feat: Support font-relative ch and ic units

components/gfx/font.rs

@@ -124,6 +124,8 @@ pub struct FontMetrics {
     pub max_advance: Au,
     pub average_advance: Au,
     pub line_gap: Au,
+    pub zero_horizontal_advance: Option<Au>,
+    pub ic_horizontal_advance: Option<Au>,
 }
 
 impl FontMetrics {
@@ -143,6 +145,8 @@ impl FontMetrics {
             max_advance: Au(0),
             average_advance: Au(0),
             line_gap: Au(0),
+            zero_horizontal_advance: None,
+            ic_horizontal_advance: None,
         }
     }
 }

components/gfx/platform/freetype/font.rs

@@ -260,10 +260,16 @@ impl PlatformFontMethods for PlatformFont {
             x_height = self.font_units_to_au(os2.sx_height as f64);
         }
 
-        let average_advance = self
+        let zero_horizontal_advance = self
             .glyph_index('0')
             .and_then(|idx| self.glyph_h_advance(idx))
-            .map_or(max_advance, |advance| self.font_units_to_au(advance));
+            .map(Au::from_f64_px);
+        let ic_horizontal_advance = self
+            .glyph_index('\u{6C34}')
+            .and_then(|idx| self.glyph_h_advance(idx))
+            .map(Au::from_f64_px);
+
+        let average_advance = zero_horizontal_advance.unwrap_or(max_advance);
 
         let metrics = FontMetrics {
             underline_size,
@@ -278,6 +284,8 @@ impl PlatformFontMethods for PlatformFont {
             max_advance,
             average_advance,
             line_gap: height,
+            zero_horizontal_advance,
+            ic_horizontal_advance,
         };
 
         debug!("Font metrics (@{}px): {:?}", em_size.to_f32_px(), metrics);

components/gfx/platform/macos/font.rs

@@ -258,11 +258,15 @@ impl PlatformFontMethods for PlatformFont {
         let line_gap = (ascent + descent + leading + 0.5).floor();
 
         let max_advance = Au::from_f64_px(self.ctfont.bounding_box().size.width);
-        let average_advance = self
+        let zero_horizontal_advance = self
             .glyph_index('0')
             .and_then(|idx| self.glyph_h_advance(idx))
-            .map(Au::from_f64_px)
-            .unwrap_or(max_advance);
+            .map(Au::from_f64_px);
+        let ic_horizontal_advance = self
+            .glyph_index('\u{6C34}')
+            .and_then(|idx| self.glyph_h_advance(idx))
+            .map(Au::from_f64_px);
+        let average_advance = zero_horizontal_advance.unwrap_or(max_advance);
 
         let metrics = FontMetrics {
             underline_size: Au::from_f64_au(underline_thickness),
@@ -285,6 +289,8 @@ impl PlatformFontMethods for PlatformFont {
             max_advance,
             average_advance,
             line_gap: Au::from_f64_px(line_gap),
+            zero_horizontal_advance,
+            ic_horizontal_advance,
         };
         debug!(
             "Font metrics (@{} pt): {:?}",

components/gfx/platform/windows/font.rs

@@ -231,6 +231,15 @@ impl PlatformFontMethods for PlatformFont {
         // is pulled out here for clarity
         let leading = dm.ascent - dm.capHeight;
 
+        let zero_horizontal_advance = self
+            .glyph_index('0')
+            .and_then(|idx| self.glyph_h_advance(idx))
+            .map(Au::from_f64_px);
+        let ic_horizontal_advance = self
+            .glyph_index('\u{6C34}')
+            .and_then(|idx| self.glyph_h_advance(idx))
+            .map(Au::from_f64_px);
+
         let metrics = FontMetrics {
             underline_size: au_from_du(dm.underlineThickness as i32),
             underline_offset: au_from_du_s(dm.underlinePosition as i32),
@@ -244,6 +253,8 @@ impl PlatformFontMethods for PlatformFont {
             max_advance: au_from_pt(0.0),     // FIXME
             average_advance: au_from_pt(0.0), // FIXME
             line_gap: au_from_du_s((dm.ascent + dm.descent + dm.lineGap as u16) as i32),
+            zero_horizontal_advance,
+            ic_horizontal_advance,
         };
         debug!("Font metrics (@{} pt): {:?}", self.em_size * 12., metrics);
         metrics

components/layout_thread_2020/lib.rs

@@ -1247,8 +1247,9 @@ impl FontMetricsProvider for LayoutFontMetricsProvider {
         _retrieve_math_scales: bool,
     ) -> FontMetrics {
         layout::context::with_thread_local_font_context(&self.0, move |font_context| {
-            let Some(servo_metrics) = font_context
-                .font_group_with_size(ServoArc::new(font.clone()), base_size.into())
+            let font_group =
+                font_context.font_group_with_size(ServoArc::new(font.clone()), base_size.into());
+            let Some(first_font_metrics) = font_group
                 .borrow_mut()
                 .first(font_context)
                 .map(|font| font.borrow().metrics.clone())
@@ -1258,16 +1259,39 @@ impl FontMetricsProvider for LayoutFontMetricsProvider {
 
             // Only use the x-height of this font if it is non-zero. Some fonts return
             // inaccurate metrics, which shouldn't be used.
-            let x_height = Some(servo_metrics.x_height)
+            let x_height = Some(first_font_metrics.x_height)
                 .filter(|x_height| !x_height.is_zero())
                 .map(CSSPixelLength::from);
 
+            let zero_advance_measure = first_font_metrics
+                .zero_horizontal_advance
+                .or_else(|| {
+                    font_group
+                        .borrow_mut()
+                        .find_by_codepoint(font_context, '0')?
+                        .borrow()
+                        .metrics
+                        .zero_horizontal_advance
+                })
+                .map(CSSPixelLength::from);
+            let ic_width = first_font_metrics
+                .ic_horizontal_advance
+                .or_else(|| {
+                    font_group
+                        .borrow_mut()
+                        .find_by_codepoint(font_context, '\u{6C34}')?
+                        .borrow()
+                        .metrics
+                        .ic_horizontal_advance
+                })
+                .map(CSSPixelLength::from);
+
             FontMetrics {
                 x_height,
-                zero_advance_measure: None,
+                zero_advance_measure,
                 cap_height: None,
-                ic_width: None,
-                ascent: servo_metrics.ascent.into(),
+                ic_width,
+                ascent: first_font_metrics.ascent.into(),
                 script_percent_scale_down: None,
                 script_script_percent_scale_down: None,
             }

tests/wpt/meta/css/css-text/white-space/text-wrap-balance-overflow-002.html.ini

@@ -0,0 +1,2 @@
+[text-wrap-balance-overflow-002.html]
+  expected: FAIL

tests/wpt/meta/css/css-text/white-space/trailing-space-position-001.html.ini

@@ -1,6 +1,3 @@
 [trailing-space-position-001.html]
-  [CSS Test: Positions of trailing collapsible spaces 1]
-    expected: FAIL
-
   [CSS Test: Positions of trailing collapsible spaces 3]
     expected: FAIL