Use MaybeUninit<u8> for IpDisplayBuffer.

Author: reitermarkus

library/std/src/lib.rs

@@ -294,6 +294,8 @@
 #![feature(std_internals)]
 #![feature(str_internals)]
 #![feature(strict_provenance)]
+#![feature(maybe_uninit_uninit_array)]
+#![feature(const_maybe_uninit_uninit_array)]
 //
 // Library features (alloc):
 #![feature(alloc_layout_extra)]

library/std/src/net/ip/display_buffer.rs

@@ -1,31 +1,37 @@
 use crate::fmt;
+use crate::mem::MaybeUninit;
 use crate::str;
 
 /// Used for slow path in `Display` implementations when alignment is required.
 pub struct IpDisplayBuffer<const SIZE: usize> {
-    buf: [u8; SIZE],
+    buf: [MaybeUninit<u8>; SIZE],
     len: usize,
 }
 
 impl<const SIZE: usize> IpDisplayBuffer<SIZE> {
     #[inline(always)]
     pub const fn new(_ip: &[u8; SIZE]) -> Self {
-        Self { buf: [0; SIZE], len: 0 }
+        Self { buf: MaybeUninit::uninit_array::<SIZE>(), len: 0 }
     }
 
     #[inline(always)]
     pub fn as_str(&self) -> &str {
         // SAFETY: `buf` is only written to by the `fmt::Write::write_str` implementation
         // which writes a valid UTF-8 string to `buf` and correctly sets `len`.
-        unsafe { str::from_utf8_unchecked(&self.buf[..self.len]) }
+        unsafe {
+            let s = MaybeUninit::slice_assume_init_ref(&self.buf[..self.len]);
+            str::from_utf8_unchecked(s)
+        }
     }
 }
 
 impl<const SIZE: usize> fmt::Write for IpDisplayBuffer<SIZE> {
     fn write_str(&mut self, s: &str) -> fmt::Result {
-        if let Some(buf) = self.buf.get_mut(self.len..(self.len + s.len())) {
-            buf.copy_from_slice(s.as_bytes());
-            self.len += s.len();
+        let bytes = s.as_bytes();
+
+        if let Some(buf) = self.buf.get_mut(self.len..(self.len + bytes.len())) {
+            MaybeUninit::write_slice(buf, bytes);
+            self.len += bytes.len();
             Ok(())
         } else {
             Err(fmt::Error)