Make "align descendants" rule use parent's text-align.

Flows never care about their own text-align, only the text-align of
their parent; change the text-align flags to account for that.  Make the
"align descendants" rule use the flags instead of the current node's style.

Fixes #7301.

components/layout/block.rs

@@ -1466,8 +1466,9 @@ impl BlockFlow {
 
             // Per CSS 2.1 § 16.3.1, text alignment propagates to all children in flow.
             //
-            // TODO(#2018, pcwalton): Do this in the cascade instead.
-            flow::mut_base(kid).flags.propagate_text_alignment_from_parent(flags.clone());
+            // TODO(#2265, pcwalton): Do this in the cascade instead.
+            let containing_block_text_align = self.fragment.style().get_inheritedtext().text_align;
+            flow::mut_base(kid).flags.set_text_align(containing_block_text_align);
 
             // Handle `text-indent` on behalf of any inline children that we have. This is
             // necessary because any percentages are relative to the containing block, which only
@@ -2276,9 +2277,6 @@ pub trait ISizeAndMarginsComputer {
             (_, box_sizing::T::content_box) => {}
         }
 
-        // The text alignment of a block flow is the text alignment of its box's style.
-        block.base.flags.set_text_align(style.get_inheritedtext().text_align);
-
         let margin = style.logical_margin();
         let position = style.logical_position();
 
@@ -2442,6 +2440,7 @@ pub trait ISizeAndMarginsComputer {
         // Check for direction of parent flow (NOT Containing Block)
         let block_mode = block.base.writing_mode;
         let container_mode = block.base.block_container_writing_mode;
+        let block_align = block.base.flags.text_align();
 
         // FIXME (mbrubeck): Handle vertical writing modes.
         let parent_has_same_direction = container_mode.is_bidi_ltr() == block_mode.is_bidi_ltr();
@@ -2472,9 +2471,6 @@ pub trait ISizeAndMarginsComputer {
                  MaybeAuto::Specified(margin_end)) => {
                     // servo_left, servo_right, and servo_center are used to implement
                     // the "align descendants" rule in HTML5 § 14.2.
-                    // FIXME(#7301): block_align is supposed to be the text-align of the
-                    // parent, not the current node.
-                    let block_align = input.text_align;
                     if block_align == text_align::T::servo_center {
                         // Ignore any existing margins, and make the inline-start and
                         // inline-end margins equal.

components/layout/flow.rs

@@ -655,14 +655,6 @@ static HAS_FLOATED_DESCENDANTS_BITMASK: FlowFlags = FlowFlags { bits: 0b0000_001
 static TEXT_ALIGN_SHIFT: usize = 11;
 
 impl FlowFlags {
-    /// Propagates text alignment flags from an appropriate parent flow per CSS 2.1.
-    ///
-    /// FIXME(#2265, pcwalton): It would be cleaner and faster to make this a derived CSS property
-    /// `-servo-text-align-in-effect`.
-    pub fn propagate_text_alignment_from_parent(&mut self, parent_flags: FlowFlags) {
-        self.set_text_align_override(parent_flags);
-    }
-
     #[inline]
     pub fn text_align(self) -> text_align::T {
         text_align::T::from_u32((self & TEXT_ALIGN).bits() >> TEXT_ALIGN_SHIFT).unwrap()
@@ -674,11 +666,6 @@ impl FlowFlags {
                 FlowFlags::from_bits(value.to_u32() << TEXT_ALIGN_SHIFT).unwrap();
     }
 
-    #[inline]
-    pub fn set_text_align_override(&mut self, parent: FlowFlags) {
-        self.insert(parent & TEXT_ALIGN);
-    }
-
     #[inline]
     pub fn union_floated_descendants_flags(&mut self, other: FlowFlags) {
         self.insert(other & HAS_FLOATED_DESCENDANTS_BITMASK);