[ARC] Type-bound assign op is not being generated

[ghost]

This fails to compile while it shouldn't. Found in https://github.com/paranim/pararules

Example

type
  MemoryNode = ref object

proc main() =
  var node: ptr MemoryNode
  var data: seq[(MemoryNode, string)]
  data.add((node: node[], text: "hello"))

main()

Current Output

/home/dian/Projects/stuff/a.nim(7, 23) Error: internal error: '=' operator not found for type MemoryNode

Expected Output

No compilation error, but of course it'll crash at runtime because it's dereferencing a null pointer.

$ nim -v
Nim Compiler Version 1.3.7 [Linux: amd64]
Compiled at 2020-10-07
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: acbe27b082c202895df1b78a82951389b4a232a0
active boot switches: -d:release -d:danger

[ghost]

Full version of the original proc:

proc fireRules*[T](session: var Session[T]) =
  # find all nodes with `then` blocks that need executed
  var thenNodes: seq[ptr MemoryNode[T]]
  for node in session.thenNodes[].items:
    thenNodes.add(node)
  if thenNodes.len == 0:
    return
  session.thenNodes[].clear
  # collect all nodes/vars to be executed
  var thenQueue: seq[(MemoryNode[T], Vars[T])]
  for node in thenNodes:
    node.trigger = false
    for match in node.matches.values:
      if match.enabled:
        thenQueue.add((node: node[], vars: match.vars)) # compiler fails on this line
  # execute `then` blocks
  for (node, vars) in thenQueue:
    node.callback(vars)
  # recur because there may be new `then` blocks to execute
  session.fireRules()