Auto merge of #7177 - pcwalton:intervening-inline-block, r=mbrubeck

layout: Improve our handling of inline absolute containing blocks.

Several issues are addressed in this commit:

* Inline flows now bubble up their absolute descendants instead of
  making the inline flow the containing block for them. (In the future,
  we will need to make the inline flow *sometimes* be the containing
  block for them, but for now it improves sites to unconditionally
  bubble up.)

* Fragments now look at their inline fragment context to determine
  whether they are positioned.

* Inline flows now push the stacking-relative position of the absolute
  containing block down to their inline-block fragments.

* Inline absolute hypothetical fragments can be containing blocks.

* Fixes the logic in
  `containing_block_range_for_flow_surrounding_fragment_at_index`. The
  condition to determine whether fragments are positioned was inverted!

* `Descendants`/`AbsDescendants` has been refactored in order to become
  more friendly to inline absolute containing blocks in the future.

Improves the inline position of the green drop-down arrow in the Google
SERPs. (The block position is still wrong.)

r? @mbrubeck

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10 files changed, 235 insertions, 92 deletions

diff --git a/components/layout/block.rs b/components/layout/block.rs
index fdfec58e776..c73f97a821b 100644
--- a/components/layout/block.rs
+++ b/components/layout/block.rs
@@ -708,9 +708,9 @@ impl BlockFlow {
 
     /// Return true if this has a replaced fragment.
     ///
-    /// Text, Images, Inline Block and
-    //  Canvas (https://html.spec.whatwg.org/multipage/#replaced-elements)
-    //  fragments are considered as replaced fragments
+    /// Text, Images, Inline Block and Canvas
+    /// (https://html.spec.whatwg.org/multipage/#replaced-elements) fragments are considered as
+    /// replaced fragments.
     fn is_replaced_content(&self) -> bool {
         match self.fragment.specific {
             SpecificFragmentInfo::ScannedText(_) |
diff --git a/components/layout/construct.rs b/components/layout/construct.rs
index a918e35463b..c9934510424 100644
--- a/components/layout/construct.rs
+++ b/components/layout/construct.rs
@@ -17,10 +17,8 @@ use block::BlockFlow;
 use context::LayoutContext;
 use data::{HAS_NEWLY_CONSTRUCTED_FLOW, LayoutDataWrapper};
 use floats::FloatKind;
-use flow::{Descendants, AbsDescendants};
-use flow::{Flow, ImmutableFlowUtils, MutableFlowUtils, MutableOwnedFlowUtils};
-use flow::{IS_ABSOLUTELY_POSITIONED};
-use flow;
+use flow::{self, AbsoluteDescendants, Flow, ImmutableFlowUtils, IS_ABSOLUTELY_POSITIONED};
+use flow::{MutableFlowUtils, MutableOwnedFlowUtils};
 use flow_ref::FlowRef;
 use fragment::{Fragment, GeneratedContentInfo, IframeFragmentInfo};
 use fragment::{CanvasFragmentInfo, ImageFragmentInfo, InlineAbsoluteFragmentInfo};
@@ -72,7 +70,7 @@ pub enum ConstructionResult {
     /// This node contributed a flow at the proper position in the tree.
     /// Nothing more needs to be done for this node. It has bubbled up fixed
     /// and absolute descendant flows that have a containing block above it.
-    Flow(FlowRef, AbsDescendants),
+    Flow(FlowRef, AbsoluteDescendants),
 
     /// This node contributed some object or objects that will be needed to construct a proper flow
     /// later up the tree, but these objects have not yet found their home.
@@ -120,9 +118,6 @@ pub struct InlineFragmentsConstructionResult {
 
     /// Any fragments that succeed the {ib} splits.
     pub fragments: IntermediateInlineFragments,
-
-    /// Any absolute descendants that we're bubbling up.
-    pub abs_descendants: AbsDescendants,
 }
 
 /// Represents an {ib} split that has not yet found the containing block that it belongs to. This
@@ -167,14 +162,14 @@ pub struct IntermediateInlineFragments {
     pub fragments: LinkedList<Fragment>,
 
     /// The list of absolute descendants of those inline fragments.
-    pub absolute_descendants: AbsDescendants,
+    pub absolute_descendants: AbsoluteDescendants,
 }
 
 impl IntermediateInlineFragments {
     fn new() -> IntermediateInlineFragments {
         IntermediateInlineFragments {
             fragments: LinkedList::new(),
-            absolute_descendants: Descendants::new(),
+            absolute_descendants: AbsoluteDescendants::new(),
         }
     }
 
@@ -424,6 +419,7 @@ impl<'a> FlowConstructor<'a> {
                                               fragment_accumulator: InlineFragmentsAccumulator,
                                               flow: &mut FlowRef,
                                               flow_list: &mut Vec<FlowRef>,
+                                              absolute_descendants: &mut AbsoluteDescendants,
                                               node: &ThreadSafeLayoutNode) {
         let mut fragments = fragment_accumulator.to_intermediate_inline_fragments();
         if fragments.is_empty() {
@@ -432,7 +428,8 @@ impl<'a> FlowConstructor<'a> {
 
         strip_ignorable_whitespace_from_start(&mut fragments.fragments);
         strip_ignorable_whitespace_from_end(&mut fragments.fragments);
-        if fragments.is_empty() {
+        if fragments.fragments.is_empty() {
+            absolute_descendants.push_descendants(fragments.absolute_descendants);
             return
         }
 
@@ -469,11 +466,18 @@ impl<'a> FlowConstructor<'a> {
         }
 
         // Set up absolute descendants as necessary.
-        let contains_positioned_fragments = inline_flow_ref.contains_positioned_fragments();
-        if contains_positioned_fragments {
-            // This is the containing block for all the absolute descendants.
-            inline_flow_ref.set_absolute_descendants(fragments.absolute_descendants);
-        }
+        //
+        // TODO(pcwalton): The inline flow itself may need to become the containing block for
+        // absolute descendants in order to handle cases like:
+        //
+        //      <div>
+        //          <span style="position: relative">
+        //              <span style="position: absolute; ..."></span>
+        //          </span>
+        //      </div>
+        //
+        // See the comment above `flow::AbsoluteDescendantInfo` for more information.
+        absolute_descendants.push_descendants(fragments.absolute_descendants);
 
         {
             let inline_flow = inline_flow_ref.as_inline();
@@ -503,7 +507,7 @@ impl<'a> FlowConstructor<'a> {
             node: &ThreadSafeLayoutNode,
             kid: ThreadSafeLayoutNode,
             inline_fragment_accumulator: &mut InlineFragmentsAccumulator,
-            abs_descendants: &mut Descendants) {
+            abs_descendants: &mut AbsoluteDescendants) {
         match kid.swap_out_construction_result() {
             ConstructionResult::None => {}
             ConstructionResult::Flow(mut kid_flow, kid_abs_descendants) => {
@@ -512,7 +516,7 @@ impl<'a> FlowConstructor<'a> {
                 if flow.is_table() && kid_flow.is_table_caption() {
                     self.set_flow_construction_result(&kid,
                                                       ConstructionResult::Flow(kid_flow,
-                                                                               Descendants::new()))
+                                                                               AbsoluteDescendants::new()))
                 } else if flow.need_anonymous_flow(&*kid_flow) {
                     consecutive_siblings.push(kid_flow)
                 } else {
@@ -520,11 +524,14 @@ impl<'a> FlowConstructor<'a> {
                     // handle {ib} splits.
                     debug!("flushing {} inline box(es) to flow A",
                            inline_fragment_accumulator.fragments.fragments.len());
-                    self.flush_inline_fragments_to_flow_or_list(
+                    let old_inline_fragment_accumulator =
                         mem::replace(inline_fragment_accumulator,
-                                     InlineFragmentsAccumulator::new()),
+                                     InlineFragmentsAccumulator::new());
+                    self.flush_inline_fragments_to_flow_or_list(
+                        old_inline_fragment_accumulator,
                         flow,
                         consecutive_siblings,
+                        abs_descendants,
                         node);
                     if !consecutive_siblings.is_empty() {
                         let consecutive_siblings = mem::replace(consecutive_siblings, vec!());
@@ -539,7 +546,6 @@ impl<'a> FlowConstructor<'a> {
                     InlineFragmentsConstructionResult {
                         splits,
                         fragments: successor_fragments,
-                        abs_descendants: kid_abs_descendants,
                     })) => {
                 // Add any {ib} splits.
                 for split in splits.into_iter() {
@@ -554,11 +560,14 @@ impl<'a> FlowConstructor<'a> {
                     // Flush any inline fragments that we were gathering up.
                     debug!("flushing {} inline box(es) to flow A",
                            inline_fragment_accumulator.fragments.fragments.len());
+                    let old_inline_fragment_accumulator =
+                        mem::replace(inline_fragment_accumulator,
+                                     InlineFragmentsAccumulator::new());
                     self.flush_inline_fragments_to_flow_or_list(
-                            mem::replace(inline_fragment_accumulator,
-                                         InlineFragmentsAccumulator::new()),
+                            old_inline_fragment_accumulator,
                             flow,
                             consecutive_siblings,
+                            &mut inline_fragment_accumulator.fragments.absolute_descendants,
                             node);
 
                     // Push the flow generated by the {ib} split onto our list of
@@ -572,7 +581,6 @@ impl<'a> FlowConstructor<'a> {
 
                 // Add the fragments to the list we're maintaining.
                 inline_fragment_accumulator.push_all(successor_fragments);
-                abs_descendants.push_descendants(kid_abs_descendants);
             }
             ConstructionResult::ConstructionItem(ConstructionItem::Whitespace(
                     whitespace_node,
@@ -614,7 +622,7 @@ impl<'a> FlowConstructor<'a> {
         inline_fragment_accumulator.fragments.push_all(initial_fragments);
 
         // List of absolute descendants, in tree order.
-        let mut abs_descendants = Descendants::new();
+        let mut abs_descendants = AbsoluteDescendants::new();
         for kid in node.children() {
             if kid.get_pseudo_element_type() != PseudoElementType::Normal {
                 self.process(&kid);
@@ -634,6 +642,7 @@ impl<'a> FlowConstructor<'a> {
         self.flush_inline_fragments_to_flow_or_list(inline_fragment_accumulator,
                                                     &mut flow,
                                                     &mut consecutive_siblings,
+                                                    &mut abs_descendants,
                                                     node);
         if !consecutive_siblings.is_empty() {
             self.generate_anonymous_missing_child(consecutive_siblings, &mut flow, node);
@@ -649,7 +658,7 @@ impl<'a> FlowConstructor<'a> {
             // This is the containing block for all the absolute descendants.
             flow.set_absolute_descendants(abs_descendants);
 
-            abs_descendants = Descendants::new();
+            abs_descendants = AbsoluteDescendants::new();
             if is_absolutely_positioned {
                 // This is now the only absolute flow in the subtree which hasn't yet
                 // reached its CB.
@@ -784,7 +793,7 @@ impl<'a> FlowConstructor<'a> {
         let mut fragment_accumulator = InlineFragmentsAccumulator::from_inline_node(node);
         fragment_accumulator.bidi_control_chars = bidi_control_chars(&*node.style());
 
-        let mut abs_descendants = Descendants::new();
+        let mut abs_descendants = AbsoluteDescendants::new();
 
         // Concatenate all the fragments of our kids, creating {ib} splits as necessary.
         for kid in node.children() {
@@ -830,7 +839,6 @@ impl<'a> FlowConstructor<'a> {
                         InlineFragmentsConstructionResult {
                             splits,
                             fragments: successors,
-                            abs_descendants: kid_abs_descendants,
                         })) => {
 
                     // Bubble up {ib} splits.
@@ -841,7 +849,6 @@ impl<'a> FlowConstructor<'a> {
 
                     // Push residual fragments.
                     fragment_accumulator.push_all(successors);
-                    abs_descendants.push_descendants(kid_abs_descendants);
                 }
                 ConstructionResult::ConstructionItem(ConstructionItem::Whitespace(
                         whitespace_node,
@@ -869,11 +876,11 @@ impl<'a> FlowConstructor<'a> {
         // Finally, make a new construction result.
         if opt_inline_block_splits.len() > 0 || !fragment_accumulator.fragments.is_empty()
                 || abs_descendants.len() > 0 {
+            fragment_accumulator.fragments.absolute_descendants.push_descendants(abs_descendants);
             let construction_item = ConstructionItem::InlineFragments(
                     InlineFragmentsConstructionResult {
                 splits: opt_inline_block_splits,
                 fragments: fragment_accumulator.to_intermediate_inline_fragments(),
-                abs_descendants: abs_descendants,
             });
             ConstructionResult::ConstructionItem(construction_item)
         } else {
@@ -924,7 +931,6 @@ impl<'a> FlowConstructor<'a> {
             ConstructionItem::InlineFragments(InlineFragmentsConstructionResult {
                 splits: LinkedList::new(),
                 fragments: fragments,
-                abs_descendants: Descendants::new(),
             });
         ConstructionResult::ConstructionItem(construction_item)
     }
@@ -950,12 +956,12 @@ impl<'a> FlowConstructor<'a> {
         let mut fragment_accumulator =
             InlineFragmentsAccumulator::from_inline_node_and_style(node, modified_style);
         fragment_accumulator.fragments.fragments.push_back(fragment);
+        fragment_accumulator.fragments.absolute_descendants.push_descendants(abs_descendants);
 
         let construction_item =
             ConstructionItem::InlineFragments(InlineFragmentsConstructionResult {
                 splits: LinkedList::new(),
                 fragments: fragment_accumulator.to_intermediate_inline_fragments(),
-                abs_descendants: abs_descendants,
             });
         ConstructionResult::ConstructionItem(construction_item)
     }
@@ -976,12 +982,12 @@ impl<'a> FlowConstructor<'a> {
 
         let mut fragment_accumulator = InlineFragmentsAccumulator::from_inline_node(node);
         fragment_accumulator.fragments.fragments.push_back(fragment);
+        fragment_accumulator.fragments.absolute_descendants.push_descendants(abs_descendants);
 
         let construction_item =
             ConstructionItem::InlineFragments(InlineFragmentsConstructionResult {
                 splits: LinkedList::new(),
                 fragments: fragment_accumulator.to_intermediate_inline_fragments(),
-                abs_descendants: abs_descendants,
             });
         ConstructionResult::ConstructionItem(construction_item)
     }
@@ -1069,8 +1075,8 @@ impl<'a> FlowConstructor<'a> {
         // First populate the table flow with its children.
         let construction_result = self.build_flow_for_block_like(table_flow, node);
 
-        let mut abs_descendants = Descendants::new();
-        let mut fixed_descendants = Descendants::new();
+        let mut abs_descendants = AbsoluteDescendants::new();
+        let mut fixed_descendants = AbsoluteDescendants::new();
 
         // The order of the caption and the table are not necessarily the same order as in the DOM
         // tree. All caption blocks are placed before or after the table flow, depending on the
@@ -1102,7 +1108,7 @@ impl<'a> FlowConstructor<'a> {
             // This is the containing block for all the absolute descendants.
             wrapper_flow.set_absolute_descendants(abs_descendants);
 
-            abs_descendants = Descendants::new();
+            abs_descendants = AbsoluteDescendants::new();
 
             if is_fixed_positioned {
                 // Send itself along with the other fixed descendants.
@@ -1267,7 +1273,7 @@ impl<'a> FlowConstructor<'a> {
         let mut flow = FlowRef::new(flow as Box<Flow>);
         flow.finish();
 
-        ConstructionResult::Flow(flow, Descendants::new())
+        ConstructionResult::Flow(flow, AbsoluteDescendants::new())
     }
 
     /// Attempts to perform incremental repair to account for recent changes to this node. This
diff --git a/components/layout/flow.rs b/components/layout/flow.rs
index 445a3e5a49c..6b11bee1f8c 100644
--- a/components/layout/flow.rs
+++ b/components/layout/flow.rs
@@ -499,7 +499,7 @@ pub trait MutableOwnedFlowUtils {
     /// Set absolute descendants for this flow.
     ///
     /// Set this flow as the Containing Block for all the absolute descendants.
-    fn set_absolute_descendants(&mut self, abs_descendants: AbsDescendants);
+    fn set_absolute_descendants(&mut self, abs_descendants: AbsoluteDescendants);
 }
 
 #[derive(RustcEncodable, PartialEq, Debug)]
@@ -694,19 +694,17 @@ impl FlowFlags {
     }
 }
 
-/// The Descendants of a flow.
-///
-/// Also, details about their position wrt this flow.
+/// Absolutely-positioned descendants of this flow.
 #[derive(Clone)]
-pub struct Descendants {
+pub struct AbsoluteDescendants {
     /// Links to every descendant. This must be private because it is unsafe to leak `FlowRef`s to
     /// layout.
-    descendant_links: Vec<FlowRef>,
+    descendant_links: Vec<AbsoluteDescendantInfo>,
 }
 
-impl Descendants {
-    pub fn new() -> Descendants {
-        Descendants {
+impl AbsoluteDescendants {
+    pub fn new() -> AbsoluteDescendants {
+        AbsoluteDescendants {
             descendant_links: Vec::new(),
         }
     }
@@ -720,40 +718,63 @@ impl Descendants {
     }
 
     pub fn push(&mut self, given_descendant: FlowRef) {
-        self.descendant_links.push(given_descendant);
+        self.descendant_links.push(AbsoluteDescendantInfo {
+            flow: given_descendant,
+        });
     }
 
     /// Push the given descendants on to the existing descendants.
     ///
     /// Ignore any static y offsets, because they are None before layout.
-    pub fn push_descendants(&mut self, given_descendants: Descendants) {
+    pub fn push_descendants(&mut self, given_descendants: AbsoluteDescendants) {
         for elem in given_descendants.descendant_links.into_iter() {
             self.descendant_links.push(elem);
         }
     }
 
     /// Return an iterator over the descendant flows.
-    pub fn iter<'a>(&'a mut self) -> DescendantIter<'a> {
-        DescendantIter {
+    pub fn iter<'a>(&'a mut self) -> AbsoluteDescendantIter<'a> {
+        AbsoluteDescendantIter {
             iter: self.descendant_links.iter_mut(),
         }
     }
 }
 
-pub type AbsDescendants = Descendants;
+/// TODO(pcwalton): This structure is going to need a flag to record whether the absolute
+/// descendants have reached their containing block yet. The reason is so that we can handle cases
+/// like the following:
+///
+///     <div>
+///         <span id=a style="position: absolute; ...">foo</span>
+///         <span style="position: relative">
+///             <span id=b style="position: absolute; ...">bar</span>
+///         </span>
+///     </div>
+///
+/// When we go to create the `InlineFlow` for the outer `div`, our absolute descendants will
+/// be `a` and `b`. At this point, we need a way to distinguish between the two, because the
+/// containing block for `a` will be different from the containing block for `b`. Specifically,
+/// the latter's containing block is the inline flow itself, while the former's containing
+/// block is going to be some parent of the outer `div`. Hence we need this flag as a way to
+/// distinguish the two; it will be false for `a` and true for `b`.
+#[derive(Clone)]
+pub struct AbsoluteDescendantInfo {
+    /// The absolute descendant flow in question.
+    flow: FlowRef,
+}
 
-pub struct DescendantIter<'a> {
-    iter: IterMut<'a, FlowRef>,
+pub struct AbsoluteDescendantIter<'a> {
+    iter: IterMut<'a, AbsoluteDescendantInfo>,
 }
 
-impl<'a> Iterator for DescendantIter<'a> {
+impl<'a> Iterator for AbsoluteDescendantIter<'a> {
     type Item = &'a mut (Flow + 'a);
     fn next(&mut self) -> Option<&'a mut (Flow + 'a)> {
-        self.iter.next().map(|flow| &mut **flow)
+        self.iter.next().map(|info| &mut *info.flow)
     }
 }
 
-pub type DescendantOffsetIter<'a> = Zip<DescendantIter<'a>, IterMut<'a, Au>>;
+pub type AbsoluteDescendantOffsetIter<'a> = Zip<AbsoluteDescendantIter<'a>, IterMut<'a, Au>>;
 
 /// Information needed to compute absolute (i.e. viewport-relative) flow positions (not to be
 /// confused with absolutely-positioned flows).
@@ -837,7 +858,7 @@ pub struct BaseFlow {
 
     /// Details about descendants with position 'absolute' or 'fixed' for which we are the
     /// containing block. This is in tree order. This includes any direct children.
-    pub abs_descendants: AbsDescendants,
+    pub abs_descendants: AbsoluteDescendants,
 
     /// The inline-size of the block container of this flow. Used for computing percentage and
     /// automatic values for `width`.
@@ -1034,7 +1055,7 @@ impl BaseFlow {
             floats: Floats::new(writing_mode),
             collapsible_margins: CollapsibleMargins::new(),
             stacking_relative_position: Point2D::zero(),
-            abs_descendants: Descendants::new(),
+            abs_descendants: AbsoluteDescendants::new(),
             block_container_inline_size: Au(0),
             block_container_writing_mode: writing_mode,
             block_container_explicit_block_size: None,
@@ -1367,7 +1388,7 @@ impl MutableOwnedFlowUtils for FlowRef {
     /// This is called during flow construction, so nothing else can be accessing the descendant
     /// flows. This is enforced by the fact that we have a mutable `FlowRef`, which only flow
     /// construction is allowed to possess.
-    fn set_absolute_descendants(&mut self, abs_descendants: AbsDescendants) {
+    fn set_absolute_descendants(&mut self, abs_descendants: AbsoluteDescendants) {
         let this = self.clone();
         let base = mut_base(&mut **self);
         base.abs_descendants = abs_descendants;
@@ -1414,7 +1435,10 @@ impl ContainingBlockLink {
                 panic!("Link to containing block not established; perhaps you forgot to call \
                         `set_absolute_descendants`?")
             }
-            Some(ref link) => link.upgrade().unwrap().generated_containing_block_size(for_flow),
+            Some(ref link) => {
+                let flow = link.upgrade().unwrap();
+                flow.generated_containing_block_size(for_flow)
+            }
         }
     }
 
@@ -1429,6 +1453,8 @@ impl ContainingBlockLink {
                 let flow = link.upgrade().unwrap();
                 if flow.is_block_like() {
                     flow.as_immutable_block().explicit_block_containing_size(layout_context)
+                } else if flow.is_inline_flow() {
+                    Some(flow.as_immutable_inline().minimum_block_size_above_baseline)
                 } else {
                     None
                 }
diff --git a/components/layout/fragment.rs b/components/layout/fragment.rs
index 880e3b4ae4e..60b340195d7 100644
--- a/components/layout/fragment.rs
+++ b/components/layout/fragment.rs
@@ -2234,6 +2234,22 @@ impl Fragment {
     pub fn margin_box_inline_size(&self) -> Au {
         self.border_box.size.inline + self.margin.inline_start_end()
     }
+
+    /// Returns true if this node *or any of the nodes within its inline fragment context* have
+    /// non-`static` `position`.
+    pub fn is_positioned(&self) -> bool {
+        if self.style.get_box().position != position::T::static_ {
+            return true
+        }
+        if let Some(ref inline_context) = self.inline_context {
+            for node in inline_context.nodes.iter() {
+                if node.style.get_box().position != position::T::static_ {
+                    return true
+                }
+            }
+        }
+        false
+    }
 }
 
 impl fmt::Debug for Fragment {
diff --git a/components/layout/inline.rs b/components/layout/inline.rs
index fe1b19001af..39a000d742e 100644
--- a/components/layout/inline.rs
+++ b/components/layout/inline.rs
@@ -1262,19 +1262,13 @@ impl InlineFlow {
         while start_index > FragmentIndex(0) &&
                 self.fragments
                     .fragments[(start_index - FragmentIndex(1)).get() as usize]
-                    .style
-                    .get_box()
-                    .position == position::T::static_ {
+                    .is_positioned() {
             start_index = start_index - FragmentIndex(1)
         }
 
         let mut end_index = fragment_index + FragmentIndex(1);
         while end_index < FragmentIndex(self.fragments.fragments.len() as isize) &&
-                self.fragments
-                    .fragments[end_index.get() as usize]
-                    .style
-                    .get_box()
-                    .position == position::T::static_ {
+                self.fragments.fragments[end_index.get() as usize].is_positioned() {
             end_index = end_index + FragmentIndex(1)
         }
 
@@ -1287,6 +1281,10 @@ impl InlineFlow {
                 SpecificFragmentInfo::InlineAbsolute(ref inline_absolute) => {
                     OpaqueFlow::from_flow(&*inline_absolute.flow_ref) == opaque_flow
                 }
+                SpecificFragmentInfo::InlineAbsoluteHypothetical(
+                        ref inline_absolute_hypothetical) => {
+                    OpaqueFlow::from_flow(&*inline_absolute_hypothetical.flow_ref) == opaque_flow
+                }
                 _ => false,
             }
         }).expect("containing_block_range_for_flow(): couldn't find inline absolute fragment!")
@@ -1600,20 +1598,43 @@ impl Flow for InlineFlow {
 
     fn compute_absolute_position(&mut self, _: &LayoutContext) {
         // First, gather up the positions of all the containing blocks (if any).
+        //
+        // FIXME(pcwalton): This will get the absolute containing blocks inside `...` wrong in the
+        // case of something like:
+        //
+        //      <span style="position: relative">
+        //          Foo
+        //          <span style="display: inline-block">...</span>
+        //      </span>
         let mut containing_block_positions = Vec::new();
         let container_size = Size2D::new(self.base.block_container_inline_size, Au(0));
         for (fragment_index, fragment) in self.fragments.fragments.iter().enumerate() {
-            if let SpecificFragmentInfo::InlineAbsolute(_) = fragment.specific {
-                let containing_block_range =
-                    self.containing_block_range_for_flow_surrounding_fragment_at_index(
-                        FragmentIndex(fragment_index as isize));
-                let first_fragment_index = containing_block_range.begin().get() as usize;
-                debug_assert!(first_fragment_index < self.fragments.fragments.len());
-                let first_fragment = &self.fragments.fragments[first_fragment_index];
-                let padding_box_origin = (first_fragment.border_box -
-                                          first_fragment.style.logical_border_width()).start;
-                containing_block_positions.push(
-                    padding_box_origin.to_physical(self.base.writing_mode, container_size));
+            match fragment.specific {
+                SpecificFragmentInfo::InlineAbsolute(_) => {
+                    let containing_block_range =
+                        self.containing_block_range_for_flow_surrounding_fragment_at_index(
+                            FragmentIndex(fragment_index as isize));
+                    let first_fragment_index = containing_block_range.begin().get() as usize;
+                    debug_assert!(first_fragment_index < self.fragments.fragments.len());
+                    let first_fragment = &self.fragments.fragments[first_fragment_index];
+                    let padding_box_origin = (first_fragment.border_box -
+                                              first_fragment.style.logical_border_width()).start;
+                    containing_block_positions.push(
+                        padding_box_origin.to_physical(self.base.writing_mode, container_size));
+                }
+                SpecificFragmentInfo::InlineBlock(_) if fragment.is_positioned() => {
+                    let containing_block_range =
+                        self.containing_block_range_for_flow_surrounding_fragment_at_index(
+                            FragmentIndex(fragment_index as isize));
+                    let first_fragment_index = containing_block_range.begin().get() as usize;
+                    debug_assert!(first_fragment_index < self.fragments.fragments.len());
+                    let first_fragment = &self.fragments.fragments[first_fragment_index];
+                    let padding_box_origin = (first_fragment.border_box -
+                                              first_fragment.style.logical_border_width()).start;
+                    containing_block_positions.push(
+                        padding_box_origin.to_physical(self.base.writing_mode, container_size));
+                }
+                _ => {}
             }
         }
 
@@ -1632,12 +1653,23 @@ impl Flow for InlineFlow {
             let clip = fragment.clipping_region_for_children(&self.base.clip,
                                                              &stacking_relative_border_box,
                                                              false);
+            let is_positioned = fragment.is_positioned();
             match fragment.specific {
                 SpecificFragmentInfo::InlineBlock(ref mut info) => {
                     flow::mut_base(&mut *info.flow_ref).clip = clip;
 
                     let block_flow = info.flow_ref.as_block();
                     block_flow.base.absolute_position_info = self.base.absolute_position_info;
+
+                    let stacking_relative_position = self.base.stacking_relative_position;
+                    if is_positioned {
+                        let padding_box_origin = containing_block_positions.next().unwrap();
+                        block_flow.base
+                                  .absolute_position_info
+                                  .stacking_relative_position_of_absolute_containing_block =
+                            stacking_relative_position + *padding_box_origin;
+                    }
+
                     block_flow.base.stacking_relative_position =
                         stacking_relative_border_box.origin;
                     block_flow.base.stacking_relative_position_of_display_port =
@@ -1645,13 +1677,14 @@ impl Flow for InlineFlow {
                 }
                 SpecificFragmentInfo::InlineAbsoluteHypothetical(ref mut info) => {
                     flow::mut_base(&mut *info.flow_ref).clip = clip;
+
                     let block_flow = info.flow_ref.as_block();
                     block_flow.base.absolute_position_info = self.base.absolute_position_info;
+
                     block_flow.base.stacking_relative_position =
                         stacking_relative_border_box.origin;
                     block_flow.base.stacking_relative_position_of_display_port =
                         self.base.stacking_relative_position_of_display_port;
-
                 }
                 SpecificFragmentInfo::InlineAbsolute(ref mut info) => {
                     flow::mut_base(&mut *info.flow_ref).clip = clip;
diff --git a/tests/ref/absolute_hypothetical_with_intervening_inline_block_a.html b/tests/ref/absolute_hypothetical_with_intervening_inline_block_a.html
new file mode 100644
index 00000000000..587dde3c589
--- /dev/null
+++ b/tests/ref/absolute_hypothetical_with_intervening_inline_block_a.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<style>
+em {
+    position: relative;
+}
+main {
+    display: inline-block;
+}
+section {
+    display: inline;
+    position: absolute;
+    top: 0;
+    left: 0;
+    background: white;
+    width: 48px;
+    height: 48px;
+}
+strong {
+    color: red;
+}
+</style>
+There should be no red.<em><main><section></section></main></em><strong>_</strong>
+
diff --git a/tests/ref/absolute_hypothetical_with_intervening_inline_block_ref.html b/tests/ref/absolute_hypothetical_with_intervening_inline_block_ref.html
new file mode 100644
index 00000000000..985e941cdd9
--- /dev/null
+++ b/tests/ref/absolute_hypothetical_with_intervening_inline_block_ref.html
@@ -0,0 +1,3 @@
+<!DOCTYPE html>
+There should be no red.
+
diff --git a/tests/ref/absolute_inline_containing_block_a.html b/tests/ref/absolute_inline_containing_block_a.html
index 84584219490..a10d4fa9e3d 100644
--- a/tests/ref/absolute_inline_containing_block_a.html
+++ b/tests/ref/absolute_inline_containing_block_a.html
@@ -5,7 +5,6 @@
 html, body {
     margin: 0;
     font-size: 0.1px;
-    line-height: 0;
 }
 #a {
     padding-left: 100px;
@@ -21,10 +20,46 @@ html, body {
     height: 100px;
     background: purple;
 }
+.cover-up-platform-specific-differences {
+    position: absolute;
+    background: white;
+}
+#cover-up-platform-specific-differences-a, #cover-up-platform-specific-differences-b {
+    left: 0;
+    width: 300px;
+}
+#cover-up-platform-specific-differences-c, #cover-up-platform-specific-differences-d {
+    top: 0;
+    height: 300px;
+}
+#cover-up-platform-specific-differences-a {
+    top: 0;
+    height: 25px;
+}
+#cover-up-platform-specific-differences-b {
+    top: 75px;
+    height: 100px;
+}
+#cover-up-platform-specific-differences-c {
+    left: 0;
+    width: 125px;
+}
+#cover-up-platform-specific-differences-d {
+    left: 175px;
+    width: 100px;
+}
 </style>
 </head>
 <body>
-<div><span id=a>&nbsp;</span><span id=b>&nbsp;<div id=c></div></span></span></div>
+<div><span id=a>a</span><span id=b><div id=c></div></span></span></div>
+<div class=cover-up-platform-specific-differences id=cover-up-platform-specific-differences-a>
+</div>
+<div class=cover-up-platform-specific-differences id=cover-up-platform-specific-differences-b>
+</div>
+<div class=cover-up-platform-specific-differences id=cover-up-platform-specific-differences-c>
+</div>
+<div class=cover-up-platform-specific-differences id=cover-up-platform-specific-differences-d>
+</div>
 </body>
 </html>
 
diff --git a/tests/ref/absolute_inline_containing_block_ref.html b/tests/ref/absolute_inline_containing_block_ref.html
index a7b1de7e4b4..9a36136b853 100644
--- a/tests/ref/absolute_inline_containing_block_ref.html
+++ b/tests/ref/absolute_inline_containing_block_ref.html
@@ -4,20 +4,20 @@
 <style>
 html, body {
     margin: 0;
-    font-size: 0.1px;
+    font-size: 0;
 }
-#a {
+div {
     position: absolute;
-    left: 100px;
-    top: 0;
-    width: 100px;
-    height: 100px;
+    top: 25px;
+    left: 125px;
+    width: 50px;
+    height: 50px;
     background: purple;
 }
 </style>
 </head>
 <body>
-<div id=a></div>
+<div></div>
 </body>
 </html>
 
diff --git a/tests/ref/basic.list b/tests/ref/basic.list
index 3f6c6c6316f..465e1ea4501 100644
--- a/tests/ref/basic.list
+++ b/tests/ref/basic.list
@@ -10,6 +10,7 @@
 fragment=top != ../html/acid2.html acid2_ref.html
 
 == abs_rel_explicit_height.html abs_rel_explicit_height_ref.html
+== absolute_hypothetical_with_intervening_inline_block_a.html absolute_hypothetical_with_intervening_inline_block_ref.html
 == absolute_inline_containing_block_a.html absolute_inline_containing_block_ref.html
 == absolute_z_index_auto_paint_order_a.html absolute_z_index_auto_paint_order_ref.html
 == acid1_a.html acid1_b.html