Merge branch 'master' into rusty-hermit

16 files changed, 392 insertions, 253 deletions

diff --git a/src/libcore/any.rs b/src/libcore/any.rs
index 85b59162620..e2704e807d1 100644
--- a/src/libcore/any.rs
+++ b/src/libcore/any.rs
@@ -2,14 +2,14 @@
 //! of any `'static` type through runtime reflection.
 //!
 //! `Any` itself can be used to get a `TypeId`, and has more features when used
-//! as a trait object. As `&Any` (a borrowed trait object), it has the `is` and
-//! `downcast_ref` methods, to test if the contained value is of a given type,
-//! and to get a reference to the inner value as a type. As `&mut Any`, there
+//! as a trait object. As `&dyn Any` (a borrowed trait object), it has the `is`
+//! and `downcast_ref` methods, to test if the contained value is of a given type,
+//! and to get a reference to the inner value as a type. As `&mut dyn Any`, there
 //! is also the `downcast_mut` method, for getting a mutable reference to the
-//! inner value. `Box<Any>` adds the `downcast` method, which attempts to
+//! inner value. `Box<dyn Any>` adds the `downcast` method, which attempts to
 //! convert to a `Box<T>`. See the [`Box`] documentation for the full details.
 //!
-//! Note that &Any is limited to testing whether a value is of a specified
+//! Note that `&dyn Any` is limited to testing whether a value is of a specified
 //! concrete type, and cannot be used to test whether a type implements a trait.
 //!
 //! [`Box`]: ../../std/boxed/struct.Box.html
@@ -445,6 +445,15 @@ impl TypeId {
 ///
 /// The current implementation uses the same infrastructure as compiler
 /// diagnostics and debuginfo, but this is not guaranteed.
+///
+/// # Example
+///
+/// ```rust
+/// assert_eq!(
+///     std::any::type_name::<Option<String>>(),
+///     "core::option::Option<alloc::string::String>",
+/// );
+/// ```
 #[stable(feature = "type_name", since = "1.38.0")]
 #[rustc_const_unstable(feature = "const_type_name")]
 pub const fn type_name<T: ?Sized>() -> &'static str {
diff --git a/src/libcore/cell.rs b/src/libcore/cell.rs
index 8579dbf353e..fda103a52d8 100644
--- a/src/libcore/cell.rs
+++ b/src/libcore/cell.rs
@@ -229,52 +229,6 @@ pub struct Cell<T: ?Sized> {
     value: UnsafeCell<T>,
 }
 
-impl<T:Copy> Cell<T> {
-    /// Returns a copy of the contained value.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::cell::Cell;
-    ///
-    /// let c = Cell::new(5);
-    ///
-    /// let five = c.get();
-    /// ```
-    #[inline]
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn get(&self) -> T {
-        unsafe{ *self.value.get() }
-    }
-
-    /// Updates the contained value using a function and returns the new value.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(cell_update)]
-    ///
-    /// use std::cell::Cell;
-    ///
-    /// let c = Cell::new(5);
-    /// let new = c.update(|x| x + 1);
-    ///
-    /// assert_eq!(new, 6);
-    /// assert_eq!(c.get(), 6);
-    /// ```
-    #[inline]
-    #[unstable(feature = "cell_update", issue = "50186")]
-    pub fn update<F>(&self, f: F) -> T
-    where
-        F: FnOnce(T) -> T,
-    {
-        let old = self.get();
-        let new = f(old);
-        self.set(new);
-        new
-    }
-}
-
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: ?Sized> Send for Cell<T> where T: Send {}
 
@@ -448,6 +402,52 @@ impl<T> Cell<T> {
     }
 }
 
+impl<T:Copy> Cell<T> {
+    /// Returns a copy of the contained value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::cell::Cell;
+    ///
+    /// let c = Cell::new(5);
+    ///
+    /// let five = c.get();
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn get(&self) -> T {
+        unsafe{ *self.value.get() }
+    }
+
+    /// Updates the contained value using a function and returns the new value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(cell_update)]
+    ///
+    /// use std::cell::Cell;
+    ///
+    /// let c = Cell::new(5);
+    /// let new = c.update(|x| x + 1);
+    ///
+    /// assert_eq!(new, 6);
+    /// assert_eq!(c.get(), 6);
+    /// ```
+    #[inline]
+    #[unstable(feature = "cell_update", issue = "50186")]
+    pub fn update<F>(&self, f: F) -> T
+    where
+        F: FnOnce(T) -> T,
+    {
+        let old = self.get();
+        let new = f(old);
+        self.set(new);
+        new
+    }
+}
+
 impl<T: ?Sized> Cell<T> {
     /// Returns a raw pointer to the underlying data in this cell.
     ///
diff --git a/src/libcore/char/methods.rs b/src/libcore/char/methods.rs
index a69eb0f6d4b..971d89e0044 100644
--- a/src/libcore/char/methods.rs
+++ b/src/libcore/char/methods.rs
@@ -116,9 +116,9 @@ impl char {
 
         // the code is split up here to improve execution speed for cases where
         // the `radix` is constant and 10 or smaller
-        let val = if radix <= 10  {
+        let val = if radix <= 10 {
             match self {
-                '0' ..= '9' => self as u32 - '0' as u32,
+                '0'..='9' => self as u32 - '0' as u32,
                 _ => return None,
             }
         } else {
@@ -130,8 +130,11 @@ impl char {
             }
         };
 
-        if val < radix { Some(val) }
-        else { None }
+        if val < radix {
+            Some(val)
+        } else {
+            None
+        }
     }
 
     /// Returns an iterator that yields the hexadecimal Unicode escape of a
@@ -303,8 +306,8 @@ impl char {
             '\r' => EscapeDefaultState::Backslash('r'),
             '\n' => EscapeDefaultState::Backslash('n'),
             '\\' | '\'' | '"' => EscapeDefaultState::Backslash(self),
-            '\x20' ..= '\x7e' => EscapeDefaultState::Char(self),
-            _ => EscapeDefaultState::Unicode(self.escape_unicode())
+            '\x20'..='\x7e' => EscapeDefaultState::Char(self),
+            _ => EscapeDefaultState::Unicode(self.escape_unicode()),
         };
         EscapeDefault { state: init_state }
     }
@@ -436,30 +439,31 @@ impl char {
     pub fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
         let code = self as u32;
         unsafe {
-            let len =
-            if code < MAX_ONE_B && !dst.is_empty() {
+            let len = if code < MAX_ONE_B && !dst.is_empty() {
                 *dst.get_unchecked_mut(0) = code as u8;
                 1
             } else if code < MAX_TWO_B && dst.len() >= 2 {
                 *dst.get_unchecked_mut(0) = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;
                 *dst.get_unchecked_mut(1) = (code & 0x3F) as u8 | TAG_CONT;
                 2
-            } else if code < MAX_THREE_B && dst.len() >= 3  {
+            } else if code < MAX_THREE_B && dst.len() >= 3 {
                 *dst.get_unchecked_mut(0) = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;
-                *dst.get_unchecked_mut(1) = (code >>  6 & 0x3F) as u8 | TAG_CONT;
+                *dst.get_unchecked_mut(1) = (code >> 6 & 0x3F) as u8 | TAG_CONT;
                 *dst.get_unchecked_mut(2) = (code & 0x3F) as u8 | TAG_CONT;
                 3
             } else if dst.len() >= 4 {
                 *dst.get_unchecked_mut(0) = (code >> 18 & 0x07) as u8 | TAG_FOUR_B;
                 *dst.get_unchecked_mut(1) = (code >> 12 & 0x3F) as u8 | TAG_CONT;
-                *dst.get_unchecked_mut(2) = (code >>  6 & 0x3F) as u8 | TAG_CONT;
+                *dst.get_unchecked_mut(2) = (code >> 6 & 0x3F) as u8 | TAG_CONT;
                 *dst.get_unchecked_mut(3) = (code & 0x3F) as u8 | TAG_CONT;
                 4
             } else {
-                panic!("encode_utf8: need {} bytes to encode U+{:X}, but the buffer has {}",
+                panic!(
+                    "encode_utf8: need {} bytes to encode U+{:X}, but the buffer has {}",
                     from_u32_unchecked(code).len_utf8(),
                     code,
-                    dst.len())
+                    dst.len(),
+                )
             };
             from_utf8_unchecked_mut(dst.get_unchecked_mut(..len))
         }
@@ -515,15 +519,24 @@ impl char {
                 *dst.get_unchecked_mut(1) = 0xDC00 | ((code as u16) & 0x3FF);
                 slice::from_raw_parts_mut(dst.as_mut_ptr(), 2)
             } else {
-                panic!("encode_utf16: need {} units to encode U+{:X}, but the buffer has {}",
+                panic!(
+                    "encode_utf16: need {} units to encode U+{:X}, but the buffer has {}",
                     from_u32_unchecked(code).len_utf16(),
                     code,
-                    dst.len())
+                    dst.len(),
+                )
             }
         }
     }
 
-    /// Returns `true` if this `char` is an alphabetic code point, and false if not.
+    /// Returns `true` if this `char` has the `Alphabetic` property.
+    ///
+    /// `Alphabetic` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
+    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
+    ///
+    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
     ///
     /// # Examples
     ///
@@ -547,10 +560,14 @@ impl char {
         }
     }
 
-    /// Returns `true` if this `char` is lowercase.
+    /// Returns `true` if this `char` has the `Lowercase` property.
     ///
-    /// 'Lowercase' is defined according to the terms of the Unicode Derived Core
-    /// Property `Lowercase`.
+    /// `Lowercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
+    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
+    ///
+    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
     ///
     /// # Examples
     ///
@@ -575,10 +592,14 @@ impl char {
         }
     }
 
-    /// Returns `true` if this `char` is uppercase.
+    /// Returns `true` if this `char` has the `Uppercase` property.
+    ///
+    /// `Uppercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
+    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
     ///
-    /// 'Uppercase' is defined according to the terms of the Unicode Derived Core
-    /// Property `Uppercase`.
+    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
     ///
     /// # Examples
     ///
@@ -603,10 +624,12 @@ impl char {
         }
     }
 
-    /// Returns `true` if this `char` is whitespace.
+    /// Returns `true` if this `char` has the `White_Space` property.
     ///
-    /// 'Whitespace' is defined according to the terms of the Unicode Derived Core
-    /// Property `White_Space`.
+    /// `White_Space` is specified in the [Unicode Character Database][ucd] [`PropList.txt`].
+    ///
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`PropList.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/PropList.txt
     ///
     /// # Examples
     ///
@@ -630,10 +653,10 @@ impl char {
         }
     }
 
-    /// Returns `true` if this `char` is alphanumeric.
+    /// Returns `true` if this `char` satisfies either [`is_alphabetic()`] or [`is_numeric()`].
     ///
-    /// 'Alphanumeric'-ness is defined in terms of the Unicode General Categories
-    /// `Nd`, `Nl`, `No` and the Derived Core Property `Alphabetic`.
+    /// [`is_alphabetic()`]: #method.is_alphabetic
+    /// [`is_numeric()`]: #method.is_numeric
     ///
     /// # Examples
     ///
@@ -655,10 +678,15 @@ impl char {
         self.is_alphabetic() || self.is_numeric()
     }
 
-    /// Returns `true` if this `char` is a control code point.
+    /// Returns `true` if this `char` has the general category for control codes.
+    ///
+    /// Control codes (code points with the general category of `Cc`) are described in Chapter 4
+    /// (Character Properties) of the [Unicode Standard] and specified in the [Unicode Character
+    /// Database][ucd] [`UnicodeData.txt`].
     ///
-    /// 'Control code point' is defined in terms of the Unicode General
-    /// Category `Cc`.
+    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
     ///
     /// # Examples
     ///
@@ -675,19 +703,29 @@ impl char {
         general_category::Cc(self)
     }
 
-    /// Returns `true` if this `char` is an extended grapheme character.
+    /// Returns `true` if this `char` has the `Grapheme_Extend` property.
     ///
-    /// 'Extended grapheme character' is defined in terms of the Unicode Shaping and Rendering
-    /// Category `Grapheme_Extend`.
+    /// `Grapheme_Extend` is described in [Unicode Standard Annex #29 (Unicode Text
+    /// Segmentation)][uax29] and specified in the [Unicode Character Database][ucd]
+    /// [`DerivedCoreProperties.txt`].
+    ///
+    /// [uax29]: https://www.unicode.org/reports/tr29/
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
     #[inline]
     pub(crate) fn is_grapheme_extended(self) -> bool {
         derived_property::Grapheme_Extend(self)
     }
 
-    /// Returns `true` if this `char` is numeric.
+    /// Returns `true` if this `char` has one of the general categories for numbers.
+    ///
+    /// The general categories for numbers (`Nd` for decimal digits, `Nl` for letter-like numeric
+    /// characters, and `No` for other numeric characters) are specified in the [Unicode Character
+    /// Database][ucd] [`UnicodeData.txt`].
     ///
-    /// 'Numeric'-ness is defined in terms of the Unicode General Categories
-    /// `Nd`, `Nl`, `No`.
+    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
     ///
     /// # Examples
     ///
@@ -713,25 +751,29 @@ impl char {
         }
     }
 
-    /// Returns an iterator that yields the lowercase equivalent of a `char`
-    /// as one or more `char`s.
+    /// Returns an iterator that yields the lowercase mapping of this `char` as one or more
+    /// `char`s.
     ///
-    /// If a character does not have a lowercase equivalent, the same character
-    /// will be returned back by the iterator.
+    /// If this `char` does not have a lowercase mapping, the iterator yields the same `char`.
     ///
-    /// This performs complex unconditional mappings with no tailoring: it maps
-    /// one Unicode character to its lowercase equivalent according to the
-    /// [Unicode database] and the additional complex mappings
-    /// [`SpecialCasing.txt`]. Conditional mappings (based on context or
-    /// language) are not considered here.
+    /// If this `char` has a one-to-one lowercase mapping given by the [Unicode Character
+    /// Database][ucd] [`UnicodeData.txt`], the iterator yields that `char`.
     ///
-    /// For a full reference, see [here][reference].
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
     ///
-    /// [Unicode database]: ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.txt
+    /// If this `char` requires special considerations (e.g. multiple `char`s) the iterator yields
+    /// the `char`(s) given by [`SpecialCasing.txt`].
     ///
-    /// [`SpecialCasing.txt`]: ftp://ftp.unicode.org/Public/UNIDATA/SpecialCasing.txt
+    /// [`SpecialCasing.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/SpecialCasing.txt
     ///
-    /// [reference]: http://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
+    /// This operation performs an unconditional mapping without tailoring. That is, the conversion
+    /// is independent of context and language.
+    ///
+    /// In the [Unicode Standard], Chapter 4 (Character Properties) discusses case mapping in
+    /// general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.
+    ///
+    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
     ///
     /// # Examples
     ///
@@ -774,25 +816,29 @@ impl char {
         ToLowercase(CaseMappingIter::new(conversions::to_lower(self)))
     }
 
-    /// Returns an iterator that yields the uppercase equivalent of a `char`
-    /// as one or more `char`s.
+    /// Returns an iterator that yields the uppercase mapping of this `char` as one or more
+    /// `char`s.
+    ///
+    /// If this `char` does not have a uppercase mapping, the iterator yields the same `char`.
+    ///
+    /// If this `char` has a one-to-one uppercase mapping given by the [Unicode Character
+    /// Database][ucd] [`UnicodeData.txt`], the iterator yields that `char`.
     ///
-    /// If a character does not have an uppercase equivalent, the same character
-    /// will be returned back by the iterator.
+    /// [ucd]: https://www.unicode.org/reports/tr44/
+    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
     ///
-    /// This performs complex unconditional mappings with no tailoring: it maps
-    /// one Unicode character to its uppercase equivalent according to the
-    /// [Unicode database] and the additional complex mappings
-    /// [`SpecialCasing.txt`]. Conditional mappings (based on context or
-    /// language) are not considered here.
+    /// If this `char` requires special considerations (e.g. multiple `char`s) the iterator yields
+    /// the `char`(s) given by [`SpecialCasing.txt`].
     ///
-    /// For a full reference, see [here][reference].
+    /// [`SpecialCasing.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/SpecialCasing.txt
     ///
-    /// [Unicode database]: ftp://ftp.unicode.org/Public/UNIDATA/UnicodeData.txt
+    /// This operation performs an unconditional mapping without tailoring. That is, the conversion
+    /// is independent of context and language.
     ///
-    /// [`SpecialCasing.txt`]: ftp://ftp.unicode.org/Public/UNIDATA/SpecialCasing.txt
+    /// In the [Unicode Standard], Chapter 4 (Character Properties) discusses case mapping in
+    /// general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.
     ///
-    /// [reference]: http://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
+    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
     ///
     /// # Examples
     ///
diff --git a/src/libcore/fmt/builders.rs b/src/libcore/fmt/builders.rs
index 15ce2277fa0..e6e3454b36f 100644
--- a/src/libcore/fmt/builders.rs
+++ b/src/libcore/fmt/builders.rs
@@ -775,10 +775,10 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
                reason = "recently added",
                issue = "62482")]
     pub fn key(&mut self, key: &dyn fmt::Debug) -> &mut DebugMap<'a, 'b> {
-        assert!(!self.has_key, "attempted to begin a new map entry \
-                                without completing the previous one");
-
         self.result = self.result.and_then(|_| {
+            assert!(!self.has_key, "attempted to begin a new map entry \
+                                    without completing the previous one");
+
             if self.is_pretty() {
                 if !self.has_fields {
                     self.fmt.write_str("\n")?;
@@ -839,9 +839,9 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
                reason = "recently added",
                issue = "62482")]
     pub fn value(&mut self, value: &dyn fmt::Debug) -> &mut DebugMap<'a, 'b> {
-        assert!(self.has_key, "attempted to format a map value before its key");
-
         self.result = self.result.and_then(|_| {
+            assert!(self.has_key, "attempted to format a map value before its key");
+
             if self.is_pretty() {
                 let mut slot = None;
                 let mut writer = PadAdapter::wrap(&mut self.fmt, &mut slot, &mut self.state);
@@ -924,9 +924,11 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
     /// ```
     #[stable(feature = "debug_builders", since = "1.2.0")]
     pub fn finish(&mut self) -> fmt::Result {
-        assert!(!self.has_key, "attempted to finish a map with a partial entry");
+        self.result.and_then(|_| {
+            assert!(!self.has_key, "attempted to finish a map with a partial entry");
 
-        self.result.and_then(|_| self.fmt.write_str("}"))
+            self.fmt.write_str("}")
+        })
     }
 
     fn is_pretty(&self) -> bool {
diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index 5dfdd162306..8413b2e0ac4 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -108,10 +108,10 @@ pub struct Error;
 /// [`io::Write`]: ../../std/io/trait.Write.html
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait Write {
-    /// Writes a slice of bytes into this writer, returning whether the write
+    /// Writes a string slice into this writer, returning whether the write
     /// succeeded.
     ///
-    /// This method can only succeed if the entire byte slice was successfully
+    /// This method can only succeed if the entire string slice was successfully
     /// written, and this method will not return until all data has been
     /// written or an error occurs.
     ///
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index e8c76b49a8e..30e8dddff85 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -127,7 +127,6 @@
 #![feature(adx_target_feature)]
 #![feature(maybe_uninit_slice)]
 #![feature(external_doc)]
-#![feature(mem_take)]
 #![feature(associated_type_bounds)]
 
 #[prelude_import]
diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs
index ca1b06fb81a..1320e63df06 100644
--- a/src/libcore/macros.rs
+++ b/src/libcore/macros.rs
@@ -520,18 +520,20 @@ macro_rules! unreachable {
     });
 }
 
-/// Indicates unfinished code.
+/// Indicates unfinished code by panicking with a message of "not yet implemented".
 ///
-/// This can be useful if you are prototyping and are just looking to have your
-/// code type-check, or if you're implementing a trait that requires multiple
-/// methods, and you're only planning on using one of them.
+/// This allows the your code to type-check, which is useful if you are prototyping or
+/// implementing a trait that requires multiple methods which you don't plan of using all of.
 ///
 /// There is no difference between `unimplemented!` and `todo!` apart from the
 /// name.
 ///
 /// # Panics
 ///
-/// This will always [panic!](macro.panic.html)
+/// This will always [panic!](macro.panic.html) because `unimplemented!` is just a
+/// shorthand for `panic!` with a fixed, specific message.
+///
+/// Like `panic!`, this macro has a second form for displaying custom values.
 ///
 /// # Examples
 ///
@@ -539,38 +541,53 @@ macro_rules! unreachable {
 ///
 /// ```
 /// trait Foo {
-///     fn bar(&self);
+///     fn bar(&self) -> u8;
 ///     fn baz(&self);
+///     fn qux(&self) -> Result<u64, ()>;
 /// }
 /// ```
 ///
-/// We want to implement `Foo` on one of our types, but we also want to work on
-/// just `bar()` first. In order for our code to compile, we need to implement
-/// `baz()`, so we can use `unimplemented!`:
+/// We want to implement `Foo` for 'MyStruct', but so far we only know how to
+/// implement the `bar()` function. `baz()` and `qux()` will still need to be defined
+/// in our implementation of `Foo`, but we can use `unimplemented!` in their definitions
+/// to allow our code to compile.
+///
+/// In the meantime, we want to have our program stop running once these
+/// unimplemented functions are reached.
 ///
 /// ```
 /// # trait Foo {
-/// #     fn bar(&self);
+/// #     fn bar(&self) -> u8;
 /// #     fn baz(&self);
+/// #     fn qux(&self) -> Result<u64, ()>;
 /// # }
 /// struct MyStruct;
 ///
 /// impl Foo for MyStruct {
-///     fn bar(&self) {
-///         // implementation goes here
+///     fn bar(&self) -> u8 {
+///         1 + 1
 ///     }
 ///
 ///     fn baz(&self) {
-///         // let's not worry about implementing baz() for now
+///         // We aren't sure how to even start writing baz yet,
+///         // so we have no logic here at all.
+///         // This will display "thread 'main' panicked at 'not yet implemented'".
 ///         unimplemented!();
 ///     }
+///
+///     fn qux(&self) -> Result<u64, ()> {
+///         let n = self.bar();
+///         // We have some logic here,
+///         // so we can use unimplemented! to display what we have so far.
+///         // This will display:
+///         // "thread 'main' panicked at 'not yet implemented: we need to divide by 2'".
+///         unimplemented!("we need to divide by {}", n);
+///     }
 /// }
 ///
 /// fn main() {
 ///     let s = MyStruct;
 ///     s.bar();
-///
-///     // we aren't even using baz() yet, so this is fine.
 /// }
 /// ```
 #[macro_export]
diff --git a/src/libcore/mem/mod.rs b/src/libcore/mem/mod.rs
index 95ad4272ced..c7da56aad30 100644
--- a/src/libcore/mem/mod.rs
+++ b/src/libcore/mem/mod.rs
@@ -236,7 +236,7 @@ pub fn forget_unsized<T: ?Sized>(t: T) {
 /// ```
 ///
 /// [alignment]: ./fn.align_of.html
-#[inline]
+#[inline(always)]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_promotable]
 pub const fn size_of<T>() -> usize {
@@ -328,7 +328,7 @@ pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
 ///
 /// assert_eq!(4, mem::align_of::<i32>());
 /// ```
-#[inline]
+#[inline(always)]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_promotable]
 pub const fn align_of<T>() -> usize {
@@ -520,8 +520,6 @@ pub fn swap<T>(x: &mut T, y: &mut T) {
 /// A simple example:
 ///
 /// ```
-/// #![feature(mem_take)]
-///
 /// use std::mem;
 ///
 /// let mut v: Vec<i32> = vec![1, 2];
@@ -552,8 +550,6 @@ pub fn swap<T>(x: &mut T, y: &mut T) {
 /// `self`, allowing it to be returned:
 ///
 /// ```
-/// #![feature(mem_take)]
-///
 /// use std::mem;
 ///
 /// # struct Buffer<T> { buf: Vec<T> }
@@ -572,7 +568,7 @@ pub fn swap<T>(x: &mut T, y: &mut T) {
 ///
 /// [`Clone`]: ../../std/clone/trait.Clone.html
 #[inline]
-#[unstable(feature = "mem_take", issue = "61129")]
+#[stable(feature = "mem_take", since = "1.40.0")]
 pub fn take<T: Default>(dest: &mut T) -> T {
     replace(dest, T::default())
 }
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index ebde82de834..8f4ade377e3 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -1058,7 +1058,7 @@ $EndFeature, "
             #[inline]
             pub fn saturating_mul(self, rhs: Self) -> Self {
                 self.checked_mul(rhs).unwrap_or_else(|| {
-                    if (self < 0 && rhs < 0) || (self > 0 && rhs > 0) {
+                    if (self < 0) == (rhs < 0) {
                         Self::max_value()
                     } else {
                         Self::min_value()
@@ -1864,7 +1864,7 @@ if `self < 0`, this is equal to round towards +/- infinity.
 
 # Panics
 
-This function will panic if `rhs` is 0.
+This function will panic if `rhs` is 0 or the division results in overflow.
 
 # Examples
 
@@ -1903,7 +1903,7 @@ This is done as if by the Euclidean division algorithm -- given
 
 # Panics
 
-This function will panic if `rhs` is 0.
+This function will panic if `rhs` is 0 or the division results in overflow.
 
 # Examples
 
@@ -3694,6 +3694,10 @@ Since, for the positive integers, all common
 definitions of division are equal, this
 is exactly equal to `self / rhs`.
 
+# Panics
+
+This function will panic if `rhs` is 0.
+
 # Examples
 
 Basic usage:
@@ -3719,6 +3723,10 @@ Since, for the positive integers, all common
 definitions of division are equal, this
 is exactly equal to `self % rhs`.
 
+# Panics
+
+This function will panic if `rhs` is 0.
+
 # Examples
 
 Basic usage:
diff --git a/src/libcore/num/wrapping.rs b/src/libcore/num/wrapping.rs
index 59a10ae99bb..5fe9895d8d2 100644
--- a/src/libcore/num/wrapping.rs
+++ b/src/libcore/num/wrapping.rs
@@ -437,7 +437,7 @@ assert_eq!(n.trailing_zeros(), 3);
             /// wrapping the truncated bits to the end of the resulting
             /// integer.
             ///
-            /// Please note this isn't the same operation as the `>>` shifting
+            /// Please note this isn't the same operation as the `<<` shifting
             /// operator!
             ///
             /// # Examples
@@ -463,7 +463,7 @@ assert_eq!(n.trailing_zeros(), 3);
             /// wrapping the truncated bits to the beginning of the resulting
             /// integer.
             ///
-            /// Please note this isn't the same operation as the `<<` shifting
+            /// Please note this isn't the same operation as the `>>` shifting
             /// operator!
             ///
             /// # Examples
diff --git a/src/libcore/option.rs b/src/libcore/option.rs
index 301e432c98d..47e3a0d2167 100644
--- a/src/libcore/option.rs
+++ b/src/libcore/option.rs
@@ -1102,7 +1102,6 @@ impl<T: Default> Option<T> {
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
 impl<T: Deref> Option<T> {
     /// Converts from `Option<T>` (or `&Option<T>`) to `Option<&T::Target>`.
     ///
@@ -1114,20 +1113,18 @@ impl<T: Deref> Option<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(inner_deref)]
-    ///
     /// let x: Option<String> = Some("hey".to_owned());
     /// assert_eq!(x.as_deref(), Some("hey"));
     ///
     /// let x: Option<String> = None;
     /// assert_eq!(x.as_deref(), None);
     /// ```
+    #[stable(feature = "option_deref", since = "1.40.0")]
     pub fn as_deref(&self) -> Option<&T::Target> {
         self.as_ref().map(|t| t.deref())
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
 impl<T: DerefMut> Option<T> {
     /// Converts from `Option<T>` (or `&mut Option<T>`) to `Option<&mut T::Target>`.
     ///
@@ -1137,14 +1134,13 @@ impl<T: DerefMut> Option<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(inner_deref)]
-    ///
     /// let mut x: Option<String> = Some("hey".to_owned());
     /// assert_eq!(x.as_deref_mut().map(|x| {
     ///     x.make_ascii_uppercase();
     ///     x
     /// }), Some("HEY".to_owned().as_mut_str()));
     /// ```
+    #[stable(feature = "option_deref", since = "1.40.0")]
     pub fn as_deref_mut(&mut self) -> Option<&mut T::Target> {
         self.as_mut().map(|t| t.deref_mut())
     }
diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index b5462d98837..4e79ea81204 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -63,6 +63,7 @@ impl<T> [T] {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
+    #[allow(unused_attributes)]
     #[allow_internal_unstable(const_fn_union)]
     pub const fn len(&self) -> usize {
         unsafe {
diff --git a/src/libcore/str/mod.rs b/src/libcore/str/mod.rs
index ece61dde490..885696e5acf 100644
--- a/src/libcore/str/mod.rs
+++ b/src/libcore/str/mod.rs
@@ -2167,6 +2167,7 @@ impl str {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline(always)]
     // SAFETY: const sound because we transmute two types with the same layout
+    #[allow(unused_attributes)]
     #[allow_internal_unstable(const_fn_union)]
     pub const fn as_bytes(&self) -> &[u8] {
         #[repr(C)]
diff --git a/src/libcore/sync/atomic.rs b/src/libcore/sync/atomic.rs
index c9ccef972c2..73d5abf1aed 100644
--- a/src/libcore/sync/atomic.rs
+++ b/src/libcore/sync/atomic.rs
@@ -18,11 +18,11 @@
 //!
 //! Each method takes an [`Ordering`] which represents the strength of
 //! the memory barrier for that operation. These orderings are the
-//! same as [LLVM atomic orderings][1]. For more information see the [nomicon][2].
+//! same as the [C++20 atomic orderings][1]. For more information see the [nomicon][2].
 //!
 //! [`Ordering`]: enum.Ordering.html
 //!
-//! [1]: https://llvm.org/docs/LangRef.html#memory-model-for-concurrent-operations
+//! [1]: https://en.cppreference.com/w/cpp/atomic/memory_order
 //! [2]: ../../../nomicon/atomics.html
 //!
 //! Atomic variables are safe to share between threads (they implement [`Sync`])
@@ -113,8 +113,8 @@
 //! ```
 
 #![stable(feature = "rust1", since = "1.0.0")]
-#![cfg_attr(not(target_has_atomic = "8"), allow(dead_code))]
-#![cfg_attr(not(target_has_atomic = "8"), allow(unused_imports))]
+#![cfg_attr(not(target_has_atomic_load_store = "8"), allow(dead_code))]
+#![cfg_attr(not(target_has_atomic_load_store = "8"), allow(unused_imports))]
 
 use self::Ordering::*;
 
@@ -160,14 +160,14 @@ pub fn spin_loop_hint() {
 /// This type has the same in-memory representation as a [`bool`].
 ///
 /// [`bool`]: ../../../std/primitive.bool.html
-#[cfg(target_has_atomic = "8")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[repr(C, align(1))]
 pub struct AtomicBool {
     v: UnsafeCell<u8>,
 }
 
-#[cfg(target_has_atomic = "8")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Default for AtomicBool {
     /// Creates an `AtomicBool` initialized to `false`.
@@ -177,14 +177,14 @@ impl Default for AtomicBool {
 }
 
 // Send is implicitly implemented for AtomicBool.
-#[cfg(target_has_atomic = "8")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl Sync for AtomicBool {}
 
 /// A raw pointer type which can be safely shared between threads.
 ///
 /// This type has the same in-memory representation as a `*mut T`.
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(target_pointer_width = "16", repr(C, align(2)))]
 #[cfg_attr(target_pointer_width = "32", repr(C, align(4)))]
@@ -193,7 +193,7 @@ pub struct AtomicPtr<T> {
     p: UnsafeCell<*mut T>,
 }
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Default for AtomicPtr<T> {
     /// Creates a null `AtomicPtr<T>`.
@@ -202,10 +202,10 @@ impl<T> Default for AtomicPtr<T> {
     }
 }
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T> Send for AtomicPtr<T> {}
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T> Sync for AtomicPtr<T> {}
 
@@ -217,8 +217,8 @@ unsafe impl<T> Sync for AtomicPtr<T> {}
 /// operations synchronize other memory while additionally preserving a total order of such
 /// operations across all threads.
 ///
-/// Rust's memory orderings are [the same as
-/// LLVM's](https://llvm.org/docs/LangRef.html#memory-model-for-concurrent-operations).
+/// Rust's memory orderings are [the same as those of
+/// C++20](https://en.cppreference.com/w/cpp/atomic/memory_order).
 ///
 /// For more information see the [nomicon].
 ///
@@ -231,9 +231,9 @@ unsafe impl<T> Sync for AtomicPtr<T> {}
 pub enum Ordering {
     /// No ordering constraints, only atomic operations.
     ///
-    /// Corresponds to LLVM's [`Monotonic`] ordering.
+    /// Corresponds to [`memory_order_relaxed`] in C++20.
     ///
-    /// [`Monotonic`]: https://llvm.org/docs/Atomics.html#monotonic
+    /// [`memory_order_relaxed`]: https://en.cppreference.com/w/cpp/atomic/memory_order#Relaxed_ordering
     #[stable(feature = "rust1", since = "1.0.0")]
     Relaxed,
     /// When coupled with a store, all previous operations become ordered
@@ -246,11 +246,12 @@ pub enum Ordering {
     ///
     /// This ordering is only applicable for operations that can perform a store.
     ///
-    /// Corresponds to LLVM's [`Release`] ordering.
+    /// Corresponds to [`memory_order_release`] in C++20.
     ///
-    /// [`Release`]: https://llvm.org/docs/Atomics.html#release
-    /// [`Acquire`]: https://llvm.org/docs/Atomics.html#acquire
-    /// [`Relaxed`]: https://llvm.org/docs/Atomics.html#monotonic
+    /// [`Release`]: #variant.Release
+    /// [`Acquire`]: #variant.Acquire
+    /// [`Relaxed`]: #variant.Relaxed
+    /// [`memory_order_release`]: https://en.cppreference.com/w/cpp/atomic/memory_order#Release-Acquire_ordering
     #[stable(feature = "rust1", since = "1.0.0")]
     Release,
     /// When coupled with a load, if the loaded value was written by a store operation with
@@ -263,11 +264,12 @@ pub enum Ordering {
     ///
     /// This ordering is only applicable for operations that can perform a load.
     ///
-    /// Corresponds to LLVM's [`Acquire`] ordering.
+    /// Corresponds to [`memory_order_acquire`] in C++20.
     ///
-    /// [`Acquire`]: https://llvm.org/docs/Atomics.html#acquire
-    /// [`Release`]: https://llvm.org/docs/Atomics.html#release
-    /// [`Relaxed`]: https://llvm.org/docs/Atomics.html#monotonic
+    /// [`Acquire`]: #variant.Acquire
+    /// [`Release`]: #variant.Release
+    /// [`Relaxed`]: #variant.Relaxed
+    /// [`memory_order_acquire`]: https://en.cppreference.com/w/cpp/atomic/memory_order#Release-Acquire_ordering
     #[stable(feature = "rust1", since = "1.0.0")]
     Acquire,
     /// Has the effects of both [`Acquire`] and [`Release`] together:
@@ -275,28 +277,28 @@ pub enum Ordering {
     ///
     /// Notice that in the case of `compare_and_swap`, it is possible that the operation ends up
     /// not performing any store and hence it has just [`Acquire`] ordering. However,
-    /// [`AcqRel`][`AcquireRelease`] will never perform [`Relaxed`] accesses.
+    /// `AcqRel` will never perform [`Relaxed`] accesses.
     ///
     /// This ordering is only applicable for operations that combine both loads and stores.
     ///
-    /// Corresponds to LLVM's [`AcquireRelease`] ordering.
+    /// Corresponds to [`memory_order_acq_rel`] in C++20.
     ///
-    /// [`AcquireRelease`]: https://llvm.org/docs/Atomics.html#acquirerelease
-    /// [`Acquire`]: https://llvm.org/docs/Atomics.html#acquire
-    /// [`Release`]: https://llvm.org/docs/Atomics.html#release
-    /// [`Relaxed`]: https://llvm.org/docs/Atomics.html#monotonic
+    /// [`memory_order_acq_rel`]: https://en.cppreference.com/w/cpp/atomic/memory_order#Release-Acquire_ordering
+    /// [`Acquire`]: #variant.Acquire
+    /// [`Release`]: #variant.Release
+    /// [`Relaxed`]: #variant.Relaxed
     #[stable(feature = "rust1", since = "1.0.0")]
     AcqRel,
     /// Like [`Acquire`]/[`Release`]/[`AcqRel`] (for load, store, and load-with-store
     /// operations, respectively) with the additional guarantee that all threads see all
     /// sequentially consistent operations in the same order.
     ///
-    /// Corresponds to LLVM's [`SequentiallyConsistent`] ordering.
+    /// Corresponds to [`memory_order_seq_cst`] in C++20.
     ///
-    /// [`SequentiallyConsistent`]: https://llvm.org/docs/Atomics.html#sequentiallyconsistent
-    /// [`Acquire`]: https://llvm.org/docs/Atomics.html#acquire
-    /// [`Release`]: https://llvm.org/docs/Atomics.html#release
-    /// [`AcqRel`]: https://llvm.org/docs/Atomics.html#acquirerelease
+    /// [`memory_order_seq_cst`]: https://en.cppreference.com/w/cpp/atomic/memory_order#Sequentially-consistent_ordering
+    /// [`Acquire`]: #variant.Acquire
+    /// [`Release`]: #variant.Release
+    /// [`AcqRel`]: #variant.AcqRel
     #[stable(feature = "rust1", since = "1.0.0")]
     SeqCst,
 }
@@ -304,7 +306,7 @@ pub enum Ordering {
 /// An [`AtomicBool`] initialized to `false`.
 ///
 /// [`AtomicBool`]: struct.AtomicBool.html
-#[cfg(target_has_atomic = "8")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_deprecated(
     since = "1.34.0",
@@ -313,7 +315,7 @@ pub enum Ordering {
 )]
 pub const ATOMIC_BOOL_INIT: AtomicBool = AtomicBool::new(false);
 
-#[cfg(target_has_atomic = "8")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 impl AtomicBool {
     /// Creates a new `AtomicBool`.
     ///
@@ -462,7 +464,7 @@ impl AtomicBool {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "8")]
     pub fn swap(&self, val: bool, order: Ordering) -> bool {
         unsafe { atomic_swap(self.v.get(), val as u8, order) != 0 }
     }
@@ -500,7 +502,7 @@ impl AtomicBool {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "8")]
     pub fn compare_and_swap(&self, current: bool, new: bool, order: Ordering) -> bool {
         match self.compare_exchange(current, new, order, strongest_failure_ordering(order)) {
             Ok(x) => x,
@@ -551,7 +553,7 @@ impl AtomicBool {
     /// ```
     #[inline]
     #[stable(feature = "extended_compare_and_swap", since = "1.10.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "8")]
     pub fn compare_exchange(&self,
                             current: bool,
                             new: bool,
@@ -607,7 +609,7 @@ impl AtomicBool {
     /// ```
     #[inline]
     #[stable(feature = "extended_compare_and_swap", since = "1.10.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "8")]
     pub fn compare_exchange_weak(&self,
                                  current: bool,
                                  new: bool,
@@ -658,7 +660,7 @@ impl AtomicBool {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "8")]
     pub fn fetch_and(&self, val: bool, order: Ordering) -> bool {
         unsafe { atomic_and(self.v.get(), val as u8, order) != 0 }
     }
@@ -700,7 +702,7 @@ impl AtomicBool {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "8")]
     pub fn fetch_nand(&self, val: bool, order: Ordering) -> bool {
         // We can't use atomic_nand here because it can result in a bool with
         // an invalid value. This happens because the atomic operation is done
@@ -753,7 +755,7 @@ impl AtomicBool {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "8")]
     pub fn fetch_or(&self, val: bool, order: Ordering) -> bool {
         unsafe { atomic_or(self.v.get(), val as u8, order) != 0 }
     }
@@ -794,13 +796,13 @@ impl AtomicBool {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "8")]
     pub fn fetch_xor(&self, val: bool, order: Ordering) -> bool {
         unsafe { atomic_xor(self.v.get(), val as u8, order) != 0 }
     }
 }
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 impl<T> AtomicPtr<T> {
     /// Creates a new `AtomicPtr`.
     ///
@@ -951,7 +953,7 @@ impl<T> AtomicPtr<T> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "ptr")]
     pub fn swap(&self, ptr: *mut T, order: Ordering) -> *mut T {
         unsafe { atomic_swap(self.p.get() as *mut usize, ptr as usize, order) as *mut T }
     }
@@ -987,7 +989,7 @@ impl<T> AtomicPtr<T> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "ptr")]
     pub fn compare_and_swap(&self, current: *mut T, new: *mut T, order: Ordering) -> *mut T {
         match self.compare_exchange(current, new, order, strongest_failure_ordering(order)) {
             Ok(x) => x,
@@ -1029,7 +1031,7 @@ impl<T> AtomicPtr<T> {
     /// ```
     #[inline]
     #[stable(feature = "extended_compare_and_swap", since = "1.10.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "ptr")]
     pub fn compare_exchange(&self,
                             current: *mut T,
                             new: *mut T,
@@ -1089,7 +1091,7 @@ impl<T> AtomicPtr<T> {
     /// ```
     #[inline]
     #[stable(feature = "extended_compare_and_swap", since = "1.10.0")]
-    #[cfg(target_has_atomic = "cas")]
+    #[cfg(target_has_atomic = "ptr")]
     pub fn compare_exchange_weak(&self,
                                  current: *mut T,
                                  new: *mut T,
@@ -1110,7 +1112,7 @@ impl<T> AtomicPtr<T> {
     }
 }
 
-#[cfg(target_has_atomic = "8")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 #[stable(feature = "atomic_bool_from", since = "1.24.0")]
 impl From<bool> for AtomicBool {
     /// Converts a `bool` into an `AtomicBool`.
@@ -1126,16 +1128,17 @@ impl From<bool> for AtomicBool {
     fn from(b: bool) -> Self { Self::new(b) }
 }
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[stable(feature = "atomic_from", since = "1.23.0")]
 impl<T> From<*mut T> for AtomicPtr<T> {
     #[inline]
     fn from(p: *mut T) -> Self { Self::new(p) }
 }
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 macro_rules! atomic_int {
-    ($stable:meta,
+    ($cfg_cas:meta,
+     $stable:meta,
      $stable_cxchg:meta,
      $stable_debug:meta,
      $stable_access:meta,
@@ -1356,7 +1359,7 @@ assert_eq!(some_var.swap(10, Ordering::Relaxed), 5);
 ```"),
                 #[inline]
                 #[$stable]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn swap(&self, val: $int_type, order: Ordering) -> $int_type {
                     unsafe { atomic_swap(self.v.get(), val, order) }
                 }
@@ -1396,7 +1399,7 @@ assert_eq!(some_var.load(Ordering::Relaxed), 10);
 ```"),
                 #[inline]
                 #[$stable]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn compare_and_swap(&self,
                                         current: $int_type,
                                         new: $int_type,
@@ -1454,7 +1457,7 @@ assert_eq!(some_var.load(Ordering::Relaxed), 10);
 ```"),
                 #[inline]
                 #[$stable_cxchg]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn compare_exchange(&self,
                                         current: $int_type,
                                         new: $int_type,
@@ -1506,7 +1509,7 @@ loop {
 ```"),
                 #[inline]
                 #[$stable_cxchg]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn compare_exchange_weak(&self,
                                              current: $int_type,
                                              new: $int_type,
@@ -1544,7 +1547,7 @@ assert_eq!(foo.load(Ordering::SeqCst), 10);
 ```"),
                 #[inline]
                 #[$stable]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn fetch_add(&self, val: $int_type, order: Ordering) -> $int_type {
                     unsafe { atomic_add(self.v.get(), val, order) }
                 }
@@ -1576,7 +1579,7 @@ assert_eq!(foo.load(Ordering::SeqCst), 10);
 ```"),
                 #[inline]
                 #[$stable]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn fetch_sub(&self, val: $int_type, order: Ordering) -> $int_type {
                     unsafe { atomic_sub(self.v.get(), val, order) }
                 }
@@ -1611,7 +1614,7 @@ assert_eq!(foo.load(Ordering::SeqCst), 0b100001);
 ```"),
                 #[inline]
                 #[$stable]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn fetch_and(&self, val: $int_type, order: Ordering) -> $int_type {
                     unsafe { atomic_and(self.v.get(), val, order) }
                 }
@@ -1647,7 +1650,7 @@ assert_eq!(foo.load(Ordering::SeqCst), !(0x13 & 0x31));
 ```"),
                 #[inline]
                 #[$stable_nand]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn fetch_nand(&self, val: $int_type, order: Ordering) -> $int_type {
                     unsafe { atomic_nand(self.v.get(), val, order) }
                 }
@@ -1682,7 +1685,7 @@ assert_eq!(foo.load(Ordering::SeqCst), 0b111111);
 ```"),
                 #[inline]
                 #[$stable]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn fetch_or(&self, val: $int_type, order: Ordering) -> $int_type {
                     unsafe { atomic_or(self.v.get(), val, order) }
                 }
@@ -1717,7 +1720,7 @@ assert_eq!(foo.load(Ordering::SeqCst), 0b011110);
 ```"),
                 #[inline]
                 #[$stable]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn fetch_xor(&self, val: $int_type, order: Ordering) -> $int_type {
                     unsafe { atomic_xor(self.v.get(), val, order) }
                 }
@@ -1767,7 +1770,7 @@ assert_eq!(x.load(Ordering::SeqCst), 9);
                 #[unstable(feature = "no_more_cas",
                        reason = "no more CAS loops in user code",
                        issue = "48655")]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn fetch_update<F>(&self,
                                        mut f: F,
                                        fetch_order: Ordering,
@@ -1828,7 +1831,7 @@ assert!(max_foo == 42);
                 #[unstable(feature = "atomic_min_max",
                        reason = "easier and faster min/max than writing manual CAS loop",
                        issue = "48655")]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn fetch_max(&self, val: $int_type, order: Ordering) -> $int_type {
                     unsafe { $max_fn(self.v.get(), val, order) }
                 }
@@ -1880,7 +1883,7 @@ assert_eq!(min_foo, 12);
                 #[unstable(feature = "atomic_min_max",
                        reason = "easier and faster min/max than writing manual CAS loop",
                        issue = "48655")]
-                #[cfg(target_has_atomic = "cas")]
+                #[$cfg_cas]
                 pub fn fetch_min(&self, val: $int_type, order: Ordering) -> $int_type {
                     unsafe { $min_fn(self.v.get(), val, order) }
                 }
@@ -1890,8 +1893,9 @@ assert_eq!(min_foo, 12);
     }
 }
 
-#[cfg(target_has_atomic = "8")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 atomic_int! {
+    cfg(target_has_atomic = "8"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
@@ -1906,8 +1910,9 @@ atomic_int! {
     "AtomicI8::new(0)",
     i8 AtomicI8 ATOMIC_I8_INIT
 }
-#[cfg(target_has_atomic = "8")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 atomic_int! {
+    cfg(target_has_atomic = "8"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
@@ -1922,8 +1927,9 @@ atomic_int! {
     "AtomicU8::new(0)",
     u8 AtomicU8 ATOMIC_U8_INIT
 }
-#[cfg(target_has_atomic = "16")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "16"))]
 atomic_int! {
+    cfg(target_has_atomic = "16"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
@@ -1938,8 +1944,9 @@ atomic_int! {
     "AtomicI16::new(0)",
     i16 AtomicI16 ATOMIC_I16_INIT
 }
-#[cfg(target_has_atomic = "16")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "16"))]
 atomic_int! {
+    cfg(target_has_atomic = "16"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
@@ -1954,8 +1961,9 @@ atomic_int! {
     "AtomicU16::new(0)",
     u16 AtomicU16 ATOMIC_U16_INIT
 }
-#[cfg(target_has_atomic = "32")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "32"))]
 atomic_int! {
+    cfg(target_has_atomic = "32"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
@@ -1970,8 +1978,9 @@ atomic_int! {
     "AtomicI32::new(0)",
     i32 AtomicI32 ATOMIC_I32_INIT
 }
-#[cfg(target_has_atomic = "32")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "32"))]
 atomic_int! {
+    cfg(target_has_atomic = "32"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
@@ -1986,8 +1995,12 @@ atomic_int! {
     "AtomicU32::new(0)",
     u32 AtomicU32 ATOMIC_U32_INIT
 }
-#[cfg(target_has_atomic = "64")]
+#[cfg(any(
+    all(bootstrap, target_has_atomic = "64"),
+    target_has_atomic_load_store = "64"
+))]
 atomic_int! {
+    cfg(target_has_atomic = "64"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
@@ -2002,8 +2015,12 @@ atomic_int! {
     "AtomicI64::new(0)",
     i64 AtomicI64 ATOMIC_I64_INIT
 }
-#[cfg(target_has_atomic = "64")]
+#[cfg(any(
+    all(bootstrap, target_has_atomic = "64"),
+    target_has_atomic_load_store = "64"
+))]
 atomic_int! {
+    cfg(target_has_atomic = "64"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
     stable(feature = "integer_atomics_stable", since = "1.34.0"),
@@ -2018,8 +2035,9 @@ atomic_int! {
     "AtomicU64::new(0)",
     u64 AtomicU64 ATOMIC_U64_INIT
 }
-#[cfg(target_has_atomic = "128")]
+#[cfg(target_has_atomic_load_store = "128")]
 atomic_int! {
+    cfg(target_has_atomic = "128"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -2034,8 +2052,9 @@ atomic_int! {
     "AtomicI128::new(0)",
     i128 AtomicI128 ATOMIC_I128_INIT
 }
-#[cfg(target_has_atomic = "128")]
+#[cfg(target_has_atomic_load_store = "128")]
 atomic_int! {
+    cfg(target_has_atomic = "128"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -2050,20 +2069,24 @@ atomic_int! {
     "AtomicU128::new(0)",
     u128 AtomicU128 ATOMIC_U128_INIT
 }
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[cfg(target_pointer_width = "16")]
 macro_rules! ptr_width {
     () => { 2 }
 }
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[cfg(target_pointer_width = "32")]
 macro_rules! ptr_width {
     () => { 4 }
 }
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[cfg(target_pointer_width = "64")]
 macro_rules! ptr_width {
     () => { 8 }
 }
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 atomic_int!{
+    cfg(target_has_atomic = "ptr"),
     stable(feature = "rust1", since = "1.0.0"),
     stable(feature = "extended_compare_and_swap", since = "1.10.0"),
     stable(feature = "atomic_debug", since = "1.3.0"),
@@ -2078,8 +2101,9 @@ atomic_int!{
     "AtomicIsize::new(0)",
     isize AtomicIsize ATOMIC_ISIZE_INIT
 }
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 atomic_int!{
+    cfg(target_has_atomic = "ptr"),
     stable(feature = "rust1", since = "1.0.0"),
     stable(feature = "extended_compare_and_swap", since = "1.10.0"),
     stable(feature = "atomic_debug", since = "1.3.0"),
@@ -2096,7 +2120,7 @@ atomic_int!{
 }
 
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 fn strongest_failure_ordering(order: Ordering) -> Ordering {
     match order {
         Release => Relaxed,
@@ -2130,7 +2154,7 @@ unsafe fn atomic_load<T>(dst: *const T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_swap<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_xchg_acq(dst, val),
@@ -2143,7 +2167,7 @@ unsafe fn atomic_swap<T>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// Returns the previous value (like __sync_fetch_and_add).
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_add<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_xadd_acq(dst, val),
@@ -2156,7 +2180,7 @@ unsafe fn atomic_add<T>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// Returns the previous value (like __sync_fetch_and_sub).
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_sub<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_xsub_acq(dst, val),
@@ -2168,7 +2192,7 @@ unsafe fn atomic_sub<T>(dst: *mut T, val: T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_compare_exchange<T>(dst: *mut T,
                                      old: T,
                                      new: T,
@@ -2193,7 +2217,7 @@ unsafe fn atomic_compare_exchange<T>(dst: *mut T,
 }
 
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_compare_exchange_weak<T>(dst: *mut T,
                                           old: T,
                                           new: T,
@@ -2218,7 +2242,7 @@ unsafe fn atomic_compare_exchange_weak<T>(dst: *mut T,
 }
 
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_and<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_and_acq(dst, val),
@@ -2230,7 +2254,7 @@ unsafe fn atomic_and<T>(dst: *mut T, val: T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_nand<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_nand_acq(dst, val),
@@ -2242,7 +2266,7 @@ unsafe fn atomic_nand<T>(dst: *mut T, val: T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_or<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_or_acq(dst, val),
@@ -2254,7 +2278,7 @@ unsafe fn atomic_or<T>(dst: *mut T, val: T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_xor<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_xor_acq(dst, val),
@@ -2267,7 +2291,7 @@ unsafe fn atomic_xor<T>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// returns the max value (signed comparison)
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_max<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_max_acq(dst, val),
@@ -2280,7 +2304,7 @@ unsafe fn atomic_max<T>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// returns the min value (signed comparison)
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_min<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_min_acq(dst, val),
@@ -2293,7 +2317,7 @@ unsafe fn atomic_min<T>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// returns the max value (signed comparison)
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_umax<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_umax_acq(dst, val),
@@ -2306,7 +2330,7 @@ unsafe fn atomic_umax<T>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// returns the min value (signed comparison)
 #[inline]
-#[cfg(target_has_atomic = "cas")]
+#[cfg(target_has_atomic = "8")]
 unsafe fn atomic_umin<T>(dst: *mut T, val: T, order: Ordering) -> T {
     match order {
         Acquire => intrinsics::atomic_umin_acq(dst, val),
@@ -2504,7 +2528,7 @@ pub fn compiler_fence(order: Ordering) {
 }
 
 
-#[cfg(target_has_atomic = "8")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "8"))]
 #[stable(feature = "atomic_debug", since = "1.3.0")]
 impl fmt::Debug for AtomicBool {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -2512,7 +2536,7 @@ impl fmt::Debug for AtomicBool {
     }
 }
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[stable(feature = "atomic_debug", since = "1.3.0")]
 impl<T> fmt::Debug for AtomicPtr<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -2520,7 +2544,7 @@ impl<T> fmt::Debug for AtomicPtr<T> {
     }
 }
 
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(any(bootstrap, target_has_atomic_load_store = "ptr"))]
 #[stable(feature = "atomic_pointer", since = "1.24.0")]
 impl<T> fmt::Pointer for AtomicPtr<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
diff --git a/src/libcore/task/wake.rs b/src/libcore/task/wake.rs
index 65e29364287..6f841bd2adf 100644
--- a/src/libcore/task/wake.rs
+++ b/src/libcore/task/wake.rs
@@ -217,7 +217,7 @@ impl fmt::Debug for Context<'_> {
 /// This handle encapsulates a [`RawWaker`] instance, which defines the
 /// executor-specific wakeup behavior.
 ///
-/// Implements [`Clone`], [`trait@Send`], and [`trait@Sync`].
+/// Implements [`Clone`], [`Send`], and [`Sync`].
 ///
 /// [`RawWaker`]: struct.RawWaker.html
 #[repr(transparent)]
diff --git a/src/libcore/tests/fmt/builders.rs b/src/libcore/tests/fmt/builders.rs
index 200659b91bb..25572443281 100644
--- a/src/libcore/tests/fmt/builders.rs
+++ b/src/libcore/tests/fmt/builders.rs
@@ -320,6 +320,46 @@ mod debug_map {
     }
 
     #[test]
+    fn test_entry_err() {
+        // Ensure errors in a map entry don't trigger panics (#65231)
+        use std::fmt::Write;
+
+        struct ErrorFmt;
+
+        impl fmt::Debug for ErrorFmt {
+            fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
+                Err(fmt::Error)
+            }
+        }
+
+        struct KeyValue<K, V>(usize, K, V);
+
+        impl<K, V> fmt::Debug for KeyValue<K, V>
+        where
+            K: fmt::Debug,
+            V: fmt::Debug,
+        {
+            fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+                let mut map = fmt.debug_map();
+
+                for _ in 0..self.0 {
+                    map.entry(&self.1, &self.2);
+                }
+
+                map.finish()
+            }
+        }
+
+        let mut buf = String::new();
+
+        assert!(write!(&mut buf, "{:?}", KeyValue(1, ErrorFmt, "bar")).is_err());
+        assert!(write!(&mut buf, "{:?}", KeyValue(1, "foo", ErrorFmt)).is_err());
+
+        assert!(write!(&mut buf, "{:?}", KeyValue(2, ErrorFmt, "bar")).is_err());
+        assert!(write!(&mut buf, "{:?}", KeyValue(2, "foo", ErrorFmt)).is_err());
+    }
+
+    #[test]
     #[should_panic]
     fn test_invalid_key_when_entry_is_incomplete() {
         struct Foo;