Add a **Note**: comment in documentation when the type/method/function is not always available

Author: poliorcetics

src/libcore/sync/atomic.rs

@@ -153,6 +153,8 @@ pub fn spin_loop_hint() {
 ///
 /// This type has the same in-memory representation as a [`bool`].
 ///
+/// **Note**: This type may not be available on some platforms.
+///
 /// [`bool`]: ../../../std/primitive.bool.html
 #[cfg(target_has_atomic_load_store = "8")]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -178,6 +180,9 @@ unsafe impl Sync for AtomicBool {}
 /// A raw pointer type which can be safely shared between threads.
 ///
 /// This type has the same in-memory representation as a `*mut T`.
+///
+/// **Note**: This type may not be available on some platforms. Its size depends
+/// on the target pointer's size.
 #[cfg(target_has_atomic_load_store = "ptr")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(target_pointer_width = "16", repr(C, align(2)))]
@@ -462,6 +467,8 @@ impl AtomicBool {
     /// assert_eq!(some_bool.swap(false, Ordering::Relaxed), true);
     /// assert_eq!(some_bool.load(Ordering::Relaxed), false);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg(target_has_atomic = "8")]
@@ -501,6 +508,8 @@ impl AtomicBool {
     /// assert_eq!(some_bool.compare_and_swap(true, true, Ordering::Relaxed), false);
     /// assert_eq!(some_bool.load(Ordering::Relaxed), false);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg(target_has_atomic = "8")]
@@ -552,6 +561,8 @@ impl AtomicBool {
     ///            Err(false));
     /// assert_eq!(some_bool.load(Ordering::Relaxed), false);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "extended_compare_and_swap", since = "1.10.0")]
     #[cfg(target_has_atomic = "8")]
@@ -610,6 +621,8 @@ impl AtomicBool {
     ///     }
     /// }
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "extended_compare_and_swap", since = "1.10.0")]
     #[cfg(target_has_atomic = "8")]
@@ -663,6 +676,8 @@ impl AtomicBool {
     /// assert_eq!(foo.fetch_and(false, Ordering::SeqCst), false);
     /// assert_eq!(foo.load(Ordering::SeqCst), false);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg(target_has_atomic = "8")]
@@ -706,6 +721,8 @@ impl AtomicBool {
     /// assert_eq!(foo.fetch_nand(false, Ordering::SeqCst), false);
     /// assert_eq!(foo.load(Ordering::SeqCst), true);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg(target_has_atomic = "8")]
@@ -759,6 +776,8 @@ impl AtomicBool {
     /// assert_eq!(foo.fetch_or(false, Ordering::SeqCst), false);
     /// assert_eq!(foo.load(Ordering::SeqCst), false);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg(target_has_atomic = "8")]
@@ -801,6 +820,8 @@ impl AtomicBool {
     /// assert_eq!(foo.fetch_xor(false, Ordering::SeqCst), false);
     /// assert_eq!(foo.load(Ordering::SeqCst), false);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg(target_has_atomic = "8")]
@@ -998,6 +1019,8 @@ impl<T> AtomicPtr<T> {
     ///
     /// let value = some_ptr.swap(other_ptr, Ordering::Relaxed);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg(target_has_atomic = "ptr")]
@@ -1035,6 +1058,8 @@ impl<T> AtomicPtr<T> {
     ///
     /// let value = some_ptr.compare_and_swap(ptr, other_ptr, Ordering::Relaxed);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[cfg(target_has_atomic = "ptr")]
@@ -1077,6 +1102,8 @@ impl<T> AtomicPtr<T> {
     /// let value = some_ptr.compare_exchange(ptr, other_ptr,
     ///                                       Ordering::SeqCst, Ordering::Relaxed);
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "extended_compare_and_swap", since = "1.10.0")]
     #[cfg(target_has_atomic = "ptr")]
@@ -1141,6 +1168,8 @@ impl<T> AtomicPtr<T> {
     ///     }
     /// }
     /// ```
+    ///
+    /// **Note**: This method may not be available on some platforms.
     #[inline]
     #[stable(feature = "extended_compare_and_swap", since = "1.10.0")]
     #[cfg(target_has_atomic = "ptr")]
@@ -1223,6 +1252,8 @@ macro_rules! atomic_int {
         /// non-atomic types as well as information about the portability of
         /// this type, please see the [module-level documentation].
         ///
+        /// **Note**: This type may not be available on some platforms.
+        ///
         /// [module-level documentation]: index.html
         #[$stable]
         #[repr(C, align($align))]
@@ -1421,7 +1452,9 @@ using [`Release`] makes the load part [`Relaxed`].
 let some_var = ", stringify!($atomic_type), "::new(5);
 
 assert_eq!(some_var.swap(10, Ordering::Relaxed), 5);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable]
                 #[$cfg_cas]
@@ -1462,7 +1495,9 @@ assert_eq!(some_var.load(Ordering::Relaxed), 10);
 
 assert_eq!(some_var.compare_and_swap(6, 12, Ordering::Relaxed), 10);
 assert_eq!(some_var.load(Ordering::Relaxed), 10);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable]
                 #[$cfg_cas]
@@ -1520,7 +1555,9 @@ assert_eq!(some_var.compare_exchange(6, 12,
                                      Ordering::Acquire),
            Err(10));
 assert_eq!(some_var.load(Ordering::Relaxed), 10);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable_cxchg]
                 #[$cfg_cas]
@@ -1573,7 +1610,9 @@ loop {
         Err(x) => old = x,
     }
 }
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable_cxchg]
                 #[$cfg_cas]
@@ -1612,7 +1651,9 @@ using [`Release`] makes the load part [`Relaxed`].
 let foo = ", stringify!($atomic_type), "::new(0);
 assert_eq!(foo.fetch_add(10, Ordering::SeqCst), 0);
 assert_eq!(foo.load(Ordering::SeqCst), 10);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable]
                 #[$cfg_cas]
@@ -1645,7 +1686,9 @@ using [`Release`] makes the load part [`Relaxed`].
 let foo = ", stringify!($atomic_type), "::new(20);
 assert_eq!(foo.fetch_sub(10, Ordering::SeqCst), 20);
 assert_eq!(foo.load(Ordering::SeqCst), 10);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable]
                 #[$cfg_cas]
@@ -1681,7 +1724,9 @@ using [`Release`] makes the load part [`Relaxed`].
 let foo = ", stringify!($atomic_type), "::new(0b101101);
 assert_eq!(foo.fetch_and(0b110011, Ordering::SeqCst), 0b101101);
 assert_eq!(foo.load(Ordering::SeqCst), 0b100001);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable]
                 #[$cfg_cas]
@@ -1718,7 +1763,9 @@ use std::sync::atomic::{", stringify!($atomic_type), ", Ordering};
 let foo = ", stringify!($atomic_type), "::new(0x13);
 assert_eq!(foo.fetch_nand(0x31, Ordering::SeqCst), 0x13);
 assert_eq!(foo.load(Ordering::SeqCst), !(0x13 & 0x31));
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable_nand]
                 #[$cfg_cas]
@@ -1754,7 +1801,9 @@ using [`Release`] makes the load part [`Relaxed`].
 let foo = ", stringify!($atomic_type), "::new(0b101101);
 assert_eq!(foo.fetch_or(0b110011, Ordering::SeqCst), 0b101101);
 assert_eq!(foo.load(Ordering::SeqCst), 0b111111);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable]
                 #[$cfg_cas]
@@ -1790,7 +1839,9 @@ using [`Release`] makes the load part [`Relaxed`].
 let foo = ", stringify!($atomic_type), "::new(0b101101);
 assert_eq!(foo.fetch_xor(0b110011, Ordering::SeqCst), 0b101101);
 assert_eq!(foo.load(Ordering::SeqCst), 0b011110);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[$stable]
                 #[$cfg_cas]
@@ -1837,7 +1888,9 @@ assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |_| None), Err(7))
 assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |x| Some(x + 1)), Ok(7));
 assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |x| Some(x + 1)), Ok(8));
 assert_eq!(x.load(Ordering::SeqCst), 9);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[stable(feature = "no_more_cas", since = "1.45.0")]
                 #[$cfg_cas]
@@ -1894,7 +1947,9 @@ let foo = ", stringify!($atomic_type), "::new(23);
 let bar = 42;
 let max_foo = foo.fetch_max(bar, Ordering::SeqCst).max(bar);
 assert!(max_foo == 42);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[stable(feature = "atomic_min_max", since = "1.45.0")]
                 #[$cfg_cas]
@@ -1943,7 +1998,9 @@ let foo = ", stringify!($atomic_type), "::new(23);
 let bar = 12;
 let min_foo = foo.fetch_min(bar, Ordering::SeqCst).min(bar);
 assert_eq!(min_foo, 12);
-```"),
+```
+
+**Note**: This method may not be available on some platforms."),
                 #[inline]
                 #[stable(feature = "atomic_min_max", since = "1.45.0")]
                 #[$cfg_cas]