ZDoom

That would be better than the mod aborting in the middle of gameplay.

They are defining their own texture sampler objects (instead of using the ones already defined). It happened to work in OpenGL by chance because they get automatically bound.

We could make the errors non-fatal and have it just not perform the pass if it doesn't compile.

From the looks of it these shaders are doing a few things wrong but I have no idea how to make them right again.
That said, is there a way to make a compile error of a postprocessing shader non-fatal? Aborting the game for it is not nice.

https://www.doomworld.com/idgames/levels/doom2/Ports/s-u/uof