push constants with a single type don't work

[expenses]

The following 3 tests all fail:

#[test]
fn push_constant_single_vulkan() {
    val_vulkan(
        r#"
#[derive(Copy, Clone)]
pub struct ShaderConstants {
    pub time: f32,
}
#[allow(unused_attributes)]
#[spirv(fragment)]
pub fn main(constants: PushConstant<ShaderConstants>) {
    let _constants = constants.load();
}
"#,
    );
}

thread 'test::basic::push_constant_single_vulkan' panicked at 'Vulkan validation failed:
invalid id:0:0 - PushConstant OpVariable <id> '2[%constants]' has illegal type.
From Vulkan spec, section 14.5.1:
Such variables must be typed as OpTypeStruct, or an array of this type
  %constants = OpVariable %_ptr_PushConstant_float PushConstant
', crates/spirv-builder/src/test/mod.rs:109:9
stack backtrace:
   0: rust_begin_unwind
             at /rustc/d32c320d7eee56706486fef6be778495303afe9e/library/std/src/panicking.rs:493:5
   1: std::panicking::begin_panic_fmt
             at /rustc/d32c320d7eee56706486fef6be778495303afe9e/library/std/src/panicking.rs:435:5
   2: spirv_builder::test::val_vulkan
             at ./src/test/mod.rs:109:9
   3: spirv_builder::test::basic::push_constant_single_vulkan
             at ./src/test/basic.rs:233:5
   4: spirv_builder::test::basic::push_constant_single_vulkan::{{closure}}
             at ./src/test/basic.rs:232:1
   5: core::ops::function::FnOnce::call_once
             at /home/ashley/.rustup/toolchains/nightly-2020-12-11-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
   6: core::ops::function::FnOnce::call_once
             at /rustc/d32c320d7eee56706486fef6be778495303afe9e/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

#[test]
fn push_constant_single_block_vulkan() {
    val_vulkan(
        r#"
#[derive(Copy, Clone)]
#[allow(unused_attributes)]
#[spirv(block)]
pub struct ShaderConstants {
    pub time: f32,
}
#[allow(unused_attributes)]
#[spirv(fragment)]
pub fn main(constants: PushConstant<ShaderConstants>) {
    let _constants = constants.load();
}
"#,
    );
}

error: `#[spirv(block)]` can only be used for `Sized` aggregates, but `ShaderConstants` has `Abi::Scalar(Scalar { value: F32, valid_range: 0..=4294967295 })`
   --> /home/ashley/projects/rust-gpu/crates/spirv-std/src/storage_class.rs:57:1
    |
57  | / storage_class! {
58  | |     /// Graphics uniform memory. OpenCL constant memory.
59  | |     ///
60  | |     /// Shared externally, visible across all functions in all invocations in
...   |
202 | |     #[spirv(physical_storage_buffer)] writeable storage_class PhysicalStorageBuffer;
203 | | }
    | |_^
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

#[test]
fn push_constant_value_vulkan() {
    val_vulkan(
        r#"
#[allow(unused_attributes)]
#[spirv(fragment)]
pub fn main(constants: PushConstant<f32>) {
    let _constants = constants.load();
}
"#,
    );
}

---- test::basic::push_constant_value_vulkan stdout ----
thread 'test::basic::push_constant_value_vulkan' panicked at 'Vulkan validation failed:
invalid id:0:0 - PushConstant OpVariable <id> '2[%constants]' has illegal type.
From Vulkan spec, section 14.5.1:
Such variables must be typed as OpTypeStruct, or an array of this type
  %constants = OpVariable %_ptr_PushConstant_float PushConstant
', crates/spirv-builder/src/test/mod.rs:109:9
stack backtrace:
   0: rust_begin_unwind
             at /rustc/d32c320d7eee56706486fef6be778495303afe9e/library/std/src/panicking.rs:493:5
   1: std::panicking::begin_panic_fmt
             at /rustc/d32c320d7eee56706486fef6be778495303afe9e/library/std/src/panicking.rs:435:5
   2: spirv_builder::test::val_vulkan
             at ./src/test/mod.rs:109:9
   3: spirv_builder::test::basic::push_constant_value_vulkan
             at ./src/test/basic.rs:270:5
   4: spirv_builder::test::basic::push_constant_value_vulkan::{{closure}}
             at ./src/test/basic.rs:269:1
   5: core::ops::function::FnOnce::call_once
             at /home/ashley/.rustup/toolchains/nightly-2020-12-11-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
   6: core::ops::function::FnOnce::call_once
             at /rustc/d32c320d7eee56706486fef6be778495303afe9e/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

I think it's alright for the 3rd one to fail, using PushConstants with primitives seems a little dodgy to me, but it'd be nice to fix either test 1 or 2.

[charles-r-earp]

Did you try #[repr(C)]? Yes, Rust will convert single and double field structs to scalar and scalar pairs.

[expenses]

If you add #[repr(C), you now get:

error: Cannot cast between pointer types
  --> src/lib.rs:17:22
   |
17 |     let _constants = constants.load();
   |                      ^^^^^^^^^^^^^^^^
   |
   = note: from: *{Function} struct ShaderConstants { time: f32 }
   = note: to: *{Function} u32

[XAMPPRocky]

I think this is a duplicate of #362 since you mention using Vulkan, and the original error is the same as what's mentioned there.

[khyperia]

Copying in some discussion from discord, the reason it goes from f32 to u32 in #[repr(C)] is that the call to load() has argument ABI PassMode::Cast. The fix is likely to create and hook a rustc query and revert the ABI back to PassMode::Direct or whatever.

[khyperia]

Reported #373 for the failure about casting to u32, which is unrelated

[khyperia]

I believe the ABI PassMode::Cast shenans part of this was fixed by #766. The PushConstant<f32> part (now written #[spirv(push_constant)] asdf: &f32) was I think fixed by #576, because it auto-wraps everything in a struct. Yay!