Add target attribute

[exdal]

This pull request introduces a new attribute for ScopedStatement called target. Target attribute allows programmer to write target (and optionally, it's version) specific shader code. Here is how it looks:

[entry(frag)]
fn main()
{
        [target(spirv)]
        {
                // Do some spir-v operations thats only valid on spir-v.
        }
        
        // Contents of this scope will be discarded for targets before SPIR-V 1.5.
        [target(spirv, 150)]
        {
                // Do some spir-v operations thats only valid on spir-v 1.5.
        }

        [target(glsl)]
        {
                // ...
        }

        [target(gles)]
        {
                // ...
        }
}

[SirLynix]

this sounds nice, but I have troubles to see some real-life scenarios where it would be useful as is, since most NZSL code should be portable, do you have any example?

[codecov]

Codecov Report

Attention: Patch coverage is 15.30612% with 83 lines in your changes missing coverage. Please review.

Project coverage is 76.49%. Comparing base (afc5a5f) to head (837bf5e).

Files with missing lines	Patch %	Lines
src/NZSL/Parser.cpp	7.84%	47 Missing ⚠️
src/NZSL/LangWriter.cpp	15.78%	16 Missing ⚠️
src/NZSL/GlslWriter.cpp	10.00%	9 Missing ⚠️
src/NZSL/SpirV/SpirvAstVisitor.cpp	11.11%	8 Missing ⚠️
include/NZSL/Ast/Compare.inl	50.00%	2 Missing ⚠️
include/NZSL/Lang/ErrorList.hpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #63      +/-   ##
==========================================
- Coverage   76.78%   76.49%   -0.29%     
==========================================
  Files         159      159              
  Lines       21835    21931      +96     
  Branches     6745     6790      +45     
==========================================
+ Hits        16765    16777      +12     
- Misses       4977     5061      +84     
  Partials       93       93              

Files with missing lines	Coverage Δ
include/NZSL/Ast/Nodes.hpp	45.45% <ø> (ø)
include/NZSL/LangWriter.hpp	100.00% <ø> (ø)
src/NZSL/Ast/AstSerializer.cpp	77.02% <100.00%> (+0.04%)	⬆️
src/NZSL/Ast/Cloner.cpp	87.29% <100.00%> (+0.05%)	⬆️
src/NZSL/Lang/Errors.cpp	81.81% <ø> (ø)
include/NZSL/Lang/ErrorList.hpp	35.94% <0.00%> (-0.24%)	⬇️
include/NZSL/Ast/Compare.inl	67.50% <50.00%> (-0.12%)	⬇️
src/NZSL/SpirV/SpirvAstVisitor.cpp	83.84% <11.11%> (-0.68%)	⬇️
src/NZSL/GlslWriter.cpp	84.93% <10.00%> (-0.45%)	⬇️
src/NZSL/LangWriter.cpp	87.88% <15.78%> (-1.28%)	⬇️
... and 1 more

---

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[exdal]

this sounds nice, but I have troubles to see some real-life scenarios where it would be useful as is, since most NZSL code should be portable, do you have any example?

I've been thinking of supporting interop features similar to slang's (specifically this section).

[SirLynix]

this sounds nice, but I have troubles to see some real-life scenarios where it would be useful as is, since most NZSL code should be portable, do you have any example?

I've been thinking of supporting interop features similar to slang's (specifically this section).

Sounds good to prepare the glsl/spir-v assembly feature.

Style question: should it stay a separate attribute or be merged with the cond attribute? Like

[cond(target(spirv))]
{
    // SPIR-V specific
}

Also, how to handle SPIR-V for OpenGL (with OpenGL 4.5) and SPIR-V for Vulkan?

[exdal]

Style question: should it stay a separate attribute or be merged with the cond attribute?

The cond indeed makes more sense, but it wouldn't persist when compiling NZSL -> NZSL due to it's nature. So I decided to introduce a new attribute. However this can be avoided if we handle target attribute as special case from rest of the expressions.

Also, how to handle SPIR-V for OpenGL (with OpenGL 4.5) and SPIR-V for Vulkan?

I am also thinking about this too.
For syntax, going back to my first answer; maybe(?):

[cond(target(spirv) && ???)]
{
    // GL SPIR-V specific
}

Where ??? is related to desired output instruction set of SPIR-V. Or maybe output instruction set can be determined by compiler with the information inside target scope, for example OpExtInst GLSL450 ...?

[SirLynix]

The cond indeed makes more sense, but it wouldn't persist when compiling NZSL -> NZSL due to it's nature

It's more complicated than that, cond is removed only if the compiler can reduce it to a constant boolean, for example:
https://github.com/NazaraEngine/ShaderLang/blob/main/src/NZSL/Ast/SanitizeVisitor.cpp#L1427-L1440

If we decide to add a target intrinsic it's possible to resolve it only when sanitizing the AST inside the GLSL/SPIR-V writer, it's a bit more complicated than what you've done but it should be ok.

One other option is to not add a target intrinsic but add builtin options which would be used as cond(SpirV), options that would be not set (unresolved) until the GLSL/SPIRV writer step.

Or maybe output instruction set can be determined by compiler with the information inside target scope, for example OpExtInst GLSL450 ...?

I don't think this is possible, OpExtInst GLSL450 is also used for valid Vulkan SPIR-V.

So we should probably split the GLSL/SPIR-V targets from the GL/GL ES/Vulkan environment, we also could add a way to test if an extension is present, etc.

[Kbz-8]

This could be useful for possible future backends like WGSL, MSL or HLSL that may not support combined image sampler. We could use them when targeting Vulkan/OpenGL|ES and fallback on splited textures/samplers to avoid compiler's hacky and heavy emulations (if NZSL supports splited textures/samplers someday).

[set(0), cond(target(spirv, glsl, gles))]
external
{
    [binding(0)] texture: sampler2D[f32],
}

[set(0), cond(!target(spirv, glsl, gles))]
external
{
    [binding(0)] texture: texture2D[f32],
    [binding(1)] sampler: sampler,
}