Passing Natural to bitops.BitsRange[T] parameter in generic proc is compile error

[demotomohiro]

Minimum code:

import std/bitops

testBit(1, 1.Natural)

Compile error message:

f:\temp\nim-1.5.1\lib\pure\bitops.nim(63, 37) Error: 'sizeof' requires '.importc' types to be '.completeStruct'

Minimum code without importing bitops:

type BitsRange[T] = range[0..sizeof(T)*8-1]

proc bar[T](a: T; b: BitsRange[T]) =
  discard

bar(1, 2.Natural)

Compile error message:

f:\temp\testbitr.nim(1, 36) Error: 'sizeof' requires '.importc' types to be '.completeStruct'

This code also produces same compile error:

type BitsRange[T] = range[0..sizeof(T)*8-1]

proc bar[T](a: T; b: BitsRange[T]) =
  discard

bar(1.Natural, 2.Natural)

Just converting Natural variable to BitsRange[int] doesn't make compile error.
Following code compiles without erorr.

type BitsRange[T] = range[0..sizeof(T)*8-1]

var x: BitsRange[int] = 0
x = 1.Natural
echo x

var y: BitsRange[Natural] = 0
y = 1.Natural
echo y
y = 2
echo y

proc foo(x: BitsRange[int]) =
  discard

foo(1)
foo(1.Natural)

proc foo2(x: BitsRange[Natural]) =
  discard

foo2(1)
foo2(1.Natural)

proc bar[T](a: T; b: BitsRange[T]) =
  discard

bar(1.Natural, 2)

Nim version:

f:\temp>nim -v
Nim Compiler Version 1.5.1 [Windows: amd64]
Compiled at 2021-09-08
Copyright (c) 2006-2021 by Andreas Rumpf

active boot switches: -d:release