Accessing a null MeshInstance object in BakedLightmap instead of the GeometryInstance

[Macksaur]

Godot version

3.x

System information

Linux

Issue description

mi has been checked/tested to be null, yet is accessed on the following lines:

godot/scene/3d/baked_lightmap.cpp

Line 392 in 40a348b

all_override = mi->get_material_override();

godot/scene/3d/baked_lightmap.cpp

Line 417 in 40a348b

mf.cast_shadows = mi->get_cast_shadows_setting() != GeometryInstance::SHADOW_CASTING_SETTING_OFF;

godot/scene/3d/baked_lightmap.cpp

Line 418 in 40a348b

mf.generate_lightmap = mi->get_generate_lightmap();

Should these variables be referencing gi?

Steps to reproduce

Compile with -Wnonnull. 4.0 doesn't look to be affected.

The warning is somewhat hard to trigger due to the UB involved.
Using the following command scons -j16 platform=x11 tools=no target=release_debug CCFLAGS=-Wnonnull after touching scene/3d/baked_lightmap.cpp produces (for me):

scene/3d/baked_lightmap.cpp: In member function 'void BakedLightmap::_find_meshes_and_lights(Node*, Vector<BakedLightmap::MeshesFound>&, Vector<BakedLightmap::LightsFound>&)':
scene/3d/baked_lightmap.cpp:392:73: warning: 'this' pointer is null [-Wnonnull]
  392 |                                 all_override = mi->get_material_override();
      |                                                ~~~~~~~~~~~~~~~~~~~~~~~~~^~
In file included from scene/3d/multimesh_instance.h:34,
                 from scene/3d/baked_lightmap.h:35,
                 from scene/3d/baked_lightmap.cpp:31:
./scene/3d/visual_instance.h:151:23: note: in a call to non-static member function 'Ref<Material> GeometryInstance::get_material_override() const'
  151 |         Ref<Material> get_material_override() const;
      |                       ^~~~~~~~~~~~~~~~~~~~~

scene/3d/baked_lightmap.cpp:417:87: warning: 'this' pointer is null [-Wnonnull]
  417 |                                         mf.cast_shadows = mi->get_cast_shadows_setting() != GeometryInstance::SHADOW_CASTING_SETTING_OFF;

      |                                                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
In file included from scene/3d/multimesh_instance.h:34,
                 from scene/3d/baked_lightmap.h:35,
                 from scene/3d/baked_lightmap.cpp:31:
./scene/3d/visual_instance.h:130:30: note: in a call to non-static member function 'GeometryInstance::ShadowCastingSetting GeometryInstance::get_cast_shadows_setting() const'
  130 |         ShadowCastingSetting get_cast_shadows_setting() const;
      |                              ^~~~~~~~~~~~~~~~~~~~~~~~

scene/3d/baked_lightmap.cpp:418:89: warning: 'this' pointer is null [-Wnonnull]
  418 |                                         mf.generate_lightmap = mi->get_generate_lightmap();
      |                                                                ~~~~~~~~~~~~~~~~~~~~~~~~~^~
In file included from scene/3d/multimesh_instance.h:34,
                 from scene/3d/baked_lightmap.h:35,
                 from scene/3d/baked_lightmap.cpp:31:
./scene/3d/visual_instance.h:133:14: note: in a call to non-static member function 'bool GeometryInstance::get_generate_lightmap()'
  133 |         bool get_generate_lightmap();
      |              ^~~~~~~~~~~~~~~~~~~~~

Minimal reproduction project

No response

[Calinou]

Fixed by #57110. (This issue wasn't closed because the pull request was merged on 3.x, which isn't this repository's default branch.)