Shrink arenas after building ItemTree

crates/ra_arena/src/lib.rs

@@ -116,6 +116,9 @@ pub fn iter(
     ) -> impl Iterator<Item = (Idx<T>, &T)> + ExactSizeIterator + DoubleEndedIterator {
         self.data.iter().enumerate().map(|(idx, value)| (Idx::from_raw(RawId(idx as u32)), value))
     }
+    pub fn shrink_to_fit(&mut self) {
+        self.data.shrink_to_fit();
+    }
 }
 
 impl<T> Default for Arena<T> {

crates/ra_hir_def/src/item_tree.rs

@@ -184,6 +184,7 @@ pub fn item_tree_query(db: &dyn DefDatabase, file_id: HirFileId) -> Arc<ItemTree
         if let Some(attrs) = top_attrs {
             item_tree.attrs.insert(AttrOwner::TopLevel, attrs);
         }
+        item_tree.shrink_to_fit();
         Arc::new(item_tree)
     }
 
@@ -196,6 +197,51 @@ fn empty() -> Self {
         }
     }
 
+    fn shrink_to_fit(&mut self) {
+        if let Some(data) = &mut self.data {
+            let ItemTreeData {
+                imports,
+                extern_crates,
+                functions,
+                structs,
+                fields,
+                unions,
+                enums,
+                variants,
+                consts,
+                statics,
+                traits,
+                impls,
+                type_aliases,
+                mods,
+                macro_calls,
+                exprs,
+                vis,
+                generics,
+            } = &mut **data;
+
+            imports.shrink_to_fit();
+            extern_crates.shrink_to_fit();
+            functions.shrink_to_fit();
+            structs.shrink_to_fit();
+            fields.shrink_to_fit();
+            unions.shrink_to_fit();
+            enums.shrink_to_fit();
+            variants.shrink_to_fit();
+            consts.shrink_to_fit();
+            statics.shrink_to_fit();
+            traits.shrink_to_fit();
+            impls.shrink_to_fit();
+            type_aliases.shrink_to_fit();
+            mods.shrink_to_fit();
+            macro_calls.shrink_to_fit();
+            exprs.shrink_to_fit();
+
+            vis.arena.shrink_to_fit();
+            generics.arena.shrink_to_fit();
+        }
+    }
+
     /// Returns an iterator over all items located at the top level of the `HirFileId` this
     /// `ItemTree` was created from.
     pub fn top_level_items(&self) -> &[ModItem] {