Strange memory corruption / codegen bug?

[rikki cattermole via Digitalmars-d-learn]

On 12/12/2016 12:15 AM, TheGag96 wrote:
> I was porting my Evolutionary Computing homework written in Python over
> to D, and I've come across this bug I cannot for the life of me figure out.
>
> https://gitlab.com/TheGag96/evo-pacman/blob/master/source/pacman/tree.d#L139

Not public, please pastebin.

> I don't think I could cut this down to a smaller reproducible scenario
> due to how bizarre and specific this problem is, so I apologize in
> advance if this is hard to follow.
>
> Basically, imagine that I have a binary tree class where, due to how my
> program is set up, each node will have either children on both the left
> and right side or no children at all (the latter represented by a value
> of null for Tree's left and right member). I have a member function
> called "dup" -- marked const, mind you -- that just returns a deep copy
> of the tree and SHOULDN'T make any changes to the calling object.
>
> I call this function a couple different places and it appears to
> function okay, but at the spot I linked, if I call .dup here, it will
> corrupt one of the tree's nodes and put something in its left member for
> no apparent reason. This oddly doesn't happen on every Tree calling this
> function. This could definitely be some stupid mistake on my part, but
> the fact that calling a const-marked function changes the state of the
> calling object makes me think something else is afoot here...
>
> I would greatly appreciate anyone who would be willing to take a look at
> this. This bug is driving me absolutely nuts.