perf: Cache commit counts

Author: epage

src/git/repo.rs

@@ -124,6 +124,7 @@ pub struct GitRepo {
     commits: std::cell::RefCell<std::collections::HashMap<git2::Oid, std::rc::Rc<Commit>>>,
     interned_strings: std::cell::RefCell<std::collections::HashSet<std::rc::Rc<str>>>,
     bases: std::cell::RefCell<std::collections::HashMap<(git2::Oid, git2::Oid), Option<git2::Oid>>>,
+    counts: std::cell::RefCell<std::collections::HashMap<(git2::Oid, git2::Oid), Option<usize>>>,
 }
 
 impl GitRepo {
@@ -135,6 +136,7 @@ impl GitRepo {
             commits: Default::default(),
             interned_strings: Default::default(),
             bases: Default::default(),
+            counts: Default::default(),
         }
     }
 
@@ -289,6 +291,14 @@ impl GitRepo {
             return Some(0);
         }
 
+        *self
+            .counts
+            .borrow_mut()
+            .entry((base_id, head_id))
+            .or_insert_with(|| self.commit_count_raw(base_id, head_id))
+    }
+
+    fn commit_count_raw(&self, base_id: git2::Oid, head_id: git2::Oid) -> Option<usize> {
         let merge_base_id = self.merge_base(base_id, head_id)?;
         if merge_base_id != base_id {
             return None;