style: document the sink module.

components/style/sink.rs

@@ -2,10 +2,20 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+//! Small helpers to abstract over different containers.
+#![deny(missing_docs)]
+
 use smallvec::{Array, SmallVec};
 use std::marker::PhantomData;
 
+/// A trait to abstract over a `push` method that may be implemented for
+/// different kind of types.
+///
+/// Used to abstract over `Array`, `SmallVec` and `Vec`, and also to implement a
+/// type which `push` method does only tweak a byte when we only need to check
+/// for the presence of something.
 pub trait Push<T> {
+    /// Push a value into self.
     fn push(&mut self, value: T);
 }
 
@@ -21,13 +31,16 @@ impl<A: Array> Push<A::Item> for SmallVec<A> {
     }
 }
 
+/// A struct that implements `Push`, but only stores whether it's empty.
 pub struct ForgetfulSink<T>(bool, PhantomData<T>);
 
 impl<T> ForgetfulSink<T> {
+    /// Trivially construct a new `ForgetfulSink`.
     pub fn new() -> Self {
         ForgetfulSink(true, PhantomData)
     }
 
+    /// Whether this sink is empty or not.
     pub fn is_empty(&self) -> bool {
         self.0
     }