[Webkit-unassigned] [Bug 187971] New: Move-constructing NeverDestroyed should move construct underlying object instead of copy constructing it

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=187971

            Bug ID: 187971
           Summary: Move-constructing NeverDestroyed should move construct
                    underlying object instead of copy constructing it
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Web Template Framework
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: dbates at webkit.org

Consider the following code taken from attachment #336064 (bug #175784):

static const RenderStyle& hackedDefaultStyle()
{
    static auto defaultStyle = makeNeverDestroyed([] {
        auto style = RenderStyle::create();
        style.setColor(Color { });
        style.setTextFillColor(Color { });
        style.setTextStrokeColor(Color { });
        style.setBackgroundColor(Color { });
        style.setTextEmphasisColor(Color { });
        return style;
    }());
    return defaultStyle;
}

This fails to compile on Mac, GTK, and WPE with an error of the form:

[[
/Volumes/Data/EWS/WebKit/WebKitBuild/Release/usr/local/include/wtf/NeverDestroyed.h:55:46: error: call to implicitly-deleted copy constructor of 'WebCore::RenderStyle'
        MaybeRelax<T>(new (storagePointer()) T(WTFMove(other)));
                                             ^ ~~~~~~~~~~~~~~
In file included from /Volumes/Data/EWS/WebKit/WebKitBuild/Release/DerivedSources/WebCore/unified-sources/UnifiedSource411.cpp:7:
./rendering/InlineTextBox.cpp:773:32: note: in instantiation of member function 'WTF::NeverDestroyed<WebCore::RenderStyle>::NeverDestroyed' requested here
    static auto defaultStyle = makeNeverDestroyed([] {
                               ^
In file included from /Volumes/Data/EWS/WebKit/WebKitBuild/Release/DerivedSources/WebCore/unified-sources/UnifiedSource411.cpp:2:
In file included from ./rendering/ImageQualityController.cpp:32:
In file included from ./rendering/RenderBoxModelObject.h:28:
In file included from ./rendering/RenderLayerModelObject.h:25:
In file included from ./rendering/RenderElement.h:26:
In file included from ./rendering/RenderObject.h:35:
/Volumes/Data/EWS/WebKit/Source/WebCore/rendering/style/RenderStyle.h:134:5: note: copy constructor is implicitly deleted because 'RenderStyle' has a user-declared move constructor
    RenderStyle(RenderStyle&&);
...
]]
<https://webkit-queues.webkit.org/results/7027403>

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