Infinite loop with holes due to inconsistent linked list state

[eile]

Hi,

We've hit a fairly uncommon bug when tesselating a large polygons with holes. I haven't fully figured it out, but the incoming linked list is inconsistent. See below for the workaround we applied.

For my own sanity, I ported it to typescript to understand and work on it. If you are interested in switching to TS, I can provide the typescript file.

     if (p.z === null) {
       p.z = zOrder(p.x, p.y, minX, minY, invSize);
     }
+
+    // Detect inconsistent state: Somehow this happens when holes are present. Fixup linked list and try again
+    if (p.prev.next !== p || p.next.prev !== p) {
+      p.prev.next = p;
+      p.next.prev = p;
+      return indexCurve(start, minX, minY, invSize);
+    }
     p.prevZ = p.prev;
     p.nextZ = p.next;
   }```

[mrgreywater]

Thank you for your information. In place of the workaround, could you add an assertion and dump the polygon to reproduce the issue, please?

[eile]

Might be a dup of #127 (we are colleagues). Will dump the poly in a bit.

[mourner]

Thanks a lot for the report! We're not planning on switching to TS, but very interested in any insights that could help fix the issue. Inconsistent prev/next state is a good clue — if it does fix the issue, we could try adding a bunch of asserts throughout the code to see the exact point where it becomes corrupted, and fix the root cause.

[eile]

Here is the call in question 135.log

[eile]

@mrgreywater @mourner Could you reproduce the problem? Do you have an idea on when you'll be able to fix this?

[mourner]

This may no longer be reproducible according to #148 — let's close and reopen if there's a test case that still breaks.