Fix doc nits

Many tiny changes to stdlib doc comments to make them consistent (for example
"Returns foo", rather than "Return foo"), adding missing periods, paragraph
breaks, backticks for monospace style, and other minor nits.

Author: bitfield

library/alloc/src/alloc.rs

@@ -57,7 +57,7 @@ pub struct Global;
 #[cfg(test)]
 pub use std::alloc::Global;
 
-/// Allocate memory with the global allocator.
+/// Allocates memory with the global allocator.
 ///
 /// This function forwards calls to the [`GlobalAlloc::alloc`] method
 /// of the allocator registered with the `#[global_allocator]` attribute
@@ -101,7 +101,7 @@ pub unsafe fn alloc(layout: Layout) -> *mut u8 {
     }
 }
 
-/// Deallocate memory with the global allocator.
+/// Deallocates memory with the global allocator.
 ///
 /// This function forwards calls to the [`GlobalAlloc::dealloc`] method
 /// of the allocator registered with the `#[global_allocator]` attribute
@@ -119,7 +119,7 @@ pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
     unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
 }
 
-/// Reallocate memory with the global allocator.
+/// Reallocates memory with the global allocator.
 ///
 /// This function forwards calls to the [`GlobalAlloc::realloc`] method
 /// of the allocator registered with the `#[global_allocator]` attribute
@@ -138,7 +138,7 @@ pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8
     unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
 }
 
-/// Allocate zero-initialized memory with the global allocator.
+/// Allocates zero-initialized memory with the global allocator.
 ///
 /// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
 /// of the allocator registered with the `#[global_allocator]` attribute
@@ -345,7 +345,7 @@ extern "Rust" {
     fn __rust_alloc_error_handler(size: usize, align: usize) -> !;
 }
 
-/// Signal a memory allocation error.
+/// Signals a memory allocation error.
 ///
 /// Callers of memory allocation APIs wishing to cease execution
 /// in response to an allocation error are encouraged to call this function,

library/alloc/src/boxed.rs

@@ -1189,9 +1189,11 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
     }
 
     /// Consumes and leaks the `Box`, returning a mutable reference,
-    /// `&'a mut T`. Note that the type `T` must outlive the chosen lifetime
-    /// `'a`. If the type has only static references, or none at all, then this
-    /// may be chosen to be `'static`.
+    /// `&'a mut T`.
+    ///
+    /// Note that the type `T` must outlive the chosen lifetime `'a`. If the type
+    /// has only static references, or none at all, then this may be chosen to be
+    /// `'static`.
     ///
     /// This function is mainly useful for data that lives for the remainder of
     /// the program's life. Dropping the returned reference will cause a memory
@@ -1774,7 +1776,7 @@ impl<T, const N: usize> TryFrom<Vec<T>> for Box<[T; N]> {
 }
 
 impl<A: Allocator> Box<dyn Any, A> {
-    /// Attempt to downcast the box to a concrete type.
+    /// Attempts to downcast the box to a concrete type.
     ///
     /// # Examples
     ///
@@ -1833,7 +1835,7 @@ impl<A: Allocator> Box<dyn Any, A> {
 }
 
 impl<A: Allocator> Box<dyn Any + Send, A> {
-    /// Attempt to downcast the box to a concrete type.
+    /// Attempts to downcast the box to a concrete type.
     ///
     /// # Examples
     ///
@@ -1892,7 +1894,7 @@ impl<A: Allocator> Box<dyn Any + Send, A> {
 }
 
 impl<A: Allocator> Box<dyn Any + Send + Sync, A> {
-    /// Attempt to downcast the box to a concrete type.
+    /// Attempts to downcast the box to a concrete type.
     ///
     /// # Examples
     ///