Auto merge of #18380 - dadaa:make-font-variation-settings-animatable, r=birtles

Make font-variation-settings animatable

<!-- Please describe your changes on the following line: -->
https://bugzilla.mozilla.org/show_bug.cgi?id=1390702 r=birtles

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach build-geckolib` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] `./mach test-tidy --stylo` does not report any errors
- [X] `./mach test-unit -p style` does not report any errors

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- [X] There are tests for these changes. The test codes are patch part 4 in https://bugzilla.mozilla.org/show_bug.cgi?id=1390702

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4 files changed, 243 insertions, 94 deletions

diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index 3eae30f6f9e..de1503ad5fa 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -5,7 +5,7 @@
 // `data` comes from components/style/properties.mako.rs; see build.rs for more details.
 
 <%!
-    from data import to_rust_ident, to_camel_case
+    from data import to_rust_ident, to_camel_case, to_camel_case_lower
     from data import Keyword
 %>
 <%namespace name="helpers" file="/helpers.mako.rs" />
@@ -1070,6 +1070,67 @@ impl Clone for ${style_struct.gecko_struct_name} {
     }
 </%def>
 
+<%def name="impl_font_settings(ident, tag_type)">
+    <%
+    gecko_ffi_name = to_camel_case_lower(ident)
+    %>
+
+    pub fn set_${ident}(&mut self, v: longhands::${ident}::computed_value::T) {
+        use values::generics::FontSettings;
+
+        let current_settings = &mut self.gecko.mFont.${gecko_ffi_name};
+        current_settings.clear_pod();
+
+        match v {
+            FontSettings::Normal => (), // do nothing, length is already 0
+
+            FontSettings::Tag(other_settings) => {
+                unsafe { current_settings.set_len_pod(other_settings.len() as u32) };
+
+                for (current, other) in current_settings.iter_mut().zip(other_settings) {
+                    current.mTag = other.tag;
+                    current.mValue = other.value.0;
+                }
+            }
+        };
+    }
+
+    pub fn copy_${ident}_from(&mut self, other: &Self) {
+        let current_settings = &mut self.gecko.mFont.${gecko_ffi_name};
+        let other_settings = &other.gecko.mFont.${gecko_ffi_name};
+        let settings_length = other_settings.len() as u32;
+
+        current_settings.clear_pod();
+        unsafe { current_settings.set_len_pod(settings_length) };
+
+        for (current, other) in current_settings.iter_mut().zip(other_settings.iter()) {
+            current.mTag = other.mTag;
+            current.mValue = other.mValue;
+        }
+    }
+
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
+
+    pub fn clone_${ident}(&self) -> longhands::${ident}::computed_value::T {
+        use values::generics::{FontSettings, FontSettingTag, ${tag_type}} ;
+
+        if self.gecko.mFont.${gecko_ffi_name}.len() == 0 {
+            FontSettings::Normal
+        } else {
+            FontSettings::Tag(
+                self.gecko.mFont.${gecko_ffi_name}.iter().map(|gecko_font_setting| {
+                    FontSettingTag {
+                        tag: gecko_font_setting.mTag,
+                        value: ${tag_type}(gecko_font_setting.mValue),
+                    }
+                }).collect()
+            )
+        }
+    }
+</%def>
+
 <%def name="raw_impl_trait(style_struct, skip_longhands='', skip_additionals='')">
 <%
     longhands = [x for x in style_struct.longhands
@@ -2069,98 +2130,8 @@ fn static_assert() {
     skip_longhands="${skip_font_longhands}"
     skip_additionals="*">
 
-    pub fn set_font_feature_settings(&mut self, v: longhands::font_feature_settings::computed_value::T) {
-        use values::generics::FontSettings;
-
-        let current_settings = &mut self.gecko.mFont.fontFeatureSettings;
-        current_settings.clear_pod();
-
-        match v {
-            FontSettings::Normal => (), // do nothing, length is already 0
-
-            FontSettings::Tag(feature_settings) => {
-                unsafe { current_settings.set_len_pod(feature_settings.len() as u32) };
-
-                for (current, feature) in current_settings.iter_mut().zip(feature_settings) {
-                    current.mTag = feature.tag;
-                    current.mValue = feature.value.0;
-                }
-            }
-        };
-    }
-
-    pub fn copy_font_feature_settings_from(&mut self, other: &Self) {
-        let current_settings = &mut self.gecko.mFont.fontFeatureSettings;
-        let feature_settings = &other.gecko.mFont.fontFeatureSettings;
-        let settings_length = feature_settings.len() as u32;
-
-        current_settings.clear_pod();
-        unsafe { current_settings.set_len_pod(settings_length) };
-
-        for (current, feature) in current_settings.iter_mut().zip(feature_settings.iter()) {
-            current.mTag = feature.mTag;
-            current.mValue = feature.mValue;
-        }
-    }
-
-    pub fn reset_font_feature_settings(&mut self, other: &Self) {
-        self.copy_font_feature_settings_from(other)
-    }
-
-    pub fn clone_font_feature_settings(&self) -> longhands::font_feature_settings::computed_value::T {
-        use values::generics::{FontSettings, FontSettingTag, FontSettingTagInt} ;
-
-        if self.gecko.mFont.fontFeatureSettings.len() == 0 {
-            FontSettings::Normal
-        } else {
-            FontSettings::Tag(
-                self.gecko.mFont.fontFeatureSettings.iter().map(|gecko_font_feature_setting| {
-                    FontSettingTag {
-                        tag: gecko_font_feature_setting.mTag,
-                        value: FontSettingTagInt(gecko_font_feature_setting.mValue),
-                    }
-                }).collect()
-            )
-        }
-    }
-
-    pub fn set_font_variation_settings(&mut self, v: longhands::font_variation_settings::computed_value::T) {
-        use values::generics::FontSettings;
-
-        let current_settings = &mut self.gecko.mFont.fontVariationSettings;
-        current_settings.clear_pod();
-
-        match v {
-            FontSettings::Normal => (), // do nothing, length is already 0
-
-            FontSettings::Tag(feature_settings) => {
-                unsafe { current_settings.set_len_pod(feature_settings.len() as u32) };
-
-                for (current, feature) in current_settings.iter_mut().zip(feature_settings) {
-                    current.mTag = feature.tag;
-                    current.mValue = feature.value.0;
-                }
-            }
-        };
-    }
-
-    pub fn copy_font_variation_settings_from(&mut self, other: &Self ) {
-        let current_settings = &mut self.gecko.mFont.fontVariationSettings;
-        let feature_settings = &other.gecko.mFont.fontVariationSettings;
-        let settings_length = feature_settings.len() as u32;
-
-        current_settings.clear_pod();
-        unsafe { current_settings.set_len_pod(settings_length) };
-
-        for (current, feature) in current_settings.iter_mut().zip(feature_settings.iter()) {
-            current.mTag = feature.mTag;
-            current.mValue = feature.mValue;
-        }
-    }
-
-    pub fn reset_font_variation_settings(&mut self, other: &Self) {
-        self.copy_font_variation_settings_from(other)
-    }
+    <% impl_font_settings("font_feature_settings", "FontSettingTagInt") %>
+    <% impl_font_settings("font_variation_settings", "FontSettingTagFloat") %>
 
     pub fn fixup_none_generic(&mut self, device: &Device) {
         self.gecko.mFont.systemFont = false;
diff --git a/components/style/properties/helpers/animated_properties.mako.rs b/components/style/properties/helpers/animated_properties.mako.rs
index 7cf4da4646d..0bbadbf4cba 100644
--- a/components/style/properties/helpers/animated_properties.mako.rs
+++ b/components/style/properties/helpers/animated_properties.mako.rs
@@ -20,6 +20,8 @@ use properties::longhands::background_size::computed_value::T as BackgroundSizeL
 use properties::longhands::border_spacing::computed_value::T as BorderSpacing;
 use properties::longhands::font_weight::computed_value::T as FontWeight;
 use properties::longhands::font_stretch::computed_value::T as FontStretch;
+#[cfg(feature = "gecko")]
+use properties::longhands::font_variation_settings::computed_value::T as FontVariationSettings;
 use properties::longhands::line_height::computed_value::T as LineHeight;
 use properties::longhands::transform::computed_value::ComputedMatrix;
 use properties::longhands::transform::computed_value::ComputedOperation as TransformOperation;
@@ -54,6 +56,9 @@ use values::computed::length::{NonNegativeLengthOrAuto, NonNegativeLengthOrNorma
 use values::computed::length::NonNegativeLengthOrPercentage;
 use values::computed::transform::DirectionVector;
 use values::distance::{ComputeSquaredDistance, SquaredDistance};
+#[cfg(feature = "gecko")] use values::generics::FontSettings as GenericFontSettings;
+#[cfg(feature = "gecko")] use values::generics::FontSettingTag as GenericFontSettingTag;
+#[cfg(feature = "gecko")] use values::generics::FontSettingTagFloat;
 use values::generics::NonNegative;
 use values::generics::effects::Filter;
 use values::generics::position as generic_position;
@@ -915,6 +920,177 @@ impl Into<FontStretch> for f64 {
     }
 }
 
+/// https://drafts.csswg.org/css-fonts-4/#font-variation-settings-def
+#[cfg(feature = "gecko")]
+impl Animate for FontVariationSettings {
+    #[inline]
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        FontSettingTagIter::new(self, other)?
+            .map(|r| r.and_then(|(st, ot)| st.animate(&ot, procedure)))
+            .collect::<Result<Vec<FontSettingTag>, ()>>()
+            .map(GenericFontSettings::Tag)
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl ComputeSquaredDistance for FontVariationSettings {
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        FontSettingTagIter::new(self, other)?
+            .map(|r| r.and_then(|(st, ot)| st.compute_squared_distance(&ot)))
+            .sum()
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl ToAnimatedZero for FontVariationSettings {
+    #[inline]
+    fn to_animated_zero(&self) -> Result<Self, ()> {
+        Err(())
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl Animate for FontSettingTag {
+    #[inline]
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        if self.tag != other.tag {
+            return Err(());
+        }
+        let value = self.value.animate(&other.value, procedure)?;
+        Ok(FontSettingTag {
+            tag: self.tag,
+            value,
+        })
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl ComputeSquaredDistance for FontSettingTag {
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        if self.tag != other.tag {
+            return Err(());
+        }
+        self.value.compute_squared_distance(&other.value)
+    }
+}
+
+#[cfg(feature = "gecko")]
+type FontSettingTag = GenericFontSettingTag<FontSettingTagFloat>;
+
+#[cfg(feature = "gecko")]
+struct FontSettingTagIterState<'a> {
+    tags: Vec<(&'a FontSettingTag)>,
+    index: usize,
+    prev_tag: u32,
+}
+
+#[cfg(feature = "gecko")]
+impl<'a> FontSettingTagIterState<'a> {
+    fn new(tags: Vec<(&'a FontSettingTag)>) -> FontSettingTagIterState<'a> {
+        FontSettingTagIterState {
+            index: tags.len(),
+            tags,
+            prev_tag: 0,
+        }
+    }
+}
+
+/// Iterator for font-variation-settings tag lists
+///
+/// [CSS fonts level 4](https://drafts.csswg.org/css-fonts-4/#descdef-font-face-font-variation-settings)
+/// defines the animation of font-variation-settings as follows:
+///
+///   Two declarations of font-feature-settings[sic] can be animated between if they are "like".
+///   "Like" declarations are ones where the same set of properties appear (in any order).
+///   Because succesive[sic] duplicate properties are applied instead of prior duplicate
+///   properties, two declarations can be "like" even if they have differing number of
+///   properties. If two declarations are "like" then animation occurs pairwise between
+///   corresponding values in the declarations.
+///
+/// In other words if we have the following lists:
+///
+///   "wght" 1.4, "wdth" 5, "wght" 2
+///   "wdth" 8, "wght" 4, "wdth" 10
+///
+/// We should animate between:
+///
+///   "wdth" 5, "wght" 2
+///   "wght" 4, "wdth" 10
+///
+/// This iterator supports this by sorting the two lists, then iterating them in reverse,
+/// and skipping entries with repeated tag names. It will return Some(Err()) if it reaches the
+/// end of one list before the other, or if the tag names do not match.
+///
+/// For the above example, this iterator would return:
+///
+///   Some(Ok("wght" 2, "wght" 4))
+///   Some(Ok("wdth" 5, "wdth" 10))
+///   None
+///
+#[cfg(feature = "gecko")]
+struct FontSettingTagIter<'a> {
+    a_state: FontSettingTagIterState<'a>,
+    b_state: FontSettingTagIterState<'a>,
+}
+
+#[cfg(feature = "gecko")]
+impl<'a> FontSettingTagIter<'a> {
+    fn new(
+        a_settings: &'a FontVariationSettings,
+        b_settings: &'a FontVariationSettings,
+    ) -> Result<FontSettingTagIter<'a>, ()> {
+        if let (&GenericFontSettings::Tag(ref a_tags), &GenericFontSettings::Tag(ref b_tags)) = (a_settings, b_settings)
+        {
+            fn as_new_sorted_tags(tags: &Vec<FontSettingTag>) -> Vec<(&FontSettingTag)> {
+                use std::iter::FromIterator;
+                let mut sorted_tags: Vec<(&FontSettingTag)> = Vec::from_iter(tags.iter());
+                sorted_tags.sort_by_key(|k| k.tag);
+                sorted_tags
+            };
+
+            Ok(FontSettingTagIter {
+                a_state: FontSettingTagIterState::new(as_new_sorted_tags(a_tags)),
+                b_state: FontSettingTagIterState::new(as_new_sorted_tags(b_tags)),
+            })
+        } else {
+            Err(())
+        }
+    }
+
+    fn next_tag(state: &mut FontSettingTagIterState<'a>) -> Option<(&'a FontSettingTag)> {
+        if state.index == 0 {
+            return None;
+        }
+
+        state.index -= 1;
+        let tag = state.tags[state.index];
+        if tag.tag == state.prev_tag {
+            FontSettingTagIter::next_tag(state)
+        } else {
+            state.prev_tag = tag.tag;
+            Some(tag)
+        }
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl<'a> Iterator for FontSettingTagIter<'a> {
+    type Item = Result<(&'a FontSettingTag, &'a FontSettingTag), ()>;
+
+    fn next(&mut self) -> Option<Result<(&'a FontSettingTag, &'a FontSettingTag), ()>> {
+        match (
+            FontSettingTagIter::next_tag(&mut self.a_state),
+            FontSettingTagIter::next_tag(&mut self.b_state),
+        ) {
+            (Some(at), Some(bt)) if at.tag == bt.tag => Some(Ok((at, bt))),
+            (None, None) => None,
+            _ => Some(Err(())), // Mismatch number of unique tags or tag names.
+        }
+    }
+}
+
 impl<H, V> RepeatableListAnimatable for generic_position::Position<H, V>
     where H: RepeatableListAnimatable, V: RepeatableListAnimatable {}
 
diff --git a/components/style/properties/longhand/font.mako.rs b/components/style/properties/longhand/font.mako.rs
index 9ced9950015..6418a0c8215 100644
--- a/components/style/properties/longhand/font.mako.rs
+++ b/components/style/properties/longhand/font.mako.rs
@@ -1995,7 +1995,8 @@ variation_spec = """\
 https://drafts.csswg.org/css-fonts-4/#low-level-font-variation-settings-control-the-font-variation-settings-property\
 """
 %>
-<%helpers:longhand name="font-variation-settings" products="gecko" animation_value_type="none"
+<%helpers:longhand name="font-variation-settings" products="gecko"
+                   animation_value_type="ComputedValue"
                    flags="APPLIES_TO_FIRST_LETTER APPLIES_TO_FIRST_LINE APPLIES_TO_PLACEHOLDER"
                    spec="${variation_spec}">
     use values::computed::ComputedValueAsSpecified;
diff --git a/components/style/values/generics/mod.rs b/components/style/values/generics/mod.rs
index 239b104d49d..ba39c19bd6a 100644
--- a/components/style/values/generics/mod.rs
+++ b/components/style/values/generics/mod.rs
@@ -219,6 +219,7 @@ pub struct FontSettingTagInt(pub u32);
 /// because it serializes with the preceding space
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[cfg_attr(feature = "gecko", derive(Animate, ComputeSquaredDistance))]
 pub struct FontSettingTagFloat(pub f32);
 
 impl ToCss for FontSettingTagInt {