Auto merge of #62873 - Centril:rollup-ncnuelj, r=Centril

Rollup of 14 pull requests

Successful merges:

 - #62709 (Test that maplike FromIter satisfies uniqueness)
 - #62713 (Stabilize <*mut _>::cast and <*const _>::cast)
 - #62746 ( do not use assume_init in std::io)
 - #62787 (Fix typo in src/libstd/net/udp.rs doc comment)
 - #62788 (normalize use of backticks in compiler messages for libcore/ptr)
 - #62799 (use const array repeat expressions for uninit_array)
 - #62810 (normalize use of backticks in compiler messages for librustc_lint)
 - #62812 (normalize use of backticks in compiler messages for librustc_metadata)
 - #62832 (normalize use of backticks in compiler messages for librustc_incremental)
 - #62845 (read: fix doc comment)
 - #62853 (normalize use of backticks in compiler messages for librustc/hir)
 - #62854 (Fix typo in Unicode character name)
 - #62858 (Change wrong variable name.)
 - #62870 (fix lexing of comments with many \r)

Failed merges:

r? @ghost

Author: bors

src/liballoc/collections/btree/map.rs

@@ -75,10 +75,10 @@ use Entry::*;
 ///
 /// // look up the values associated with some keys.
 /// let to_find = ["Up!", "Office Space"];
-/// for book in &to_find {
-///     match movie_reviews.get(book) {
-///        Some(review) => println!("{}: {}", book, review),
-///        None => println!("{} is unreviewed.", book)
+/// for movie in &to_find {
+///     match movie_reviews.get(movie) {
+///        Some(review) => println!("{}: {}", movie, review),
+///        None => println!("{} is unreviewed.", movie)
 ///     }
 /// }
 ///

src/liballoc/collections/btree/node.rs

@@ -106,8 +106,8 @@ impl<K, V> LeafNode<K, V> {
         LeafNode {
             // As a general policy, we leave fields uninitialized if they can be, as this should
             // be both slightly faster and easier to track in Valgrind.
-            keys: uninitialized_array![_; CAPACITY],
-            vals: uninitialized_array![_; CAPACITY],
+            keys: uninit_array![_; CAPACITY],
+            vals: uninit_array![_; CAPACITY],
             parent: ptr::null(),
             parent_idx: MaybeUninit::uninit(),
             len: 0
@@ -159,7 +159,7 @@ impl<K, V> InternalNode<K, V> {
     unsafe fn new() -> Self {
         InternalNode {
             data: LeafNode::new(),
-            edges: uninitialized_array![_; 2*B],
+            edges: uninit_array![_; 2*B],
         }
     }
 }

src/liballoc/lib.rs

@@ -77,13 +77,15 @@
 #![feature(box_syntax)]
 #![feature(cfg_target_has_atomic)]
 #![feature(coerce_unsized)]
+#![cfg_attr(not(bootstrap), feature(const_in_array_repeat_expressions))]
 #![feature(dispatch_from_dyn)]
 #![feature(core_intrinsics)]
 #![feature(dropck_eyepatch)]
 #![feature(exact_size_is_empty)]
 #![feature(fmt_internals)]
 #![feature(fn_traits)]
 #![feature(fundamental)]
+#![feature(internal_uninit_const)]
 #![feature(lang_items)]
 #![feature(libc)]
 #![feature(nll)]

src/libcore/fmt/float.rs

@@ -12,10 +12,11 @@ fn float_to_decimal_common_exact<T>(fmt: &mut Formatter<'_>, num: &T,
     unsafe {
         let mut buf = MaybeUninit::<[u8; 1024]>::uninit(); // enough for f32 and f64
         let mut parts = MaybeUninit::<[flt2dec::Part<'_>; 4]>::uninit();
-        // FIXME(#53491): Technically, this is calling `get_mut` on an uninitialized
-        // `MaybeUninit` (here and elsewhere in this file).  Revisit this once
+        // FIXME(#53491): This is calling `get_mut` on an uninitialized
+        // `MaybeUninit` (here and elsewhere in this file). Revisit this once
         // we decided whether that is valid or not.
-        // Using `freeze` is *not enough*; `flt2dec::Part` is an enum!
+        // We can do this only because we are libstd and coupled to the compiler.
+        // (FWIW, using `freeze` would not be enough; `flt2dec::Part` is an enum!)
         let formatted = flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact,
                                                     *num, sign, precision,
                                                     false, buf.get_mut(), parts.get_mut());

src/libcore/fmt/num.rs

@@ -51,7 +51,7 @@ trait GenericRadix {
         // characters for a base 2 number.
         let zero = T::zero();
         let is_nonnegative = x >= zero;
-        let mut buf = uninitialized_array![u8; 128];
+        let mut buf = [MaybeUninit::<u8>::uninit(); 128];
         let mut curr = buf.len();
         let base = T::from_u8(Self::BASE);
         if is_nonnegative {
@@ -189,7 +189,7 @@ static DEC_DIGITS_LUT: &[u8; 200] =
 macro_rules! impl_Display {
     ($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
         fn $name(mut n: $u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-            let mut buf = uninitialized_array![u8; 39];
+            let mut buf = [MaybeUninit::<u8>::uninit(); 39];
             let mut curr = buf.len() as isize;
             let buf_ptr = MaybeUninit::first_ptr_mut(&mut buf);
             let lut_ptr = DEC_DIGITS_LUT.as_ptr();

src/libcore/macros.rs

@@ -626,20 +626,37 @@ macro_rules! todo {
 /// Creates an array of [`MaybeUninit`].
 ///
 /// This macro constructs an uninitialized array of the type `[MaybeUninit<K>; N]`.
+/// It exists solely because bootstrap does not yet support const array-init expressions.
 ///
 /// [`MaybeUninit`]: mem/union.MaybeUninit.html
+// FIXME: Remove both versions of this macro once bootstrap is 1.38.
 #[macro_export]
 #[unstable(feature = "maybe_uninit_array", issue = "53491")]
-macro_rules! uninitialized_array {
+#[cfg(bootstrap)]
+macro_rules! uninit_array {
     // This `assume_init` is safe because an array of `MaybeUninit` does not
     // require initialization.
-    // FIXME(#49147): Could be replaced by an array initializer, once those can
-    // be any const expression.
     ($t:ty; $size:expr) => (unsafe {
         MaybeUninit::<[MaybeUninit<$t>; $size]>::uninit().assume_init()
     });
 }
 
+/// Creates an array of [`MaybeUninit`].
+///
+/// This macro constructs an uninitialized array of the type `[MaybeUninit<K>; N]`.
+/// It exists solely because bootstrap does not yet support const array-init expressions.
+///
+/// [`MaybeUninit`]: mem/union.MaybeUninit.html
+// FIXME: Just inline this version of the macro once bootstrap is 1.38.
+#[macro_export]
+#[unstable(feature = "maybe_uninit_array", issue = "53491")]
+#[cfg(not(bootstrap))]
+macro_rules! uninit_array {
+    ($t:ty; $size:expr) => (
+        [MaybeUninit::<$t>::UNINIT; $size]
+    );
+}
+
 /// Built-in macros to the compiler itself.
 ///
 /// These macros do not have any corresponding definition with a `macro_rules!`

src/libcore/mem/maybe_uninit.rs

@@ -252,6 +252,11 @@ impl<T> MaybeUninit<T> {
         MaybeUninit { uninit: () }
     }
 
+    /// A promotable constant, equivalent to `uninit()`.
+    #[unstable(feature = "internal_uninit_const", issue = "0",
+        reason = "hack to work around promotability")]
+    pub const UNINIT: Self = Self::uninit();
+
     /// Creates a new `MaybeUninit<T>` in an uninitialized state, with the memory being
     /// filled with `0` bytes. It depends on `T` whether that already makes for
     /// proper initialization. For example, `MaybeUninit<usize>::zeroed()` is initialized,

src/libcore/ptr/mod.rs

@@ -1043,7 +1043,7 @@ impl<T: ?Sized> *const T {
     }
 
     /// Cast to a pointer to a different type
-    #[unstable(feature = "ptr_cast", issue = "60602")]
+    #[stable(feature = "ptr_cast", since = "1.38.0")]
     #[inline]
     pub const fn cast<U>(self) -> *const U {
         self as _
@@ -1678,7 +1678,7 @@ impl<T: ?Sized> *mut T {
     }
 
     /// Cast to a pointer to a different type
-    #[unstable(feature = "ptr_cast", issue = "60602")]
+    #[stable(feature = "ptr_cast", since = "1.38.0")]
     #[inline]
     pub const fn cast<U>(self) -> *mut U {
         self as _

src/libcore/ptr/unique.rs

@@ -26,8 +26,8 @@ use crate::ptr::NonNull;
 /// Unlike `*mut T`, `Unique<T>` is covariant over `T`. This should always be correct
 /// for any type which upholds Unique's aliasing requirements.
 #[unstable(feature = "ptr_internals", issue = "0",
-           reason = "use NonNull instead and consider PhantomData<T> \
-                     (if you also use #[may_dangle]), Send, and/or Sync")]
+           reason = "use `NonNull` instead and consider `PhantomData<T>` \
+                     (if you also use `#[may_dangle]`), `Send`, and/or `Sync`")]
 #[doc(hidden)]
 #[repr(transparent)]
 #[rustc_layout_scalar_valid_range_start(1)]

src/libcore/slice/sort.rs

@@ -216,14 +216,14 @@ fn partition_in_blocks<T, F>(v: &mut [T], pivot: &T, is_less: &mut F) -> usize
     let mut block_l = BLOCK;
     let mut start_l = ptr::null_mut();
     let mut end_l = ptr::null_mut();
-    let mut offsets_l: [MaybeUninit<u8>; BLOCK] = uninitialized_array![u8; BLOCK];
+    let mut offsets_l = [MaybeUninit::<u8>::uninit(); BLOCK];
 
     // The current block on the right side (from `r.sub(block_r)` to `r`).
     let mut r = unsafe { l.add(v.len()) };
     let mut block_r = BLOCK;
     let mut start_r = ptr::null_mut();
     let mut end_r = ptr::null_mut();
-    let mut offsets_r: [MaybeUninit<u8>; BLOCK] = uninitialized_array![u8; BLOCK];
+    let mut offsets_r = [MaybeUninit::<u8>::uninit(); BLOCK];
 
     // FIXME: When we get VLAs, try creating one array of length `min(v.len(), 2 * BLOCK)` rather
     // than two fixed-size arrays of length `BLOCK`. VLAs might be more cache-efficient.