Merge pull request #2647 from dtolnay/doccfg

Render `doc(cfg(...))` on feature gated APIs in docs.rs

serde/Cargo.toml

@@ -27,9 +27,9 @@ doc-scrape-examples = false
 features = ["derive", "rc"]
 
 [package.metadata.docs.rs]
-features = ["derive"]
+features = ["derive", "rc", "unstable"]
 targets = ["x86_64-unknown-linux-gnu"]
-rustdoc-args = ["--generate-link-to-definition"]
+rustdoc-args = ["--cfg", "doc_cfg", "--generate-link-to-definition"]
 
 # This cfg cannot be enabled, but it still forces Cargo to keep serde_derive's
 # version in lockstep with serde's, even if someone depends on the two crates

serde/src/de/impls.rs

@@ -39,6 +39,7 @@ impl<'de> Deserialize<'de> for () {
 }
 
 #[cfg(feature = "unstable")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "unstable")))]
 impl<'de> Deserialize<'de> for ! {
     fn deserialize<D>(_deserializer: D) -> Result<Self, D::Error>
     where
@@ -596,6 +597,7 @@ impl<'a, 'de> Visitor<'de> for StringInPlaceVisitor<'a> {
 }
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl<'de> Deserialize<'de> for String {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
@@ -739,6 +741,7 @@ impl<'de> Visitor<'de> for CStringVisitor {
 }
 
 #[cfg(any(feature = "std", all(not(no_core_cstr), feature = "alloc")))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl<'de> Deserialize<'de> for CString {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
@@ -750,10 +753,10 @@ impl<'de> Deserialize<'de> for CString {
 
 macro_rules! forwarded_impl {
     (
-        $(#[doc = $doc:tt])*
+        $(#[$attr:meta])*
         ($($id:ident),*), $ty:ty, $func:expr
     ) => {
-        $(#[doc = $doc])*
+        $(#[$attr])*
         impl<'de $(, $id : Deserialize<'de>,)*> Deserialize<'de> for $ty {
             fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
             where
@@ -765,10 +768,15 @@ macro_rules! forwarded_impl {
     }
 }
 
-#[cfg(any(feature = "std", all(not(no_core_cstr), feature = "alloc")))]
+forwarded_impl! {
-forwarded_impl!((), Box<CStr>, CString::into_boxed_c_str);
+    #[cfg(any(feature = "std", all(not(no_core_cstr), feature = "alloc")))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    (), Box<CStr>, CString::into_boxed_c_str
+}
 
-forwarded_impl!((T), Reverse<T>, Reverse);
+forwarded_impl! {
+    (T), Reverse<T>, Reverse
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 
@@ -874,9 +882,9 @@ impl<'de, T: ?Sized> Deserialize<'de> for PhantomData<T> {
 
 ////////////////////////////////////////////////////////////////////////////////
 
-#[cfg(any(feature = "std", feature = "alloc"))]
 macro_rules! seq_impl {
     (
+        $(#[$attr:meta])*
         $ty:ident <T $(: $tbound1:ident $(+ $tbound2:ident)*)* $(, $typaram:ident : $bound1:ident $(+ $bound2:ident)*)*>,
         $access:ident,
         $clear:expr,
@@ -884,6 +892,7 @@ macro_rules! seq_impl {
         $reserve:expr,
         $insert:expr
     ) => {
+        $(#[$attr])*
         impl<'de, T $(, $typaram)*> Deserialize<'de> for $ty<T $(, $typaram)*>
         where
             T: Deserialize<'de> $(+ $tbound1 $(+ $tbound2)*)*,
@@ -971,8 +980,9 @@ macro_rules! seq_impl {
 #[cfg(any(feature = "std", feature = "alloc"))]
 fn nop_reserve<T>(_seq: T, _n: usize) {}
 
-#[cfg(any(feature = "std", feature = "alloc"))]
 seq_impl!(
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
     BinaryHeap<T: Ord>,
     seq,
     BinaryHeap::clear,
@@ -981,8 +991,9 @@ seq_impl!(
     BinaryHeap::push
 );
 
-#[cfg(any(feature = "std", feature = "alloc"))]
 seq_impl!(
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
     BTreeSet<T: Eq + Ord>,
     seq,
     BTreeSet::clear,
@@ -991,8 +1002,9 @@ seq_impl!(
     BTreeSet::insert
 );
 
-#[cfg(any(feature = "std", feature = "alloc"))]
 seq_impl!(
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
     LinkedList<T>,
     seq,
     LinkedList::clear,
@@ -1001,8 +1013,9 @@ seq_impl!(
     LinkedList::push_back
 );
 
-#[cfg(feature = "std")]
 seq_impl!(
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
     HashSet<T: Eq + Hash, S: BuildHasher + Default>,
     seq,
     HashSet::clear,
@@ -1011,8 +1024,9 @@ seq_impl!(
     HashSet::insert
 );
 
-#[cfg(any(feature = "std", feature = "alloc"))]
 seq_impl!(
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
     VecDeque<T>,
     seq,
     VecDeque::clear,
@@ -1024,6 +1038,7 @@ seq_impl!(
 ////////////////////////////////////////////////////////////////////////////////
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl<'de, T> Deserialize<'de> for Vec<T>
 where
     T: Deserialize<'de>,
@@ -1369,13 +1384,14 @@ tuple_impls! {
 
 ////////////////////////////////////////////////////////////////////////////////
 
-#[cfg(any(feature = "std", feature = "alloc"))]
 macro_rules! map_impl {
     (
+        $(#[$attr:meta])*
         $ty:ident <K $(: $kbound1:ident $(+ $kbound2:ident)*)*, V $(, $typaram:ident : $bound1:ident $(+ $bound2:ident)*)*>,
         $access:ident,
-        $with_capacity:expr
+        $with_capacity:expr,
     ) => {
+        $(#[$attr])*
         impl<'de, K, V $(, $typaram)*> Deserialize<'de> for $ty<K, V $(, $typaram)*>
         where
             K: Deserialize<'de> $(+ $kbound1 $(+ $kbound2)*)*,
@@ -1424,21 +1440,30 @@ macro_rules! map_impl {
     }
 }
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+map_impl! {
-map_impl!(BTreeMap<K: Ord, V>, map, BTreeMap::new());
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    BTreeMap<K: Ord, V>,
+    map,
+    BTreeMap::new(),
+}
 
-#[cfg(feature = "std")]
+map_impl! {
-map_impl!(
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
     HashMap<K: Eq + Hash, V, S: BuildHasher + Default>,
     map,
-    HashMap::with_capacity_and_hasher(size_hint::cautious::<(K, V)>(map.size_hint()), S::default())
+    HashMap::with_capacity_and_hasher(size_hint::cautious::<(K, V)>(map.size_hint()), S::default()),
-);
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 
-#[cfg(feature = "std")]
 macro_rules! parse_ip_impl {
-    ($expecting:tt $ty:ty; $size:tt) => {
+    (
+        $(#[$attr:meta])*
+        $ty:ty, $expecting:expr, $size:tt
+    ) => {
+        $(#[$attr])*
         impl<'de> Deserialize<'de> for $ty {
             fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
             where
@@ -1567,6 +1592,7 @@ macro_rules! deserialize_enum {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl<'de> Deserialize<'de> for net::IpAddr {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
@@ -1585,15 +1611,25 @@ impl<'de> Deserialize<'de> for net::IpAddr {
     }
 }
 
-#[cfg(feature = "std")]
+parse_ip_impl! {
-parse_ip_impl!("IPv4 address" net::Ipv4Addr; 4);
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    net::Ipv4Addr, "IPv4 address", 4
+}
 
-#[cfg(feature = "std")]
+parse_ip_impl! {
-parse_ip_impl!("IPv6 address" net::Ipv6Addr; 16);
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    net::Ipv6Addr, "IPv6 address", 16
+}
 
-#[cfg(feature = "std")]
 macro_rules! parse_socket_impl {
-    ($expecting:tt $ty:ty, $new:expr) => {
+    (
+        $(#[$attr:meta])*
+        $ty:ty, $expecting:tt,
+        $new:expr,
+    ) => {
+        $(#[$attr])*
         impl<'de> Deserialize<'de> for $ty {
             fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
             where
@@ -1610,6 +1646,7 @@ macro_rules! parse_socket_impl {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl<'de> Deserialize<'de> for net::SocketAddr {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
@@ -1628,11 +1665,19 @@ impl<'de> Deserialize<'de> for net::SocketAddr {
     }
 }
 
-#[cfg(feature = "std")]
+parse_socket_impl! {
-parse_socket_impl!("IPv4 socket address" net::SocketAddrV4, |(ip, port)| net::SocketAddrV4::new(ip, port));
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    net::SocketAddrV4, "IPv4 socket address",
+    |(ip, port)| net::SocketAddrV4::new(ip, port),
+}
 
-#[cfg(feature = "std")]
+parse_socket_impl! {
-parse_socket_impl!("IPv6 socket address" net::SocketAddrV6, |(ip, port)| net::SocketAddrV6::new(ip, port, 0, 0));
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    net::SocketAddrV6, "IPv6 socket address",
+    |(ip, port)| net::SocketAddrV6::new(ip, port, 0, 0),
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 
@@ -1665,6 +1710,7 @@ impl<'a> Visitor<'a> for PathVisitor {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl<'de: 'a, 'a> Deserialize<'de> for &'a Path {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
@@ -1719,6 +1765,7 @@ impl<'de> Visitor<'de> for PathBufVisitor {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl<'de> Deserialize<'de> for PathBuf {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
@@ -1728,8 +1775,11 @@ impl<'de> Deserialize<'de> for PathBuf {
     }
 }
 
-#[cfg(feature = "std")]
+forwarded_impl! {
-forwarded_impl!((), Box<Path>, PathBuf::into_boxed_path);
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    (), Box<Path>, PathBuf::into_boxed_path
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 
@@ -1789,6 +1839,7 @@ impl<'de> Visitor<'de> for OsStringVisitor {
 }
 
 #[cfg(all(feature = "std", any(unix, windows)))]
+#[cfg_attr(doc_cfg, doc(cfg(all(feature = "std", any(unix, windows)))))]
 impl<'de> Deserialize<'de> for OsString {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
@@ -1800,19 +1851,32 @@ impl<'de> Deserialize<'de> for OsString {
 
 ////////////////////////////////////////////////////////////////////////////////
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+forwarded_impl! {
-forwarded_impl!((T), Box<T>, Box::new);
+    #[cfg(any(feature = "std", feature = "alloc"))]
-
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
-#[cfg(any(feature = "std", feature = "alloc"))]
+    (T), Box<T>, Box::new
-forwarded_impl!((T), Box<[T]>, Vec::into_boxed_slice);
+}
-
+
-#[cfg(any(feature = "std", feature = "alloc"))]
+forwarded_impl! {
-forwarded_impl!((), Box<str>, String::into_boxed_str);
+    #[cfg(any(feature = "std", feature = "alloc"))]
-
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
-#[cfg(all(feature = "std", any(unix, windows)))]
+    (T), Box<[T]>, Vec::into_boxed_slice
-forwarded_impl!((), Box<OsStr>, OsString::into_boxed_os_str);
+}
+
+forwarded_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    (), Box<str>, String::into_boxed_str
+}
+
+forwarded_impl! {
+    #[cfg(all(feature = "std", any(unix, windows)))]
+    #[cfg_attr(doc_cfg, doc(cfg(all(feature = "std", any(unix, windows)))))]
+    (), Box<OsStr>, OsString::into_boxed_os_str
+}
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl<'de, 'a, T: ?Sized> Deserialize<'de> for Cow<'a, T>
 where
     T: ToOwned,
@@ -1834,6 +1898,10 @@ where
 ///
 /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
 #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+#[cfg_attr(
+    doc_cfg,
+    doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc"))))
+)]
 impl<'de, T: ?Sized> Deserialize<'de> for RcWeak<T>
 where
     T: Deserialize<'de>,
@@ -1852,6 +1920,10 @@ where
 ///
 /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
 #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+#[cfg_attr(
+    doc_cfg,
+    doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc"))))
+)]
 impl<'de, T: ?Sized> Deserialize<'de> for ArcWeak<T>
 where
     T: Deserialize<'de>,
@@ -1867,13 +1939,12 @@ where
 
 ////////////////////////////////////////////////////////////////////////////////
 
-#[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
 macro_rules! box_forwarded_impl {
     (
-        $(#[doc = $doc:tt])*
+        $(#[$attr:meta])*
         $t:ident
     ) => {
-        $(#[doc = $doc])*
+        $(#[$attr])*
         impl<'de, T: ?Sized> Deserialize<'de> for $t<T>
         where
             Box<T>: Deserialize<'de>,
@@ -1888,7 +1959,6 @@ macro_rules! box_forwarded_impl {
     };
 }
 
-#[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
 box_forwarded_impl! {
     /// This impl requires the [`"rc"`] Cargo feature of Serde.
     ///
@@ -1897,10 +1967,11 @@ box_forwarded_impl! {
     /// will end up with a strong count of 1.
     ///
     /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+    #[cfg_attr(doc_cfg, doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))))]
     Rc
 }
 
-#[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
 box_forwarded_impl! {
     /// This impl requires the [`"rc"`] Cargo feature of Serde.
     ///
@@ -1909,6 +1980,8 @@ box_forwarded_impl! {
     /// will end up with a strong count of 1.
     ///
     /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+    #[cfg_attr(doc_cfg, doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))))]
     Arc
 }
 
@@ -1926,13 +1999,21 @@ where
     }
 }
 
-forwarded_impl!((T), RefCell<T>, RefCell::new);
+forwarded_impl! {
+    (T), RefCell<T>, RefCell::new
+}
 
-#[cfg(feature = "std")]
+forwarded_impl! {
-forwarded_impl!((T), Mutex<T>, Mutex::new);
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    (T), Mutex<T>, Mutex::new
+}
 
-#[cfg(feature = "std")]
+forwarded_impl! {
-forwarded_impl!((T), RwLock<T>, RwLock::new);
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    (T), RwLock<T>, RwLock::new
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 
@@ -2085,6 +2166,7 @@ impl<'de> Deserialize<'de> for Duration {
 ////////////////////////////////////////////////////////////////////////////////
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl<'de> Deserialize<'de> for SystemTime {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
@@ -2920,6 +3002,7 @@ macro_rules! atomic_impl {
     ($($ty:ident $size:expr)*) => {
         $(
             #[cfg(any(no_target_has_atomic, target_has_atomic = $size))]
+            #[cfg_attr(doc_cfg, doc(cfg(all(feature = "std", target_has_atomic = $size))))]
             impl<'de> Deserialize<'de> for $ty {
                 fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
                 where

serde/src/de/mod.rs

@@ -1525,6 +1525,7 @@ pub trait Visitor<'de>: Sized {
     /// `String`.
     #[inline]
     #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
     fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
     where
         E: Error,
@@ -1583,6 +1584,7 @@ pub trait Visitor<'de>: Sized {
     /// The default implementation forwards to `visit_bytes` and then drops the
     /// `Vec<u8>`.
     #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
     fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
     where
         E: Error,

serde/src/de/value.rs

@@ -112,6 +112,7 @@ impl Debug for Error {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl error::Error for Error {
     fn description(&self) -> &str {
         &self.err
@@ -184,12 +185,14 @@ impl<E> Debug for UnitDeserializer<E> {
 
 /// A deserializer that cannot be instantiated.
 #[cfg(feature = "unstable")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "unstable")))]
 pub struct NeverDeserializer<E> {
     never: !,
     marker: PhantomData<E>,
 }
 
 #[cfg(feature = "unstable")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "unstable")))]
 impl<'de, E> IntoDeserializer<'de, E> for !
 where
     E: de::Error,
@@ -562,6 +565,7 @@ impl<'de, E> Debug for BorrowedStrDeserializer<'de, E> {
 
 /// A deserializer holding a `String`.
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 pub struct StringDeserializer<E> {
     value: String,
     marker: PhantomData<E>,
@@ -578,6 +582,7 @@ impl<E> Clone for StringDeserializer<E> {
 }
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl<'de, E> IntoDeserializer<'de, E> for String
 where
     E: de::Error,
@@ -665,6 +670,7 @@ impl<E> Debug for StringDeserializer<E> {
 
 /// A deserializer holding a `Cow<str>`.
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 pub struct CowStrDeserializer<'a, E> {
     value: Cow<'a, str>,
     marker: PhantomData<E>,
@@ -681,6 +687,7 @@ impl<'a, E> Clone for CowStrDeserializer<'a, E> {
 }
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl<'de, 'a, E> IntoDeserializer<'de, E> for Cow<'a, str>
 where
     E: de::Error,
@@ -999,6 +1006,7 @@ where
 ////////////////////////////////////////////////////////////////////////////////
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl<'de, T, E> IntoDeserializer<'de, E> for Vec<T>
 where
     T: IntoDeserializer<'de, E>,
@@ -1012,6 +1020,7 @@ where
 }
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl<'de, T, E> IntoDeserializer<'de, E> for BTreeSet<T>
 where
     T: IntoDeserializer<'de, E> + Eq + Ord,
@@ -1025,6 +1034,7 @@ where
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl<'de, T, S, E> IntoDeserializer<'de, E> for HashSet<T, S>
 where
     T: IntoDeserializer<'de, E> + Eq + Hash,
@@ -1411,6 +1421,7 @@ impl Expected for ExpectedInMap {
 ////////////////////////////////////////////////////////////////////////////////
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl<'de, K, V, E> IntoDeserializer<'de, E> for BTreeMap<K, V>
 where
     K: IntoDeserializer<'de, E> + Eq + Ord,
@@ -1425,6 +1436,7 @@ where
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl<'de, K, V, S, E> IntoDeserializer<'de, E> for HashMap<K, V, S>
 where
     K: IntoDeserializer<'de, E> + Eq + Hash,

serde/src/lib.rs

@@ -98,6 +98,8 @@
 #![doc(html_root_url = "https://docs.rs/serde/1.0.190")]
 // 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(doc_cfg, feature(doc_cfg))]
 // Unstable functionality only if the user asks for it. For tracking and
 // discussion of these features please refer to this issue:
 //
@@ -324,6 +326,7 @@ extern crate serde_derive;
 
 /// Derive macro available if serde is built with `features = ["derive"]`.
 #[cfg(feature = "serde_derive")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
 pub use serde_derive::{Deserialize, Serialize};
 
 #[cfg(all(not(no_serde_derive), any(feature = "std", feature = "alloc")))]

serde/src/ser/impls.rs

@@ -48,6 +48,7 @@ impl Serialize for str {
 }
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl Serialize for String {
     #[inline]
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
@@ -70,6 +71,7 @@ impl<'a> Serialize for fmt::Arguments<'a> {
 ////////////////////////////////////////////////////////////////////////////////
 
 #[cfg(any(feature = "std", not(no_core_cstr)))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for CStr {
     #[inline]
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
@@ -81,6 +83,7 @@ impl Serialize for CStr {
 }
 
 #[cfg(any(feature = "std", all(not(no_core_cstr), feature = "alloc")))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
 impl Serialize for CString {
     #[inline]
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
@@ -179,9 +182,13 @@ where
     }
 }
 
-#[cfg(all(any(feature = "std", feature = "alloc"), not(no_relaxed_trait_bounds)))]
+#[cfg(not(no_relaxed_trait_bounds))]
 macro_rules! seq_impl {
-    ($ty:ident <T $(: $tbound1:ident $(+ $tbound2:ident)*)* $(, $typaram:ident : $bound:ident)*>) => {
+    (
+        $(#[$attr:meta])*
+        $ty:ident <T $(: $tbound1:ident $(+ $tbound2:ident)*)* $(, $typaram:ident : $bound:ident)*>
+    ) => {
+        $(#[$attr])*
         impl<T $(, $typaram)*> Serialize for $ty<T $(, $typaram)*>
         where
             T: Serialize,
@@ -197,9 +204,13 @@ macro_rules! seq_impl {
     }
 }
 
-#[cfg(all(any(feature = "std", feature = "alloc"), no_relaxed_trait_bounds))]
+#[cfg(no_relaxed_trait_bounds)]
 macro_rules! seq_impl {
-    ($ty:ident <T $(: $tbound1:ident $(+ $tbound2:ident)*)* $(, $typaram:ident : $bound:ident)*>) => {
+    (
+        $(#[$attr:meta])*
+        $ty:ident <T $(: $tbound1:ident $(+ $tbound2:ident)*)* $(, $typaram:ident : $bound:ident)*>
+    ) => {
+        $(#[$attr])*
         impl<T $(, $typaram)*> Serialize for $ty<T $(, $typaram)*>
         where
             T: Serialize $(+ $tbound1 $(+ $tbound2)*)*,
@@ -216,23 +227,41 @@ macro_rules! seq_impl {
     }
 }
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+seq_impl! {
-seq_impl!(BinaryHeap<T: Ord>);
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    BinaryHeap<T: Ord>
+}
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+seq_impl! {
-seq_impl!(BTreeSet<T: Ord>);
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    BTreeSet<T: Ord>
+}
 
-#[cfg(feature = "std")]
+seq_impl! {
-seq_impl!(HashSet<T: Eq + Hash, H: BuildHasher>);
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    HashSet<T: Eq + Hash, H: BuildHasher>
+}
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+seq_impl! {
-seq_impl!(LinkedList<T>);
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    LinkedList<T>
+}
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+seq_impl! {
-seq_impl!(Vec<T>);
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    Vec<T>
+}
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+seq_impl! {
-seq_impl!(VecDeque<T>);
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    VecDeque<T>
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 
@@ -339,6 +368,7 @@ impl Serialize for () {
 }
 
 #[cfg(feature = "unstable")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "unstable")))]
 impl Serialize for ! {
     fn serialize<S>(&self, _serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -394,9 +424,13 @@ tuple_impls! {
 
 ////////////////////////////////////////////////////////////////////////////////
 
-#[cfg(all(any(feature = "std", feature = "alloc"), not(no_relaxed_trait_bounds)))]
+#[cfg(not(no_relaxed_trait_bounds))]
 macro_rules! map_impl {
-    ($ty:ident <K $(: $kbound1:ident $(+ $kbound2:ident)*)*, V $(, $typaram:ident : $bound:ident)*>) => {
+    (
+        $(#[$attr:meta])*
+        $ty:ident <K $(: $kbound1:ident $(+ $kbound2:ident)*)*, V $(, $typaram:ident : $bound:ident)*>
+    ) => {
+        $(#[$attr])*
         impl<K, V $(, $typaram)*> Serialize for $ty<K, V $(, $typaram)*>
         where
             K: Serialize,
@@ -413,9 +447,13 @@ macro_rules! map_impl {
     }
 }
 
-#[cfg(all(any(feature = "std", feature = "alloc"), no_relaxed_trait_bounds))]
+#[cfg(no_relaxed_trait_bounds)]
 macro_rules! map_impl {
-    ($ty:ident <K $(: $kbound1:ident $(+ $kbound2:ident)*)*, V $(, $typaram:ident : $bound:ident)*>) => {
+    (
+        $(#[$attr:meta])*
+        $ty:ident <K $(: $kbound1:ident $(+ $kbound2:ident)*)*, V $(, $typaram:ident : $bound:ident)*>
+    ) => {
+        $(#[$attr])*
         impl<K, V $(, $typaram)*> Serialize for $ty<K, V $(, $typaram)*>
         where
             K: Serialize $(+ $kbound1 $(+ $kbound2)*)*,
@@ -433,20 +471,26 @@ macro_rules! map_impl {
     }
 }
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+map_impl! {
-map_impl!(BTreeMap<K: Ord, V>);
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    BTreeMap<K: Ord, V>
+}
 
-#[cfg(feature = "std")]
+map_impl! {
-map_impl!(HashMap<K: Eq + Hash, V, H: BuildHasher>);
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    HashMap<K: Eq + Hash, V, H: BuildHasher>
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 
 macro_rules! deref_impl {
     (
-        $(#[doc = $doc:tt])*
+        $(#[$attr:meta])*
         <$($desc:tt)+
     ) => {
-        $(#[doc = $doc])*
+        $(#[$attr])*
         impl <$($desc)+ {
             #[inline]
             fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
@@ -459,13 +503,20 @@ macro_rules! deref_impl {
     };
 }
 
-deref_impl!(<'a, T: ?Sized> Serialize for &'a T where T: Serialize);
+deref_impl! {
-deref_impl!(<'a, T: ?Sized> Serialize for &'a mut T where T: Serialize);
+    <'a, T: ?Sized> Serialize for &'a T where T: Serialize
+}
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+deref_impl! {
-deref_impl!(<T: ?Sized> Serialize for Box<T> where T: Serialize);
+    <'a, T: ?Sized> Serialize for &'a mut T where T: Serialize
+}
+
+deref_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    <T: ?Sized> Serialize for Box<T> where T: Serialize
+}
 
-#[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
 deref_impl! {
     /// This impl requires the [`"rc"`] Cargo feature of Serde.
     ///
@@ -475,10 +526,11 @@ deref_impl! {
     /// repeated data.
     ///
     /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+    #[cfg_attr(doc_cfg, doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))))]
     <T: ?Sized> Serialize for Rc<T> where T: Serialize
 }
 
-#[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
 deref_impl! {
     /// This impl requires the [`"rc"`] Cargo feature of Serde.
     ///
@@ -488,11 +540,16 @@ deref_impl! {
     /// repeated data.
     ///
     /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+    #[cfg_attr(doc_cfg, doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))))]
     <T: ?Sized> Serialize for Arc<T> where T: Serialize
 }
 
-#[cfg(any(feature = "std", feature = "alloc"))]
+deref_impl! {
-deref_impl!(<'a, T: ?Sized> Serialize for Cow<'a, T> where T: Serialize + ToOwned);
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    <'a, T: ?Sized> Serialize for Cow<'a, T> where T: Serialize + ToOwned
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 
@@ -500,6 +557,10 @@ deref_impl!(<'a, T: ?Sized> Serialize for Cow<'a, T> where T: Serialize + ToOwne
 ///
 /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
 #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+#[cfg_attr(
+    doc_cfg,
+    doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc"))))
+)]
 impl<T: ?Sized> Serialize for RcWeak<T>
 where
     T: Serialize,
@@ -516,6 +577,10 @@ where
 ///
 /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
 #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+#[cfg_attr(
+    doc_cfg,
+    doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc"))))
+)]
 impl<T: ?Sized> Serialize for ArcWeak<T>
 where
     T: Serialize,
@@ -592,6 +657,7 @@ where
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl<T: ?Sized> Serialize for Mutex<T>
 where
     T: Serialize,
@@ -608,6 +674,7 @@ where
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl<T: ?Sized> Serialize for RwLock<T>
 where
     T: Serialize,
@@ -661,6 +728,7 @@ impl Serialize for Duration {
 ////////////////////////////////////////////////////////////////////////////////
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for SystemTime {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -705,6 +773,7 @@ macro_rules! serialize_display_bounded_length {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for net::IpAddr {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -775,6 +844,7 @@ fn test_format_u8() {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for net::Ipv4Addr {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -799,6 +869,7 @@ impl Serialize for net::Ipv4Addr {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for net::Ipv6Addr {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -815,6 +886,7 @@ impl Serialize for net::Ipv6Addr {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for net::SocketAddr {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -839,6 +911,7 @@ impl Serialize for net::SocketAddr {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for net::SocketAddrV4 {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -855,6 +928,7 @@ impl Serialize for net::SocketAddrV4 {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for net::SocketAddrV6 {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -876,6 +950,7 @@ impl Serialize for net::SocketAddrV6 {
 ////////////////////////////////////////////////////////////////////////////////
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for Path {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -889,6 +964,7 @@ impl Serialize for Path {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
 impl Serialize for PathBuf {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -899,6 +975,7 @@ impl Serialize for PathBuf {
 }
 
 #[cfg(all(feature = "std", any(unix, windows)))]
+#[cfg_attr(doc_cfg, doc(cfg(all(feature = "std", any(unix, windows)))))]
 impl Serialize for OsStr {
     #[cfg(unix)]
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
@@ -921,6 +998,7 @@ impl Serialize for OsStr {
 }
 
 #[cfg(all(feature = "std", any(unix, windows)))]
+#[cfg_attr(doc_cfg, doc(cfg(all(feature = "std", any(unix, windows)))))]
 impl Serialize for OsString {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -965,6 +1043,7 @@ macro_rules! atomic_impl {
     ($($ty:ident $size:expr)*) => {
         $(
             #[cfg(any(no_target_has_atomic, target_has_atomic = $size))]
+            #[cfg_attr(doc_cfg, doc(cfg(all(feature = "std", target_has_atomic = $size))))]
             impl Serialize for $ty {
                 fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
                 where