Can't call `.len()` on an array

[Jasper-Bekkers]

Compiling this gives the following compilation errors.

const OFFSETS : [f32; 18] = [0.000000, 1.494118, 3.486275, 5.478431, 7.470588, 9.462745, 11.454902, 13.447059, 15.439216, 17.431373, 19.423529, 21.415686, 23.407843, 25.400000, 27.392157, 29.384314, 31.376471, 33.368627];

#[allow(unused_attributes)]
#[spirv(fragment)]
pub fn ps_main(
) {
    OFFSETS.len();
}

Errors:

error: Cannot cast between pointer types
  --> C:\Users\Jasper\.rustup\toolchains\nightly-2020-11-24-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\slice\mod.rs:95:18
   |
95 |         unsafe { crate::ptr::Repr { rust: self }.raw.len }
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: from: *{Function} [u8; 8]
   = note: to: *{Function} struct *const [f32] { *{Function} [f32], u32 }

error: Cannot cast between pointer types
  --> C:\Users\Jasper\.rustup\toolchains\nightly-2020-11-24-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\slice\mod.rs:95:18
   |
95 |         unsafe { crate::ptr::Repr { rust: self }.raw.len }
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: from: *{Function} [u8; 8]
   = note: to: *{Function} struct core::ptr::FatPtr<f32> { *{Function} f32, u32 }

error: Cannot cast between pointer types
 --> src\guassian.rs:8:5
  |
8 |     OFFSETS.len();
  |     ^^^^^^^
  |
  = note: from: *{Function} [f32; 18]
  = note: to: *{Function} [f32]

error: aborting due to 3 previous errors; 1 warning emitted

Obviously this can be worked around by just hardcoding the length directly.

[DJMcNab]

It might be possible to use const len: usize = OFFSETS.len();, to force the length to be const evaluated, as another workaround?

[zicklag]

Also getting this with the following shader:

#![cfg_attr(
    target_arch = "spirv",
    feature(register_attr),
    register_attr(spirv),
    no_std
)]
extern crate spirv_std;
#[cfg(not(target_arch = "spirv"))]
use spirv_std::macros::spirv;

use glam::UVec3;
use spirv_std::glam;

#[spirv(compute(threads(1)))]
pub fn main_cs(
    #[spirv(global_invocation_id)] id: UVec3,
    #[spirv(storage_buffer, descriptor_set = 0, binding = 0)] numbers: &mut [u32],
) {
    let idx = id.x as usize;
    if idx + 1 < numbers.len() {
        numbers[idx] = numbers[idx + 1];
    }
}

In this case there's no good workaround because the buffer length is dynamic.

[zicklag]

If anybody could give me some pointers on what might need to be done to fix this, I might have the time to see if I could make a fix for this. I've never worked on Rust GPU's source before so any quick hints would be useful. :)

[khyperia]

If anybody could give me some pointers on what might need to be done to fix this, I might have the time to see if I could make a fix for this. I've never worked on Rust GPU's source before so any quick hints would be useful. :)

Unfortunately the reason it hasn't been fixed yet is because it's a pretty complicated problem to solve, can't really give many quick or easy hints :(

[khyperia]

Strangely, this compiles now! wha. Wild guess here, maybe this was fixed by #469?