Compiler refuses to apply a converter when the input is an Array or Openarray

[ReneSac]

Here an example where, depending how you use it, the converter works or fails:

See also: https://github.com/micklat/NimBorg/blob/master/nim_py/high_level.nim
(search for the line with: " # doesn't work as a converter, I don't know why ")

import opengl, glfw/glfw

type
  TCoord = enum
    x, y, z

  TVertex = object
    pos: array[TCoord, GLfloat]
    normal: array[TCoord, GLfloat]


var
  vertices: array[NumVertices, TVertex]  

converter toGlVec(a: Array[3, int]) : array[TCoord, GLfloat] = 
  return [a[x.ord].GlFloat, a[y.ord].GlFloat, a[z.ord].GlFloat]

# Call:
newVertexGroup([0, 0, 1] , [-1, -1, 1] , [1, -1, 1] , [1, 1, 1] , [-1, 1, 1] )

#Works:
proc newVertexGroup(normal: Array[3, int], pos: varargs[Array[3, int]]) =
  var curVertex {.global.} = 0
  for p in pos:
    vertices[curVertex] = TVertex(pos: p, normal: normal)
    curVertex.inc


#Fails:
proc newVertexGroup(normal: array[TCoord, GLfloat], pos: varargs[array[TCoord, GLfloat]]) =
  var curVertex {.global.} = 0
  for p in pos:
    vertices[curVertex] = TVertex(pos: p, normal: normal)
    curVertex.inc

# Error: type mismatch: got (Array constructor[0..2, int], Array constructor[0..2, int], Array constructor[0..2, int], Array constructor[0..2, int], Array constructor[0..2, int])
#but expected one of: 
#N.newVertexGroup(normal: array[TCoord, GLfloat], pos: varargs[array[TCoord, GLfloat]])

[micklat]

current link to the additional (supposed) example of the same problem:
https://github.com/micklat/NimBorg/blob/master/nimborg/py/high_level.nim

[Araq]

Converters do not lift to array construction. It's easy enough to use varargs[typ, op].

[ReneSac]

I don't see how it would apply to my example above:

proc newVertexGroup(normal: array[TCoord, GLfloat], pos: varargs[array[TCoord, GLfloat]])

Varargs is very limited. It can only be used once as the last parameter on a call. With varargs you also don't have control over the number of elements you receive. It should be used when you want varargs, not when you want to use Array or OpenArray.

EDIT: Looking at micklat use case, it also don't seems to fit.