style: Use used, rather than computed font-size for font-metric dependent units

Differential Revision: https://phabricator.services.mozilla.com/D165737

11 files changed, 64 insertions, 39 deletions

diff --git a/components/style/matching.rs b/components/style/matching.rs
index a22dba26808..fa757693e5b 100644
--- a/components/style/matching.rs
+++ b/components/style/matching.rs
@@ -924,7 +924,7 @@ pub trait MatchMethods: TElement {
                 if is_root {
                     let device = context.shared.stylist.device();
                     debug_assert!(self.owner_doc_matches_for_testing(device));
-                    device.set_root_font_size(new_font_size.size().into());
+                    device.set_root_font_size(new_font_size.computed_size().into());
                     if device.used_root_font_size() {
                         // If the root font-size changed since last time, and something
                         // in the document did use rem units, ensure we recascade the
diff --git a/components/style/properties/cascade.rs b/components/style/properties/cascade.rs
index dfd063ba8a5..ce8973f4939 100644
--- a/components/style/properties/cascade.rs
+++ b/components/style/properties/cascade.rs
@@ -983,7 +983,7 @@ impl<'a, 'b: 'a> Cascade<'a, 'b> {
                 },
             };
 
-            if font.gecko().mScriptUnconstrainedSize == new_size.size {
+            if font.gecko().mScriptUnconstrainedSize == new_size.computed_size {
                 return;
             }
 
diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index 03301cc07d2..05f2d3223bd 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -863,6 +863,8 @@ fn static_assert() {
         self.gecko.mScriptUnconstrainedSize = other.gecko.mScriptUnconstrainedSize;
 
         self.gecko.mSize = other.gecko.mScriptUnconstrainedSize;
+        // NOTE: Intentionally not copying from mFont.size. The cascade process
+        // recomputes the used size as needed.
         self.gecko.mFont.size = other.gecko.mSize;
         self.gecko.mFontSizeKeyword = other.gecko.mFontSizeKeyword;
 
@@ -876,12 +878,14 @@ fn static_assert() {
     }
 
     pub fn set_font_size(&mut self, v: FontSize) {
-        let size = v.size;
-        self.gecko.mScriptUnconstrainedSize = size;
+        let computed_size = v.computed_size;
+        self.gecko.mScriptUnconstrainedSize = computed_size;
 
         // These two may be changed from Cascade::fixup_font_stuff.
-        self.gecko.mSize = size;
-        self.gecko.mFont.size = size;
+        self.gecko.mSize = computed_size;
+        // NOTE: Intentionally not copying from used_size. The cascade process
+        // recomputes the used size as needed.
+        self.gecko.mFont.size = computed_size;
 
         self.gecko.mFontSizeKeyword = v.keyword_info.kw;
         self.gecko.mFontSizeFactor = v.keyword_info.factor;
@@ -892,7 +896,8 @@ fn static_assert() {
         use crate::values::specified::font::KeywordInfo;
 
         FontSize {
-            size: self.gecko.mSize,
+            computed_size: self.gecko.mSize,
+            used_size: self.gecko.mFont.size,
             keyword_info: KeywordInfo {
                 kw: self.gecko.mFontSizeKeyword,
                 factor: self.gecko.mFontSizeFactor,
diff --git a/components/style/properties/longhands/font.mako.rs b/components/style/properties/longhands/font.mako.rs
index 67e8db666ef..e987a42b652 100644
--- a/components/style/properties/longhands/font.mako.rs
+++ b/components/style/properties/longhands/font.mako.rs
@@ -382,10 +382,12 @@ pub mod system_font {
                 );
                 &mut *system.as_mut_ptr()
             };
+            let size = NonNegative(cx.maybe_zoom_text(system.size.0));
             let ret = ComputedSystemFont {
                 font_family: system.family.clone(),
                 font_size: FontSize {
-                    size: NonNegative(cx.maybe_zoom_text(system.size.0)),
+                    computed_size: size,
+                    used_size: size,
                     keyword_info: KeywordInfo::none()
                 },
                 font_weight: system.weight,
diff --git a/components/style/rule_cache.rs b/components/style/rule_cache.rs
index 24039fb94f7..604a92b724a 100644
--- a/components/style/rule_cache.rs
+++ b/components/style/rule_cache.rs
@@ -53,7 +53,7 @@ impl RuleCacheConditions {
         }
 
         if let Some(fs) = self.font_size {
-            if style.get_font().clone_font_size().size != fs {
+            if style.get_font().clone_font_size().computed_size != fs {
                 return false;
             }
         }
diff --git a/components/style/values/computed/font.rs b/components/style/values/computed/font.rs
index 43f12a2f6cb..8fe54445d05 100644
--- a/components/style/values/computed/font.rs
+++ b/components/style/values/computed/font.rs
@@ -226,8 +226,13 @@ impl FontWeight {
 #[cfg_attr(feature = "servo", derive(Serialize, Deserialize))]
 /// The computed value of font-size
 pub struct FontSize {
-    /// The size.
-    pub size: NonNegativeLength,
+    /// The computed size, that we use to compute ems etc. This accounts for
+    /// e.g., text-zoom.
+    pub computed_size: NonNegativeLength,
+    /// The actual used size. This is the computed font size, potentially
+    /// constrained by other factors like minimum font-size settings and so on.
+    #[css(skip)]
+    pub used_size: NonNegativeLength,
     /// If derived from a keyword, the keyword and additional transformations applied to it
     #[css(skip)]
     pub keyword_info: KeywordInfo,
@@ -236,15 +241,22 @@ pub struct FontSize {
 impl FontSize {
     /// The actual computed font size.
     #[inline]
-    pub fn size(&self) -> Length {
-        self.size.0
+    pub fn computed_size(&self) -> Length {
+        self.computed_size.0
+    }
+
+    /// The actual used font size.
+    #[inline]
+    pub fn used_size(&self) -> Length {
+        self.used_size.0
     }
 
     #[inline]
     /// Get default value of font size.
     pub fn medium() -> Self {
         Self {
-            size: NonNegative(Length::new(specified::FONT_MEDIUM_PX)),
+            computed_size: NonNegative(Length::new(specified::FONT_MEDIUM_PX)),
+            used_size: NonNegative(Length::new(specified::FONT_MEDIUM_PX)),
             keyword_info: KeywordInfo::medium(),
         }
     }
@@ -255,13 +267,14 @@ impl ToAnimatedValue for FontSize {
 
     #[inline]
     fn to_animated_value(self) -> Self::AnimatedValue {
-        self.size.0
+        self.computed_size.0
     }
 
     #[inline]
     fn from_animated_value(animated: Self::AnimatedValue) -> Self {
         FontSize {
-            size: NonNegative(animated.clamp_to_non_negative()),
+            computed_size: NonNegative(animated.clamp_to_non_negative()),
+            used_size: NonNegative(animated.clamp_to_non_negative()),
             keyword_info: KeywordInfo::none(),
         }
     }
@@ -839,7 +852,7 @@ impl ToComputedValue for specified::MozScriptMinSize {
         match self.0 {
             NoCalcLength::FontRelative(value) => value.to_computed_value(cx, base_size),
             NoCalcLength::ServoCharacterWidth(value) => {
-                value.to_computed_value(base_size.resolve(cx))
+                value.to_computed_value(base_size.resolve(cx).computed_size())
             },
             ref l => l.to_computed_value(cx),
         }
diff --git a/components/style/values/computed/length.rs b/components/style/values/computed/length.rs
index 29bed80d926..4f68e1c4593 100644
--- a/components/style/values/computed/length.rs
+++ b/components/style/values/computed/length.rs
@@ -58,7 +58,7 @@ impl specified::NoCalcLength {
                 length.to_computed_value(context)
             },
             specified::NoCalcLength::ServoCharacterWidth(length) => {
-                length.to_computed_value(context.style().get_font().clone_font_size().size())
+                length.to_computed_value(context.style().get_font().clone_font_size().computed_size())
             },
         }
     }
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index de5c1e5a374..dac4c4f2467 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -327,7 +327,7 @@ impl<'a> Context<'a> {
             FontBaseSize::CurrentStyle => ComputedValueFlags::DEPENDS_ON_SELF_FONT_METRICS,
             FontBaseSize::InheritedStyle => ComputedValueFlags::DEPENDS_ON_INHERITED_FONT_METRICS,
         });
-        let size = base_size.resolve(self);
+        let size = base_size.resolve(self).used_size();
         let style = self.style();
 
         let (wm, font) = match base_size {
diff --git a/components/style/values/specified/font.rs b/components/style/values/specified/font.rs
index d2e47bf7dfc..f61f1c5abaa 100644
--- a/components/style/values/specified/font.rs
+++ b/components/style/values/specified/font.rs
@@ -907,11 +907,11 @@ impl FontSize {
                 // If the parent font was keyword-derived, this is too.
                 // Tack the % onto the factor
                 info = compose_keyword(pc.0);
-                (base_size.resolve(context) * pc.0).normalized()
+                (base_size.resolve(context).computed_size() * pc.0).normalized()
             },
             FontSize::Length(LengthPercentage::Calc(ref calc)) => {
                 let calc = calc.to_computed_value_zoomed(context, base_size);
-                calc.resolve(base_size.resolve(context))
+                calc.resolve(base_size.resolve(context).computed_size())
             },
             FontSize::Keyword(i) => {
                 // As a specified keyword, this is keyword derived
@@ -940,13 +940,13 @@ impl FontSize {
                         .as_ref()
                         .unwrap()
                         .font_size
-                        .size
-                        .0
+                        .computed_size()
                 }
             },
         };
         computed::FontSize {
-            size: NonNegative(size),
+            computed_size: NonNegative(size),
+            used_size: NonNegative(size),
             keyword_info: info,
         }
     }
@@ -963,7 +963,7 @@ impl ToComputedValue for FontSize {
     #[inline]
     fn from_computed_value(computed: &computed::FontSize) -> Self {
         FontSize::Length(LengthPercentage::Length(
-            ToComputedValue::from_computed_value(&computed.size.0),
+            ToComputedValue::from_computed_value(&computed.computed_size()),
         ))
     }
 }
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index ea96ef7426e..2d0a031953f 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -77,12 +77,10 @@ pub enum FontBaseSize {
 
 impl FontBaseSize {
     /// Calculate the actual size for a given context
-    pub fn resolve(&self, context: &Context) -> computed::Length {
+    pub fn resolve(&self, context: &Context) -> computed::FontSize {
         match *self {
-            FontBaseSize::CurrentStyle => context.style().get_font().clone_font_size().size(),
-            FontBaseSize::InheritedStyle => {
-                context.style().get_parent_font().clone_font_size().size()
-            },
+            FontBaseSize::CurrentStyle => context.style().get_font().clone_font_size(),
+            FontBaseSize::InheritedStyle => context.style().get_parent_font().clone_font_size(),
         }
     }
 }
@@ -167,11 +165,11 @@ impl FontRelativeLength {
                         context
                             .rule_cache_conditions
                             .borrow_mut()
-                            .set_font_size_dependency(reference_font_size.into());
+                            .set_font_size_dependency(reference_font_size.computed_size);
                     }
                 }
 
-                (reference_font_size, length)
+                (reference_font_size.computed_size(), length)
             },
             FontRelativeLength::Ex(length) => {
                 // The x-height is an intrinsically horizontal metric.
@@ -184,7 +182,9 @@ impl FontRelativeLength {
                     //     determine the x-height, a value of 0.5em must be
                     //     assumed.
                     //
-                    reference_font_size * 0.5
+                    // (But note we use 0.5em of the used, not computed
+                    // font-size)
+                    reference_font_size.used_size() * 0.5
                 });
                 (reference_size, length)
             },
@@ -212,11 +212,13 @@ impl FontRelativeLength {
                     //     writing-mode is vertical-rl or vertical-lr and
                     //     text-orientation is upright).
                     //
+                    // Same caveat about computed vs. used font-size applies
+                    // above.
                     let wm = context.style().writing_mode;
                     if wm.is_vertical() && wm.is_upright() {
-                        reference_font_size
+                        reference_font_size.used_size()
                     } else {
-                        reference_font_size * 0.5
+                        reference_font_size.used_size() * 0.5
                     }
                 });
                 (reference_size, length)
@@ -228,7 +230,8 @@ impl FontRelativeLength {
                     // https://drafts.csswg.org/css-values/#cap
                     //
                     //     In the cases where it is impossible or impractical to
-                    //     determine the cap-height, the font’s ascent must be used.
+                    //     determine the cap-height, the font’s ascent must be
+                    //     used.
                     //
                     metrics.ascent
                 });
@@ -247,7 +250,9 @@ impl FontRelativeLength {
                     //     determine the ideographic advance measure, it must be
                     //     assumed to be 1em.
                     //
-                    reference_font_size
+                    // Same caveat about computed vs. used as for other
+                    // metric-dependent units.
+                    reference_font_size.used_size()
                 });
                 (reference_size, length)
             },
@@ -259,7 +264,7 @@ impl FontRelativeLength {
                 //     value.
                 //
                 let reference_size = if context.builder.is_root_element || context.in_media_query {
-                    reference_font_size
+                    reference_font_size.computed_size()
                 } else {
                     context.device().root_font_size()
                 };
diff --git a/components/style/values/specified/text.rs b/components/style/values/specified/text.rs
index 5f21c774372..b782780c955 100644
--- a/components/style/values/specified/text.rs
+++ b/components/style/values/specified/text.rs
@@ -123,7 +123,7 @@ impl ToComputedValue for LineHeight {
                     LengthPercentage::Calc(ref calc) => {
                         let computed_calc =
                             calc.to_computed_value_zoomed(context, FontBaseSize::CurrentStyle);
-                        let base = context.style().get_font().clone_font_size().size();
+                        let base = context.style().get_font().clone_font_size().computed_size();
                         computed_calc.resolve(base)
                     },
                 };