Make rand dependency optional (but enabled by default)

Most users probably don't use the rand impls, so the `rand` crate pulls
a large number of dependencies into the dependency tree which is just
wasted compilation time.

Cargo.toml

@@ -17,6 +17,7 @@ keywords = ["gamedev", "math", "matrix", "vector", "quaternion"]
 name = "cgmath"
 
 [features]
+default = ["rand"]
 unstable = []
 swizzle = []
 
@@ -24,7 +25,7 @@ swizzle = []
 approx = "0.3"
 mint = { version = "0.5", optional = true }
 num-traits = "0.2"
-rand = "0.6"
+rand = { version = "0.6", optional = true }
 serde = { version = "1.0", features = ["serde_derive"], optional = true }
 simd = { version = "0.2", optional = true }
 

src/angle.rs

@@ -20,9 +20,11 @@ use std::f64;
 use std::iter;
 use std::ops::*;
 
-use rand::Rng;
+#[cfg(feature = "rand")]
-use rand::distributions::{Distribution, Standard};
+use rand::{
-use rand::distributions::uniform::SampleUniform;
+    Rng,
+    distributions::{Distribution, Standard, uniform::SampleUniform},
+};
 use num_traits::{cast, Bounded};
 
 use structure::*;
@@ -209,6 +211,7 @@ macro_rules! impl_angle {
             }
         }
 
+        #[cfg(feature = "rand")]
         impl<S> Distribution<$Angle<S>> for Standard
             where Standard: Distribution<S>,
                 S: BaseFloat + SampleUniform {

src/euler.rs

@@ -13,8 +13,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use rand::distributions::{Distribution, Standard};
+#[cfg(feature = "rand")]
-use rand::Rng;
+use rand::{
+    Rng,
+    distributions::{Distribution, Standard},
+};
 use num_traits::cast;
 
 use structure::*;
@@ -186,6 +189,7 @@ impl<A: Angle> approx::UlpsEq for Euler<A> {
     }
 }
 
+#[cfg(feature = "rand")]
 impl<A> Distribution<Euler<A>> for Standard
     where Standard: Distribution<A>,
         A: Angle {

src/lib.rs

@@ -58,6 +58,7 @@ extern crate approx;
 #[cfg(feature = "mint")]
 pub extern crate mint;
 
+#[cfg(feature = "rand")]
 extern crate rand;
 pub extern crate num_traits;
 

src/matrix.rs

@@ -13,8 +13,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use rand::distributions::{Standard, Distribution};
+#[cfg(feature = "rand")]
-use rand::Rng;
+use rand::{
+    Rng,
+    distributions::{Standard, Distribution},
+};
 use num_traits::{cast, NumCast};
 use std::fmt;
 use std::iter;
@@ -1536,6 +1539,7 @@ impl<S: fmt::Debug> fmt::Debug for Matrix4<S> {
     }
 }
 
+#[cfg(feature = "rand")]
 impl<S> Distribution<Matrix2<S>> for Standard
     where
         Standard: Distribution<Vector2<S>>,
@@ -1549,6 +1553,7 @@ impl<S> Distribution<Matrix2<S>> for Standard
     }
 }
 
+#[cfg(feature = "rand")]
 impl<S> Distribution<Matrix3<S>> for Standard
     where Standard: Distribution<Vector3<S>>,
         S: BaseFloat {
@@ -1562,6 +1567,7 @@ impl<S> Distribution<Matrix3<S>> for Standard
     }
 }
 
+#[cfg(feature = "rand")]
 impl<S> Distribution<Matrix4<S>> for Standard
     where Standard: Distribution<Vector4<S>>,
         S: BaseFloat {

src/quaternion.rs

@@ -17,8 +17,11 @@ use std::iter;
 use std::mem;
 use std::ops::*;
 
-use rand::distributions::{Distribution, Standard};
+#[cfg(feature = "rand")]
-use rand::Rng;
+use rand::{
+    Rng,
+    distributions::{Distribution, Standard},
+};
 use num_traits::{cast, NumCast};
 
 use structure::*;
@@ -870,6 +873,7 @@ index_operators!(S, [S], RangeTo<usize>);
 index_operators!(S, [S], RangeFrom<usize>);
 index_operators!(S, [S], RangeFull);
 
+#[cfg(feature = "rand")]
 impl<S> Distribution<Quaternion<S>> for Standard
     where Standard: Distribution<S>,
         Standard: Distribution<Vector3<S>>,

src/vector.rs

@@ -13,8 +13,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use rand::distributions::{Distribution, Standard};
+#[cfg(feature = "rand")]
-use rand::Rng;
+use rand::{
+    Rng,
+    distributions::{Distribution, Standard},
+};
 use num_traits::{Bounded, NumCast};
 use std::fmt;
 use std::iter;
@@ -245,6 +248,7 @@ macro_rules! impl_vector {
             }
         }
 
+        #[cfg(feature = "rand")]
         impl<S> Distribution<$VectorN<S>> for Standard
             where Standard: Distribution<S>,
                 S: BaseFloat {
@@ -502,6 +506,7 @@ macro_rules! impl_vector_default {
             }
         }
 
+        #[cfg(feature = "rand")]
         impl<S> Distribution<$VectorN<S>> for Standard
             where S: BaseFloat,
                 Standard: Distribution<S>  {