index: fix check for adding existing commit to index

The check for adding an existing commit to the index only checked if
the commit was already in the `MutableIndex`, not if it was already in
the parent `ReadonlyIndex`.

lib/src/index.rs

@@ -384,7 +384,7 @@ impl MutableIndex {
     }
 
     fn add_commit_data(&mut self, id: CommitId, parent_ids: Vec<CommitId>) {
-        if self.lookup.contains_key(&id) {
+        if self.has_id(&id) {
             return;
         }
         let mut entry = MutableGraphEntry {
@@ -1182,8 +1182,7 @@ impl ReadonlyIndex {
             }
             Some(parent_op_id) => {
                 let parent_file = Arc::new(
-                    ReadonlyIndex::load_at_operation(dir.clone(), hash_length, &parent_op_id)
-                        .unwrap(),
+                    ReadonlyIndex::load_at_operation(dir.clone(), hash_length, &parent_op_id).unwrap(),
                 );
                 maybe_parent_file = Some(parent_file.clone());
                 data = MutableIndex::incremental(parent_file)

lib/tests/test_index.rs

@@ -394,3 +394,29 @@ fn test_index_commits_incremental_empty_transaction(use_git: bool) {
     assert_eq!(generation_number(index.clone(), root_commit.id()), 0);
     assert_eq!(generation_number(index.clone(), commit_a.id()), 1);
 }
+
+#[test_case(false ; "local store")]
+#[test_case(true ; "git store")]
+fn test_index_commits_incremental_already_indexed(use_git: bool) {
+    // Tests that trying to add a commit that's already been added is a no-op.
+    let settings = testutils::user_settings();
+    let (_temp_dir, mut repo) = testutils::init_repo(&settings, use_git);
+
+    // Create A in one operation, then try to add it again an new transaction.
+    // o A
+    // | o working copy
+    // |/
+    // o root
+
+    let root_commit = repo.store().root_commit();
+    let commit_a =
+        child_commit(&settings, &repo, &root_commit).write_to_new_transaction(&repo, "test");
+    Arc::get_mut(&mut repo).unwrap().reload();
+
+    assert!(repo.index().has_id(commit_a.id()));
+    assert_eq!(repo.index().num_commits(), 2 + 1);
+    let mut tx = repo.start_transaction("test");
+    tx.add_head(&commit_a);
+    assert_eq!(tx.index().num_commits(), 2 + 1);
+    tx.discard();
+}