Executing RigidBody.new()._direct_state_changed(BoxShape.new()) crashes Godot

[qarmin]

Godot version:
Godot 3.2.4 rc 2

Issue description:
Executing

RigidBody.new()._direct_state_changed(BoxShape.new())

crashes with backtrace

scene/3d/physics_body.cpp:453:44: runtime error: member call on null pointer of type 'struct PhysicsDirectBodyState'
scene/3d/physics_body.cpp:453:44: runtime error: member access within null pointer of type 'struct PhysicsDirectBodyState'
handle_crash: Program crashed with signal 11
Dumping the backtrace. Please include this when reporting the bug on https://github.com/godotengine/godot/issues
[1] godots() [0x16f757a] (/mnt/Miecz/godot3.2/platform/x11/crash_handler_x11.cpp:54)
[2] /lib/x86_64-linux-gnu/libc.so.6(+0x46210) [0x7f7e6f8a4210] (??:0)
[3] RigidBody::_direct_state_changed(Object*) (/mnt/Miecz/godot3.2/scene/3d/physics_body.cpp:453)
[4] MethodBind1<Object*>::call(Object*, Variant const**, int, Variant::CallError&) (/mnt/Miecz/godot3.2/./core/method_bind.gen.inc:775 (discriminator 12))
[5] Object::call(StringName const&, Variant const**, int, Variant::CallError&) (/mnt/Miecz/godot3.2/core/object.cpp:919 (discriminator 1))
[6] Variant::call_ptr(StringName const&, Variant const**, int, Variant*, Variant::CallError&) (/mnt/Miecz/godot3.2/core/variant_call.cpp:1129 (discriminator 1))
[7] GDScriptFunction::call(GDScriptInstance*, Variant const**, int, Variant::CallError&, GDScriptFunction::CallState*) (/mnt/Miecz/godot3.2/modules/gdscript/gdscript_function.cpp:1089)
[8] GDScriptInstance::_ml_call_reversed(GDScript*, StringName const&, Variant const**, int) (/mnt/Miecz/godot3.2/modules/gdscript/gdscript.cpp:1269)
[9] GDScriptInstance::call_multilevel_reversed(StringName const&, Variant const**, int) (/mnt/Miecz/godot3.2/modules/gdscript/gdscript.cpp:1278)
[10] Node::_notification(int) (/mnt/Miecz/godot3.2/scene/main/node.cpp:152)
[11] Node::_notificationv(int, bool) (/mnt/Miecz/godot3.2/./scene/main/node.h:46 (discriminator 14))
[12] CanvasItem::_notificationv(int, bool) (/mnt/Miecz/godot3.2/./scene/2d/canvas_item.h:166 (discriminator 3))
[13] Node2D::_notificationv(int, bool) (/mnt/Miecz/godot3.2/./scene/2d/node_2d.h:38 (discriminator 3))
[14] Object::notification(int, bool) (/mnt/Miecz/godot3.2/core/object.cpp:931)
[15] Node::_propagate_ready() (/mnt/Miecz/godot3.2/scene/main/node.cpp:197)
[16] Node::_propagate_ready() (/mnt/Miecz/godot3.2/scene/main/node.cpp:186 (discriminator 2))
[17] Node::_set_tree(SceneTree*) (/mnt/Miecz/godot3.2/scene/main/node.cpp:2560)
[18] SceneTree::init() (/mnt/Miecz/godot3.2/scene/main/scene_tree.cpp:464)
[19] OS_X11::run() (/mnt/Miecz/godot3.2/platform/x11/os_x11.cpp:3628)
[20] godots(main+0x331) [0x16ee467] (/mnt/Miecz/godot3.2/platform/x11/godot_x11.cpp:57)
[21] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf3) [0x7f7e6f8850b3] (??:0)
[22] godots(_start+0x2e) [0x16ee07e] (??:?)

[rafallus]

_direct_state_changed() should receive a PhysicsDirectBodyState object, not a BoxShape one. As the argument is not what expected, it's casted into a null object, making Godot to crash when trying to access it. Should the function just return and do nothing if the argument is not of type PhysicsDirectBodyState?

[qarmin]

Function should in most situations return default value(e.g 0, false, empty Array etc.) and print error.
This is done(usually) by one of ERR_FAIL macros

[madmiraal]

The real question is: why is this method exposed? It's used internally by the physics engine to trigger an update in the scene. It's a hidden method, so not something that would normally be called, but I can't think of a reason that a user would want to call this method.

[akien-mga]

The real question is: why is this method exposed? It's used internally by the physics engine to trigger an update in the scene. It's a hidden method, so not something that would normally be called, but I can't think of a reason that a user would want to call this method.

It's because it's used as a callback that goes through the method bindings:

scene/3d/physics_body.cpp
1076:   PhysicsServer::get_singleton()->body_set_force_integration_callback(get_rid(), this, "_direct_state_changed");

In master this can maybe be changed to use callable_mp so that the callback uses a function pointer, but in 3.x that's not possible. So we have a number of internal methods exposed publicly because they're used as callbacks by engine internals (see godotengine/godot-proposals#2285 which discusses it in reaction to this type of issue).

[qarmin]

Looks that in 3.x branch there is for now 671 methods which starts with _(_ready etc. are also counted)
List of all functions - godotengine/godot-proposals#2285 (comment)