Document tuple impls as fake variadic

Author: dtolnay

serde/src/de/impls.rs

@@ -1393,7 +1393,19 @@ array_impls! {
 macro_rules! tuple_impls {
     ($($len:tt => ($($n:tt $name:ident)+))+) => {
         $(
-            impl<'de, $($name: Deserialize<'de>),+> Deserialize<'de> for ($($name,)+) {
+            #[cfg_attr(docsrs, doc(hidden))]
+            impl<'de, $($name),+> Deserialize<'de> for ($($name,)+)
+            where
+                $($name: Deserialize<'de>,)+
+            {
+                tuple_impl_body!($len => ($($n $name)+));
+            }
+        )+
+    };
+}
+
+macro_rules! tuple_impl_body {
+    ($len:tt => ($($n:tt $name:ident)+)) => {
                 #[inline]
                 fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
                 where
@@ -1462,13 +1474,22 @@ macro_rules! tuple_impls {
 
                     deserializer.deserialize_tuple($len, TupleInPlaceVisitor(place))
                 }
-            }
-        )+
-    }
+    };
+}
+
+#[cfg_attr(docsrs, doc(fake_variadic))]
+#[cfg_attr(
+    docsrs,
+    doc = "This trait is implemented for tuples up to 16 items long."
+)]
+impl<'de, T> Deserialize<'de> for (T,)
+where
+    T: Deserialize<'de>,
+{
+    tuple_impl_body!(1 => (0 T));
 }
 
 tuple_impls! {
-    1  => (0 T0)
     2  => (0 T0 1 T1)
     3  => (0 T0 1 T1 2 T2)
     4  => (0 T0 1 T1 2 T2 3 T3)

serde/src/lib.rs

@@ -99,7 +99,8 @@
 // Support using Serde without the standard library!
 #![cfg_attr(not(feature = "std"), no_std)]
 // Show which crate feature enables conditionally compiled APIs in documentation.
-#![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg, rustdoc_internals))]
+#![cfg_attr(docsrs, allow(internal_features))]
 // Unstable functionality only if the user asks for it. For tracking and
 // discussion of these features please refer to this issue:
 //

serde/src/ser/impls.rs

@@ -386,10 +386,19 @@ impl Serialize for ! {
 macro_rules! tuple_impls {
     ($($len:expr => ($($n:tt $name:ident)+))+) => {
         $(
+            #[cfg_attr(docsrs, doc(hidden))]
             impl<$($name),+> Serialize for ($($name,)+)
             where
                 $($name: Serialize,)+
             {
+                tuple_impl_body!($len => ($($n)+));
+            }
+        )+
+    };
+}
+
+macro_rules! tuple_impl_body {
+    ($len:expr => ($($n:tt)+)) => {
                 #[inline]
                 fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
                 where
@@ -401,13 +410,22 @@ macro_rules! tuple_impls {
                     )+
                     tuple.end()
                 }
-            }
-        )+
-    }
+    };
+}
+
+#[cfg_attr(docsrs, doc(fake_variadic))]
+#[cfg_attr(
+    docsrs,
+    doc = "This trait is implemented for tuples up to 16 items long."
+)]
+impl<T> Serialize for (T,)
+where
+    T: Serialize,
+{
+    tuple_impl_body!(1 => (0));
 }
 
 tuple_impls! {
-    1 => (0 T0)
     2 => (0 T0 1 T1)
     3 => (0 T0 1 T1 2 T2)
     4 => (0 T0 1 T1 2 T2 3 T3)