I recently found that some of my OSL shaders don’t work in Blender 2.83.
More specifically, shaders compiled with Blender 2.83 had their microfacet bsdf not recognized by the renderer and return 0.
* Shaders that were compiled by previous versions did work.
Looking into the problem I found that the OSL source files that ship with Blender 2.83 are significantly different than the files shipped with previous versions.
Copy the stdosl.h and oslutil.h from Blender 2.82 to 2.83.
On Windows these files are found in this folder:
C:\Program Files\Blender Foundation\Blender 2.83\2.83\scripts\addons\cycles\shader
* I’m not suggesting to download the files strait from ImageWorks GitHub because I’m not sure the ones that ship with Blender & Cycles are not modified.
I have reported the bug here.