auto merge of #1349 : dhedlund/servo/issue_222, r=jdm,me

Fixes #222.

Implements 'text-align' inheritance for inline elements.  The text alignment code has been changed a couple of times since the ticket was originally opened and was improved to inherit the text-align property from from an ancestor element.  This addressed the issue, so long as no inline elements had a text-align property defined.  Both Firefox and Chromium ignore any text-align properties attached to inline elements, but none of the specs are explicit about ignoring the property or inheriting only from non-inline elements:
http://www.w3.org/TR/CSS2/visuren.html#inline-formatting
http://www.w3.org/TR/CSS2/text.html#propdef-text-align

This is my first stab at writing any code that touches the DOM node tree.  Based on a few observations, I made the assumption that the `self.base.node` of a InlineFlow always corresponds to a BlockFlow-based node, no matter how deep inline DOM elements are nested; there was no obvious way to traverse Flow-traited objects directly and I'm not sure if it's possible to get from a FlowData struct back to a non-child {Block,Inline}Flow (probably intentionally).

I could've kept traversing the node tree directly, checking against each node style to ensure it didn't have an inline display property, but I could not create a scenario where the `base.node` was ever an inline.  It also feels like a code smell to be walking up the tree at all, especially for stylesheet properties.  Feels like it should eventually be handled in style::properties directly as being conditional inherited?

4 files changed, 46 insertions, 14 deletions

diff --git a/src/components/main/layout/inline.rs b/src/components/main/layout/inline.rs
index aa5b5825070..861fa93a1c9 100644
--- a/src/components/main/layout/inline.rs
+++ b/src/components/main/layout/inline.rs
@@ -579,22 +579,10 @@ impl InlineFlow {
     }
 
     /// Sets box X positions based on alignment for one line.
-    fn set_horizontal_box_positions(boxes: &[Box], line: &LineBox) {
+    fn set_horizontal_box_positions(boxes: &[Box], line: &LineBox, linebox_align: text_align::T) {
         // Figure out how much width we have.
         let slack_width = Au::max(Au(0), line.green_zone.width - line.bounds.size.width);
 
-        // Get the text alignment.
-        //
-        // TODO(burg, issue #222): use 'text-align' property from `InlineFlow`'s block container,
-        // not from the style of the first box child.
-        let linebox_align = if line.range.begin() < boxes.len() {
-            let first_box = &boxes[line.range.begin()];
-            first_box.style().Text.text_align
-        } else {
-            // Nothing to lay out, so assume left alignment.
-            text_align::left
-        };
-
         // Set the box x positions based on that alignment.
         let mut offset_x = line.bounds.origin.x;
         offset_x = offset_x + match linebox_align {
@@ -712,10 +700,13 @@ impl Flow for InlineFlow {
 
         let mut line_height_offset = Au::new(0);
 
+        // All lines use text alignment from base (non-inline) node
+        let text_align = self.base.node.style().get().Text.text_align;
+
         // Now, go through each line and lay out the boxes inside.
         for line in self.lines.mut_iter() {
             // Lay out boxes horizontally.
-            InlineFlow::set_horizontal_box_positions(self.boxes, line);
+            InlineFlow::set_horizontal_box_positions(self.boxes, line, text_align);
 
             // Set the top y position of the current linebox.
             // `line_height_offset` is updated at the end of the previous loop.
diff --git a/src/test/ref/basic.list b/src/test/ref/basic.list
index f4d2b5aaacc..787823656c2 100644
--- a/src/test/ref/basic.list
+++ b/src/test/ref/basic.list
@@ -18,3 +18,4 @@
 == border_style_none_a.html border_style_none_b.html
 == acid1_a.html acid1_b.html
 == text_decoration_propagation_a.html text_decoration_propagation_b.html
+== inline_text_align_a.html inline_text_align_b.html
diff --git a/src/test/ref/inline_text_align_a.html b/src/test/ref/inline_text_align_a.html
new file mode 100644
index 00000000000..57fc40b7448
--- /dev/null
+++ b/src/test/ref/inline_text_align_a.html
@@ -0,0 +1,24 @@
+<html>
+  <head>
+    <style>
+      .right {
+        text-align: right;
+      }
+      .left {
+        text-align: left;
+      }
+      .inline {
+        display: inline;
+      }
+    </style>
+  </head>
+  <body>
+    <div class="right">
+      <span class="left"> <!-- should ignore 'text-align' of inline elements -->
+        <div class="inline left"> <!-- ... and those explicitly defined as inline -->
+          <span>hello, wide world</span>
+        </span>
+      </span>
+    </div>
+  </body>
+</html>
diff --git a/src/test/ref/inline_text_align_b.html b/src/test/ref/inline_text_align_b.html
new file mode 100644
index 00000000000..72ab836ae04
--- /dev/null
+++ b/src/test/ref/inline_text_align_b.html
@@ -0,0 +1,16 @@
+<html>
+  <head>
+    <style>
+      .right {
+        text-align: right;
+      }
+    </style>
+  </head>
+  <body>
+    <div class="right">
+      <span class="right">
+        hello, wide world
+      </span>
+    </div>
+  </body>
+</html>