Merge from rustc

Author: RalfJung

Cargo.lock

@@ -1,3 +1,5 @@
+cargo-features = ["public-dependency"]
+
 [package]
 name = "alloc"
 version = "0.0.0"
@@ -9,8 +11,8 @@ autobenches = false
 edition = "2021"
 
 [dependencies]
-core = { path = "../core" }
-compiler_builtins = { version = "=0.1.146", features = ['rustc-dep-of-std'] }
+core = { path = "../core", public = true }
+compiler_builtins = { version = "=0.1.147", features = ['rustc-dep-of-std'] }
 
 [dev-dependencies]
 rand = { version = "0.9.0", default-features = false, features = ["alloc"] }

alloc/Cargo.toml

@@ -237,23 +237,13 @@ pub struct Box<
 /// the newly allocated memory. This is an intrinsic to avoid unnecessary copies.
 ///
 /// This is the surface syntax for `box <expr>` expressions.
-#[cfg(not(bootstrap))]
 #[rustc_intrinsic]
 #[rustc_intrinsic_must_be_overridden]
 #[unstable(feature = "liballoc_internals", issue = "none")]
 pub fn box_new<T>(_x: T) -> Box<T> {
     unreachable!()
 }
 
-/// Transition function for the next bootstrap bump.
-#[cfg(bootstrap)]
-#[unstable(feature = "liballoc_internals", issue = "none")]
-#[inline(always)]
-pub fn box_new<T>(x: T) -> Box<T> {
-    #[rustc_box]
-    Box::new(x)
-}
-
 impl<T> Box<T> {
     /// Allocates memory on the heap and then places `x` into it.
     ///
@@ -1689,7 +1679,20 @@ impl<T: Default> Default for Box<T> {
     /// Creates a `Box<T>`, with the `Default` value for T.
     #[inline]
     fn default() -> Self {
-        Box::write(Box::new_uninit(), T::default())
+        let mut x: Box<mem::MaybeUninit<T>> = Box::new_uninit();
+        unsafe {
+            // SAFETY: `x` is valid for writing and has the same layout as `T`.
+            // If `T::default()` panics, dropping `x` will just deallocate the Box as `MaybeUninit<T>`
+            // does not have a destructor.
+            //
+            // We use `ptr::write` as `MaybeUninit::write` creates
+            // extra stack copies of `T` in debug mode.
+            //
+            // See https://github.com/rust-lang/rust/issues/136043 for more context.
+            ptr::write(&raw mut *x as *mut T, T::default());
+            // SAFETY: `x` was just initialized above.
+            x.assume_init()
+        }
     }
 }
 

alloc/src/boxed.rs

@@ -105,6 +105,7 @@
 #![feature(box_uninit_write)]
 #![feature(bstr)]
 #![feature(bstr_internals)]
+#![feature(char_max_len)]
 #![feature(clone_to_uninit)]
 #![feature(coerce_unsized)]
 #![feature(const_eval_select)]
@@ -136,7 +137,6 @@
 #![feature(pointer_like_trait)]
 #![feature(ptr_internals)]
 #![feature(ptr_metadata)]
-#![feature(ptr_sub_ptr)]
 #![feature(set_ptr_value)]
 #![feature(sized_type_properties)]
 #![feature(slice_from_ptr_range)]

alloc/src/lib.rs

@@ -27,7 +27,7 @@ pub use core::slice::ArrayChunksMut;
 pub use core::slice::ArrayWindows;
 #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
 pub use core::slice::EscapeAscii;
-#[stable(feature = "get_many_mut", since = "CURRENT_RUSTC_VERSION")]
+#[stable(feature = "get_many_mut", since = "1.86.0")]
 pub use core::slice::GetDisjointMutError;
 #[stable(feature = "slice_get_slice", since = "1.28.0")]
 pub use core::slice::SliceIndex;

alloc/src/slice.rs

@@ -1419,7 +1419,9 @@ impl String {
     pub fn push(&mut self, ch: char) {
         match ch.len_utf8() {
             1 => self.vec.push(ch as u8),
-            _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
+            _ => {
+                self.vec.extend_from_slice(ch.encode_utf8(&mut [0; char::MAX_LEN_UTF8]).as_bytes())
+            }
         }
     }
 
@@ -1716,7 +1718,7 @@ impl String {
     #[rustc_confusables("set")]
     pub fn insert(&mut self, idx: usize, ch: char) {
         assert!(self.is_char_boundary(idx));
-        let mut bits = [0; 4];
+        let mut bits = [0; char::MAX_LEN_UTF8];
         let bits = ch.encode_utf8(&mut bits).as_bytes();
 
         unsafe {
@@ -2797,7 +2799,7 @@ impl SpecToString for core::ascii::Char {
 impl SpecToString for char {
     #[inline]
     fn spec_to_string(&self) -> String {
-        String::from(self.encode_utf8(&mut [0; 4]))
+        String::from(self.encode_utf8(&mut [0; char::MAX_LEN_UTF8]))
     }
 }
 
@@ -3155,6 +3157,24 @@ impl From<String> for Vec<u8> {
     }
 }
 
+#[stable(feature = "try_from_vec_u8_for_string", since = "CURRENT_RUSTC_VERSION")]
+impl TryFrom<Vec<u8>> for String {
+    type Error = FromUtf8Error;
+    /// Converts the given [`Vec<u8>`] into a  [`String`] if it contains valid UTF-8 data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let s1 = b"hello world".to_vec();
+    /// let v1 = String::try_from(s1).unwrap();
+    /// assert_eq!(v1, "hello world");
+    ///
+    /// ```
+    fn try_from(bytes: Vec<u8>) -> Result<Self, Self::Error> {
+        Self::from_utf8(bytes)
+    }
+}
+
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Write for String {

alloc/src/string.rs

@@ -232,7 +232,7 @@ impl<T, A: Allocator> Drop for Drain<'_, T, A> {
             // it from the original vec but also avoid creating a &mut to the front since that could
             // invalidate raw pointers to it which some unsafe code might rely on.
             let vec_ptr = vec.as_mut().as_mut_ptr();
-            let drop_offset = drop_ptr.sub_ptr(vec_ptr);
+            let drop_offset = drop_ptr.offset_from_unsigned(vec_ptr);
             let to_drop = ptr::slice_from_raw_parts_mut(vec_ptr.add(drop_offset), drop_len);
             ptr::drop_in_place(to_drop);
         }

alloc/src/vec/drain.rs

@@ -379,7 +379,7 @@ where
         let sink =
             self.try_fold::<_, _, Result<_, !>>(sink, write_in_place_with_drop(end)).into_ok();
         // iteration succeeded, don't drop head
-        unsafe { ManuallyDrop::new(sink).dst.sub_ptr(dst_buf) }
+        unsafe { ManuallyDrop::new(sink).dst.offset_from_unsigned(dst_buf) }
     }
 }
 

alloc/src/vec/in_place_collect.rs

@@ -14,7 +14,7 @@ pub(super) struct InPlaceDrop<T> {
 
 impl<T> InPlaceDrop<T> {
     fn len(&self) -> usize {
-        unsafe { self.dst.sub_ptr(self.inner) }
+        unsafe { self.dst.offset_from_unsigned(self.inner) }
     }
 }
 

alloc/src/vec/in_place_drop.rs

@@ -179,7 +179,7 @@ impl<T, A: Allocator> IntoIter<T, A> {
                 // say that they're all at the beginning of the "allocation".
                 0..this.len()
             } else {
-                this.ptr.sub_ptr(this.buf)..this.end.sub_ptr(buf)
+                this.ptr.offset_from_unsigned(this.buf)..this.end.offset_from_unsigned(buf)
             };
             let cap = this.cap;
             let alloc = ManuallyDrop::take(&mut this.alloc);
@@ -230,7 +230,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         let exact = if T::IS_ZST {
             self.end.addr().wrapping_sub(self.ptr.as_ptr().addr())
         } else {
-            unsafe { non_null!(self.end, T).sub_ptr(self.ptr) }
+            unsafe { non_null!(self.end, T).offset_from_unsigned(self.ptr) }
         };
         (exact, Some(exact))
     }