Specialization constants need to be supported on all backends, including non-Vulkan GLSL, HLSL and C++

[smarton-sc]

As a follow-on to #5725, we need specialization constant support via #if expressions for backends that don't have native specialization constant constructs.

[csyonghe]

Please note that non-vulkan GLSL is not an officially supported backend, so it would not be possible to add without the fundamentals to add traditional GLSL as a dedicated backend first.

[smarton-sc]

Oof. I was not aware. That's another hard blocker for us. We use desktop 120 (hopefully not for long) and 430, as well as ES 300 and 310.
We actually wouldn't use the HLSL and C++ backends, so spec consts in those languages are not useful for us, I just added them for completeness, ie: that slang should support specialization universally in principle.
I don't want to sound demanding, just offering context. I understand you probably have bigger fish to fry.

[bmillsNV]

Thank you for filing this issue. This is worth resolving, but we don’t have current available bandwidth – moving to the backlog for now. Please do feel welcome to propose a solution if you’re able to before it makes it out of the backlog!

[steel3d]

Thanks! Will do.