Fix jj-vcs#2476, change ids

lib/src/id_prefix.rs

@@ -168,13 +168,14 @@ impl IdPrefixContext {
         prefix: &HexPrefix,
     ) -> PrefixResolution<Vec<CommitId>> {
         if let Some(indexes) = self.disambiguation_indexes(repo) {
-            let resolution = indexes.change_index.resolve_prefix_with(
-                &*indexes.commit_change_ids,
-                prefix,
-                |(commit_id, _)| commit_id.clone(),
-            );
-            if let PrefixResolution::SingleMatch((_, ids)) = resolution {
-                return PrefixResolution::SingleMatch(ids);
+            let resolution = indexes
+                .change_index
+                .resolve_prefix_to_key(&*indexes.commit_change_ids, prefix);
+            if let PrefixResolution::SingleMatch(change_id) = resolution {
+                // There may be more commits with this change id outside the narrower sets.
+                return PrefixResolution::SingleMatch(repo.resolve_change_id(&change_id).expect(
+                    "Change ids present in narrower search set should be present globally.",
+                ));
             }
         }
         repo.resolve_change_id_prefix(prefix)

lib/tests/test_id_prefix.rs

@@ -377,10 +377,13 @@ fn test_id_prefix_divergent() {
         SingleMatch(vec![first_commit.id().clone()])
     );
     // Short prefix does not find the first commit. (This is correct)
-    // TODO(#2476): Looking up the divergent commits by their change id prefix only
-    // finds the id within the lookup set.
+    // We find both commits with this change ids, even though
+    // `third_commit_divergent_with_second` is not in the short prefix set (#2476).
     assert_eq!(
         c.resolve_change_prefix(repo.as_ref(), &prefix("7")),
-        SingleMatch(vec![second_commit.id().clone()])
+        SingleMatch(vec![
+            second_commit.id().clone(),
+            third_commit_divergent_with_second.id().clone()
+        ])
     );
 }