sampling `sm::Texture<_, _, sm::Multi>` with `MipFn::Level` needs nicer error messages

[RayMarch]

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this program creates an error message that is technically correct, but not ideal for guiding the user to the required fix:

use shame as sm;

fn main() -> Result<(), sm::EncodingErrors>  {
    let _pipeline = {
        let mut enc = sm::start_encoding(Default::default())?;
        let mut dispatch = enc.new_compute_pipeline([4, 4]);
        let mut bindings = dispatch.bind_groups.next();
        
        let ms_tex: sm::Texture<sm::tf::Rg8Unorm, _, sm::Multi> = bindings.next();
        let filter: sm::Sampler<sm::Filtering> = bindings.next();

        filter.sample(ms_tex, sm::MipFn::zero(), sm::f32x2::zero());
        
        enc.finish()?
    };
    Ok(())
}

yields error:

shame encoding error:
  --> src/main.rs:12:16
   |
12 >        filter.sample(ms_tex, sm::MipFn::zero(), sm::f32x2::zero());
   |               ^
   |
no matching function call for `TextureSampleLevel { uvw_offset: None }` with argument types

[Store(Handle(SampledTexture(_2D, Nearest { len: X2, channel_type: F32 }, Multi))), Store(Handle(Sampler(Filtering))), Store(Sized(Vector(X2, F32))), Store(Sized(Vector(X1, F32)))]

a 2ch nearest f32-sampled texture is incompatible with a filtering sampler

the texture format sm::tf::Rg8Unorm itself causes no nearest requirement on the sampler, but sm::Multi-sampling does.

once the sampler type is adjusted to Sampler<Nearest> the real issue is presented, which is

no matching function call for `TextureSampleLevel { uvw_offset: None }` with argument types

[Store(Handle(SampledTexture(_2D, Nearest { len: X2, channel_type: F32 }, Multi))), Store(Handle(Sampler(NonFiltering))), Store(Sized(Vector(X2, F32))), Store(Sized(Vector(X1, F32)))]

first argument must be a sampleable texture with a single sample per pixel

Once Multi is changed back to Single the pipeline encoding succeeds. Encountering a runtime typechecker error is always a bug if encountered through use of the statically typed rust api.

Potential solutions:

• add a custom error message before the runtime typechecker is entered for multisampled textures in particular
• make fn sample require single sampled textures and provide a separate function for multisampled textures which offers an alternative MipFn-like enum for the subset of mip functions supported by those textures (if there are multiple).
• switch the order of error generation in the runtime typechecker somehow, so that the "first argument must be a sampleable texture with a single sample per pixel" error check happens before the "a 2ch nearest f32-sampled texture is incompatible with a filtering sampler" error