3 files changed, 85 insertions, 4 deletions

diff --git a/lib/arena/Cargo.toml b/lib/arena/Cargo.toml
index 183a5bb6a..d47366b0b 100644
--- a/lib/arena/Cargo.toml
+++ b/lib/arena/Cargo.toml
@@ -5,6 +5,3 @@ description = "Thy rope of sands..."
 license = "MIT OR Apache-2.0"
 authors = ["rust-analyzer developers"]
 edition = "2018"
-
-[lib]
-doctest = false
diff --git a/lib/arena/src/lib.rs b/lib/arena/src/lib.rs
index 3169aa5b8..78a147c7d 100644
--- a/lib/arena/src/lib.rs
+++ b/lib/arena/src/lib.rs
@@ -1,4 +1,6 @@
-//! Yet another index-based arena.
+//! Yet another ID-based arena.
+
+#![warn(missing_docs)]
 
 use std::{
     fmt,
@@ -10,6 +12,7 @@ use std::{
 
 pub mod map;
 
+/// The raw ID of a value in an arena.
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct RawId(u32);
 
@@ -37,6 +40,7 @@ impl fmt::Display for RawId {
     }
 }
 
+/// The ID of a value allocated in an arena that holds `T`s.
 pub struct Idx<T> {
     raw: RawId,
     _ty: PhantomData<fn() -> T>,
@@ -73,14 +77,18 @@ impl<T> fmt::Debug for Idx<T> {
 }
 
 impl<T> Idx<T> {
+    /// Creates a new ID from a [`RawId`].
     pub fn from_raw(raw: RawId) -> Self {
         Idx { raw, _ty: PhantomData }
     }
+
+    /// Converts this ID into the underlying [`RawId`].
     pub fn into_raw(self) -> RawId {
         self.raw
     }
 }
 
+/// Yet another ID-based arena.
 #[derive(Clone, PartialEq, Eq)]
 pub struct Arena<T> {
     data: Vec<T>,
@@ -93,29 +101,99 @@ impl<T: fmt::Debug> fmt::Debug for Arena<T> {
 }
 
 impl<T> Arena<T> {
+    /// Creates a new empty arena.
+    ///
+    /// ```
+    /// let arena: la_arena::Arena<i32> = la_arena::Arena::new();
+    /// assert!(arena.is_empty());
+    /// ```
     pub const fn new() -> Arena<T> {
         Arena { data: Vec::new() }
     }
+
+    /// Empties the arena, removing all contained values.
+    ///
+    /// ```
+    /// let mut arena = la_arena::Arena::new();
+    ///
+    /// arena.alloc(1);
+    /// arena.alloc(2);
+    /// arena.alloc(3);
+    /// assert_eq!(arena.len(), 3);
+    ///
+    /// arena.clear();
+    /// assert!(arena.is_empty());
+    /// ```
     pub fn clear(&mut self) {
         self.data.clear();
     }
 
+    /// Returns the length of the arena.
+    ///
+    /// ```
+    /// let mut arena = la_arena::Arena::new();
+    /// assert_eq!(arena.len(), 0);
+    ///
+    /// arena.alloc("foo");
+    /// assert_eq!(arena.len(), 1);
+    ///
+    /// arena.alloc("bar");
+    /// assert_eq!(arena.len(), 2);
+    ///
+    /// arena.alloc("baz");
+    /// assert_eq!(arena.len(), 3);
+    /// ```
     pub fn len(&self) -> usize {
         self.data.len()
     }
+
+    /// Returns whether the arena contains no elements.
+    ///
+    /// ```
+    /// let mut arena = la_arena::Arena::new();
+    /// assert!(arena.is_empty());
+    ///
+    /// arena.alloc(0.5);
+    /// assert!(!arena.is_empty());
+    /// ```
     pub fn is_empty(&self) -> bool {
         self.data.is_empty()
     }
+
+    /// Allocates a new value on the arena, returning the value’s ID.
+    ///
+    /// ```
+    /// let mut arena = la_arena::Arena::new();
+    /// let id = arena.alloc(50);
+    ///
+    /// assert_eq!(arena[id], 50);
+    /// ```
     pub fn alloc(&mut self, value: T) -> Idx<T> {
         let id = RawId(self.data.len() as u32);
         self.data.push(value);
         Idx::from_raw(id)
     }
+
+    /// Returns an iterator over the arena’s elements.
+    ///
+    /// ```
+    /// let mut arena = la_arena::Arena::new();
+    /// let id1 = arena.alloc(20);
+    /// let id2 = arena.alloc(40);
+    /// let id3 = arena.alloc(60);
+    ///
+    /// let mut iterator = arena.iter();
+    /// assert_eq!(iterator.next(), Some((id1, &20)));
+    /// assert_eq!(iterator.next(), Some((id2, &40)));
+    /// assert_eq!(iterator.next(), Some((id3, &60)));
+    /// ```
     pub fn iter(
         &self,
     ) -> impl Iterator<Item = (Idx<T>, &T)> + ExactSizeIterator + DoubleEndedIterator {
         self.data.iter().enumerate().map(|(idx, value)| (Idx::from_raw(RawId(idx as u32)), value))
     }
+
+    /// Reallocates the arena to make it take up as little space as possible.
     pub fn shrink_to_fit(&mut self) {
         self.data.shrink_to_fit();
     }
diff --git a/lib/arena/src/map.rs b/lib/arena/src/map.rs
index 0f33907c0..980198247 100644
--- a/lib/arena/src/map.rs
+++ b/lib/arena/src/map.rs
@@ -12,6 +12,7 @@ pub struct ArenaMap<ID, V> {
 }
 
 impl<T, V> ArenaMap<Idx<T>, V> {
+    /// Inserts a value associated with a given arena ID into the map.
     pub fn insert(&mut self, id: Idx<T>, t: V) {
         let idx = Self::to_idx(id);
 
@@ -19,22 +20,27 @@ impl<T, V> ArenaMap<Idx<T>, V> {
         self.v[idx] = Some(t);
     }
 
+    /// Returns a reference to the value associated with the provided ID if it is present.
     pub fn get(&self, id: Idx<T>) -> Option<&V> {
         self.v.get(Self::to_idx(id)).and_then(|it| it.as_ref())
     }
 
+    /// Returns a mutable reference to the value associated with the provided ID if it is present.
     pub fn get_mut(&mut self, id: Idx<T>) -> Option<&mut V> {
         self.v.get_mut(Self::to_idx(id)).and_then(|it| it.as_mut())
     }
 
+    /// Returns an iterator over the values in the map.
     pub fn values(&self) -> impl Iterator<Item = &V> {
         self.v.iter().filter_map(|o| o.as_ref())
     }
 
+    /// Returns an iterator over mutable references to the values in the map.
     pub fn values_mut(&mut self) -> impl Iterator<Item = &mut V> {
         self.v.iter_mut().filter_map(|o| o.as_mut())
     }
 
+    /// Returns an iterator over the arena IDs and values in the map.
     pub fn iter(&self) -> impl Iterator<Item = (Idx<T>, &V)> {
         self.v.iter().enumerate().filter_map(|(idx, o)| Some((Self::from_idx(idx), o.as_ref()?)))
     }