Properly make stacking contexts for inlines

Instead of making a stacking context out of inline fragments parent
flow, make the inline fragment itself the stacking context. This fixes
positioning and rendering of these sort of fragments and prevents
over-layerization.

Fixes #7424.
Fixes #5812.

components/layout/display_list_builder.rs

@@ -1738,19 +1738,20 @@ impl BlockFlowDisplayListBuilding for BlockFlow {
 }
 
 pub trait InlineFlowDisplayListBuilding {
+    fn build_display_list_for_inline_fragment_at_index(&mut self,
+                                                       index: usize,
+                                                       display_list: &mut DisplayList,
+                                                       layout_context: &LayoutContext);
     fn build_display_list_for_inline(&mut self, layout_context: &LayoutContext);
 }
 
 impl InlineFlowDisplayListBuilding for InlineFlow {
-    fn build_display_list_for_inline(&mut self, layout_context: &LayoutContext) {
+    fn build_display_list_for_inline_fragment_at_index(&mut self,
-        // TODO(#228): Once we form lines and have their cached bounds, we can be smarter and
+                                                       index: usize,
-        // not recurse on a line if nothing in it can intersect the dirty region.
+                                                       display_list: &mut DisplayList,
-        debug!("Flow: building display list for {} inline fragments", self.fragments.len());
+                                                       layout_context: &LayoutContext) {
-
+        let fragment = self.fragments.fragments.get_mut(index).unwrap();
-        let mut display_list = box DisplayList::new();
+        fragment.build_display_list(display_list,
-        let mut has_stacking_context = false;
-        for fragment in &mut self.fragments.fragments {
-            fragment.build_display_list(&mut *display_list,
                                     layout_context,
                                     &self.base.stacking_relative_position,
                                     &self.base
@@ -1764,8 +1765,6 @@ impl InlineFlowDisplayListBuilding for InlineFlow {
                                     &self.base.clip,
                                     &self.base.stacking_relative_position_of_display_port);
 
-            has_stacking_context = fragment.establishes_stacking_context();
-
         match fragment.specific {
             SpecificFragmentInfo::InlineBlock(ref mut block_flow) => {
                 let block_flow = flow_ref::deref_mut(&mut block_flow.flow_ref);
@@ -1786,35 +1785,51 @@ impl InlineFlowDisplayListBuilding for InlineFlow {
         }
     }
 
+    fn build_display_list_for_inline(&mut self, layout_context: &LayoutContext) {
+        // TODO(#228): Once we form lines and have their cached bounds, we can be smarter and
+        // not recurse on a line if nothing in it can intersect the dirty region.
+        debug!("Flow: building display list for {} inline fragments", self.fragments.len());
+
+        let mut display_list = box DisplayList::new();
+
+        // We iterate using an index here, because we want to avoid doing a doing
+        // a double-borrow of self (one mutable for the method call and one immutable
+        // for the self.fragments.fragment iterator itself).
+        for index in (0..self.fragments.fragments.len()) {
+            let establishes_stacking_context = {
+                let fragment = self.fragments.fragments.get(index).unwrap();
+                match fragment.specific {
+                    SpecificFragmentInfo::InlineBlock(_) |
+                        SpecificFragmentInfo::InlineAbsoluteHypothetical(_) => false,
+                    _ => fragment.establishes_stacking_context(),
+                }
+            };
+
+            if establishes_stacking_context {
+                let mut fragment_display_list = box DisplayList::new();
+                self.build_display_list_for_inline_fragment_at_index(index,
+                                                                     &mut *fragment_display_list,
+                                                                     layout_context);
+                let fragment = self.fragments.fragments.get(index).unwrap();
+                display_list.positioned_content.push_back(DisplayItem::StackingContextClass(
+                    fragment.create_stacking_context(
+                        &self.base,
+                        fragment_display_list,
+                        ScrollPolicy::Scrollable,
+                        StackingContextCreationMode::Normal)));
+            } else {
+                self.build_display_list_for_inline_fragment_at_index(index,
+                                                                     &mut *display_list,
+                                                                     layout_context);
+            }
+        }
+
         if !self.fragments.fragments.is_empty() {
             self.base.build_display_items_for_debugging_tint(&mut *display_list,
                                                              self.fragments.fragments[0].node);
         }
 
-        // FIXME(Savago): fix Fragment::establishes_stacking_context() for absolute positioned item
+        self.base.display_list_building_result = Some(display_list);
-        // and remove the check for filter presence. Further details on #5812.
-        //
-        // FIXME(#7424, pcwalton): This is terribly bogus! What is even going on here?
-        if has_stacking_context {
-            match self.fragments.fragments[0].specific {
-                SpecificFragmentInfo::Canvas(_) | SpecificFragmentInfo::Iframe(_) => {}
-                _ => {
-                    has_stacking_context =
-                        !self.fragments.fragments[0].style().get_effects().filter.is_empty()
-                }
-            }
-        }
-
-        self.base.display_list_building_result = if has_stacking_context {
-            Some(DisplayList::new_with_stacking_context(
-                self.fragments.fragments[0].create_stacking_context(
-                    &self.base,
-                    display_list,
-                    ScrollPolicy::Scrollable,
-                    StackingContextCreationMode::Normal)))
-        } else {
-            Some(display_list)
-        };
 
         if opts::get().validate_display_list_geometry {
             self.base.validate_display_list_geometry();

tests/wpt/mozilla/meta/MANIFEST.json

@@ -2015,6 +2015,18 @@
             "url": "/_mozilla/css/inline_padding_a.html"
           }
         ],
+        "css/inline_stacking_context.html": [
+          {
+            "path": "css/inline_stacking_context.html",
+            "references": [
+              [
+                "/_mozilla/css/inline_stacking_context_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/inline_stacking_context.html"
+          }
+        ],
         "css/inline_text_align_a.html": [
           {
             "path": "css/inline_text_align_a.html",
@@ -6948,6 +6960,18 @@
           "url": "/_mozilla/css/inline_padding_a.html"
         }
       ],
+      "css/inline_stacking_context.html": [
+        {
+          "path": "css/inline_stacking_context.html",
+          "references": [
+            [
+              "/_mozilla/css/inline_stacking_context_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/inline_stacking_context.html"
+        }
+      ],
       "css/inline_text_align_a.html": [
         {
           "path": "css/inline_text_align_a.html",

tests/wpt/mozilla/tests/css/inline_stacking_context.html

@@ -0,0 +1,14 @@
+<!doctype html>
+<html>
+    <head>
+        <meta charset="utf-8">
+        <title>Inline stacking context positioned correctly</title>
+        <link rel=match href="inline_stacking_context_ref.html">
+    </head>
+    <body>
+        <div style="font-size: 25px">
+            <span style="color: transparent;"><img src="100x100_green.png"></span>
+            <img style="filter: blur(0px);" src="100x100_green.png">
+        </div>
+    </body>
+</html>

tests/wpt/mozilla/tests/css/inline_stacking_context_ref.html

@@ -0,0 +1,12 @@
+<!doctype html>
+<html>
+    <head>
+        <meta charset="utf-8">
+    </head>
+    <body>
+        <div style="font-size: 25px">
+            <span style="color: transparent;"><img src="100x100_green.png"></span>
+            <img src="100x100_green.png">
+        </div>
+    </body>
+</html>