Handle cases where the layout root is None. Fixes #6375.

components/layout/block.rs

@@ -2436,7 +2436,7 @@ pub trait ISizeAndMarginsComputer {
 
         // Invariant: inline-start_margin + inline-size + inline-end_margin ==
         // available_inline-size
-        let (inline_start_margin, mut inline_size, inline_end_margin) =
+        let (inline_start_margin, inline_size, inline_end_margin) =
             match (inline_start_margin, computed_inline_size, inline_end_margin) {
                 // If all have a computed value other than 'auto', the system is over-constrained.
                 (MaybeAuto::Specified(margin_start),
@@ -2922,7 +2922,7 @@ impl ISizeAndMarginsComputer for InlineBlockNonReplaced {
                                      block: &mut BlockFlow,
                                      input: &ISizeConstraintInput)
                                      -> ISizeConstraintSolution {
-        let (mut computed_inline_size,
+        let (computed_inline_size,
              inline_start_margin,
              inline_end_margin,
              available_inline_size) =
@@ -2963,7 +2963,7 @@ impl ISizeAndMarginsComputer for InlineBlockReplaced {
             MaybeAuto::Auto => false,
         });
 
-        let (mut computed_inline_size,
+        let (computed_inline_size,
              inline_start_margin,
              inline_end_margin,
              available_inline_size) =

components/layout/layout_task.rs

@@ -156,6 +156,14 @@ pub struct LayoutTaskData {
     pub visible_rects: Arc<HashMap<LayerId, Rect<Au>, DefaultState<FnvHasher>>>,
 }
 
+impl LayoutTaskData {
+    pub fn layout_root(&self) -> Option<FlowRef> {
+        self.root_flow.as_ref().map(|root_flow| {
+            root_flow.clone()
+        })
+    }
+}
+
 /// Information needed by the layout task.
 pub struct LayoutTask {
     /// The ID of the pipeline that we belong to.
@@ -786,10 +794,6 @@ impl LayoutTask {
         Some(flow)
     }
 
-    fn get_layout_root(&self, node: LayoutNode) -> FlowRef {
-        self.try_get_layout_root(node).expect("no layout root")
-    }
-
     /// Performs layout constraint solving.
     ///
     /// This corresponds to `Reflow()` in Gecko and `layout()` in WebKit/Blink and should be
@@ -1161,7 +1165,7 @@ impl LayoutTask {
             });
 
             // Retrieve the (possibly rebuilt) root flow.
-            rw_data.root_flow = Some(self.get_layout_root((*node).clone()));
+            rw_data.root_flow = self.try_get_layout_root((*node).clone());
 
             // Kick off animations if any were triggered.
             animation::process_new_animations(&mut *rw_data, self.id);
@@ -1178,7 +1182,7 @@ impl LayoutTask {
                                                      &mut rw_data,
                                                      &mut shared_layout_context);
 
-        let mut root_flow = (*rw_data.root_flow.as_ref().unwrap()).clone();
+        if let Some(mut root_flow) = rw_data.layout_root() {
             match data.query_type {
                 ReflowQueryType::ContentBoxQuery(node) =>
                     process_content_box_request(node, &mut root_flow, &mut rw_data),
@@ -1192,7 +1196,7 @@ impl LayoutTask {
                     self.process_offset_parent_query(node, &mut root_flow, &mut rw_data),
                 ReflowQueryType::NoQuery => {}
             }
-
+        }
 
         // Tell script that we're done.
         //
@@ -1279,14 +1283,8 @@ impl LayoutTask {
                                                                   &self.url,
                                                                   reflow_info.goal);
 
-        match rw_data.root_flow.as_ref() {
+        if let Some(mut root_flow) = rw_data.layout_root() {
-            None => {
-                // We haven't performed a single layout yet! Do nothing.
-                return
-            }
-            Some(ref root_flow) => {
             // Perform an abbreviated style recalc that operates without access to the DOM.
-                let mut root_flow = (*root_flow).clone();
             let animations = &*rw_data.running_animations;
             profile(time::ProfilerCategory::LayoutStyleRecalc,
                     self.profiler_metadata(),
@@ -1296,7 +1294,6 @@ impl LayoutTask {
                                                                animations)
                     });
         }
-        }
 
         self.perform_post_style_recalc_layout_passes(&reflow_info,
                                                      &mut *rw_data,
@@ -1307,7 +1304,7 @@ impl LayoutTask {
                                                    data: &Reflow,
                                                    rw_data: &mut LayoutTaskData,
                                                    layout_context: &mut SharedLayoutContext) {
-        let mut root_flow = (*rw_data.root_flow.as_ref().unwrap()).clone();
+        if let Some(mut root_flow) = rw_data.layout_root() {
             profile(time::ProfilerCategory::LayoutRestyleDamagePropagation,
                     self.profiler_metadata(),
                     self.time_profiler_chan.clone(),
@@ -1356,13 +1353,14 @@ impl LayoutTask {
 
             self.perform_post_main_layout_passes(data, rw_data, layout_context);
         }
+    }
 
     fn perform_post_main_layout_passes<'a>(&'a self,
                                            data: &Reflow,
                                            rw_data: &mut LayoutTaskData,
                                            layout_context: &mut SharedLayoutContext) {
         // Build the display list if necessary, and send it to the painter.
-        let mut root_flow = (*rw_data.root_flow.as_ref().unwrap()).clone();
+        if let Some(mut root_flow) = rw_data.layout_root() {
             self.compute_abs_pos_and_build_display_list(data,
                                                         &mut root_flow,
                                                         &mut *layout_context,
@@ -1379,6 +1377,7 @@ impl LayoutTask {
 
             rw_data.generation += 1;
         }
+    }
 
     unsafe fn dirty_all_nodes(node: &mut LayoutNode) {
         for node in node.traverse_preorder() {

tests/wpt/metadata-css/css21_dev/html4/root-box-003.htm.ini

@@ -1,3 +1,3 @@
 [root-box-003.htm]
   type: reftest
-  expected: CRASH
+  expected: TIMEOUT

tests/wpt/metadata/dom/nodes/Document-createElement-namespace.html.ini

@@ -1,3 +1,104 @@
 [Document-createElement-namespace.html]
   type: testharness
-  disabled: Issue 6386
+  [Created element's namespace in created XML document]
+    expected: FAIL
+
+  [Created element's namespace in created XHTML document]
+    expected: FAIL
+
+  [Created element's namespace in created SVG document]
+    expected: FAIL
+
+  [Created element's namespace in created MathML document]
+    expected: FAIL
+
+  [Created element's namespace in empty.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in empty.xml]
+    expected: FAIL
+
+  [Created element's namespace in empty.svg]
+    expected: FAIL
+
+  [Created element's namespace in minimal_html.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in minimal_html.xml]
+    expected: FAIL
+
+  [Created element's namespace in minimal_html.svg]
+    expected: FAIL
+
+  [Created element's namespace in xhtml.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in xhtml.xml]
+    expected: FAIL
+
+  [Created element's namespace in xhtml.svg]
+    expected: FAIL
+
+  [Created element's namespace in svg.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in svg.xml]
+    expected: FAIL
+
+  [Created element's namespace in svg.svg]
+    expected: FAIL
+
+  [Created element's namespace in mathml.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in mathml.xml]
+    expected: FAIL
+
+  [Created element's namespace in mathml.svg]
+    expected: FAIL
+
+  [Created element's namespace in bare_xhtml.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in bare_xhtml.xml]
+    expected: FAIL
+
+  [Created element's namespace in bare_xhtml.svg]
+    expected: FAIL
+
+  [Created element's namespace in bare_svg.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in bare_svg.xml]
+    expected: FAIL
+
+  [Created element's namespace in bare_svg.svg]
+    expected: FAIL
+
+  [Created element's namespace in bare_mathml.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in bare_mathml.xml]
+    expected: FAIL
+
+  [Created element's namespace in bare_mathml.svg]
+    expected: FAIL
+
+  [Created element's namespace in xhtml_ns_removed.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in xhtml_ns_removed.xml]
+    expected: FAIL
+
+  [Created element's namespace in xhtml_ns_removed.svg]
+    expected: FAIL
+
+  [Created element's namespace in xhtml_ns_changed.xhtml]
+    expected: FAIL
+
+  [Created element's namespace in xhtml_ns_changed.xml]
+    expected: FAIL
+
+  [Created element's namespace in xhtml_ns_changed.svg]
+    expected: FAIL
+