From 253117ece652a416f3fca48056462b2f57087717 Mon Sep 17 00:00:00 2001
From: Martin Robinson <mrobinson@igalia.com>
Date: Fri, 22 Jun 2018 17:59:35 +0200
Subject: [PATCH] New reference frames should create containing blocks

Transforms should always create containing blocks. This bug already
existed in Servo, but was covered up by the reference frame id
replacement feature in WebRender. Now that we create reference frames
manually we need to fix it.
---
 components/layout/display_list/builder.rs | 18 ++++++++++++++----
 components/layout/table_rowgroup.rs       |  2 +-
 components/layout/table_wrapper.rs        |  2 +-
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/components/layout/display_list/builder.rs b/components/layout/display_list/builder.rs
index 5d9a738606e..c963322323a 100644
--- a/components/layout/display_list/builder.rs
+++ b/components/layout/display_list/builder.rs
@@ -79,8 +79,13 @@ use webrender_api::StickyOffsetBounds;
 fn establishes_containing_block_for_absolute(
     flags: StackingContextCollectionFlags,
     positioning: StylePosition,
+    established_reference_frame: bool,
 ) -> bool {
-    !flags.contains(StackingContextCollectionFlags::NEVER_CREATES_CONTAINING_BLOCK) &&
+    if established_reference_frame {
+        return true;
+    }
+
+    !flags.contains(StackingContextCollectionFlags::POSITION_NEVER_CREATES_CONTAINING_BLOCK) &&
         StylePosition::Static != positioning
 }
 
@@ -2167,7 +2172,7 @@ impl FragmentDisplayListBuilding for Fragment {
 bitflags! {
     pub struct StackingContextCollectionFlags: u8 {
         /// This flow never establishes a containing block.
-        const NEVER_CREATES_CONTAINING_BLOCK = 0b001;
+        const POSITION_NEVER_CREATES_CONTAINING_BLOCK = 0b001;
         /// This flow never creates a ClipScrollNode.
         const NEVER_CREATES_CLIP_SCROLL_NODE = 0b010;
         /// This flow never creates a stacking context.
@@ -2445,7 +2450,11 @@ impl BlockFlowDisplayListBuilding for BlockFlow {
             flags,
         );
 
-        if establishes_containing_block_for_absolute(flags, self.positioning()) {
+        if establishes_containing_block_for_absolute(
+            flags,
+            self.positioning(),
+            established_reference_frame.is_some()
+        ) {
             state.containing_block_clipping_and_scrolling = state.current_clipping_and_scrolling;
         }
 
@@ -2534,7 +2543,7 @@ impl BlockFlowDisplayListBuilding for BlockFlow {
 
         // We keep track of our position so that any stickily positioned elements can
         // properly determine the extent of their movement relative to scrolling containers.
-        if !flags.contains(StackingContextCollectionFlags::NEVER_CREATES_CONTAINING_BLOCK) {
+        if !flags.contains(StackingContextCollectionFlags::POSITION_NEVER_CREATES_CONTAINING_BLOCK) {
             let border_box = if self.fragment.establishes_stacking_context() {
                 stacking_relative_border_box
             } else {
@@ -2911,6 +2920,7 @@ impl InlineFlowDisplayListBuilding for InlineFlow {
             if establishes_containing_block_for_absolute(
                 StackingContextCollectionFlags::empty(),
                 fragment.style.get_box().position,
+                false,
             ) {
                 state.containing_block_clipping_and_scrolling =
                     state.current_clipping_and_scrolling;
diff --git a/components/layout/table_rowgroup.rs b/components/layout/table_rowgroup.rs
index 85bccb18ade..8934f77a266 100644
--- a/components/layout/table_rowgroup.rs
+++ b/components/layout/table_rowgroup.rs
@@ -186,7 +186,7 @@ impl Flow for TableRowGroupFlow {
 
     fn collect_stacking_contexts(&mut self, state: &mut StackingContextCollectionState) {
         self.block_flow.collect_stacking_contexts_for_block(state,
-            StackingContextCollectionFlags::NEVER_CREATES_CONTAINING_BLOCK);
+            StackingContextCollectionFlags::POSITION_NEVER_CREATES_CONTAINING_BLOCK);
     }
 
     fn repair_style(&mut self, new_style: &::ServoArc<ComputedValues>) {
diff --git a/components/layout/table_wrapper.rs b/components/layout/table_wrapper.rs
index 7336efa41e9..90be14876cc 100644
--- a/components/layout/table_wrapper.rs
+++ b/components/layout/table_wrapper.rs
@@ -464,7 +464,7 @@ impl Flow for TableWrapperFlow {
     fn collect_stacking_contexts(&mut self, state: &mut StackingContextCollectionState) {
         self.block_flow.collect_stacking_contexts_for_block(
             state,
-            StackingContextCollectionFlags::NEVER_CREATES_CONTAINING_BLOCK |
+            StackingContextCollectionFlags::POSITION_NEVER_CREATES_CONTAINING_BLOCK |
             StackingContextCollectionFlags::NEVER_CREATES_CLIP_SCROLL_NODE);
     }