GDScript debugger crashes the instant a doubly linked list is made using a Dictionary.

[SamuelNewhouse]

Godot version:
v3.1.1.stable.official

OS/device including version:
Windows 10 Home, Version 1809, OS Build 17763.914

Issue description:
If run normally the game will not crash, but stepping through the code with the GDScript debugger causes the debugger to crash the instant a doubly linked list is made using a Dictionary. The moment the list is linked both forwards and backwards, the debugger crashes.

Steps to reproduce:

1. Use a dictionary with "next" and "previous" keys as a structure for a doubly linked list.
2. Use a loop inside _ready() to create the doubly linked list.
3. Run the game and it will not crash.
4. Step through code with the debugger and it will crash on the second loop when "previous" is assigned to the first list item.

Minimal reproduction project:
Doubly Linked.zip

[Zylann]

A doubly-linked list in GDScript calls for reference cycles (as in a graph). Item 1 references item 0, item 0 references item 1. The debugger may be fixed to not crash in this case, but you still have a memory leak problem.
To workaround this:

• Change your list items to derive from Object (if they don't already), but take care freeing them after use
• Or have your items in a separate array, and store indexes to that array in your list items

[SamuelNewhouse]

Thanks Zylann. I created a new listItem derived from Object and it no longer crashes when stepping through the code.

[bojidar-bg]

Duplicate of #1289.