servo: Merge #15941 - style: Fix media query parsing when invalid queries are present (from emilio:media); r=heycam

Fixes [bug 1347273](https://bugzil.la/1347273).

Source-Repo: https://github.com/servo/servo
Source-Revision: 304cafe57d45921e460ff408ae18138f4eca10df

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 8afc7ff724ff4f89d1f6d17ca27f74d09fafc1fd

servo/components/style/media_queries.rs

@@ -243,19 +243,13 @@ pub fn parse_media_query_list(input: &mut Parser) -> MediaList {
     }
 
     let mut media_queries = vec![];
-    let mut found_invalid = false;
     loop {
         match input.parse_until_before(Delimiter::Comma, MediaQuery::parse) {
-            Ok(mq) => if !found_invalid {
+            Ok(mq) => {
                 media_queries.push(mq);
             },
-            Err(..) => if !found_invalid {
-                media_queries.clear();
+            Err(..) => {
                 media_queries.push(MediaQuery::never_matching());
-                // Consume the rest of the input as if they were valid
-                // expressions (they might be, they might not), but ignore the
-                // result, this allows correctly parsing invalid media queries.
-                found_invalid = true;
             },
         }
 
@@ -266,8 +260,6 @@ pub fn parse_media_query_list(input: &mut Parser) -> MediaList {
         }
     }
 
-    debug_assert!(!found_invalid || media_queries.len() == 1);
-
     MediaList {
         media_queries: media_queries,
     }

servo/tests/unit/style/media_queries.rs

@@ -321,11 +321,12 @@ fn test_mq_multiple_expressions() {
 #[test]
 fn test_mq_malformed_expressions() {
     fn check_malformed_expr(list: &MediaList, css: &str) {
-        assert!(list.media_queries.len() == 1, css.to_owned());
-        let q = &list.media_queries[0];
-        assert!(q.qualifier == Some(Qualifier::Not), css.to_owned());
-        assert!(q.media_type == MediaQueryType::All, css.to_owned());
-        assert!(q.expressions.len() == 0, css.to_owned());
+        assert!(!list.media_queries.is_empty(), css.to_owned());
+        for mq in &list.media_queries {
+            assert!(mq.qualifier == Some(Qualifier::Not), css.to_owned());
+            assert!(mq.media_type == MediaQueryType::All, css.to_owned());
+            assert!(mq.expressions.is_empty(), css.to_owned());
+        }
     }
 
     for rule in &[
@@ -335,8 +336,6 @@ fn test_mq_malformed_expressions() {
         "@media not {}",
         "@media not (min-width: 300px) {}",
         "@media , {}",
-        "@media screen 4px, print {}",
-        "@media screen, {}",
     ] {
         test_media_rule(rule, check_malformed_expr);
     }