servo: Merge #18158 - style: Skip state pseudo-classes when finding a pseudo-element (from emilio:pseudo-crash); r=heycam

Bug: 1391577
Reviewed-by: heycam
MozReview-Commit-ID: 1ICBijtcf2b
Source-Repo: https://github.com/servo/servo
Source-Revision: 4f3fb904ae6863aa86bb3c8b7abee5533478af13

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 7158d74b7fcc082a2086e639df09b0bf83175977

servo/components/style/invalidation/element/invalidator.rs

@@ -595,14 +595,27 @@ impl<'a, 'b: 'a, E> TreeStyleInvalidator<'a, 'b, E>
                 matched = true;
 
                 if matches!(next_combinator, Combinator::PseudoElement) {
+                    // This will usually be the very next component, except for
+                    // the fact that we store compound selectors the other way
+                    // around, so there could also be state pseudo-classes.
                     let pseudo_selector =
                         invalidation.selector
                             .iter_raw_parse_order_from(next_combinator_offset - 1)
+                            .skip_while(|c| matches!(**c, Component::NonTSPseudoClass(..)))
                             .next()
                             .unwrap();
+
                     let pseudo = match *pseudo_selector {
                         Component::PseudoElement(ref pseudo) => pseudo,
-                        _ => unreachable!("Someone seriously messed up selector parsing"),
+                        _ => {
+                            unreachable!(
+                                "Someone seriously messed up selector parsing: \
+                                {:?} at offset {:?}: {:?}",
+                                invalidation.selector,
+                                next_combinator_offset,
+                                pseudo_selector,
+                            )
+                        }
                     };
 
                     // FIXME(emilio): This is not ideal, and could not be