rust-ancestors: duplicate loop that visits parents of revs/bases

As the inline comment says, it can't be cleanly implemented in Rust. It's
better to duplicate the code instead of inserting "if"s. The loop will be
cleaned up by future commits.

rust/hg-core/src/ancestors.rs

@@ -345,14 +345,6 b' impl<G: Graph> MissingAncestors<G> {'
             if revs_visit.remove(&curr) {
                 missing.push(curr);
                 this_visit_is_revs = true;
-            } else if bases_visit.contains(&curr) {
-                this_visit_is_revs = false;
-            } else {
-                // not an ancestor of revs or bases: ignore
-                continue;
-            }
-
-            {
                 for p in self.graph.parents(curr)?.iter().cloned() {
                     if p == NULL_REVISION {
                         continue;
@@ -378,6 +370,35 b' impl<G: Graph> MissingAncestors<G> {'
                         }
                     }
                 }
+            } else if bases_visit.contains(&curr) {
+                this_visit_is_revs = false;
+                for p in self.graph.parents(curr)?.iter().cloned() {
+                    if p == NULL_REVISION {
+                        continue;
+                    }
+                    let in_other_visit = if this_visit_is_revs {
+                        bases_visit.contains(&p)
+                    } else {
+                        revs_visit.contains(&p)
+                    };
+                    if in_other_visit || both_visit.contains(&p) {
+                        // p is implicitely in this_visit.
+                        // This means p is or should be in bothvisit
+                        // TODO optim: hence if bothvisit, we look up twice
+                        revs_visit.remove(&p);
+                        bases_visit.insert(p);
+                        both_visit.insert(p);
+                    } else {
+                        // visit later
+                        if this_visit_is_revs {
+                            revs_visit.insert(p);
+                        } else {
+                            bases_visit.insert(p);
+                        }
+                    }
+                }
+            } else {
+                // not an ancestor of revs or bases: ignore
             }
         }
         missing.reverse();