Compile-time checks to ensure structs conform to WGSL's memory layout rules

The core of this crate is the [ShaderLayout], [ShaderLayoutCompat] derive proc-macros (or declarative macros if derive feature is disabled), and the [ShaderLayout], [ShaderLayoutCompat] traits.

ShaderLayout corresponds to https://www.w3.org/TR/WGSL/#alignment-and-size.

ShaderLayoutCompat is a stricter subset that enforces the uniform address space layout constraints (without the uniform_buffer_standard_layout extension). Every type implementing ShaderLayoutCompat also implements ShaderLayout.

Both macros validate every field's alignment and the overall struct size at compile time. If a constraint is violated, compilation fails with a clear error message:

shader_layout! {
    pub struct OffsetUnaligned {
        a1: f32,        // align 4
        a4: glam::Vec3, // align 16 — offset 4 is not a multiple of 16!
    }
}
// error[E0080]: evaluation panicked: Failed to implement `ShaderLayout`: field `OffsetUnaligned::a4` (`glam::Vec3`) is not properly aligned. The offset is 4 but required align is 16

use const_shader_layout::{shader_layout, shader_layout_compat, ShaderLayout, ShaderLayoutCompat};
use glam::{Vec2, Vec3, Vec4};

// Use derive proc-macros
#[derive(Clone, Copy, ShaderLayout)]
#[repr(C)]
pub struct MyStorage {
    a1: f32,
    a2: [f32; 2],
    a3: [f32; 1],
    a4: Vec3,
    a5: f32,
    a6: Vec3,
    p1: f32, // Padding needed otherwise struct size (44) won't match shader size (48).
}

// Or use declarative macros
shader_layout_compat! {
    pub struct Nested {
        a1: [Vec4; 2],
        a2: Vec3,
        a3: f32
    }
}

shader_layout_compat! {
    pub struct MyUniform {
        a1: Nested,
        a2: Vec3,
        // Padding is implicit, because struct size is 64 aligned to 16 in `repr(C)` which matches shader size (64).
    }
}

See https://github.com/beicause/const_shader_layout/tree/master/tests for what this supports and checks.

Features

Feature	Description
derive(default)	Enable ShaderLayout, ShaderLayoutCompat derive macros
glam (default)	Implements ShaderLayout/ShaderLayoutCompat for glam types
half	Implements ShaderLayout/ShaderLayoutCompat for half::f16 and array of it
std (default), libm, nostd-libm	Re-export glam's corresponding features

This crate focuses on layout validation only. For safe cast/transmute utilities, pair it with other crates like bytemuck.