Auto merge of #18075 - upsuper:text-in-ruby, r=Manishearth

Apply line break suppression to text when in any ruby

This should fix [bug 1388904](https://bugzilla.mozilla.org/show_bug.cgi?id=1388904).

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components/style/style_adjuster.rs

@@ -108,8 +108,9 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
     ///
     /// Note that this, for Gecko, comes through Servo_ComputedValues_Inherit.
     #[cfg(feature = "gecko")]
-    pub fn adjust_for_text(&mut self) {
+    pub fn adjust_for_text(&mut self, parent_style: &ComputedValues) {
         self.adjust_for_text_combine_upright();
+        self.adjust_for_text_in_ruby(parent_style);
         self.set_bits();
     }
 
@@ -138,6 +139,19 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
         }
     }
 
+    /// Applies the line break suppression flag to text if it is in any ruby
+    /// box. This is necessary because its parent may not itself have the flag
+    /// set (e.g. ruby or ruby containers), thus we may not inherit the flag
+    /// from them.
+    #[cfg(feature = "gecko")]
+    fn adjust_for_text_in_ruby(&mut self, parent_style: &ComputedValues) {
+        use properties::computed_value_flags::SHOULD_SUPPRESS_LINEBREAK;
+        let parent_display = parent_style.get_box().clone_display();
+        if parent_display.is_ruby_type() {
+            self.style.flags.insert(SHOULD_SUPPRESS_LINEBREAK);
+        }
+    }
+
     /// https://drafts.csswg.org/css-writing-modes-3/#block-flow:
     ///
     ///    If a box has a different writing-mode value than its containing

ports/geckolib/glue.rs

@@ -1821,7 +1821,7 @@ pub extern "C" fn Servo_ComputedValues_Inherit(
 
         if for_text {
             StyleAdjuster::new(&mut style)
-                .adjust_for_text();
+                .adjust_for_text(reference);
         }
 
         style.build()