Auto merge of rust-lang#117050 - c410-f3r:here-we-go-again, r=petrochenkov

[`RFC 3086`] Attempt to try to resolve blocking concerns

Implements what is described at rust-lang#83527 (comment) to hopefully make some progress.

It is unknown if such approach is or isn't desired due to the lack of further feedback, as such, it is probably best to nominate this PR to the official entities.

`@rustbot` labels +I-compiler-nominated

Author: bors

core/src/tuple.rs

@@ -8,6 +8,7 @@ use crate::marker::{StructuralEq, StructuralPartialEq};
 //
 // Also provides implementations for tuples with lesser arity. For example, tuple_impls!(A B C)
 // will implement everything for (A, B, C), (A, B) and (A,).
+#[cfg(bootstrap)]
 macro_rules! tuple_impls {
     // Stopping criteria (1-ary tuple)
     ($T:ident) => {
@@ -142,6 +143,148 @@ macro_rules! tuple_impls {
     }
 }
 
+// Recursive macro for implementing n-ary tuple functions and operations
+//
+// Also provides implementations for tuples with lesser arity. For example, tuple_impls!(A B C)
+// will implement everything for (A, B, C), (A, B) and (A,).
+#[cfg(not(bootstrap))]
+macro_rules! tuple_impls {
+    // Stopping criteria (1-ary tuple)
+    ($T:ident) => {
+        tuple_impls!(@impl $T);
+    };
+    // Running criteria (n-ary tuple, with n >= 2)
+    ($T:ident $( $U:ident )+) => {
+        tuple_impls!($( $U )+);
+        tuple_impls!(@impl $T $( $U )+);
+    };
+    // "Private" internal implementation
+    (@impl $( $T:ident )+) => {
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<$($T: PartialEq),+> PartialEq for ($($T,)+)
+            where
+                last_type!($($T,)+): ?Sized
+            {
+                #[inline]
+                fn eq(&self, other: &($($T,)+)) -> bool {
+                    $( ${ignore($T)} self.${index()} == other.${index()} )&&+
+                }
+                #[inline]
+                fn ne(&self, other: &($($T,)+)) -> bool {
+                    $( ${ignore($T)} self.${index()} != other.${index()} )||+
+                }
+            }
+        }
+
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<$($T: Eq),+> Eq for ($($T,)+)
+            where
+                last_type!($($T,)+): ?Sized
+            {}
+        }
+
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[unstable(feature = "structural_match", issue = "31434")]
+            impl<$($T: ConstParamTy),+> ConstParamTy for ($($T,)+)
+            {}
+        }
+
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[unstable(feature = "structural_match", issue = "31434")]
+            impl<$($T),+> StructuralPartialEq for ($($T,)+)
+            {}
+        }
+
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[unstable(feature = "structural_match", issue = "31434")]
+            impl<$($T),+> StructuralEq for ($($T,)+)
+            {}
+        }
+
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<$($T: PartialOrd),+> PartialOrd for ($($T,)+)
+            where
+                last_type!($($T,)+): ?Sized
+            {
+                #[inline]
+                fn partial_cmp(&self, other: &($($T,)+)) -> Option<Ordering> {
+                    lexical_partial_cmp!($( ${ignore($T)} self.${index()}, other.${index()} ),+)
+                }
+                #[inline]
+                fn lt(&self, other: &($($T,)+)) -> bool {
+                    lexical_ord!(lt, Less, $( ${ignore($T)} self.${index()}, other.${index()} ),+)
+                }
+                #[inline]
+                fn le(&self, other: &($($T,)+)) -> bool {
+                    lexical_ord!(le, Less, $( ${ignore($T)} self.${index()}, other.${index()} ),+)
+                }
+                #[inline]
+                fn ge(&self, other: &($($T,)+)) -> bool {
+                    lexical_ord!(ge, Greater, $( ${ignore($T)} self.${index()}, other.${index()} ),+)
+                }
+                #[inline]
+                fn gt(&self, other: &($($T,)+)) -> bool {
+                    lexical_ord!(gt, Greater, $( ${ignore($T)} self.${index()}, other.${index()} ),+)
+                }
+            }
+        }
+
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<$($T: Ord),+> Ord for ($($T,)+)
+            where
+                last_type!($($T,)+): ?Sized
+            {
+                #[inline]
+                fn cmp(&self, other: &($($T,)+)) -> Ordering {
+                    lexical_cmp!($( ${ignore($T)} self.${index()}, other.${index()} ),+)
+                }
+            }
+        }
+
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<$($T: Default),+> Default for ($($T,)+) {
+                #[inline]
+                fn default() -> ($($T,)+) {
+                    ($({ let x: $T = Default::default(); x},)+)
+                }
+            }
+        }
+
+        #[stable(feature = "array_tuple_conv", since = "1.71.0")]
+        impl<T> From<[T; ${count($T)}]> for ($(${ignore($T)} T,)+) {
+            #[inline]
+            #[allow(non_snake_case)]
+            fn from(array: [T; ${count($T)}]) -> Self {
+                let [$($T,)+] = array;
+                ($($T,)+)
+            }
+        }
+
+        #[stable(feature = "array_tuple_conv", since = "1.71.0")]
+        impl<T> From<($(${ignore($T)} T,)+)> for [T; ${count($T)}] {
+            #[inline]
+            #[allow(non_snake_case)]
+            fn from(tuple: ($(${ignore($T)} T,)+)) -> Self {
+                let ($($T,)+) = tuple;
+                [$($T,)+]
+            }
+        }
+    }
+}
+
 // If this is a unary tuple, it adds a doc comment.
 // Otherwise, it hides the docs entirely.
 macro_rules! maybe_tuple_doc {