Improve the tuple and unit trait docs

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -401,6 +401,11 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                     let msg = "`#[doc(keyword)]` is meant for internal use only";
                     gate_feature_post!(self, rustdoc_internals, attr.span, msg);
                 }
+
+                if nested_meta.has_name(sym::tuple_variadic) {
+                    let msg = "`#[doc(tuple_variadic)]` is meant for internal use only";
+                    gate_feature_post!(self, rustdoc_internals, attr.span, msg);
+                }
             }
         }
 

compiler/rustc_passes/src/check_attr.rs

@@ -804,6 +804,37 @@ impl CheckAttrVisitor<'_> {
         true
     }
 
+    fn check_doc_tuple_variadic(&self, meta: &NestedMetaItem, hir_id: HirId) -> bool {
+        match self.tcx.hir().find(hir_id).and_then(|node| match node {
+            hir::Node::Item(item) => Some(&item.kind),
+            _ => None,
+        }) {
+            Some(ItemKind::Impl(ref i)) => {
+                if !matches!(&i.self_ty.kind, hir::TyKind::Tup([_])) {
+                    self.tcx
+                        .sess
+                        .struct_span_err(
+                            meta.span(),
+                            "`#[doc(tuple_variadic)]` must be used on the first of a set of tuple trait impls with varying arity",
+                        )
+                        .emit();
+                    return false;
+                }
+            }
+            _ => {
+                self.tcx
+                    .sess
+                    .struct_span_err(
+                        meta.span(),
+                        "`#[doc(keyword = \"...\")]` can only be used on impl blocks",
+                    )
+                    .emit();
+                return false;
+            }
+        }
+        true
+    }
+
     /// Checks `#[doc(inline)]`/`#[doc(no_inline)]` attributes. Returns `true` if valid.
     ///
     /// A doc inlining attribute is invalid if it is applied to a non-`use` item, or
@@ -1064,6 +1095,13 @@ impl CheckAttrVisitor<'_> {
                             is_valid = false
                         }
 
+                        sym::tuple_variadic
+                            if !self.check_attr_not_crate_level(meta, hir_id, "tuple_variadic")
+                                || !self.check_doc_tuple_variadic(meta, hir_id) =>
+                        {
+                            is_valid = false
+                        }
+
                         sym::html_favicon_url
                         | sym::html_logo_url
                         | sym::html_playground_url
@@ -1117,7 +1155,8 @@ impl CheckAttrVisitor<'_> {
                         | sym::no_inline
                         | sym::notable_trait
                         | sym::passes
-                        | sym::plugins => {}
+                        | sym::plugins
+                        | sym::tuple_variadic => {}
 
                         sym::test => {
                             if !self.check_test_attr(meta, hir_id) {

compiler/rustc_span/src/symbol.rs

@@ -1439,6 +1439,7 @@ symbols! {
         tuple,
         tuple_from_req,
         tuple_indexing,
+        tuple_variadic,
         two_phase,
         ty,
         type_alias_enum_variants,

library/core/src/clone.rs

@@ -95,7 +95,6 @@ use crate::marker::Destruct;
 ///
 /// * Function item types (i.e., the distinct types defined for each function)
 /// * Function pointer types (e.g., `fn() -> i32`)
-/// * Tuple types, if each component also implements `Clone` (e.g., `()`, `(i32, bool)`)
 /// * Closure types, if they capture no value from the environment
 ///   or if all such captured values implement `Clone` themselves.
 ///   Note that variables captured by shared reference always implement `Clone`

library/core/src/fmt/mod.rs

@@ -2313,29 +2313,46 @@ macro_rules! peel {
 macro_rules! tuple {
     () => ();
     ( $($name:ident,)+ ) => (
-        #[stable(feature = "rust1", since = "1.0.0")]
-        impl<$($name:Debug),+> Debug for ($($name,)+) where last_type!($($name,)+): ?Sized {
-            #[allow(non_snake_case, unused_assignments)]
-            fn fmt(&self, f: &mut Formatter<'_>) -> Result {
-                let mut builder = f.debug_tuple("");
-                let ($(ref $name,)+) = *self;
-                $(
-                    builder.field(&$name);
-                )+
-
-                builder.finish()
+        maybe_tuple_doc! {
+            $($name)+ @
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<$($name:Debug),+> Debug for ($($name,)+) where last_type!($($name,)+): ?Sized {
+                #[allow(non_snake_case, unused_assignments)]
+                fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+                    let mut builder = f.debug_tuple("");
+                    let ($(ref $name,)+) = *self;
+                    $(
+                        builder.field(&$name);
+                    )+
+
+                    builder.finish()
+                }
             }
         }
         peel! { $($name,)+ }
     )
 }
 
+macro_rules! maybe_tuple_doc {
+    ($a:ident @ #[$meta:meta] $item:item) => {
+        #[cfg_attr(not(bootstrap), doc(tuple_variadic))]
+        #[doc = "This trait is implemented for tuples up to twelve items long."]
+        #[$meta]
+        $item
+    };
+    ($a:ident $($rest_a:ident)+ @ #[$meta:meta] $item:item) => {
+        #[doc(hidden)]
+        #[$meta]
+        $item
+    };
+}
+
 macro_rules! last_type {
     ($a:ident,) => { $a };
     ($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
 }
 
-tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }
+tuple! { E, D, C, B, A, Z, Y, X, W, V, U, T, }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Debug> Debug for [T] {

library/core/src/hash/mod.rs

@@ -883,36 +883,53 @@ mod impls {
         );
 
         ( $($name:ident)+) => (
-            #[stable(feature = "rust1", since = "1.0.0")]
-            impl<$($name: Hash),+> Hash for ($($name,)+) where last_type!($($name,)+): ?Sized {
-                #[allow(non_snake_case)]
-                #[inline]
-                fn hash<S: Hasher>(&self, state: &mut S) {
-                    let ($(ref $name,)+) = *self;
-                    $($name.hash(state);)+
+            maybe_tuple_doc! {
+                $($name)+ @
+                #[stable(feature = "rust1", since = "1.0.0")]
+                impl<$($name: Hash),+> Hash for ($($name,)+) where last_type!($($name,)+): ?Sized {
+                    #[allow(non_snake_case)]
+                    #[inline]
+                    fn hash<S: Hasher>(&self, state: &mut S) {
+                        let ($(ref $name,)+) = *self;
+                        $($name.hash(state);)+
+                    }
                 }
             }
         );
     }
 
+    macro_rules! maybe_tuple_doc {
+        ($a:ident @ #[$meta:meta] $item:item) => {
+            #[cfg_attr(not(bootstrap), doc(tuple_variadic))]
+            #[doc = "This trait is implemented for tuples up to twelve items long."]
+            #[$meta]
+            $item
+        };
+        ($a:ident $($rest_a:ident)+ @ #[$meta:meta] $item:item) => {
+            #[doc(hidden)]
+            #[$meta]
+            $item
+        };
+    }
+
     macro_rules! last_type {
         ($a:ident,) => { $a };
         ($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
     }
 
     impl_hash_tuple! {}
-    impl_hash_tuple! { A }
-    impl_hash_tuple! { A B }
-    impl_hash_tuple! { A B C }
-    impl_hash_tuple! { A B C D }
-    impl_hash_tuple! { A B C D E }
-    impl_hash_tuple! { A B C D E F }
-    impl_hash_tuple! { A B C D E F G }
-    impl_hash_tuple! { A B C D E F G H }
-    impl_hash_tuple! { A B C D E F G H I }
-    impl_hash_tuple! { A B C D E F G H I J }
-    impl_hash_tuple! { A B C D E F G H I J K }
-    impl_hash_tuple! { A B C D E F G H I J K L }
+    impl_hash_tuple! { T }
+    impl_hash_tuple! { T B }
+    impl_hash_tuple! { T B C }
+    impl_hash_tuple! { T B C D }
+    impl_hash_tuple! { T B C D E }
+    impl_hash_tuple! { T B C D E F }
+    impl_hash_tuple! { T B C D E F G }
+    impl_hash_tuple! { T B C D E F G H }
+    impl_hash_tuple! { T B C D E F G H I }
+    impl_hash_tuple! { T B C D E F G H I J }
+    impl_hash_tuple! { T B C D E F G H I J K }
+    impl_hash_tuple! { T B C D E F G H I J K L }
 
     #[stable(feature = "rust1", since = "1.0.0")]
     impl<T: Hash> Hash for [T] {

library/core/src/marker.rs

@@ -359,7 +359,6 @@ pub trait StructuralEq {
 ///
 /// * Function item types (i.e., the distinct types defined for each function)
 /// * Function pointer types (e.g., `fn() -> i32`)
-/// * Tuple types, if each component also implements `Copy` (e.g., `()`, `(i32, bool)`)
 /// * Closure types, if they capture no value from the environment
 ///   or if all such captured values implement `Copy` themselves.
 ///   Note that variables captured by shared reference always implement `Copy`

library/core/src/primitive_docs.rs

@@ -439,6 +439,27 @@ mod prim_char {}
 #[stable(feature = "rust1", since = "1.0.0")]
 mod prim_unit {}
 
+// Required to make auto trait impls render.
+// See src/librustdoc/passes/collect_trait_impls.rs:collect_trait_impls
+#[doc(hidden)]
+impl () {}
+
+// Fake impl that's only really used for docs.
+#[cfg(doc)]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Clone for () {
+    fn clone(&self) -> Self {
+        loop {}
+    }
+}
+
+// Fake impl that's only really used for docs.
+#[cfg(doc)]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Copy for () {
+    // empty
+}
+
 #[doc(primitive = "pointer")]
 #[doc(alias = "ptr")]
 #[doc(alias = "*")]
@@ -893,13 +914,18 @@ mod prim_str {}
 ///
 /// For more about tuples, see [the book](../book/ch03-02-data-types.html#the-tuple-type).
 ///
+// Hardcoded anchor in src/librustdoc/html/format.rs
+// linked to as `#trait-implementations-1`
 /// # Trait implementations
 ///
-/// If every type inside a tuple implements one of the following traits, then a
-/// tuple itself also implements it.
+/// In this documentation the shorthand `(T₁, T₂, …, Tₙ)` is used to represent tuples of varying
+/// length. When that is used, any trait bound expressed on `T` applies to each element of the
+/// tuple independently. Note that this is a convenience notation to avoid repetitive
+/// documentation, not valid Rust syntax.
+///
+/// Due to a temporary restriction in Rust’s type system, the following traits are only
+/// implemented on tuples of arity 12 or less. In the future, this may change:
 ///
-/// * [`Clone`]
-/// * [`Copy`]
 /// * [`PartialEq`]
 /// * [`Eq`]
 /// * [`PartialOrd`]
@@ -911,8 +937,21 @@ mod prim_str {}
 /// [`Debug`]: fmt::Debug
 /// [`Hash`]: hash::Hash
 ///
-/// Due to a temporary restriction in Rust's type system, these traits are only
-/// implemented on tuples of arity 12 or less. In the future, this may change.
+/// The following traits are implemented for tuples of any length. These traits have
+/// implementations that are automatically generated by the compiler, so are not limited by
+/// missing language features.
+///
+/// * [`Clone`]
+/// * [`Copy`]
+/// * [`Send`]
+/// * [`Sync`]
+/// * [`Unpin`]
+/// * [`UnwindSafe`]
+/// * [`RefUnwindSafe`]
+///
+/// [`Unpin`]: marker::Unpin
+/// [`UnwindSafe`]: panic::UnwindSafe
+/// [`RefUnwindSafe`]: panic::RefUnwindSafe
 ///
 /// # Examples
 ///
@@ -949,6 +988,31 @@ mod prim_str {}
 #[stable(feature = "rust1", since = "1.0.0")]
 mod prim_tuple {}
 
+// Required to make auto trait impls render.
+// See src/librustdoc/passes/collect_trait_impls.rs:collect_trait_impls
+#[doc(hidden)]
+impl<T> (T,) {}
+
+// Fake impl that's only really used for docs.
+#[cfg(doc)]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(bootstrap), doc(tuple_variadic))]
+/// This trait is implemented on arbitrary-length tuples.
+impl<T: Clone> Clone for (T,) {
+    fn clone(&self) -> Self {
+        loop {}
+    }
+}
+
+// Fake impl that's only really used for docs.
+#[cfg(doc)]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(bootstrap), doc(tuple_variadic))]
+/// This trait is implemented on arbitrary-length tuples.
+impl<T: Copy> Copy for (T,) {
+    // empty
+}
+
 #[doc(primitive = "f32")]
 /// A 32-bit floating point type (specifically, the "binary32" type defined in IEEE 754-2008).
 ///