Compiler Seg faulting when using "object" instead of "ref object" for nested object

[davidbruce]

Originally from: https://forum.nim-lang.org/t/6679

I ran into a incredible frustrating issue where my compiler was seg faulting due to missing a ref in a type declaration. In the below code just swapping Node[T] = object to Node[T] = ref object stops the seg fault and compiles and runs as expected. In fact on MacOS I don't even get the segfault error, Segmentation fault (core dumped), instead the compiler just mysteriously stopped. The same thing happens with the devel branch I grabbed from choosenim.

type
  Node[T] = object
      item: T
      next: Node[T]
  Bag*[T] = ref object
      first: Node[T]
      size: int

Example

You can reproduce the seg fault here: https://play.nim-lang.org/#ix=2u3O

import random

type
  Node[T] = object
      item: T
      next: Node[T]
  Bag*[T] = ref object
      first: Node[T]
      size: int

func isEmpty*(bag: Bag): bool =
   bag.first == nil

func size*(bag: Bag): int =
   bag.size

func add*[T](bag: Bag[T], item: T): void =
   var oldFirst = bag.first
   bag.first = new(Node[T])
   bag.first.item = item
   bag.first.next = oldFirst
   bag.size += 1


var testBag = new(Bag[int])
for i in 1 .. 10:
  randomize()
  testBag.add(i * rand(100))

echo "Is the bag empty: " & $testBag.isEmpty
echo "Bag size: " & $testBag.size

Current Output

Segmentation fault (core dumped)

Expected Output

An error of some kind pointing out the need for a reference.

Nim Compiler Version 1.0 and beyond

[metagn]

Still an issue, same as #14646.