#34161: Keep a weak reference to orphan subclasses to reuse on class reload

[ChibiDenDen]

This change is a second attempt to fix #34161
first attempt is here: #35027

Bugsquad edit: also fixes #30557.

In this change, when a GDScript is destroyed, an ObjectID is kept on GDScriptLanguage for each subclass that is still in use.
when the GDScript is loaded again, it checks if an orphan subclass is still available and reuses it.

To be considered:
the ObjectID is kept in a Map where the Key is a string in the format CLASS:SUBCLASS, this means that there is no support for multiple levels of subclasses, only one.
IMO, every class should keep a fully qualified name, or some other UNIQUE_ID that is stable and reproducible without requiring a full load of the subclass.

[ChibiDenDen]

I have tested and this seems to fix #30557 as well

[akien-mga]

See also #35096 which is @vnen's attempt at solving the same issue (I don't know if it addresses #30557 too).

[vnen]

This is better but I fear it has the same problem as the other PR: references are kept alive forever. The difference here is that only some inner classes will be kept. But once they are in that list, they'll only be freed when the application ends.

Maybe we can do a similar thing but only in smaller contexts. For instance, keep this list for the parser while it's running. Or for the compiler it can keep a list of external references in the actual GDScript, so it can take them away when it's freed.

Still, I'm not confident in merging such a solution for 3.2 this close to the release.

[ChibiDenDen]

Why do you think that they are kept alive forever?
this is just the objectid, this does not keep reference.
I can create a test case that shows that.

[vnen]

I see, I should have another coffee before reading the code.

I guess this is a good solution, since it avoids recreating the inner classes when the owner script is reloaded, so the memory address don't change.

[vnen]

Also, #35122 should be merged first, so this PR can be updated to use the fully qualified names.

[vnen]

Looks good, thanks. Just need to squash the commits into one. See http://docs.godotengine.org/en/latest/community/contributing/pr_workflow.html#mastering-the-pr-workflow-the-rebase

[ChibiDenDen]

Looks good, thanks. Just need to squash the commits into one. See http://docs.godotengine.org/en/latest/community/contributing/pr_workflow.html#mastering-the-pr-workflow-the-rebase

Done, its a single commit now

[vnen]

Looks good. It's a clever solution while we don't have the proper ScriptCache.

[akien-mga]

Thanks!