Bug 1829430 - Fix @import supports() parsing position r=emilio

Fixed @import supports() being parsed in the incorrect position as per spec.

Also added more WPT tests for layer and supports in one @import.

Differential Revision: https://phabricator.services.mozilla.com/D176193

servo/components/style/stylesheets/rule_parser.rs

@@ -241,6 +241,21 @@ impl<'a, 'i> AtRuleParser<'i> for TopLevelRuleParser<'a> {
                 let url_string = input.expect_url_or_string()?.as_ref().to_owned();
                 let url = CssUrl::parse_from_string(url_string, &self.context, CorsMode::None);
 
+                let layer = if input.try_parse(|input| input.expect_ident_matching("layer")).is_ok() {
+                    Some(ImportLayer {
+                        name: None,
+                    })
+                } else {
+                    input.try_parse(|input| {
+                        input.expect_function_matching("layer")?;
+                        input.parse_nested_block(|input| {
+                            LayerName::parse(&self.context, input)
+                        }).map(|name| ImportLayer {
+                            name: Some(name),
+                        })
+                    }).ok()
+                };
+
                 let supports = if !static_prefs::pref!("layout.css.import-supports.enabled") {
                     None
                 } else {
@@ -259,21 +274,6 @@ impl<'a, 'i> AtRuleParser<'i> for TopLevelRuleParser<'a> {
                     }).ok()
                 };
 
-                let layer = if input.try_parse(|input| input.expect_ident_matching("layer")).is_ok() {
-                    Some(ImportLayer {
-                        name: None,
-                    })
-                } else {
-                    input.try_parse(|input| {
-                        input.expect_function_matching("layer")?;
-                        input.parse_nested_block(|input| {
-                            LayerName::parse(&self.context, input)
-                        }).map(|name| ImportLayer {
-                            name: Some(name),
-                        })
-                    }).ok()
-                };
-
                 let media = MediaList::parse(&self.context, input);
                 let media = Arc::new(self.shared_lock.wrap(media));
 

testing/web-platform/tests/css/css-cascade/import-conditions.html

@@ -99,6 +99,14 @@
       importCondition: "supports(font-format(invalid))",
       matches: false
     },
+    {
+      importCondition: "layer(A.B) supports(font-format(opentype))",
+      matches: true
+    },
+    {
+      importCondition: "layer supports(selector(a))",
+      matches: true
+    },
   ];
   let target = document.getElementById("target");
   for (let testCase of testCases) {