Metal half name reserved

[BenjaminSchaaf]

Description
Writing a wgpu shader using a variable with the name half doesn't work under metal, as half is a reserved name.

Repro steps
Use the hello_triangle example, with the following shader on macOS (using metal):

@vertex
fn vs_main(@builtin(vertex_index) in_vertex_index: u32) -> @builtin(position) vec4<f32> {
    let x = f32(i32(in_vertex_index) - 1);
    let y = f32(i32(in_vertex_index & 1u) * 2 - 1);
    return vec4<f32>(x, y, 0.0, 1.0);
}

@fragment
fn fs_main() -> @location(0) vec4<f32> {
    let half = 0.5;
    return vec4<f32>(half, 0.0, 0.0, 1.0);
}

Apologies if this doesn't reproduce, I'm reporting this from memory of testing on someone else's mac

Expected vs observed behavior
The shader should work, half works with other backends. Instead it fails to compile the shader once it gets to the metal backend compiler.

Platform
macOS, wgpu 0.18.0, naga 0.14.2

[teoxoy]

I think this has been fixed with #4707. Could you try latest trunk?

[BenjaminSchaaf]

Apologies, I should have found that duplicate. I can't test right now, but I'm sure it's fixed.