fix #14339

[ringabout]

ref: #14339

[Varriount]

• Why does this work?
• Wouldn't a better solution be to change the implementation, or extend the VM? I don't think introducing functionality in the standard library that's solely meant to work around compiler issues is a good idea. One the issue is fixed (hopefully) the functionality becomes pointless.

[ringabout]

The get in CritBitTree returns var T which somehow can't be used in VM.
So there are three solutions:

1. Make a version of get which doesn't use var T as return type.
2. Extend VM which is hard for me :)
3. Make get return T which is a break change, namely change to proc []*[T](c: var CritBitTree[T], key: string): T {.inline.}.

proc `[]`*[T](c: var CritBitTree[T], key: string): var T 

I will try to find the reason which cause this problem.

[ringabout]

It seems to be related to generics templates. Moving codes in templates to [] proc seems to work. I don't know how to deal with it.

# template get[T](c: CritBitTree[T], key: string): T =
#   let n = rawGet(c, key)
#   if n == nil:
#     when compiles($key):
#       raise newException(KeyError, "key not found: " & $key)
#     else:
#       raise newException(KeyError, "key not found")
#   n.val

proc `[]`*[T](c: var CritBitTree[T], key: string): var T {.inline.} =
  # get(c, key)
  let n = rawGet(c, key)
  if n == nil:
    when compiles($key):
      raise newException(KeyError, "key not found: " & $key)
    else:
      raise newException(KeyError, "key not found")
  result = n.val

[timotheecour]

It seems to be related to generics templates.

no, see #14339 (comment)

(always minimize examples to maximum extent before jumping to conclusions / bugfixes ;-) )

[timotheecour]

superseded by #16002 (which makes VM support this)