Rollup merge of #144478 - joshtriplett:doc-code-formatting-prep, r=Amanieu

Improve formatting of doc code blocks

We don't currently apply automatic formatting to doc comment code blocks. As a
result, it has built up various idiosyncracies, which make such automatic
formatting difficult. Some of those idiosyncracies also make things harder for
human readers or other tools.

This PR makes a few improvements to doc code formatting, in the hopes of making
future automatic formatting easier, as well as in many cases providing net
readability improvements.

I would suggest reading each commit separately, as each commit contains one
class of changes.

9 files changed, 29 insertions, 25 deletions

diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs
index d6d1bf2effa..d67408cae1b 100644
--- a/library/core/src/cell.rs
+++ b/library/core/src/cell.rs
@@ -2068,9 +2068,9 @@ impl<T: ?Sized + fmt::Display> fmt::Display for RefMut<'_, T> {
 /// implies exclusive access to its `T`:
 ///
 /// ```rust
-/// #![forbid(unsafe_code)] // with exclusive accesses,
-///                         // `UnsafeCell` is a transparent no-op wrapper,
-///                         // so no need for `unsafe` here.
+/// #![forbid(unsafe_code)]
+/// // with exclusive accesses, `UnsafeCell` is a transparent no-op wrapper, so no need for
+/// // `unsafe` here.
 /// use std::cell::UnsafeCell;
 ///
 /// let mut x: UnsafeCell<i32> = 42.into();
diff --git a/library/core/src/hint.rs b/library/core/src/hint.rs
index 696d323c66d..c72eeb9a9c9 100644
--- a/library/core/src/hint.rs
+++ b/library/core/src/hint.rs
@@ -649,8 +649,6 @@ pub const fn must_use<T>(value: T) -> T {
 ///     }
 /// }
 /// ```
-///
-///
 #[unstable(feature = "likely_unlikely", issue = "136873")]
 #[inline(always)]
 pub const fn likely(b: bool) -> bool {
diff --git a/library/core/src/iter/mod.rs b/library/core/src/iter/mod.rs
index 7ca41d224a0..56ca1305b60 100644
--- a/library/core/src/iter/mod.rs
+++ b/library/core/src/iter/mod.rs
@@ -233,10 +233,12 @@
 //!
 //! ```
 //! let mut values = vec![41];
-//! for x in &mut values { // same as `values.iter_mut()`
+//! for x in &mut values {
+//!     //   ^ same as `values.iter_mut()`
 //!     *x += 1;
 //! }
-//! for x in &values { // same as `values.iter()`
+//! for x in &values {
+//!     //   ^ same as `values.iter()`
 //!     assert_eq!(*x, 42);
 //! }
 //! assert_eq!(values.len(), 1);
diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs
index 10f9d464f7d..29313867ff2 100644
--- a/library/core/src/iter/traits/iterator.rs
+++ b/library/core/src/iter/traits/iterator.rs
@@ -807,7 +807,7 @@ pub trait Iterator {
     /// might be preferable to keep a functional style with longer iterators:
     ///
     /// ```
-    /// (0..5).flat_map(|x| x * 100 .. x * 110)
+    /// (0..5).flat_map(|x| (x * 100)..(x * 110))
     ///       .enumerate()
     ///       .filter(|&(i, x)| (i + x) % 3 == 0)
     ///       .for_each(|(i, x)| println!("{i}:{x}"));
diff --git a/library/core/src/macros/mod.rs b/library/core/src/macros/mod.rs
index 3d57da63683..c59290a757b 100644
--- a/library/core/src/macros/mod.rs
+++ b/library/core/src/macros/mod.rs
@@ -271,7 +271,10 @@ pub macro cfg_select($($tt:tt)*) {
 /// // expression given.
 /// debug_assert!(true);
 ///
-/// fn some_expensive_computation() -> bool { true } // a very simple function
+/// fn some_expensive_computation() -> bool {
+///     // Some expensive computation here
+///     true
+/// }
 /// debug_assert!(some_expensive_computation());
 ///
 /// // assert with a custom message
@@ -1547,7 +1550,10 @@ pub(crate) mod builtin {
     /// // expression given.
     /// assert!(true);
     ///
-    /// fn some_computation() -> bool { true } // a very simple function
+    /// fn some_computation() -> bool {
+    ///     // Some expensive computation here
+    ///     true
+    /// }
     ///
     /// assert!(some_computation());
     ///
diff --git a/library/core/src/marker.rs b/library/core/src/marker.rs
index 45277a1c82d..ba00ee17b65 100644
--- a/library/core/src/marker.rs
+++ b/library/core/src/marker.rs
@@ -138,8 +138,7 @@ unsafe impl<T: Sync + PointeeSized> Send for &T {}
 /// impl Bar for Impl { }
 ///
 /// let x: &dyn Foo = &Impl;    // OK
-/// // let y: &dyn Bar = &Impl; // error: the trait `Bar` cannot
-///                             // be made into an object
+/// // let y: &dyn Bar = &Impl; // error: the trait `Bar` cannot be made into an object
 /// ```
 ///
 /// [trait object]: ../../book/ch17-02-trait-objects.html
diff --git a/library/core/src/mem/maybe_uninit.rs b/library/core/src/mem/maybe_uninit.rs
index 34d8370da7e..c160360cfac 100644
--- a/library/core/src/mem/maybe_uninit.rs
+++ b/library/core/src/mem/maybe_uninit.rs
@@ -773,8 +773,7 @@ impl<T> MaybeUninit<T> {
     /// // Initialize the `MaybeUninit` using `Cell::set`:
     /// unsafe {
     ///     b.assume_init_ref().set(true);
-    ///    // ^^^^^^^^^^^^^^^
-    ///    // Reference to an uninitialized `Cell<bool>`: UB!
+    ///     //^^^^^^^^^^^^^^^ Reference to an uninitialized `Cell<bool>`: UB!
     /// }
     /// ```
     #[stable(feature = "maybe_uninit_ref", since = "1.55.0")]
@@ -864,9 +863,9 @@ impl<T> MaybeUninit<T> {
     /// {
     ///     let mut buffer = MaybeUninit::<[u8; 64]>::uninit();
     ///     reader.read_exact(unsafe { buffer.assume_init_mut() })?;
-    ///                             // ^^^^^^^^^^^^^^^^^^^^^^^^
-    ///                             // (mutable) reference to uninitialized memory!
-    ///                             // This is undefined behavior.
+    ///     //                         ^^^^^^^^^^^^^^^^^^^^^^^^
+    ///     // (mutable) reference to uninitialized memory!
+    ///     // This is undefined behavior.
     ///     Ok(unsafe { buffer.assume_init() })
     /// }
     /// ```
@@ -884,13 +883,13 @@ impl<T> MaybeUninit<T> {
     /// let foo: Foo = unsafe {
     ///     let mut foo = MaybeUninit::<Foo>::uninit();
     ///     ptr::write(&mut foo.assume_init_mut().a as *mut u32, 1337);
-    ///                  // ^^^^^^^^^^^^^^^^^^^^^
-    ///                  // (mutable) reference to uninitialized memory!
-    ///                  // This is undefined behavior.
+    ///     //              ^^^^^^^^^^^^^^^^^^^^^
+    ///     // (mutable) reference to uninitialized memory!
+    ///     // This is undefined behavior.
     ///     ptr::write(&mut foo.assume_init_mut().b as *mut u8, 42);
-    ///                  // ^^^^^^^^^^^^^^^^^^^^^
-    ///                  // (mutable) reference to uninitialized memory!
-    ///                  // This is undefined behavior.
+    ///     //              ^^^^^^^^^^^^^^^^^^^^^
+    ///     // (mutable) reference to uninitialized memory!
+    ///     // This is undefined behavior.
     ///     foo.assume_init()
     /// };
     /// ```
diff --git a/library/core/src/primitive_docs.rs b/library/core/src/primitive_docs.rs
index 9a1ba7d1728..1c824e336be 100644
--- a/library/core/src/primitive_docs.rs
+++ b/library/core/src/primitive_docs.rs
@@ -271,6 +271,7 @@ mod prim_bool {}
 /// When the compiler sees a value of type `!` in a [coercion site], it implicitly inserts a
 /// coercion to allow the type checker to infer any type:
 ///
+// FIXME: use `core::convert::absurd` here instead, once it's merged
 /// ```rust,ignore (illustrative-and-has-placeholders)
 /// // this
 /// let x: u8 = panic!();
@@ -281,7 +282,6 @@ mod prim_bool {}
 /// // where absurd is a function with the following signature
 /// // (it's sound, because `!` always marks unreachable code):
 /// fn absurd<T>(_: !) -> T { ... }
-// FIXME: use `core::convert::absurd` here instead, once it's merged
 /// ```
 ///
 /// This can lead to compilation errors if the type cannot be inferred:
diff --git a/library/core/src/result.rs b/library/core/src/result.rs
index 812fc0d9819..474f86395ae 100644
--- a/library/core/src/result.rs
+++ b/library/core/src/result.rs
@@ -1631,7 +1631,7 @@ impl<T, E> Result<T, E> {
     ///
     /// ```no_run
     /// let x: Result<u32, &str> = Err("emergency failure");
-    /// unsafe { x.unwrap_unchecked(); } // Undefined behavior!
+    /// unsafe { x.unwrap_unchecked() }; // Undefined behavior!
     /// ```
     #[inline]
     #[track_caller]