style: Add some flags to the computed values.

This will allow us to fix propagation of text-decoration, and also to implement
inlinization of ruby kids.

Signed-off-by: Emilio Cobos Álvarez <emilio@crisal.io>

components/style/properties/computed_value_flags.rs

@@ -0,0 +1,45 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Misc information about a given computed style.
+
+use properties::{ComputedValues, StyleBuilder};
+
+bitflags! {
+    /// Misc information about a given computed style.
+    pub flags ComputedValueFlags: u8 {
+        /// Whether the style or any of the ancestors has a text-decoration
+        /// property that should get propagated to descendants.
+        ///
+        /// text-decoration is a reset property, but gets propagated in the
+        /// frame/box tree.
+        const HAS_TEXT_DECORATION_LINE = 1 << 0,
+    }
+}
+
+impl ComputedValueFlags {
+    /// Get the computed value flags for the initial style.
+    pub fn initial() -> Self {
+        Self::empty()
+    }
+
+    /// Compute the flags for this style, given the parent style.
+    pub fn compute(
+        this_style: &StyleBuilder,
+        parent_style: &ComputedValues,
+    ) -> Self {
+        let mut ret = Self::empty();
+
+        // FIXME(emilio): This feels like it wants to look at the
+        // layout_parent_style, but the way it works in Gecko means it's not
+        // needed (we'd recascade a bit more when it changes, but that's fine),
+        // and this way it simplifies the code for text styles and similar.
+        if parent_style.flags.contains(HAS_TEXT_DECORATION_LINE) ||
+           !this_style.get_text().clone_text_decoration_line().is_empty() {
+            ret.insert(HAS_TEXT_DECORATION_LINE);
+        }
+
+        ret
+    }
+}

components/style/properties/gecko.mako.rs

@@ -54,9 +54,8 @@ use gecko::values::round_border_to_device_pixels;
 use logical_geometry::WritingMode;
 use media_queries::Device;
 use properties::animated_properties::TransitionProperty;
-use properties::longhands;
-use properties:: FontComputationData;
-use properties::{Importance, LonghandId};
+use properties::computed_value_flags::ComputedValueFlags;
+use properties::{longhands, FontComputationData, Importance, LonghandId};
 use properties::{PropertyDeclaration, PropertyDeclarationBlock, PropertyDeclarationId};
 use rule_tree::StrongRuleNode;
 use std::fmt::{self, Debug};
@@ -75,16 +74,16 @@ pub mod style_structs {
     % endfor
 }
 
-
+// FIXME(emilio): Unify both definitions, since they're equal now.
 #[derive(Clone)]
 pub struct ComputedValues {
     % for style_struct in data.style_structs:
     ${style_struct.ident}: Arc<style_structs::${style_struct.name}>,
     % endfor
-
     custom_properties: Option<Arc<ComputedValuesMap>>,
     pub writing_mode: WritingMode,
     pub font_computation_data: FontComputationData,
+    pub flags: ComputedValueFlags,
 
     /// The rule node representing the ordered list of rules matched for this
     /// node.  Can be None for default values and text nodes.  This is
@@ -100,6 +99,7 @@ impl ComputedValues {
     pub fn new(custom_properties: Option<Arc<ComputedValuesMap>>,
                writing_mode: WritingMode,
                font_size_keyword: Option<(longhands::font_size::KeywordSize, f32)>,
+               flags: ComputedValueFlags,
                rules: Option<StrongRuleNode>,
                visited_style: Option<Arc<ComputedValues>>,
                % for style_struct in data.style_structs:
@@ -107,13 +107,14 @@ impl ComputedValues {
                % endfor
     ) -> Self {
         ComputedValues {
-            custom_properties: custom_properties,
-            writing_mode: writing_mode,
+            custom_properties,
+            writing_mode,
             font_computation_data: FontComputationData::new(font_size_keyword),
-            rules: rules,
+            flags,
+            rules,
             visited_style: visited_style,
             % for style_struct in data.style_structs:
-            ${style_struct.ident}: ${style_struct.ident},
+            ${style_struct.ident},
             % endfor
         }
     }

components/style/properties/longhand/text.mako.rs

@@ -150,6 +150,7 @@ ${helpers.single_keyword("unicode-bidi",
 
 <%helpers:longhand name="text-decoration-line"
                    custom_cascade="${product == 'servo'}"
+                   need_clone=True
                    animation_value_type="discrete"
                    spec="https://drafts.csswg.org/css-text-decor/#propdef-text-decoration-line">
     use std::fmt;

components/style/properties/properties.mako.rs

@@ -44,6 +44,7 @@ use values::generics::text::LineHeight;
 use values::computed;
 use cascade_info::CascadeInfo;
 use rule_tree::{CascadeLevel, StrongRuleNode};
+use self::computed_value_flags::ComputedValueFlags;
 use style_adjuster::StyleAdjuster;
 #[cfg(feature = "servo")] use values::specified::BorderStyle;
 
@@ -77,6 +78,8 @@ macro_rules! impl_bitflags_conversions {
     import os.path
 %>
 
+#[path="${repr(os.path.join(os.path.dirname(__file__), 'computed_value_flags.rs'))[1:-1]}"]
+pub mod computed_value_flags;
 #[path="${repr(os.path.join(os.path.dirname(__file__), 'declaration_block.rs'))[1:-1]}"]
 pub mod declaration_block;
 
@@ -1823,10 +1826,14 @@ pub struct ComputedValues {
     /// The keyword behind the current font-size property, if any
     pub font_computation_data: FontComputationData,
 
+    /// A set of flags we use to store misc information regarding this style.
+    pub flags: ComputedValueFlags,
+
     /// The rule node representing the ordered list of rules matched for this
     /// node.  Can be None for default values and text nodes.  This is
     /// essentially an optimization to avoid referencing the root rule node.
     pub rules: Option<StrongRuleNode>,
+
     /// The element's computed values if visited, only computed if there's a
     /// relevant link for this element. A element's "relevant link" is the
     /// element being matched if it is a link or the nearest ancestor link.
@@ -1836,23 +1843,27 @@ pub struct ComputedValues {
 #[cfg(feature = "servo")]
 impl ComputedValues {
     /// Construct a `ComputedValues` instance.
-    pub fn new(custom_properties: Option<Arc<::custom_properties::ComputedValuesMap>>,
+    pub fn new(
+        custom_properties: Option<Arc<::custom_properties::ComputedValuesMap>>,
         writing_mode: WritingMode,
         font_size_keyword: Option<(longhands::font_size::KeywordSize, f32)>,
+        flags: ComputedValueFlags,
         rules: Option<StrongRuleNode>,
         visited_style: Option<Arc<ComputedValues>>,
         % for style_struct in data.active_style_structs():
         ${style_struct.ident}: Arc<style_structs::${style_struct.name}>,
         % endfor
     ) -> Self {
+        let font_computation_data = FontComputationData::new(font_size_keyword);
         ComputedValues {
-            custom_properties: custom_properties,
-            writing_mode: writing_mode,
-            font_computation_data: FontComputationData::new(font_size_keyword),
-            rules: rules,
-            visited_style: visited_style,
+            custom_properties,
+            writing_mode,
+            font_computation_data,
+            flags,
+            rules,
+            visited_style,
         % for style_struct in data.active_style_structs():
-            ${style_struct.ident}: ${style_struct.ident},
+            ${style_struct.ident},
         % endfor
         }
     }
@@ -2297,6 +2308,8 @@ impl<'a, T: 'a> Deref for StyleStructRef<'a, T> {
 /// actually cloning them, until we either build the style, or mutate the
 /// inherited value.
 pub struct StyleBuilder<'a> {
+    /// The style we're inheriting from.
+    inherited_style: &'a ComputedValues,
     /// The rule node representing the ordered list of rules matched for this
     /// node.
     rules: Option<StrongRuleNode>,
@@ -2318,24 +2331,28 @@ pub struct StyleBuilder<'a> {
 
 impl<'a> StyleBuilder<'a> {
     /// Trivially construct a `StyleBuilder`.
-    pub fn new(
+    fn new(
+        inherited_style: &'a ComputedValues,
+        reset_style: &'a ComputedValues,
         rules: Option<StrongRuleNode>,
         custom_properties: Option<Arc<::custom_properties::ComputedValuesMap>>,
         writing_mode: WritingMode,
         font_size_keyword: Option<(longhands::font_size::KeywordSize, f32)>,
         visited_style: Option<Arc<ComputedValues>>,
-        % for style_struct in data.active_style_structs():
-            ${style_struct.ident}: &'a Arc<style_structs::${style_struct.name}>,
-        % endfor
     ) -> Self {
         StyleBuilder {
-            rules: rules,
-            custom_properties: custom_properties,
-            writing_mode: writing_mode,
-            font_size_keyword: font_size_keyword,
-            visited_style: visited_style,
+            inherited_style,
+            rules,
+            custom_properties,
+            writing_mode,
+            font_size_keyword,
+            visited_style,
             % for style_struct in data.active_style_structs():
-            ${style_struct.ident}: StyleStructRef::Borrowed(${style_struct.ident}),
+            % if style_struct.inherited:
+            ${style_struct.ident}: StyleStructRef::Borrowed(inherited_style.${style_struct.name_lower}_arc()),
+            % else:
+            ${style_struct.ident}: StyleStructRef::Borrowed(reset_style.${style_struct.name_lower}_arc()),
+            % endif
             % endfor
         }
     }
@@ -2348,19 +2365,18 @@ impl<'a> StyleBuilder<'a> {
 
     /// Inherits style from the parent element, accounting for the default
     /// computed values that need to be provided as well.
-    pub fn for_inheritance(parent: &'a ComputedValues, default: &'a ComputedValues) -> Self {
-        Self::new(/* rules = */ None,
+    pub fn for_inheritance(
+        parent: &'a ComputedValues,
+        default: &'a ComputedValues
+    ) -> Self {
+        Self::new(
+            parent,
+            default,
+            /* rules = */ None,
             parent.custom_properties(),
             parent.writing_mode,
             parent.font_computation_data.font_size_keyword,
-                  parent.clone_visited_style(),
-                  % for style_struct in data.active_style_structs():
-                  % if style_struct.inherited:
-                  parent.${style_struct.name_lower}_arc(),
-                  % else:
-                  default.${style_struct.name_lower}_arc(),
-                  % endif
-                  % endfor
+            parent.clone_visited_style()
         )
     }
 
@@ -2423,9 +2439,11 @@ impl<'a> StyleBuilder<'a> {
 
     /// Turns this `StyleBuilder` into a proper `ComputedValues` instance.
     pub fn build(self) -> ComputedValues {
+        let flags = ComputedValueFlags::compute(&self, &self.inherited_style);
         ComputedValues::new(self.custom_properties,
                             self.writing_mode,
                             self.font_size_keyword,
+                            flags,
                             self.rules,
                             self.visited_style,
                             % for style_struct in data.active_style_structs():
@@ -2453,6 +2471,7 @@ mod lazy_static_module {
     use logical_geometry::WritingMode;
     use stylearc::Arc;
     use super::{ComputedValues, longhands, style_structs, FontComputationData};
+    use super::computed_value_flags::ComputedValueFlags;
 
     /// The initial values for all style structs as defined by the specification.
     lazy_static! {
@@ -2469,6 +2488,7 @@ mod lazy_static_module {
             % endfor
             custom_properties: None,
             writing_mode: WritingMode::empty(),
+            flags: ComputedValueFlags::initial(),
             font_computation_data: FontComputationData::default_values(),
             rules: None,
             visited_style: None,
@@ -2634,33 +2654,10 @@ pub fn apply_declarations<'a, F, I>(device: &Device,
         ::custom_properties::finish_cascade(
             custom_properties, &inherited_custom_properties);
 
-    // We'd really like to own the rules here to avoid refcount traffic, but
-    // animation's usage of `apply_declarations` make this tricky. See bug
-    // 1375525.
-    let builder = if !flags.contains(INHERIT_ALL) {
-        StyleBuilder::new(Some(rules.clone()),
-                          custom_properties,
-                          WritingMode::empty(),
-                          inherited_style.font_computation_data.font_size_keyword,
-                          visited_style,
-                          % for style_struct in data.active_style_structs():
-                              % if style_struct.inherited:
-                                  inherited_style.${style_struct.name_lower}_arc(),
-                              % else:
-                                  default_style.${style_struct.name_lower}_arc(),
-                              % endif
-                          % endfor
-                          )
+    let reset_style = if flags.contains(INHERIT_ALL) {
+        inherited_style
     } else {
-        StyleBuilder::new(Some(rules.clone()),
-                          custom_properties,
-                          WritingMode::empty(),
-                          inherited_style.font_computation_data.font_size_keyword,
-                          visited_style,
-                          % for style_struct in data.active_style_structs():
-                              inherited_style.${style_struct.name_lower}_arc(),
-                          % endfor
-                          )
+        default_style
     };
 
     let mut context = computed::Context {
@@ -2668,7 +2665,18 @@ pub fn apply_declarations<'a, F, I>(device: &Device,
         device: device,
         inherited_style: inherited_style,
         layout_parent_style: layout_parent_style,
-        style: builder,
+        // We'd really like to own the rules here to avoid refcount traffic, but
+        // animation's usage of `apply_declarations` make this tricky. See bug
+        // 1375525.
+        style: StyleBuilder::new(
+            inherited_style,
+            reset_style,
+            Some(rules.clone()),
+            custom_properties,
+            WritingMode::empty(),
+            inherited_style.font_computation_data.font_size_keyword,
+            visited_style,
+        ),
         font_metrics_provider: font_metrics_provider,
         cached_system_font: None,
         in_media_query: false,
@@ -2701,9 +2709,8 @@ pub fn apply_declarations<'a, F, I>(device: &Device,
     // virtual dispatch instead.
     % for category_to_cascade_now in ["early", "other"]:
         % if category_to_cascade_now == "early":
-            // Pull these out so that we can
-            // compute them in a specific order without
-            // introducing more iterations
+            // Pull these out so that we can compute them in a specific order
+            // without introducing more iterations.
             let mut font_size = None;
             let mut font_family = None;
         % endif