refactor: add wgpu_types::size module

Author: ErichDonGubler

wgpu-types/src/lib.rs

@@ -44,6 +44,7 @@ mod render;
 #[doc(hidden)] // without this we get spurious missing_docs warnings
 mod send_sync;
 mod shader;
+pub mod size;
 mod surface;
 mod texture;
 mod tokens;

wgpu-types/src/size.rs

@@ -0,0 +1,18 @@
+//! Utilities for converting between [`usize`]s and fixed-size integrals in wgpu, mostly
+//! [`usize_from_u32`].
+//!
+//! wgpu crates only support 32-bit targets. This module both enforces this at compile time, and
+//! offers conveniences for converting between [`u32`] and [`usize`] that [`core`] cannot provide,
+//! because Rust's minimum assumed word size is 16 bits.
+
+/// This is the load-bearing constant type assertion for the rest of the module. If this is true,
+/// then everything else should Just Work™.
+const _: () = assert!(
+    size_of::<usize>() >= size_of::<u32>(),
+    "word sizes < 32 bits are not supported in wgpu crates"
+);
+
+/// Convert a [`u32`] to a [`usize`].
+pub const fn usize_from_u32(n: u32) -> usize {
+    n as usize
+}