3 files changed, 17 insertions, 5 deletions
diff --git a/library/std/src/io/error.rs b/library/std/src/io/error.rs
index ff7fdcae1..3cabf2449 100644
--- a/library/std/src/io/error.rs
+++ b/library/std/src/io/error.rs
@@ -76,6 +76,14 @@ impl fmt::Debug for Error {
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl From<alloc::ffi::NulError> for Error {
+    /// Converts a [`alloc::ffi::NulError`] into a [`Error`].
+    fn from(_: alloc::ffi::NulError) -> Error {
+        const_io_error!(ErrorKind::InvalidInput, "data provided contains a nul byte")
+    }
+}
+
 // Only derive debug in tests, to make sure it
 // doesn't accidentally get printed.
 #[cfg_attr(test, derive(Debug))]
@@ -379,7 +387,7 @@ pub enum ErrorKind {
 impl ErrorKind {
     pub(crate) fn as_str(&self) -> &'static str {
         use ErrorKind::*;
-        // Strictly alphabetical, please.  (Sadly rustfmt cannot do this yet.)
+        // tidy-alphabetical-start
         match *self {
             AddrInUse => "address in use",
             AddrNotAvailable => "address not available",
@@ -423,6 +431,7 @@ impl ErrorKind {
             WouldBlock => "operation would block",
             WriteZero => "write zero",
         }
+        // tidy-alphabetical-end
     }
 }
 
@@ -473,6 +482,7 @@ impl Error {
     /// originate from the OS itself. The `error` argument is an arbitrary
     /// payload which will be contained in this [`Error`].
     ///
+    /// Note that this function allocates memory on the heap.
     /// If no extra payload is required, use the `From` conversion from
     /// `ErrorKind`.
     ///
@@ -487,7 +497,7 @@ impl Error {
     /// // errors can also be created from other errors
     /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
     ///
-    /// // creating an error without payload
+    /// // creating an error without payload (and without memory allocation)
     /// let eof_error = Error::from(ErrorKind::UnexpectedEof);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -564,6 +574,8 @@ impl Error {
     /// println!("last OS error: {os_error:?}");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[doc(alias = "GetLastError")]
+    #[doc(alias = "errno")]
     #[must_use]
     #[inline]
     pub fn last_os_error() -> Error {
diff --git a/library/std/src/io/error/repr_bitpacked.rs b/library/std/src/io/error/repr_bitpacked.rs
index 292bf4826..781ae03ad 100644
--- a/library/std/src/io/error/repr_bitpacked.rs
+++ b/library/std/src/io/error/repr_bitpacked.rs
@@ -269,10 +269,10 @@ where
         }
         TAG_SIMPLE_MESSAGE => ErrorData::SimpleMessage(&*ptr.cast::<SimpleMessage>().as_ptr()),
         TAG_CUSTOM => {
-            // It would be correct for us to use `ptr::sub` here (see the
+            // It would be correct for us to use `ptr::byte_sub` here (see the
             // comment above the `wrapping_add` call in `new_custom` for why),
             // but it isn't clear that it makes a difference, so we don't.
-            let custom = ptr.as_ptr().cast::<u8>().wrapping_sub(TAG_CUSTOM).cast::<Custom>();
+            let custom = ptr.as_ptr().wrapping_byte_sub(TAG_CUSTOM).cast::<Custom>();
             ErrorData::Custom(make_custom(custom))
         }
         _ => {
diff --git a/library/std/src/io/error/tests.rs b/library/std/src/io/error/tests.rs
index c897a5e87..16c634e9a 100644
--- a/library/std/src/io/error/tests.rs
+++ b/library/std/src/io/error/tests.rs
@@ -86,7 +86,7 @@ fn test_errorkind_packing() {
     assert_eq!(Error::from(ErrorKind::NotFound).kind(), ErrorKind::NotFound);
     assert_eq!(Error::from(ErrorKind::PermissionDenied).kind(), ErrorKind::PermissionDenied);
     assert_eq!(Error::from(ErrorKind::Uncategorized).kind(), ErrorKind::Uncategorized);
-    // Check that the innards look like like what we want.
+    // Check that the innards look like what we want.
     assert_matches!(
         Error::from(ErrorKind::OutOfMemory).repr.data(),
         ErrorData::Simple(ErrorKind::OutOfMemory),