1 files changed, 100 insertions, 0 deletions

diff --git a/crates/ra_db/src/loc2id.rs b/crates/ra_db/src/loc2id.rs
new file mode 100644
index 000000000..69ba43d0f
--- /dev/null
+++ b/crates/ra_db/src/loc2id.rs
@@ -0,0 +1,100 @@
+use parking_lot::Mutex;
+
+use std::hash::Hash;
+
+use rustc_hash::FxHashMap;
+
+/// There are two principle ways to refer to things:
+///   - by their locatinon (module in foo/bar/baz.rs at line 42)
+///   - by their numeric id (module `ModuleId(42)`)
+///
+/// The first one is more powerful (you can actually find the thing in question
+/// by id), but the second one is so much more compact.
+///
+/// `Loc2IdMap` allows us to have a cake an eat it as well: by maintaining a
+/// bidirectional mapping between positional and numeric ids, we can use compact
+/// representation wich still allows us to get the actual item
+#[derive(Debug)]
+struct Loc2IdMap<LOC, ID>
+where
+    ID: NumericId,
+    LOC: Clone + Eq + Hash,
+{
+    loc2id: FxHashMap<LOC, ID>,
+    id2loc: FxHashMap<ID, LOC>,
+}
+
+impl<LOC, ID> Default for Loc2IdMap<LOC, ID>
+where
+    ID: NumericId,
+    LOC: Clone + Eq + Hash,
+{
+    fn default() -> Self {
+        Loc2IdMap {
+            loc2id: FxHashMap::default(),
+            id2loc: FxHashMap::default(),
+        }
+    }
+}
+
+impl<LOC, ID> Loc2IdMap<LOC, ID>
+where
+    ID: NumericId,
+    LOC: Clone + Eq + Hash,
+{
+    pub fn loc2id(&mut self, loc: &LOC) -> ID {
+        match self.loc2id.get(loc) {
+            Some(id) => return id.clone(),
+            None => (),
+        }
+        let id = self.loc2id.len();
+        assert!(id < u32::max_value() as usize);
+        let id = ID::from_u32(id as u32);
+        self.loc2id.insert(loc.clone(), id.clone());
+        self.id2loc.insert(id.clone(), loc.clone());
+        id
+    }
+
+    pub fn id2loc(&self, id: ID) -> LOC {
+        self.id2loc[&id].clone()
+    }
+}
+
+pub trait NumericId: Clone + Eq + Hash {
+    fn from_u32(id: u32) -> Self;
+    fn to_u32(self) -> u32;
+}
+
+#[derive(Debug)]
+pub struct LocationIntener<LOC, ID>
+where
+    ID: NumericId,
+    LOC: Clone + Eq + Hash,
+{
+    map: Mutex<Loc2IdMap<LOC, ID>>,
+}
+
+impl<LOC, ID> Default for LocationIntener<LOC, ID>
+where
+    ID: NumericId,
+    LOC: Clone + Eq + Hash,
+{
+    fn default() -> Self {
+        LocationIntener {
+            map: Default::default(),
+        }
+    }
+}
+
+impl<LOC, ID> LocationIntener<LOC, ID>
+where
+    ID: NumericId,
+    LOC: Clone + Eq + Hash,
+{
+    pub fn loc2id(&self, loc: &LOC) -> ID {
+        self.map.lock().loc2id(loc)
+    }
+    pub fn id2loc(&self, id: ID) -> LOC {
+        self.map.lock().id2loc(id)
+    }
+}