Rollup of 6 pull requests

library/alloc/src/collections/btree/map.rs

@@ -194,6 +194,9 @@ pub struct BTreeMap<
     root: Option<Root<K, V>>,
     length: usize,
     /// `ManuallyDrop` to control drop order (needs to be dropped after all the nodes).
+    // Although some of the accessory types store a copy of the allocator, the nodes do not.
+    // Because allocations will remain live as long as any copy (like this one) of the allocator
+    // is live, it's unnecessary to store the allocator in each node.
     pub(super) alloc: ManuallyDrop<A>,
     // For dropck; the `Box` avoids making the `Unpin` impl more strict than before
     _marker: PhantomData<crate::boxed::Box<(K, V), A>>,

library/alloc/src/collections/btree/node.rs

@@ -225,7 +225,11 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::Leaf> {
     }
 
     fn from_new_leaf<A: Allocator + Clone>(leaf: Box<LeafNode<K, V>, A>) -> Self {
-        NodeRef { height: 0, node: NonNull::from(Box::leak(leaf)), _marker: PhantomData }
+        // The allocator must be dropped, not leaked.  See also `BTreeMap::alloc`.
+        let (leaf, _alloc) = Box::into_raw_with_allocator(leaf);
+        // SAFETY: the node was just allocated.
+        let node = unsafe { NonNull::new_unchecked(leaf) };
+        NodeRef { height: 0, node, _marker: PhantomData }
     }
 }
 
@@ -243,7 +247,11 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::Internal> {
         height: usize,
     ) -> Self {
         debug_assert!(height > 0);
-        let node = NonNull::from(Box::leak(internal)).cast();
+        // The allocator must be dropped, not leaked.  See also `BTreeMap::alloc`.
+        let (internal, _alloc) = Box::into_raw_with_allocator(internal);
+        // SAFETY: the node was just allocated.
+        let internal = unsafe { NonNull::new_unchecked(internal) };
+        let node = internal.cast();
         let mut this = NodeRef { height, node, _marker: PhantomData };
         this.borrow_mut().correct_all_childrens_parent_links();
         this

library/alloc/src/vec/extract_if.rs

@@ -64,27 +64,37 @@ where
     type Item = T;
 
     fn next(&mut self) -> Option<T> {
-        unsafe {
-            while self.idx < self.end {
-                let i = self.idx;
-                let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
-                let drained = (self.pred)(&mut v[i]);
-                // Update the index *after* the predicate is called. If the index
-                // is updated prior and the predicate panics, the element at this
-                // index would be leaked.
-                self.idx += 1;
-                if drained {
-                    self.del += 1;
-                    return Some(ptr::read(&v[i]));
-                } else if self.del > 0 {
-                    let del = self.del;
-                    let src: *const T = &v[i];
-                    let dst: *mut T = &mut v[i - del];
-                    ptr::copy_nonoverlapping(src, dst, 1);
+        while self.idx < self.end {
+            let i = self.idx;
+            // SAFETY:
+            //  We know that `i < self.end` from the if guard and that `self.end <= self.old_len` from
+            //  the validity of `Self`. Therefore `i` points to an element within `vec`.
+            //
+            //  Additionally, the i-th element is valid because each element is visited at most once
+            //  and it is the first time we access vec[i].
+            //
+            //  Note: we can't use `vec.get_unchecked_mut(i)` here since the precondition for that
+            //  function is that i < vec.len(), but we've set vec's length to zero.
+            let cur = unsafe { &mut *self.vec.as_mut_ptr().add(i) };
+            let drained = (self.pred)(cur);
+            // Update the index *after* the predicate is called. If the index
+            // is updated prior and the predicate panics, the element at this
+            // index would be leaked.
+            self.idx += 1;
+            if drained {
+                self.del += 1;
+                // SAFETY: We never touch this element again after returning it.
+                return Some(unsafe { ptr::read(cur) });
+            } else if self.del > 0 {
+                // SAFETY: `self.del` > 0, so the hole slot must not overlap with current element.
+                // We use copy for move, and never touch this element again.
+                unsafe {
+                    let hole_slot = self.vec.as_mut_ptr().add(i - self.del);
+                    ptr::copy_nonoverlapping(cur, hole_slot, 1);
                 }
             }
-            None
         }
+        None
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
@@ -95,14 +105,18 @@ where
 #[stable(feature = "extract_if", since = "1.87.0")]
 impl<T, F, A: Allocator> Drop for ExtractIf<'_, T, F, A> {
     fn drop(&mut self) {
-        unsafe {
-            if self.idx < self.old_len && self.del > 0 {
-                let ptr = self.vec.as_mut_ptr();
-                let src = ptr.add(self.idx);
-                let dst = src.sub(self.del);
-                let tail_len = self.old_len - self.idx;
-                src.copy_to(dst, tail_len);
+        if self.del > 0 {
+            // SAFETY: Trailing unchecked items must be valid since we never touch them.
+            unsafe {
+                ptr::copy(
+                    self.vec.as_ptr().add(self.idx),
+                    self.vec.as_mut_ptr().add(self.idx - self.del),
+                    self.old_len - self.idx,
+                );
             }
+        }
+        // SAFETY: After filling holes, all items are in contiguous memory.
+        unsafe {
             self.vec.set_len(self.old_len - self.del);
         }
     }

library/alloc/src/vec/mod.rs

@@ -2173,9 +2173,37 @@ impl<T, A: Allocator> Vec<T, A> {
             panic!("removal index (is {index}) should be < len (is {len})");
         }
 
+        match self.try_remove(index) {
+            Some(elem) => elem,
+            None => assert_failed(index, self.len()),
+        }
+    }
+
+    /// Remove and return the element at position `index` within the vector,
+    /// shifting all elements after it to the left, or [`None`] if it does not
+    /// exist.
+    ///
+    /// Note: Because this shifts over the remaining elements, it has a
+    /// worst-case performance of *O*(*n*). If you'd like to remove
+    /// elements from the beginning of the `Vec`, consider using
+    /// [`VecDeque::pop_front`] instead.
+    ///
+    /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(vec_try_remove)]
+    /// let mut v = vec![1, 2, 3];
+    /// assert_eq!(v.try_remove(0), Some(1));
+    /// assert_eq!(v.try_remove(2), None);
+    /// ```
+    #[unstable(feature = "vec_try_remove", issue = "146954")]
+    #[rustc_confusables("delete", "take", "remove")]
+    pub fn try_remove(&mut self, index: usize) -> Option<T> {
         let len = self.len();
         if index >= len {
-            assert_failed(index, len);
+            return None;
         }
         unsafe {
             // infallible
@@ -2191,7 +2219,7 @@ impl<T, A: Allocator> Vec<T, A> {
                 ptr::copy(ptr.add(1), ptr, len - index - 1);
             }
             self.set_len(len - 1);
-            ret
+            Some(ret)
         }
     }
 

library/alloctests/tests/lib.rs

@@ -41,6 +41,7 @@
 #![feature(unique_rc_arc)]
 #![feature(macro_metavar_expr_concat)]
 #![feature(vec_peek_mut)]
+#![feature(vec_try_remove)]
 #![allow(internal_features)]
 #![deny(fuzzy_provenance_casts)]
 #![deny(unsafe_op_in_unsafe_fn)]

library/alloctests/tests/vec.rs

@@ -630,6 +630,21 @@ fn test_swap_remove_empty() {
     vec.swap_remove(0);
 }
 
+#[test]
+fn test_try_remove() {
+    let mut vec = vec![1, 2, 3];
+    // We are attempting to remove vec[0] which contains 1
+    assert_eq!(vec.try_remove(0), Some(1));
+    // Now `vec` looks like: [2, 3]
+    // We will now try to remove vec[2] which does not exist
+    // This should return `None`
+    assert_eq!(vec.try_remove(2), None);
+
+    // We will try the same thing with an empty vector
+    let mut v: Vec<u8> = vec![];
+    assert!(v.try_remove(0).is_none());
+}
+
 #[test]
 fn test_move_items() {
     let vec = vec![1, 2, 3];

library/core/src/num/nonzero.rs

@@ -548,6 +548,18 @@ macro_rules! nonzero_integer {
         #[doc = concat!("assert_eq!(align_of::<", stringify!($Ty), ">(), align_of::<Option<", stringify!($Ty), ">>());")]
         /// ```
         ///
+        /// # Compile-time creation
+        ///
+        /// Since both [`Option::unwrap()`] and [`Option::expect()`] are `const`, it is possible to
+        /// define a new
+        #[doc = concat!("`", stringify!($Ty), "`")]
+        /// at compile time via:
+        /// ```
+        #[doc = concat!("use std::num::", stringify!($Ty), ";")]
+        ///
+        #[doc = concat!("const TEN: ", stringify!($Ty), " = ", stringify!($Ty) , r#"::new(10).expect("ten is non-zero");"#)]
+        /// ```
+        ///
         /// [null pointer optimization]: crate::option#representation
         #[$stability]
         pub type $Ty = NonZero<$Int>;

src/doc/rustdoc/src/advanced-features.md

@@ -89,20 +89,30 @@ https://doc.rust-lang.org/stable/std/?search=%s&go_to_first=true
 This URL adds the `go_to_first=true` query parameter which can be appended to any `rustdoc` search URL
 to automatically go to the first result.
 
-## `#[repr(transparent)]`: Documenting the transparent representation
+## `#[repr(...)]`: Documenting the representation of a type
+
+Generally, rustdoc only displays the representation of a given type if none of its variants are
+`#[doc(hidden)]` and if all of its fields are public and not `#[doc(hidden)]` since it's likely
+not meant to be considered part of the public ABI otherwise.
+
+Note that there's no way to overwrite that heuristic and force rustdoc to show the representation
+regardless.
+
+### `#[repr(transparent)]`
 
 You can read more about `#[repr(transparent)]` itself in the [Rust Reference][repr-trans-ref] and
 in the [Rustonomicon][repr-trans-nomicon].
 
 Since this representation is only considered part of the public ABI if the single field with non-trivial
-size or alignment is public and if the documentation does not state otherwise, Rustdoc helpfully displays
-the attribute if and only if the non-1-ZST field is public or at least one field is public in case all
-fields are 1-ZST fields. The term *1-ZST* refers to types that are one-aligned and zero-sized.
+size or alignment is public and if the documentation does not state otherwise, rustdoc helpfully displays
+the attribute if and only if the non-1-ZST field is public and not `#[doc(hidden)]` or
+– in case all fields are 1-ZST fields — at least one field is public and not `#[doc(hidden)]`.
+The term *1-ZST* refers to types that are one-aligned and zero-sized.
 
 It would seem that one can manually hide the attribute with `#[cfg_attr(not(doc), repr(transparent))]`
 if one wishes to declare the representation as private even if the non-1-ZST field is public.
 However, due to [current limitations][cross-crate-cfg-doc], this method is not always guaranteed to work.
-Therefore, if you would like to do so, you should always write it down in prose independently of whether
+Therefore, if you would like to do so, you should always write that down in prose independently of whether
 you use `cfg_attr` or not.
 
 [repr-trans-ref]: https://doc.rust-lang.org/reference/type-layout.html#the-transparent-representation

src/librustdoc/clean/types.rs

@@ -794,50 +794,6 @@ impl Item {
         Some(tcx.visibility(def_id))
     }
 
-    /// Get a list of attributes excluding `#[repr]` to display.
-    ///
-    /// Only used by the HTML output-format.
-    fn attributes_without_repr(&self) -> Vec<String> {
-        self.attrs
-            .other_attrs
-            .iter()
-            .filter_map(|attr| match attr {
-                hir::Attribute::Parsed(AttributeKind::LinkSection { name, .. }) => {
-                    Some(format!("#[unsafe(link_section = \"{name}\")]"))
-                }
-                hir::Attribute::Parsed(AttributeKind::NoMangle(..)) => {
-                    Some("#[unsafe(no_mangle)]".to_string())
-                }
-                hir::Attribute::Parsed(AttributeKind::ExportName { name, .. }) => {
-                    Some(format!("#[unsafe(export_name = \"{name}\")]"))
-                }
-                hir::Attribute::Parsed(AttributeKind::NonExhaustive(..)) => {
-                    Some("#[non_exhaustive]".to_string())
-                }
-                _ => None,
-            })
-            .collect()
-    }
-
-    /// Get a list of attributes to display on this item.
-    ///
-    /// Only used by the HTML output-format.
-    pub(crate) fn attributes(&self, tcx: TyCtxt<'_>, cache: &Cache) -> Vec<String> {
-        let mut attrs = self.attributes_without_repr();
-
-        if let Some(repr_attr) = self.repr(tcx, cache) {
-            attrs.push(repr_attr);
-        }
-        attrs
-    }
-
-    /// Returns a stringified `#[repr(...)]` attribute.
-    ///
-    /// Only used by the HTML output-format.
-    pub(crate) fn repr(&self, tcx: TyCtxt<'_>, cache: &Cache) -> Option<String> {
-        repr_attributes(tcx, cache, self.def_id()?, self.type_())
-    }
-
     pub fn is_doc_hidden(&self) -> bool {
         self.attrs.is_doc_hidden()
     }
@@ -847,74 +803,6 @@ impl Item {
     }
 }
 
-/// Return a string representing the `#[repr]` attribute if present.
-///
-/// Only used by the HTML output-format.
-pub(crate) fn repr_attributes(
-    tcx: TyCtxt<'_>,
-    cache: &Cache,
-    def_id: DefId,
-    item_type: ItemType,
-) -> Option<String> {
-    use rustc_abi::IntegerType;
-
-    if !matches!(item_type, ItemType::Struct | ItemType::Enum | ItemType::Union) {
-        return None;
-    }
-    let adt = tcx.adt_def(def_id);
-    let repr = adt.repr();
-    let mut out = Vec::new();
-    if repr.c() {
-        out.push("C");
-    }
-    if repr.transparent() {
-        // Render `repr(transparent)` iff the non-1-ZST field is public or at least one
-        // field is public in case all fields are 1-ZST fields.
-        let render_transparent = cache.document_private
-            || adt
-                .all_fields()
-                .find(|field| {
-                    let ty = field.ty(tcx, ty::GenericArgs::identity_for_item(tcx, field.did));
-                    tcx.layout_of(ty::TypingEnv::post_analysis(tcx, field.did).as_query_input(ty))
-                        .is_ok_and(|layout| !layout.is_1zst())
-                })
-                .map_or_else(
-                    || adt.all_fields().any(|field| field.vis.is_public()),
-                    |field| field.vis.is_public(),
-                );
-
-        if render_transparent {
-            out.push("transparent");
-        }
-    }
-    if repr.simd() {
-        out.push("simd");
-    }
-    let pack_s;
-    if let Some(pack) = repr.pack {
-        pack_s = format!("packed({})", pack.bytes());
-        out.push(&pack_s);
-    }
-    let align_s;
-    if let Some(align) = repr.align {
-        align_s = format!("align({})", align.bytes());
-        out.push(&align_s);
-    }
-    let int_s;
-    if let Some(int) = repr.int {
-        int_s = match int {
-            IntegerType::Pointer(is_signed) => {
-                format!("{}size", if is_signed { 'i' } else { 'u' })
-            }
-            IntegerType::Fixed(size, is_signed) => {
-                format!("{}{}", if is_signed { 'i' } else { 'u' }, size.size().bytes() * 8)
-            }
-        };
-        out.push(&int_s);
-    }
-    if !out.is_empty() { Some(format!("#[repr({})]", out.join(", "))) } else { None }
-}
-
 #[derive(Clone, Debug)]
 pub(crate) enum ItemKind {
     ExternCrateItem {