Auto merge of #11303 - mbrubeck:last-resort, r=pcwalton

Always include the last-resort font

This is used as a fallback for any characters that don't have glyphs in the specified font.  Without this, per-glyph font fallback doesn't work because the FontGroup always contains only one font.  Fixes missing glyphs on many pages on my Linux box.

As a follow-up, we should probably have a smarter strategy for finding fallback fonts, possibly varying by script.  (Currently we just have a few hard-coded family names.)

r? @glennw

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components/gfx/font_context.rs

@@ -223,38 +223,35 @@ impl FontContext {
             }
         }
 
-        // If unable to create any of the specified fonts, create one from the
-        // list of last resort fonts for this platform.
-        if fonts.is_empty() {
-            let mut cache_hit = false;
-            for cached_font_entry in &self.fallback_font_cache {
-                let cached_font = cached_font_entry.font.borrow();
-                if cached_font.descriptor == desc &&
-                            cached_font.requested_pt_size == style.font_size &&
-                            cached_font.variant == style.font_variant {
-                    fonts.push(cached_font_entry.font.clone());
-                    cache_hit = true;
-                    break;
-                }
+        // Add a last resort font as a fallback option.
+        let mut cache_hit = false;
+        for cached_font_entry in &self.fallback_font_cache {
+            let cached_font = cached_font_entry.font.borrow();
+            if cached_font.descriptor == desc &&
+                        cached_font.requested_pt_size == style.font_size &&
+                        cached_font.variant == style.font_variant {
+                fonts.push(cached_font_entry.font.clone());
+                cache_hit = true;
+                break;
             }
+        }
 
-            if !cache_hit {
-                let template_info = self.font_cache_thread.last_resort_font_template(desc.clone());
-                let layout_font = self.create_layout_font(template_info.font_template,
-                                                          desc.clone(),
-                                                          style.font_size,
-                                                          style.font_variant,
-                                                          template_info.font_key);
-                match layout_font {
-                    Ok(layout_font) => {
-                        let layout_font = Rc::new(RefCell::new(layout_font));
-                        self.fallback_font_cache.push(FallbackFontCacheEntry {
-                            font: layout_font.clone(),
-                        });
-                        fonts.push(layout_font);
-                    }
-                    Err(_) => debug!("Failed to create fallback layout font!")
+        if !cache_hit {
+            let template_info = self.font_cache_thread.last_resort_font_template(desc.clone());
+            let layout_font = self.create_layout_font(template_info.font_template,
+                                                      desc.clone(),
+                                                      style.font_size,
+                                                      style.font_variant,
+                                                      template_info.font_key);
+            match layout_font {
+                Ok(layout_font) => {
+                    let layout_font = Rc::new(RefCell::new(layout_font));
+                    self.fallback_font_cache.push(FallbackFontCacheEntry {
+                        font: layout_font.clone(),
+                    });
+                    fonts.push(layout_font);
                 }
+                Err(_) => debug!("Failed to create fallback layout font!")
             }
         }
 

components/layout/fragment.rs

@@ -1971,6 +1971,11 @@ impl Fragment {
                 }
             }
             SpecificFragmentInfo::ScannedText(ref text_fragment) => {
+                // Fragments with no glyphs don't contribute any inline metrics.
+                // TODO: Filter out these fragments during flow construction?
+                if text_fragment.content_size.inline == Au(0) {
+                    return InlineMetrics::new(Au(0), Au(0), Au(0));
+                }
                 // See CSS 2.1 § 10.8.1.
                 let line_height = self.calculate_line_height(layout_context);
                 let font_derived_metrics =

components/layout/text.rs

@@ -197,17 +197,12 @@ impl TextRunScanner {
                 for (byte_index, character) in text.char_indices() {
                     // Search for the first font in this font group that contains a glyph for this
                     // character.
-                    let mut font_index = 0;
+                    let font_index = fontgroup.fonts.iter().position(|font| {
+                        font.borrow().glyph_index(character).is_some()
+                    }).unwrap_or(0);
+
                     // The following code panics one way or another if this condition isn't met.
                     assert!(fontgroup.fonts.len() > 0);
-                    while font_index < fontgroup.fonts.len() - 1 {
-                        if fontgroup.fonts.get(font_index).unwrap().borrow()
-                                          .glyph_index(character)
-                                          .is_some() {
-                            break
-                        }
-                        font_index += 1;
-                    }
 
                     let bidi_level = match bidi_levels {
                         Some(levels) => levels[*paragraph_bytes_processed],

tests/wpt/metadata-css/css-color-3_dev/html4/t422-rgba-onscreen-multiple-boxes-c.htm.ini

@@ -0,0 +1,3 @@
+[t422-rgba-onscreen-multiple-boxes-c.htm]
+  type: reftest
+  expected: FAIL

tests/wpt/metadata-css/css-color-3_dev/html4/t425-hsla-onscreen-multiple-boxes-c.htm.ini

@@ -0,0 +1,3 @@
+[t425-hsla-onscreen-multiple-boxes-c.htm]
+  type: reftest
+  expected: FAIL

tests/wpt/metadata-css/css-text-3_dev/html/css3-text-line-break-jazh-059.htm.ini

@@ -1,3 +1,4 @@
 [css3-text-line-break-jazh-059.htm]
   type: reftest
-  expected: FAIL
+  expected:
+    if os == "mac": FAIL