Regression: "Object Position" node in Light Function materials did not compile up to UE 5.0. Starting with 5.1, it compiles but outputs garbage values

Up to UE 5.0, when the "Object Position" node is used in the Material Editor as part of a material with Light Function domain, attempting to compile the material results in the following error: "[SM5] /Engine/Generated/Material.ush: error X3004: undeclared identifier 'GetObjectWorldPosition'".

Starting with UE 5.1, however, that (probably unsupported) use-case does compile, but the node outputs garbage values (probably coming from an invalid memory access). This behavior was introduced by CL 21757684 in ue5-main in an attempt to address issue [Link Removed]. As part of this CL, the definition of function "GetObjectWorldPosition()" in file "MaterialTemplate.ush" became no longer protected by "#if HAS_PRIMITIVE_UNIFORM_BUFFER". Similarly, in file "MaterialExpressions.cpp", function "UMaterialExpressionObjectPositionWS::Compile()" lost a check against its usage on the "MD_DeferredDecal" material domain, which is probably related to the goal of the CL (maybe a new check against "LightFunction" could be added?).

As a side-note, a UDN licensee would also be interested in being able to access the world-space position of a light source when evaluating a Light Function material, if possible.

• Create a new Material
• Set it to use the "Light Function" material domain
• Implement "ObjectPosition (Absolute)" – "Component Mask (R)" – "Debug Scalar Values" – "Emissive Color" attribute
• Compile the material. Compilation will (incorrectly?) succeed.
• Create a new basic level
• Place a spotlight pointing down near the ground
• Apply the created Material as its Light Function
• The visualization will show continuously-changing garbage values