Beeware application crashes when attempting to click and drag item out of toga.Table and toga.Tree

[chk-n]

After installing the toga demo file from the toga repository and playing around with it I noticed that when I attempted to click and drag an item in a Tree or Table the app would crash saying 'Python quit unexpectedly.'.

Steps to reproduce the behavior:

1. Install demo
2. Run > briefcase dev
3. Click on item in list or Tree and attempt to drag it out

Environment:

• Operating System: MacOSX 10.15.7
• Python version: 3.8.6
• Software versions:
  - Briefcase: 0.3.3
  - Toga: Alpha

[freakboy3742]

Thanks for the report! A hard segfault crash definitely isn't the desired behavior, so at the very least there's an error that needs to be caught.

[freakboy3742]

Some initial investigation work: I thought we might be able to work around this by defining canDragRowsWithIndexes:atPoint: with a return value of False - however, this turns the problem in to an immediate segfault on the first click in the table.

[freakboy3742]

@samschott Any chance you have some free time to take a look at this one? I'm not having much luck hunting it down - mostly because there's almost no breadcrumb trail indicating the source of the problem, just a hard segfault as soon as a drag action is detected.

[samschott]

@freakboy3742, I'll have a look.

[freakboy3742]

Looks like I was mistaken - the fix is with canDragRowsWithIndexes:atPoint:. Not sure what I did with my previous experiment, but #2291 implements the fix, and it seems to work. I'm assuming I got the type definitions wrong on my previous attempt, and as a result, the method wasn't actually being used.