libc: add padding struct

Author: mbyx

libc-test/test/check_style.rs

@@ -20,7 +20,7 @@ use style::{Result, StyleChecker};
 const SKIP_PREFIXES: &[&str] = &[
     // Don't run the style checker on the reorganized portion of the crate while we figure
     // out what style we want.
-    "new/",
+    "new/", "types.rs",
 ];
 
 #[test]

src/lib.rs

@@ -43,6 +43,8 @@ pub use core::ffi::c_void;
 #[allow(unused_imports)] // needed while the module is empty on some platforms
 pub use new::*;
 
+mod types;
+
 cfg_if! {
     if #[cfg(windows)] {
         mod primitives;

src/macros.rs

@@ -80,6 +80,9 @@ macro_rules! prelude {
             #[allow(unused_imports)]
             pub(crate) use mem::{align_of, align_of_val, size_of, size_of_val};
 
+            #[allow(unused_imports)]
+            pub(crate) use crate::types::Padding;
+
             // Commonly used types defined in this crate
             #[allow(unused_imports)]
             pub(crate) use crate::{

src/types.rs

@@ -0,0 +1,20 @@
+//! Platform-agnostic support types.
+
+use core::clone::Clone;
+use core::default::Default;
+use core::marker::Copy;
+use core::mem::MaybeUninit;
+use core::prelude::rust_2024::derive;
+
+/// A transparent wrapper over `MaybeUninit<T>` to represent uninitialized padding
+/// while providing `Default`.
+#[allow(unused)]
+#[repr(transparent)]
+#[derive(Clone, Copy)]
+pub(crate) struct Padding<T: Copy>(MaybeUninit<T>);
+
+impl<T: Copy> Default for Padding<T> {
+    fn default() -> Self {
+        Self(MaybeUninit::zeroed())
+    }
+}