[Webkit-unassigned] [Bug 93411] New: percentage margins + flex incorrectly overflows the flexbox

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=93411

           Summary: percentage margins + flex incorrectly overflows the
                    flexbox
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
               URL: http://plexode.com/u/#2W%3C2V%3E2U%222T%3B-SpxQRKJ7(1I
                    *902Q%0AfPO8100SJwiM90rONumn)olor(salmonrNL7-direction
                    (colrMdth(300STIQrL4Udisplay%3A7JEKHsolid6JT!EIUVrH)ol
                    G!border(2S!rGor(orange85STr9!!!!4Umargin(1Y8Jheight(b
                    7-webkit-flexn4Wdiv!style%3Dn*W%2FdivVQr)Jbackground-c
                    6(%3A!2!%20~http://plexode.com/eval3/#ht=PSRSKI**WbrVQ
                    QP%25R%25KI**Q
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: ojan at chromium.org
                CC: esprehn at gmail.com, tony at chromium.org,
                    jchaffraix at webkit.org, tabatkins at google.com
            Blocks: 62048


See the test-case in the URL field.

The problem is that RenderFlexibleBox::computeMainAxisPreferredSizes incorrectly uses the height for computing percentage margin-top/bottom in column flexboxes. As per CSS2.1 percentage margins and padding should always be computed WRT the containing block's width.

When we call layoutIfNeeded in layoutAndPlaceChildren, the margin-top/bottom gets correctly set to the right value, so the flex items size and place correctly, but we compute the wrong preferred child size in RenderFlexibleBox::computeNextFlexLine if there is actually flex on any child.

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