Auto merge of #16294 - hiikezoe:make-word-spacing-animatable, r=emilio

Make word spacing animatable

<!-- Please describe your changes on the following line: -->
This is a PR for https://bugzilla.mozilla.org/show_bug.cgi?id=1354053

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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- [X] There are tests for these changes, a test case will be landed in web-platform-tests in https://bugzilla.mozilla.org/show_bug.cgi?id=1354053

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components/style/properties/gecko.mako.rs

@@ -2885,11 +2885,12 @@ fn static_assert() {
 
     pub fn clone_letter_spacing(&self) -> longhands::letter_spacing::computed_value::T {
         use properties::longhands::letter_spacing::computed_value::T;
-        match self.gecko.mLetterSpacing.as_value() {
-            CoordDataValue::Normal => T(None),
-            CoordDataValue::Coord(coord) => T(Some(Au(coord))),
-            _ => unreachable!("Unexpected computed value for letter-spacing"),
-        }
+        debug_assert!(
+            matches!(self.gecko.mLetterSpacing.as_value(),
+                     CoordDataValue::Normal |
+                     CoordDataValue::Coord(_)),
+            "Unexpected computed value for letter-spacing");
+        T(Au::from_gecko_style_coord(&self.gecko.mLetterSpacing))
     }
 
     <%call expr="impl_coord_copy('letter_spacing', 'mLetterSpacing')"></%call>
@@ -2902,6 +2903,19 @@ fn static_assert() {
         }
     }
 
+    pub fn clone_word_spacing(&self) -> longhands::word_spacing::computed_value::T {
+        use properties::longhands::word_spacing::computed_value::T;
+        use values::computed::LengthOrPercentage;
+        debug_assert!(
+            matches!(self.gecko.mWordSpacing.as_value(),
+                     CoordDataValue::Normal |
+                     CoordDataValue::Coord(_) |
+                     CoordDataValue::Percent(_) |
+                     CoordDataValue::Calc(_)),
+            "Unexpected computed value for word-spacing");
+        T(LengthOrPercentage::from_gecko_style_coord(&self.gecko.mWordSpacing))
+    }
+
     <%call expr="impl_coord_copy('word_spacing', 'mWordSpacing')"></%call>
 
     fn clear_text_emphasis_style_if_string(&mut self) {

components/style/properties/helpers.mako.rs

@@ -736,3 +736,26 @@
     %>
 </%def>
 
+/// Macro for defining Interpolate trait for tuple struct which has Option<T>,
+/// e.g. struct T(pub Option<Au>).
+<%def name="impl_interpolate_for_option_tuple(value_for_none)">
+    impl Interpolate for T {
+        #[inline]
+        fn interpolate(&self, other: &Self, progress: f64) -> Result<Self, ()> {
+            match (self, other) {
+                (&T(Some(ref this)), &T(Some(ref other))) => {
+                    Ok(T(this.interpolate(other, progress).ok()))
+                },
+                (&T(Some(ref this)), &T(None)) => {
+                    Ok(T(this.interpolate(&${value_for_none}, progress).ok()))
+                },
+                (&T(None), &T(Some(ref other))) => {
+                    Ok(T(${value_for_none}.interpolate(other, progress).ok()))
+                },
+                (&T(None), &T(None)) => {
+                    Ok(T(None))
+                },
+            }
+        }
+    }
+</%def>

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

@@ -445,26 +445,7 @@ ${helpers.single_keyword("text-align-last",
         #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
         pub struct T(pub Option<Au>);
 
-        impl Interpolate for T {
-            #[inline]
-            fn interpolate(&self, other: &Self, progress: f64) -> Result<Self, ()> {
-                match (self, other) {
-                    (&T(Some(ref this)), &T(Some(ref other))) => {
-                        Ok(T(this.interpolate(other, progress).ok()))
-                    },
-                    (&T(Some(ref this)), &T(None)) => {
-                        Ok(T(this.interpolate(&Au(0), progress).ok()))
-                    },
-                    (&T(None), &T(Some(ref other))) => {
-                        Ok(T(Au(0).interpolate(other, progress).ok()))
-                    },
-                    (&T(None), &T(None)) => {
-                        Ok(T(None))
-                    },
-                }
-            }
-        }
-
+        ${helpers.impl_interpolate_for_option_tuple('Au(0)')}
     }
 
     impl ToCss for computed_value::T {
@@ -510,7 +491,7 @@ ${helpers.single_keyword("text-align-last",
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="word-spacing" animation_type="none"
+<%helpers:longhand name="word-spacing" animation_type="normal"
                    spec="https://drafts.csswg.org/css-text/#propdef-word-spacing">
     use std::fmt;
     use style_traits::ToCss;
@@ -542,10 +523,13 @@ ${helpers.single_keyword("text-align-last",
     }
 
     pub mod computed_value {
+        use properties::animated_properties::Interpolate;
         use values::computed::LengthOrPercentage;
         #[derive(Debug, Clone, PartialEq)]
         #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
         pub struct T(pub Option<LengthOrPercentage>);
+
+        ${helpers.impl_interpolate_for_option_tuple('LengthOrPercentage::zero()')}
     }
 
     impl ToCss for computed_value::T {