2 files changed, 79 insertions, 54 deletions

diff --git a/crates/ra_arena/src/lib.rs b/crates/ra_arena/src/lib.rs
index fc0f7c12f..ea98d5444 100644
--- a/crates/ra_arena/src/lib.rs
+++ b/crates/ra_arena/src/lib.rs
@@ -2,6 +2,7 @@
 
 use std::{
     fmt,
+    hash::{Hash, Hasher},
     iter::FromIterator,
     marker::PhantomData,
     ops::{Index, IndexMut},
@@ -36,86 +37,110 @@ impl fmt::Display for RawId {
     }
 }
 
-#[derive(Clone, PartialEq, Eq)]
-pub struct Arena<ID, T> {
-    data: Vec<T>,
-    _ty: PhantomData<ID>,
+pub struct Idx<T> {
+    raw: RawId,
+    _ty: PhantomData<fn() -> T>,
 }
 
-impl<ID: ArenaId, T: fmt::Debug> fmt::Debug for Arena<ID, T> {
-    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        fmt.debug_struct("Arena").field("len", &self.len()).field("data", &self.data).finish()
+impl<T> Clone for Idx<T> {
+    fn clone(&self) -> Self {
+        *self
     }
 }
+impl<T> Copy for Idx<T> {}
 
-#[macro_export]
-macro_rules! impl_arena_id {
-    ($name:ident) => {
-        impl $crate::ArenaId for $name {
-            fn from_raw(raw: $crate::RawId) -> Self {
-                $name(raw)
-            }
-            fn into_raw(self) -> $crate::RawId {
-                self.0
-            }
+impl<T> PartialEq for Idx<T> {
+    fn eq(&self, other: &Idx<T>) -> bool {
+        self.raw == other.raw
+    }
+}
+impl<T> Eq for Idx<T> {}
+
+impl<T> Hash for Idx<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.raw.hash(state)
+    }
+}
+
+impl<T> fmt::Debug for Idx<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut type_name = std::any::type_name::<T>();
+        if let Some(idx) = type_name.rfind(':') {
+            type_name = &type_name[idx + 1..]
         }
-    };
+        write!(f, "Idx::<{}>({})", type_name, self.raw)
+    }
 }
 
-pub trait ArenaId {
-    fn from_raw(raw: RawId) -> Self;
-    fn into_raw(self) -> RawId;
+impl<T> Idx<T> {
+    pub fn from_raw(raw: RawId) -> Self {
+        Idx { raw, _ty: PhantomData }
+    }
+    pub fn into_raw(self) -> RawId {
+        self.raw
+    }
+}
+
+#[derive(Clone, PartialEq, Eq)]
+pub struct Arena<T> {
+    data: Vec<T>,
 }
 
-impl<ID, T> Arena<ID, T> {
-    pub const fn new() -> Arena<ID, T> {
-        Arena { data: Vec::new(), _ty: PhantomData }
+impl<T: fmt::Debug> fmt::Debug for Arena<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt.debug_struct("Arena").field("len", &self.len()).field("data", &self.data).finish()
     }
 }
 
-impl<ID: ArenaId, T> Arena<ID, T> {
+impl<T> Arena<T> {
+    pub const fn new() -> Arena<T> {
+        Arena { data: Vec::new() }
+    }
+
     pub fn len(&self) -> usize {
         self.data.len()
     }
     pub fn is_empty(&self) -> bool {
         self.data.is_empty()
     }
-    pub fn alloc(&mut self, value: T) -> ID {
+    pub fn alloc(&mut self, value: T) -> Idx<T> {
         let id = RawId(self.data.len() as u32);
         self.data.push(value);
-        ID::from_raw(id)
+        Idx::from_raw(id)
     }
-    pub fn iter(&self) -> impl Iterator<Item = (ID, &T)> + ExactSizeIterator + DoubleEndedIterator {
-        self.data.iter().enumerate().map(|(idx, value)| (ID::from_raw(RawId(idx as u32)), value))
+    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))
     }
 }
 
-impl<ID: ArenaId, T> Default for Arena<ID, T> {
-    fn default() -> Arena<ID, T> {
-        Arena { data: Vec::new(), _ty: PhantomData }
+impl<T> Default for Arena<T> {
+    fn default() -> Arena<T> {
+        Arena { data: Vec::new() }
     }
 }
 
-impl<ID: ArenaId, T> Index<ID> for Arena<ID, T> {
+impl<T> Index<Idx<T>> for Arena<T> {
     type Output = T;
-    fn index(&self, idx: ID) -> &T {
+    fn index(&self, idx: Idx<T>) -> &T {
         let idx = idx.into_raw().0 as usize;
         &self.data[idx]
     }
 }
 
-impl<ID: ArenaId, T> IndexMut<ID> for Arena<ID, T> {
-    fn index_mut(&mut self, idx: ID) -> &mut T {
+impl<T> IndexMut<Idx<T>> for Arena<T> {
+    fn index_mut(&mut self, idx: Idx<T>) -> &mut T {
         let idx = idx.into_raw().0 as usize;
         &mut self.data[idx]
     }
 }
 
-impl<ID: ArenaId, T> FromIterator<T> for Arena<ID, T> {
+impl<T> FromIterator<T> for Arena<T> {
     fn from_iter<I>(iter: I) -> Self
     where
         I: IntoIterator<Item = T>,
     {
-        Arena { data: Vec::from_iter(iter), _ty: PhantomData }
+        Arena { data: Vec::from_iter(iter) }
     }
 }
diff --git a/crates/ra_arena/src/map.rs b/crates/ra_arena/src/map.rs
index b73d4e365..5e764113d 100644
--- a/crates/ra_arena/src/map.rs
+++ b/crates/ra_arena/src/map.rs
@@ -2,17 +2,17 @@
 
 use std::marker::PhantomData;
 
-use super::ArenaId;
+use crate::Idx;
 
 /// A map from arena IDs to some other type. Space requirement is O(highest ID).
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct ArenaMap<ID, T> {
-    v: Vec<Option<T>>,
+pub struct ArenaMap<ID, V> {
+    v: Vec<Option<V>>,
     _ty: PhantomData<ID>,
 }
 
-impl<ID: ArenaId, T> ArenaMap<ID, T> {
-    pub fn insert(&mut self, id: ID, t: T) {
+impl<T, V> ArenaMap<Idx<T>, V> {
+    pub fn insert(&mut self, id: Idx<T>, t: V) {
         let idx = Self::to_idx(id);
         if self.v.capacity() <= idx {
             self.v.reserve(idx + 1 - self.v.capacity());
@@ -25,43 +25,43 @@ impl<ID: ArenaId, T> ArenaMap<ID, T> {
         self.v[idx] = Some(t);
     }
 
-    pub fn get(&self, id: ID) -> Option<&T> {
+    pub fn get(&self, id: Idx<T>) -> Option<&V> {
         self.v.get(Self::to_idx(id)).and_then(|it| it.as_ref())
     }
 
-    pub fn get_mut(&mut self, id: ID) -> Option<&mut T> {
+    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())
     }
 
-    pub fn values(&self) -> impl Iterator<Item = &T> {
+    pub fn values(&self) -> impl Iterator<Item = &V> {
         self.v.iter().filter_map(|o| o.as_ref())
     }
 
-    pub fn values_mut(&mut self) -> impl Iterator<Item = &mut T> {
+    pub fn values_mut(&mut self) -> impl Iterator<Item = &mut V> {
         self.v.iter_mut().filter_map(|o| o.as_mut())
     }
 
-    pub fn iter(&self) -> impl Iterator<Item = (ID, &T)> {
+    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()?)))
     }
 
-    fn to_idx(id: ID) -> usize {
+    fn to_idx(id: Idx<T>) -> usize {
         u32::from(id.into_raw()) as usize
     }
 
-    fn from_idx(idx: usize) -> ID {
-        ID::from_raw((idx as u32).into())
+    fn from_idx(idx: usize) -> Idx<T> {
+        Idx::from_raw((idx as u32).into())
     }
 }
 
-impl<ID: ArenaId, T> std::ops::Index<ID> for ArenaMap<ID, T> {
+impl<T, V> std::ops::Index<Idx<V>> for ArenaMap<Idx<V>, T> {
     type Output = T;
-    fn index(&self, id: ID) -> &T {
+    fn index(&self, id: Idx<V>) -> &T {
         self.v[Self::to_idx(id)].as_ref().unwrap()
     }
 }
 
-impl<ID, T> Default for ArenaMap<ID, T> {
+impl<T, V> Default for ArenaMap<Idx<V>, T> {
     fn default() -> Self {
         ArenaMap { v: Vec::new(), _ty: PhantomData }
     }