[Webkit-unassigned] [Bug 61997] New: Cloning elements with shadow DOM does redundant element creation

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=61997

           Summary: Cloning elements with shadow DOM does redundant
                    element creation
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: HTML DOM
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: dominicc at chromium.org
            Blocks: 61983


Cloning an element with shadow DOM typically does redundant element creation.

For example, cloning an <input type="range" style="…"> creates one shadow slider element during the HTMLInputElement clone when it clones its type attribute (which creates a RangeInputType, which creates a shadow subtree for the slider.) Then Element::copyNonAttributeProperties destroys that shadow subtree and creates another shadow subtree that is a clone of the shadow subtree of the original node.

We only need one of these two shadow trees.

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