Auto merge of #53832 - pietroalbini:rollup, r=pietroalbini

Rollup of 20 pull requests

Successful merges:

 - #51760 (Add another PartialEq example)
 - #53113 (Add example for Cow)
 - #53129 (remove `let x = baz` which was obscuring the real error)
 - #53389 (document effect of join on memory ordering)
 - #53472 (Use FxHash{Map,Set} instead of the default Hash{Map,Set} everywhere in rustc.)
 - #53476 (Add partialeq implementation for TryFromIntError type)
 - #53513 (Force-inline `shallow_resolve` at its hottest call site.)
 - #53655 (set applicability)
 - #53702 (Fix stabilisation version for macro_vis_matcher.)
 - #53727 (Do not suggest dereferencing in macro)
 - #53732 (save-analysis: Differentiate foreign functions and statics.)
 - #53740 (add llvm-readobj to llvm-tools-preview)
 - #53743 (fix a typo: taget_env -> target_env)
 - #53747 (Rustdoc fixes)
 - #53753 (expand keep-stage --help text)
 - #53756 (Fix typo in comment)
 - #53768 (move file-extension based .gitignore down to src/)
 - #53785 (Fix a comment in src/libcore/slice/mod.rs)
 - #53786 (Replace usages of 'bad_style' with 'nonstandard_style'.)
 - #53806 (Fix UI issues on Implementations on Foreign types)

Failed merges:

r? @ghost

3 files changed, 86 insertions, 8 deletions

diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
index 58d6c4f5e09..ef7d83a0993 100644
--- a/src/libcore/cmp.rs
+++ b/src/libcore/cmp.rs
@@ -75,7 +75,12 @@ use self::Ordering::*;
 /// the same book if their ISBN matches, even if the formats differ:
 ///
 /// ```
-/// enum BookFormat { Paperback, Hardback, Ebook }
+/// enum BookFormat {
+///     Paperback,
+///     Hardback,
+///     Ebook,
+/// }
+///
 /// struct Book {
 ///     isbn: i32,
 ///     format: BookFormat,
@@ -95,6 +100,84 @@ use self::Ordering::*;
 /// assert!(b1 != b3);
 /// ```
 ///
+/// ## How can I compare two different types?
+///
+/// The type you can compare with is controlled by `PartialEq`'s type parameter.
+/// For example, let's tweak our previous code a bit:
+///
+/// ```
+/// enum BookFormat {
+///     Paperback,
+///     Hardback,
+///     Ebook,
+/// }
+///
+/// struct Book {
+///     isbn: i32,
+///     format: BookFormat,
+/// }
+///
+/// impl PartialEq<BookFormat> for Book {
+///     fn eq(&self, other: &BookFormat) -> bool {
+///         match (&self.format, other) {
+///            (BookFormat::Paperback, BookFormat::Paperback) => true,
+///            (BookFormat::Hardback,  BookFormat::Hardback)  => true,
+///            (BookFormat::Ebook,     BookFormat::Ebook)     => true,
+///            (_, _) => false,
+///         }
+///     }
+/// }
+///
+/// let b1 = Book { isbn: 3, format: BookFormat::Paperback };
+///
+/// assert!(b1 == BookFormat::Paperback);
+/// assert!(b1 != BookFormat::Ebook);
+/// ```
+///
+/// By changing `impl PartialEq for Book` to `impl PartialEq<BookFormat> for Book`,
+/// we've changed what type we can use on the right side of the `==` operator.
+/// This lets us use it in the `assert!` statements at the bottom.
+///
+/// You can also combine these implementations to let the `==` operator work with
+/// two different types:
+///
+/// ```
+/// enum BookFormat {
+///     Paperback,
+///     Hardback,
+///     Ebook,
+/// }
+///
+/// struct Book {
+///     isbn: i32,
+///     format: BookFormat,
+/// }
+///
+/// impl PartialEq<BookFormat> for Book {
+///     fn eq(&self, other: &BookFormat) -> bool {
+///         match (&self.format, other) {
+///            (&BookFormat::Paperback, &BookFormat::Paperback) => true,
+///            (&BookFormat::Hardback,  &BookFormat::Hardback)  => true,
+///            (&BookFormat::Ebook,     &BookFormat::Ebook)     => true,
+///            (_, _) => false,
+///         }
+///     }
+/// }
+///
+/// impl PartialEq for Book {
+///     fn eq(&self, other: &Book) -> bool {
+///         self.isbn == other.isbn
+///     }
+/// }
+///
+/// let b1 = Book { isbn: 3, format: BookFormat::Paperback };
+/// let b2 = Book { isbn: 3, format: BookFormat::Ebook };
+///
+/// assert!(b1 == BookFormat::Paperback);
+/// assert!(b1 != BookFormat::Ebook);
+/// assert!(b1 == b2);
+/// ```
+///
 /// # Examples
 ///
 /// ```
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index b93428c6321..fc405881b28 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -4323,7 +4323,7 @@ from_str_radix_int_impl! { isize i8 i16 i32 i64 i128 usize u8 u16 u32 u64 u128 }
 
 /// The error type returned when a checked integral type conversion fails.
 #[unstable(feature = "try_from", issue = "33417")]
-#[derive(Debug, Copy, Clone)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub struct TryFromIntError(());
 
 impl TryFromIntError {
diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index 3366c4a3e66..f8c3feba74c 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -21,14 +21,9 @@
 // The library infrastructure for slices is fairly messy. There's
 // a lot of stuff defined here. Let's keep it clean.
 //
-// Since slices don't support inherent methods; all operations
-// on them are defined on traits, which are then re-exported from
-// the prelude for convenience. So there are a lot of traits here.
-//
 // The layout of this file is thus:
 //
-// * Slice-specific 'extension' traits and their implementations. This
-//   is where most of the slice API resides.
+// * Inherent methods. This is where most of the slice API resides.
 // * Implementations of a few common traits with important slice ops.
 // * Definitions of a bunch of iterators.
 // * Free functions.