MSL does not have an implicit global scope, this is emulated via macro's adding an indirection for uniforms, attributes, shader stage inputs and outputs such as:
#define roughness shaderinst->roughness.
Variables in GLSL which exist within uniform blocks can be directly referenced via the global scope, unlike standard C++. This means that variable name pollution occurs if subsequent local variables in the code use the same name, resulting in compilation errors.
A number of these conflicting names have been renamed to ensure unique naming and no further scope pollution.
Ref T96261
Reviewed By: fclem
Maniphest Tasks: T96261
Differential Revision: https://developer.blender.org/D14452
49bc640b76