-im/nim-chronos#261, which allows to cleanup the opensyms:

proc cleanupOpenSymChoice(node: NimNode): NimNode {.compileTime.} =
  if node.kind in nnkCallKinds and
    node[0].kind == nnkOpenSymChoice and node[0].eqIdent("[]"):
    result = newNimNode(nnkBracketExpr)
    for child in node[1..^1]:
      result.add(cleanupOpenSymChoice(child))
  else:
    result = node.copyNimNode()
    for child in node:
      result.add(cleanupOpenSymChoice(child))

With

  prc.body.add(nnkCall.newTree(
    cleanupOpenSymChoice(prc.params[0])

The first code now compiles correctly.

[metagn]

Works in devel probably because of #23983