Fix checking for empty set for getElementsByClassName

Because empty set with `.all(predicate)` will always return `true`, it
will result in always filtering wrong elements when the classes is empty
set.

Thus, we return earlier with `always_empty` HTMLCollection in the mpety
classes case so that we can avoid filtering on empty sets.

1 files changed, 6 insertions, 0 deletions

diff --git a/components/script/dom/htmlcollection.rs b/components/script/dom/htmlcollection.rs
index d5198b94986..f1eb1fdd706 100644
--- a/components/script/dom/htmlcollection.rs
+++ b/components/script/dom/htmlcollection.rs
@@ -252,11 +252,17 @@ impl HTMLCollection {
                 let case_sensitivity = document_from_node(elem)
                     .quirks_mode()
                     .classes_and_ids_case_sensitivity();
+
                 self.classes
                     .iter()
                     .all(|class| elem.has_class(class, case_sensitivity))
             }
         }
+
+        if classes.is_empty() {
+            return HTMLCollection::always_empty(window, root);
+        }
+
         let filter = ClassNameFilter { classes: classes };
         HTMLCollection::create(window, root, Box::new(filter))
     }