Changeset 271053 in webkit

Timestamp:

Dec 22, 2020 8:09:03 AM (19 months ago)

Author:

Simon Fraser

Message:

Layout overflow is computed incorrectly inside flexbox (breaks sticky positioning)
​https://bugs.webkit.org/show_bug.cgi?id=220075
Source/WebCore:

<rdar://problem/70956639>

Reviewed by Zalan Bujtas.

RenderBlock::endAndCommitUpdateScrollInfoAfterLayoutTransaction(), which is only called by grid
and flexbox layout, would unconditionally clear layout overflow on boxes with overflow clipping,
which resulted in incorrect sticky positioning because RenderBoxModelObject::computeStickyPositionConstraints()
consults layout overflow.

It was only through happenstance that overflow:scroll worked correctly, relying on the fact
that updateScrollInfoAfterLayout() would trigger caching of scroll dimensions on RenderLayer.

This clearing was added in r151360 but seems incorrect; layout overflow should be preserved
after layout.

Test: fast/flexbox/preserve-layout-overflow.html

• rendering/RenderBlock.cpp:

(WebCore::RenderBlock::endAndCommitUpdateScrollInfoAfterLayoutTransaction):

LayoutTests:

Reviewed by Zalan Bujtas.

• fast/flexbox/preserve-layout-overflow-expected.txt: Added.
• fast/flexbox/preserve-layout-overflow.html: Added.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/fast/flexbox/preserve-layout-overflow-expected.txt (added)
• LayoutTests/fast/flexbox/preserve-layout-overflow.html (added)
• Source/WebCore/ChangeLog (modified) (1 diff)
• Source/WebCore/rendering/RenderBlock.cpp (modified) (1 diff)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2020-12-22  Simon Fraser  <simon.fraser@apple.com>
+
+        Layout overflow is computed incorrectly inside flexbox (breaks sticky positioning)
+        https://bugs.webkit.org/show_bug.cgi?id=220075
+
+        Reviewed by Zalan Bujtas.
+
+        * fast/flexbox/preserve-layout-overflow-expected.txt: Added.
+        * fast/flexbox/preserve-layout-overflow.html: Added.
+
 2020-12-21  Beth Dakin  <bdakin@apple.com>
 

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2020-12-22  Simon Fraser  <simon.fraser@apple.com>
+
+        Layout overflow is computed incorrectly inside flexbox (breaks sticky positioning)
+        https://bugs.webkit.org/show_bug.cgi?id=220075
+        <rdar://problem/70956639>
+
+        Reviewed by Zalan Bujtas.
+
+        RenderBlock::endAndCommitUpdateScrollInfoAfterLayoutTransaction(), which is only called by grid
+        and flexbox layout, would unconditionally clear layout overflow on boxes with overflow clipping,
+        which resulted in incorrect sticky positioning because RenderBoxModelObject::computeStickyPositionConstraints()
+        consults layout overflow.
+
+        It was only through happenstance that overflow:scroll worked correctly, relying on the fact
+        that updateScrollInfoAfterLayout() would trigger caching of scroll dimensions on RenderLayer.
+
+        This clearing was added in r151360 but seems incorrect; layout overflow should be preserved
+        after layout.
+
+        Test: fast/flexbox/preserve-layout-overflow.html
+
+        * rendering/RenderBlock.cpp:
+        (WebCore::RenderBlock::endAndCommitUpdateScrollInfoAfterLayoutTransaction):
+
 2020-12-22  Zalan Bujtas  <zalan@apple.com>
 

trunk/Source/WebCore/rendering/RenderBlock.cpp

@@ -555 +555 @@
         ASSERT(block->hasOverflowClip());
         block->layer()->updateScrollInfoAfterLayout();
-        block->clearLayoutOverflow();
     }
 }