style: Make viewport-relative units zoomable via "zoom text only"

They're not font relative, so it we probably want them to be zoomed.

Differential Revision: https://phabricator.services.mozilla.com/D148796

components/style/values/computed/length.rs

@@ -31,10 +31,22 @@ impl ToComputedValue for specified::NoCalcLength {
 
     #[inline]
     fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
+        self.to_computed_value_with_base_size(context, FontBaseSize::CurrentStyle)
+    }
+
+    #[inline]
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        specified::NoCalcLength::Absolute(AbsoluteLength::Px(computed.px()))
+    }
+}
+
+impl specified::NoCalcLength {
+    /// Computes a length with a given font-relative base size.
+    pub fn to_computed_value_with_base_size(&self, context: &Context, base_size: FontBaseSize) -> Length {
         match *self {
             specified::NoCalcLength::Absolute(length) => length.to_computed_value(context),
             specified::NoCalcLength::FontRelative(length) => {
-                length.to_computed_value(context, FontBaseSize::CurrentStyle)
+                length.to_computed_value(context, base_size)
             },
             specified::NoCalcLength::ViewportPercentage(length) => {
                 context
@@ -47,11 +59,6 @@ impl ToComputedValue for specified::NoCalcLength {
             },
         }
     }
-
-    #[inline]
-    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
-        specified::NoCalcLength::Absolute(AbsoluteLength::Px(computed.px()))
-    }
 }
 
 impl ToComputedValue for specified::Length {

components/style/values/computed/length_percentage.rs

@@ -730,14 +730,16 @@ impl specified::CalcLengthPercentage {
         F: Fn(Length) -> Length,
     {
         use crate::values::specified::calc::Leaf;
-        use crate::values::specified::length::NoCalcLength;
 
         let node = self.node.map_leaves(|leaf| match *leaf {
             Leaf::Percentage(p) => CalcLengthPercentageLeaf::Percentage(Percentage(p)),
-            Leaf::Length(l) => CalcLengthPercentageLeaf::Length(match l {
+            Leaf::Length(l) => CalcLengthPercentageLeaf::Length({
-                NoCalcLength::Absolute(ref abs) => zoom_fn(abs.to_computed_value(context)),
+                let result = l.to_computed_value_with_base_size(context, base_size);
-                NoCalcLength::FontRelative(ref fr) => fr.to_computed_value(context, base_size),
+                if l.should_zoom_text() {
-                other => other.to_computed_value(context),
+                    zoom_fn(result)
+                } else {
+                    result
+                }
             }),
             Leaf::Number(..) | Leaf::Angle(..) | Leaf::Time(..) => {
                 unreachable!("Shouldn't have parsed")
@@ -755,7 +757,7 @@ impl specified::CalcLengthPercentage {
     ) -> LengthPercentage {
         self.to_computed_value_with_zoom(
             context,
-            |abs| context.maybe_zoom_text(abs.into()),
+            |abs| context.maybe_zoom_text(abs),
             base_size,
         )
     }

components/style/values/specified/font.rs

@@ -916,21 +916,21 @@ impl FontSize {
         };
         let mut info = KeywordInfo::none();
         let size = match *self {
-            FontSize::Length(LengthPercentage::Length(NoCalcLength::FontRelative(value))) => {
+            FontSize::Length(LengthPercentage::Length(ref l)) => {
-                if let FontRelativeLength::Em(em) = value {
+                if let NoCalcLength::FontRelative(ref value) = *l {
-                    // If the parent font was keyword-derived, this is too.
+                    if let FontRelativeLength::Em(em) = *value {
-                    // Tack the em unit onto the factor
+                        // If the parent font was keyword-derived, this is
-                    info = compose_keyword(em);
+                        // too. Tack the em unit onto the factor
+                        info = compose_keyword(em);
+                    }
+                }
+                let result = l.to_computed_value_with_base_size(context, base_size);
+                if l.should_zoom_text() {
+                    context.maybe_zoom_text(result)
+                } else {
+                    result
                 }
-                value.to_computed_value(context, base_size)
             },
-            FontSize::Length(LengthPercentage::Length(NoCalcLength::ServoCharacterWidth(
-                value,
-            ))) => value.to_computed_value(base_size.resolve(context)),
-            FontSize::Length(LengthPercentage::Length(NoCalcLength::Absolute(ref l))) => {
-                context.maybe_zoom_text(l.to_computed_value(context))
-            },
-            FontSize::Length(LengthPercentage::Length(ref l)) => l.to_computed_value(context),
             FontSize::Length(LengthPercentage::Percentage(pc)) => {
                 // If the parent font was keyword-derived, this is too.
                 // Tack the % onto the factor

components/style/values/specified/length.rs

@@ -790,6 +790,19 @@ impl NoCalcLength {
         }
     }
 
+    /// Whether text-only zoom should be applied to this length.
+    ///
+    /// Generally, font-dependent/relative units don't get text-only-zoomed,
+    /// because the font they're relative to should be zoomed already.
+    pub fn should_zoom_text(&self) -> bool {
+        match *self {
+            Self::Absolute(..) |
+            Self::ViewportPercentage(..) => true,
+            Self::ServoCharacterWidth(..) |
+            Self::FontRelative(..) => false,
+        }
+    }
+
     /// Parse a given absolute or relative dimension.
     pub fn parse_dimension(
         context: &ParserContext,