Simplify documentation for Extend impl for tuples

Author: shahn

library/core/src/iter/traits/collect.rs

@@ -494,25 +494,17 @@ impl Extend<()> for () {
 
 macro_rules! spec_tuple_impl {
     ( ($ty_name:ident, $var_name:ident, $extend_ty_name: ident, $trait_name:ident, $default_fn_name:ident, $cnt:tt), ) => {
-        spec_tuple_impl!($trait_name, $default_fn_name, #[stable(feature = "extend_for_more_tuples", since = "CURRENT_RUSTC_VERSION")] #[doc(fake_variadic)] #[doc = "This trait is implemented for tuples up to twelve items long."] => ($ty_name, $var_name, $extend_ty_name, $cnt),);
-    };
-    // Special case (A, B) as this was stabilized earlier
-    ( ($ty_name:ident, $var_name:ident, $extend_ty_name: ident, $trait_name:ident, $default_fn_name:ident, $cnt:tt),
-      ($ty_names:ident, $var_names:ident, $extend_ty_names: ident, $trait_names:ident, $default_fn_names:ident, $cnts:tt),) => {
-
-        spec_tuple_impl!(($ty_names, $var_names, $extend_ty_names, $trait_names, $default_fn_names, $cnts),);
-        spec_tuple_impl!($trait_name, $default_fn_name, #[stable(feature = "extend_for_tuple", since = "1.56.0")] => ($ty_name, $var_name, $extend_ty_name, $cnt), ($ty_names, $var_names, $extend_ty_names, $cnts),);
+        spec_tuple_impl!($trait_name, $default_fn_name, #[doc(fake_variadic)] #[doc = "This trait is implemented for tuples up to twelve items long. The `impl`s for 1- and 3- through 12-ary tuples were stabilized after 2-tuples, in RUSTC_CURRENT_VERSION."] => ($ty_name, $var_name, $extend_ty_name, $cnt),);
     };
     ( ($ty_name:ident, $var_name:ident, $extend_ty_name: ident, $trait_name:ident, $default_fn_name:ident, $cnt:tt), $(($ty_names:ident, $var_names:ident,  $extend_ty_names:ident, $trait_names:ident, $default_fn_names:ident, $cnts:tt),)*) => {
 
         spec_tuple_impl!($(($ty_names, $var_names, $extend_ty_names, $trait_names, $default_fn_names, $cnts),)*);
-        spec_tuple_impl!($trait_name, $default_fn_name, #[stable(feature = "extend_for_more_tuples", since = "CURRENT_RUSTC_VERSION")] #[doc(hidden)] => ($ty_name, $var_name, $extend_ty_name, $cnt), $(($ty_names, $var_names, $extend_ty_names, $cnts),)*);
+        spec_tuple_impl!($trait_name, $default_fn_name, #[doc(hidden)] => ($ty_name, $var_name, $extend_ty_name, $cnt), $(($ty_names, $var_names, $extend_ty_names, $cnts),)*);
     };
-    ($trait_name:ident, $default_fn_name:ident, #[$stable:meta] $(#[$meta:meta] $(#[$doctext:meta])?)? => $(($ty_names:ident, $var_names:ident, $extend_ty_names:ident, $cnts:tt),)*) => {
-        $(#[$meta]
-            $(#[$doctext])?
-        )?
-        #[$stable]
+    ($trait_name:ident, $default_fn_name:ident, #[$meta:meta] $(#[$doctext:meta])? => $(($ty_names:ident, $var_names:ident, $extend_ty_names:ident, $cnts:tt),)*) => {
+        #[$meta]
+        $(#[$doctext])?
+        #[stable(feature = "extend_for_tuple", since = "1.56.0")]
         impl<$($ty_names,)* $($extend_ty_names,)*> Extend<($($ty_names,)*)> for ($($extend_ty_names,)*)
         where
             $($extend_ty_names: Extend<$ty_names>,)*