Add support for static variables in GDScript

[vnen]

Which allows editable data associated with a particular class instead of the instance. Scripts with static variables are kept in memory indefinitely unless the @static_unload annotation is used or the static_unload() method is called on the GDScript.

If the custom function _static_init() exists it will be called when the class is loaded, after the static variables are set.

Closes godotengine/godot-proposals#6156

Note: During development I noticed a problem with GDScriptCache that is keeping all scripts in memory even after not being referenced anymore, so the static_unload implemented here (both method and annotation) won't be effective until the problem is fixed.

[vnen]

I think I fixed the leak now.

[dalexeev]

1. Runtime error when using a static function in a static variable initializer.

extends Node

static func f():
    return "test"

static var s = f() # Runtime Error: Invalid call. Nonexistent function 'f' in base 'Nil'.

func _ready() -> void:
    print(s)

2. Static variables of inner classes are not initialized.

extends Node

class A:
    static var a := 42

func _ready() -> void:
    print(A.a) # <null>

3. Static variables do not appear in autocompletion when accessed from outside.

4. _static_init() and unload_static() do not appear in autocompletion.

[adamscott]

Note: During development I noticed a problem with GDScriptCache that is keeping all scripts in memory even after not being referenced anymore, so the static_unload implemented here (both method and annotation) won't be effective until the problem is fixed.

It's in my "garbage collection" todo list.

[adamscott]

Approved by the GDScript team in a PR meeting.

Thank you George for this big PR. Truly a great job. What would we do without you!

[vnen]

Updated the code to fix some of the mentioned issues. I did not touch autocompletion yet (other than adding _static_init()) but can be done at a later step if this is merged.

[akien-mga]

Needs rebase, then should be ready to merge I think.

[vnen]

Rebased.

[akien-mga]

Thanks!

[shendo]

Hi, this appears to have broken android template_debug builds on master, due to the mix of TOOLS_ENABLED/DEBUG_ENABLED conditions. eg.

scons platform=android target=template_debug arch=armv7
...
modules/gdscript/gdscript.cpp:746:3: error: use of undeclared identifier '_save_old_static_data'
                _save_old_static_data();
                ^
modules/gdscript/gdscript.cpp:823:3: error: use of undeclared identifier '_restore_old_static_data'
                _restore_old_static_data();
                ^
2 errors generated.
scons: *** [modules/gdscript/gdscript.android.template_debug.arm32.o] Error 1
scons: building terminated because of errors.

[akien-mga]

@shendo Fixed with 7780926.

[atirut-w]

How easily can this be ported to 4.x in the future?

[dalexeev]

How easily can this be ported to 4.x in the future?

This has already been merged for 4.1 (and therefore also for 4.x). You probably mean backport for 4.0.x. I think this is against Godot release policy, as this change is too big and risky for patch releases, and most importantly, it's a feature implementation, not a bug fix. But the good news is that you won't have to wait very long for 4.1!

[atirut-w]

This was merged into master though?

[Zireael07]

@atirut-w Master will become 4.1