revset: for roots:heads, terminate ancestor lookup at min(roots)

lib/src/default_revset_engine.rs

@@ -825,9 +825,14 @@ impl<'index, 'heads> EvaluationContext<'index, 'heads> {
         S: InternalRevset<'a> + ?Sized,
         T: InternalRevset<'b> + ?Sized,
     {
-        let mut reachable: HashSet<_> = root_set.iter().map(|entry| entry.position()).collect();
+        let root_positions = root_set.iter().map(|entry| entry.position()).collect_vec();
+        let bottom_position = *root_positions.last().unwrap_or(&IndexPosition::MAX);
+        let mut reachable: HashSet<_> = root_positions.into_iter().collect();
         let mut index_entries = vec![];
-        let candidates = self.walk_ancestors(head_set).collect_vec();
+        let candidates = self
+            .walk_ancestors(head_set)
+            .take_while(|entry| entry.position() >= bottom_position)
+            .collect_vec();
         for candidate in candidates.into_iter().rev() {
             if reachable.contains(&candidate.position())
                 || candidate

lib/tests/test_revset.rs

@@ -976,6 +976,30 @@ fn test_evaluate_expression_dag_range(use_git: bool) {
         vec![]
     );
 
+    // Empty root
+    assert_eq!(
+        resolve_commit_ids(mut_repo, &format!("none():{}", commit5.id().hex())),
+        vec![],
+    );
+
+    // Multiple root, commit1 shouldn't be hidden by commit2
+    assert_eq!(
+        resolve_commit_ids(
+            mut_repo,
+            &format!(
+                "({}|{}):{}",
+                commit1.id().hex(),
+                commit2.id().hex(),
+                commit3.id().hex()
+            )
+        ),
+        vec![
+            commit3.id().clone(),
+            commit2.id().clone(),
+            commit1.id().clone()
+        ]
+    );
+
     // Including a merge
     assert_eq!(
         resolve_commit_ids(

testing/bench-revsets-git.txt

@@ -13,6 +13,7 @@ v2.40.0
 v2.39.0..v2.40.0
 :v2.40.0 ~ :v2.39.0
 v2.39.0:v2.40.0
+v2.40.0+
 # Tags and branches
 tags()
 branches()