[Webkit-unassigned] [Bug 224185] New: Interoperability issue in margin collapsing with overflow:hidden elements

Mon Apr 5 08:18:46 PDT 2021

https://bugs.webkit.org/show_bug.cgi?id=224185

            Bug ID: 224185
           Summary: Interoperability issue in margin collapsing with
                    overflow:hidden elements
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: svillar at igalia.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 425153

  --> https://bugs.webkit.org/attachment.cgi?id=425153&action=review

Margin collapsing issue

See the attached example. It's basically a couple of blocks separated by a special block element with overflow:hidden.

A non visual overflow in theory creates a new formatting context, and thus should prevent margins between siblings from collapsing. That's how current Chrome and Firefox behave. However WebKit does not check the overflow value at all and thus goes on collapsing margins.

It's easy to add a new condition to RenderBox[1] to check for overflow != visible. However that brings additional issues in the case of the body being the element with non visual overflow. Chrome added long time ago some code [2][3][4] that makes a non-visual overflow not creating a new formatting context in cases like the one mentioned above (<body> being the element with non-visual overflow).

[1] https://webkit-search.igalia.com/webkit/source/Source/WebCore/rendering/RenderBox.cpp#4676
[2] https://source.chromium.org/chromium/chromium/src/+/master:third_party/blink/renderer/core/dom/document.cc;l=3587;drc=9ba6750ad3912c31b2c411cb309f724293859c41;bpv=1;bpt=1?q=viewportdefiningelement&sq=&ss=chromium%2Fchromium%2Fsrc
[3] https://source.chromium.org/chromium/chromium/src/+/master:third_party/blink/renderer/core/layout/layout_block.cc;drc=9ba6750ad3912c31b2c411cb309f724293859c41;bpv=1;bpt=1;l=256?q=sethasnonvisibleoverflow&ss=chromium%2Fchromium%2Fsrc
[4] https://source.chromium.org/chromium/chromium/src/+/master:third_party/blink/renderer/core/layout/layout_object.h;l=1649;drc=9ba6750ad3912c31b2c411cb309f724293859c41;bpv=1;bpt=1?q=isscrollcontainer&sq=&ss=chromium%2Fchromium%2Fsrc

-- 
You are receiving this mail because:
You are the assignee for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.webkit.org/pipermail/webkit-unassigned/attachments/20210405/f4811be6/attachment.htm>