GDExtension call to method of Variant return type fails with singletons

[konczg]

Godot version

v4.2.dev.custom_build (544601a686eed6b35a346de1f7a5b607fcf8ce97)

System information

Ubuntu 20.04.6 LTS (Focal Fossa)

Issue description

The attached example project demonstrates a specific crash when a function with Variant return type is called on a registered singleton. This happens as MethodBind::bind_ptrcall() is called with r_return == nullptr.

Steps to reproduce

Commit IDs where the issue CAN be reproduced:

• godot: 6b727eb
• godot-cpp: ef2f63a00c5496cc325e8546acd743787e87a83d

Commit IDs where the issue CANNOT be reproduced:

• godot: 3cf1bc0
• godot-cpp: ef2f63a00c5496cc325e8546acd743787e87a83d

Steps to reproduce:

• Build the project: scons .
• Open and run in Godot 4.x

Expected result:

• The project starts without issue

Actual result:

• The project crashes with the following backtrace:

================================================================
handle_crash: Program crashed with signal 11
Engine version: Godot Engine v4.2.dev.custom_build (544601a686eed6b35a346de1f7a5b607fcf8ce97)
Dumping the backtrace. Please include this when reporting the bug to the project developer.
[1] /lib/x86_64-linux-gnu/libc.so.6(+0x43090) [0x7f4f6fa50090] (??:0)
[2] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x481bd44) [0x561fb48f3d44] (??:0)
[3] godot::Variant::clear() (??:0)
[4] godot::Variant::operator=(godot::Variant const&) (??:0)
[5] godot::MethodBindTR<godot::Variant>::ptrcall(void*, void const* const*, void*) const (??:0)
[6] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x4802c71) [0x561fb48dac71] (??:0)
[7] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x919517) [0x561fb09f1517] (??:0)
[8] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x7ab488) [0x561fb0883488] (??:0)
[9] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x26c250b) [0x561fb279a50b] (??:0)
[10] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x2ccdfea) [0x561fb2da5fea] (??:0)
[11] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x48502d0) [0x561fb49282d0] (??:0)
[12] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x26afb16) [0x561fb2787b16] (??:0)
[13] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x26afab8) [0x561fb2787ab8] (??:0)
[14] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x26b1417) [0x561fb2789417] (??:0)
[15] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x56e32d) [0x561fb064632d] (??:0)
[16] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x55ac61) [0x561fb0632c61] (??:0)
[17] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf3) [0x7f4f6fa31083] (??:0)
[18] /godot/godot/bin/godot.linuxbsd.editor.x86_64(+0x56bfce) [0x561fb0643fce] (??:0)
-- END OF BACKTRACE --
================================================================

Minimal reproduction project

gdextension_crash_example.zip

[dsnopek]

Thanks for the MRP!

I'm not sure what makes your example different than a very similar function in the automated tests for godot-cpp, but I can definitely get it to crash with your project.

I've updated PR #83054 with a change that fixes the crash for me