An occurence of a bug which was fixed in DMD a while ago

[Iain Buclaw via D.gnu]

On 20 Nov 2014 01:45, "Koz Ross via D.gnu" <d.gnu at puremagic.com> wrote:
>
> The bug is similar to https://issues.dlang.org/show_bug.cgi?id=6998.
Specifically, here is the code that can be used to demonstrate it. I'm
using GDC 4.9.1 (according to gdc --version).
>
> module badbh;
>
> import std.container, std.string, std.stdio;
>
> class Node {
>   size_t val;
>   Node next;
>
>   this (size_t val) {
>     this.val = val;
>   }
>
>   override string toString() {
>     if (next is null) {
>       return format("%s", val);
>     } else {
>       return format("%s, %s", val, next.toString());
>     }
>   }
> }
>
> void main () {
>   //sets up the demo structure
>   auto n = new Node(40);
>   n.next = new Node(30);
>   n.next.next = new Node(10);
>   n.next.next.next = new Node(20);
>   writeln(n); //should yield "40, 30, 10, 20"
>   auto t2 = top2(n);
>   writeln(n); //watch the segfaults
> }
>
> Node[] top2 (Node n) {
>   auto heap = BinaryHeap!(Array!Node, function bool (Node a, Node
b){return a.val > b.val;})();
>   Node[] nodes;
>   auto ptr = n;
>   while (ptr !is null) {
>     heap.insert(ptr);
>     ptr = ptr.next;
>   }
>   for (auto i = 0; i < 2; i++) {
>     nodes ~= heap.front;
>     heap.removeFront;
>   }
>   assert(nodes.length == 2);
>   //some sanity checks to show my code isn't logically FUBAR
>   assert(nodes[0] !is null);
>   assert(nodes[1] !is null);
>   assert(nodes[0].val == 10);
>   assert(nodes[1].val == 20);
>   return nodes;
> }
>
> The comments are self-explanatory. This destructive behaviour occurs
*only* when the heap is in a different scope to the structure - if you were
to copy all the code in top2 into main, the segfault wouldn't happen.
>
> I know that this is definitely a GDC thing - the same code under DMD
works correctly (i.e. prints the whole linked structure and doesn't
segfault).

Looking at the date it was fixed in DMD, the next release merge should
resolve that.

Iain.
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