When self-referenced optional field is defined inside a ref type then the option type behaves in a wrong way during an assignment

[KarolBajkowski]

Description

When the type contains a self-referenced optional field then during the variable assignment (value copy takes place I believe), the field 'isSome' has a wrong value. Below are the examples:

This works fine:

import options

type Foo = ref object
    name: string

var foo1: Option[Foo] = none(Foo)
var foo2: Option[Foo] = foo1
if foo2.isSome:
    echo "SHOULD NOT BE REACHABLE"
else:
    echo "OK"

It will print: "OK"

however, when I add 'prev' field, this program misbehaves:

import options

type Foo = ref object
    name: string
    prev: Option[Foo]    # <-- this has been added

var foo1: Option[Foo] = none(Foo)
var foo2: Option[Foo] = foo1
if foo2.isSome:
    echo "SHOULD NOT BE REACHABLE"
else:
    echo "OK"

It will print "SHOULD NOT BE REACHABLE" which is an unexpected result.

Nim Version

Nim Compiler Version 2.0.8 [Windows: amd64] Compiled at 2024-07-03 Copyright (c) 2006-2023 by Andreas Rumpf

Current Output

No response

Expected Output

No response

Known Workarounds

import options

type 
    Foo = ref FooObj
    FooObj = object
        name: string
        abc: Option[Foo]

var foo1: Option[Foo] = none(Foo)
var foo2: Option[Foo] = foo1
if foo2.isSome:
    echo "SHOULD NOT BE REACHABLE"
else:
    echo "OK"

Additional Information

No response

[metagn]

Related #16754

[KarolBajkowski]

@metagn Actually it might be exactly the same. I refined my example. It looks like this one also misbehaves:

import options

type Foo = ref object
    name: string
    abc: Option[Foo]

var foo1: Option[Foo] = none(Foo)
var foo2: Option[Foo] = foo1
if foo2.isSome:
    echo "SHOULD NOT BE REACHABLE"
else:
    echo "OK"

It prints "SHOULD NOT BE REACHABLE" as well.