style: Share code to parse @import layer + supports()

The duplication was slightly annoying me :)

Differential Revision: https://phabricator.services.mozilla.com/D176564

components/style/stylesheets/import_rule.rs

@@ -7,14 +7,17 @@
 //! [import]: https://drafts.csswg.org/css-cascade-3/#at-import
 
 use crate::media_queries::MediaList;
-use crate::shared_lock::{DeepCloneParams, DeepCloneWithLock};
+use crate::parser::{Parse, ParserContext};
-use crate::shared_lock::{SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
+use crate::shared_lock::{
+    DeepCloneParams, DeepCloneWithLock, SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard,
+};
 use crate::str::CssStringWriter;
-use crate::stylesheets::supports_rule::SupportsCondition;
+use crate::stylesheets::{
-use crate::stylesheets::layer_rule::LayerName;
+    layer_rule::LayerName, stylesheet::Namespaces, supports_rule::SupportsCondition, CssRule,
-use crate::stylesheets::{CssRule, StylesheetInDocument};
+    CssRuleType, StylesheetInDocument,
+};
 use crate::values::CssUrl;
-use cssparser::SourceLocation;
+use cssparser::{Parser, SourceLocation};
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
 use to_shmem::{self, SharedMemoryBuilder, ToShmem};
@@ -62,8 +65,7 @@ impl ImportSheet {
                 }
                 Some(s)
             },
-            ImportSheet::Refused |
+            ImportSheet::Refused | ImportSheet::Pending => None,
-            ImportSheet::Pending => None,
         }
     }
 
@@ -181,7 +183,7 @@ pub struct ImportSupportsCondition {
     pub condition: SupportsCondition,
 
     /// If the import is enabled, from the result of the import condition.
-    pub enabled: bool
+    pub enabled: bool,
 }
 
 impl ToCss for ImportLayer {
@@ -223,6 +225,54 @@ pub struct ImportRule {
     pub source_location: SourceLocation,
 }
 
+impl ImportRule {
+    /// Parses the layer() / layer / supports() part of the import header, as per
+    /// https://drafts.csswg.org/css-cascade-5/#at-import:
+    ///
+    ///     [ layer | layer(<layer-name>) ]?
+    ///     [ supports([ <supports-condition> | <declaration> ]) ]?
+    ///
+    /// We do this here so that the import preloader can look at this without having to parse the
+    /// whole import rule or parse the media query list or what not.
+    pub fn parse_layer_and_supports<'i, 't>(
+        input: &mut Parser<'i, 't>,
+        context: &ParserContext,
+        namespaces: &Namespaces,
+    ) -> (Option<ImportLayer>, Option<ImportSupportsCondition>) {
+        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(context, input))
+                        .map(|name| ImportLayer { name: Some(name) })
+                })
+                .ok()
+        };
+
+        let supports = if !static_prefs::pref!("layout.css.import-supports.enabled") {
+            None
+        } else {
+            input
+                .try_parse(SupportsCondition::parse_for_import)
+                .map(|condition| {
+                    let eval_context =
+                        ParserContext::new_with_rule_type(context, CssRuleType::Style, namespaces);
+                    let enabled = condition.eval(&eval_context, namespaces);
+                    ImportSupportsCondition { condition, enabled }
+                })
+                .ok()
+        };
+
+        (layer, supports)
+    }
+}
+
 impl ToShmem for ImportRule {
     fn to_shmem(&self, _builder: &mut SharedMemoryBuilder) -> to_shmem::Result<Self> {
         Err(String::from(

components/style/stylesheets/rule_parser.rs

@@ -16,7 +16,7 @@ use crate::str::starts_with_ignore_ascii_case;
 use crate::stylesheets::container_rule::{ContainerCondition, ContainerRule};
 use crate::stylesheets::document_rule::DocumentCondition;
 use crate::stylesheets::font_feature_values_rule::parse_family_name_list;
-use crate::stylesheets::import_rule::{ImportLayer, ImportSupportsCondition};
+use crate::stylesheets::import_rule::{ImportRule, ImportLayer, ImportSupportsCondition};
 use crate::stylesheets::keyframes_rule::parse_keyframe_list;
 use crate::stylesheets::layer_rule::{LayerBlockRule, LayerName, LayerStatementRule};
 use crate::stylesheets::stylesheet::Namespaces;
@@ -241,43 +241,7 @@ 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() {
+                let (layer, supports) = ImportRule::parse_layer_and_supports(input, &self.context, self.namespaces);
-                    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()
-                };
-
-                #[cfg(feature = "gecko")]
-                let supports_enabled = static_prefs::pref!("layout.css.import-supports.enabled");
-                #[cfg(feature = "servo")]
-                let supports_enabled = false;
-
-                let supports = if !supports_enabled {
-                    None
-                } else {
-                    input.try_parse(SupportsCondition::parse_for_import).map(|condition| {
-                        let eval_context = ParserContext::new_with_rule_type(
-                            &self.context,
-                            CssRuleType::Style,
-                            self.namespaces,
-                        );
-
-                        let enabled = condition.eval(&eval_context, self.namespaces);
-                        ImportSupportsCondition {
-                            condition,
-                            enabled
-                        }
-                    }).ok()
-                };
 
                 let media = MediaList::parse(&self.context, input);
                 let media = Arc::new(self.shared_lock.wrap(media));