[Webkit-unassigned] [Bug 256413] New: Incorrect rerender when element with box-shadow and height:auto changes size

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=256413

            Bug ID: 256413
           Summary: Incorrect rerender when element with box-shadow and
                    height:auto changes size
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Mac (Apple Silicon)
                OS: macOS 13
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: me at std4453.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 466243

  --> https://bugs.webkit.org/attachment.cgi?id=466243&action=review

Reproduction code

When an element that:
- has `box-shadow`
- is `height: auto`
- its content changes size
- has non-zero `padding`
part of the element does not get rerendered, resulting in a visual artifact

This can be reproduced with the attached file, simply by hovering on the blue part.

Screenshot: https://i.imgur.com/81vzF8t.png

This is observed on Safari 16.4 only (and Safari Technical Preview, Release 169, WebKit 18616.1.12.2), not on Safari 16.3.

And on MacBook Pro M2 and iPad Pro M1, but not on iPhone 12. 

It seems that X px of box-shadow offset-y creates such an erroneous area of (2*X) px.

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