Make note about traits that can be derived

in their API docs

Fixes #29711

src/libcore/clone.rs

@@ -24,6 +24,8 @@
 use marker::Sized;
 
 /// A common trait for cloning an object.
+///
+/// This trait can be used with `#[derive]`.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait Clone : Sized {
     /// Returns a copy of the value.

src/libcore/cmp.rs

@@ -43,6 +43,8 @@
 /// in terms of it by default. Any manual implementation of `ne` *must* respect
 /// the rule that `eq` is a strict inverse of `ne`; that is, `!(a == b)` if and
 /// only if `a != b`.
+///
+/// This trait can be used with `#[derive]`.
 #[lang = "eq"]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait PartialEq<Rhs: ?Sized = Self> {
@@ -69,6 +71,8 @@ fn ne(&self, other: &Rhs) -> bool { !self.eq(other) }
 ///
 /// This property cannot be checked by the compiler, and therefore `Eq` implies
 /// `PartialEq`, and has no extra methods.
+///
+/// This trait can be used with `#[derive]`.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait Eq: PartialEq<Self> {
     // FIXME #13101: this method is used solely by #[deriving] to
@@ -171,6 +175,8 @@ pub fn reverse(self) -> Ordering {
 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
 ///
 /// When this trait is `derive`d, it produces a lexicographic ordering.
+///
+/// This trait can be used with `#[derive]`.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait Ord: Eq + PartialOrd<Self> {
     /// This method returns an `Ordering` between `self` and `other`.
@@ -227,6 +233,8 @@ fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> {
 /// However it remains possible to implement the others separately for types which do not have a
 /// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 ==
 /// false` (cf. IEEE 754-2008 section 5.11).
+///
+/// This trait can be used with `#[derive]`.
 #[lang = "ord"]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {

src/libcore/fmt/mod.rs

@@ -300,6 +300,8 @@ fn fmt(&self, fmt: &mut Formatter) -> Result {
 ///
 /// [module]: ../../std/fmt/index.html
 ///
+/// This trait can be used with `#[derive]`.
+///
 /// # Examples
 ///
 /// Deriving an implementation:

src/libcore/hash/mod.rs

@@ -93,6 +93,8 @@
 ///
 /// In other words, if two keys are equal, their hashes should also be equal.
 /// `HashMap` and `HashSet` both rely on this behavior.
+///
+/// This trait can be used with `#[derive]`.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait Hash {
     /// Feeds this value into the state given, updating the hasher as necessary.

src/libcore/marker.rs

@@ -165,6 +165,10 @@ pub trait Unsize<T: ?Sized> {
 /// to consider though: if you think your type may _not_ be able to implement `Copy` in the future,
 /// then it might be prudent to not implement `Copy`. This is because removing `Copy` is a breaking
 /// change: that second example would fail to compile if we made `Foo` non-`Copy`.
+///
+/// # Derivable
+///
+/// This trait can be used with `#[derive]`.
 #[stable(feature = "rust1", since = "1.0.0")]
 #[lang = "copy"]
 pub trait Copy : Clone {