[Webkit-unassigned] [Bug 195548] New: WebKit failed with error C2440 under /std:c++latest when built by msvc on Windows

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=195548

            Bug ID: 195548
           Summary: WebKit failed with error C2440 under /std:c++latest
                    when built by msvc on Windows
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: PC
                OS: Windows 10
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CMake
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: 1998zhangyi at gmail.com

Created attachment 364242

  --> https://bugs.webkit.org/attachment.cgi?id=364242&action=review

p1008r1.pdf

Hi all,

A paper(see attachment) voted into the C++20 working draft changes the definition of aggregate such that classes with any user-declared ctors are no longer aggregates. 

The MSVC team builds WebKit regularly to detect regressions, and found this failure under our build configuration with the /std:c++latest switch. Not sure if you are interented in upstreaming it if C++20 compatibility is on the library's radar. I still reported this issue. If not, we will try "/std:c++17".

Repro steps:
1. git clone https://github.com/WebKit/webkit d:\WebKit\src
2. open a VS 2017 x86 command prompt as admin and browse to D:\Webkit
3. extra WebKitLibrary\win to D:\WebKit\src\WebKitLibraries\win
4. set path=C:\gnuwin32\bin;%path%
5. set _CL_=/std:c++latest
6. cmake -G "Visual Studio 15 2017" -DCMAKE_SYSTEM_VERSION=10.0.17134.0 -DCMAKE_BUILD_TYPE=Release -DRUBY_LIBRARY=C:\Ruby25-x64\lib -DPORT="AppleWin" ..\src
7. msbuild /p:Configuration=Release;Platform=Win32 WebKit.sln /t:Rebuild

Failures:
D:\WebKit\build_x86\DerivedSources\ForwardingHeaders\pal/spi/cf/CFNetworkSPI.h(26): warning C4068: unknown pragma
D:\WebKit\src\Source\WebCore\html/canvas/CanvasStyle.cpp(93): error C2440: 'initializing': cannot convert from 'initializer list' to 'WebCore::CanvasStyle::CMYKAColor'
D:\WebKit\src\Source\WebCore\html/canvas/CanvasStyle.cpp(93): note: No constructor could take the source type, or constructor overload resolution was ambiguous

D:\WebKit\src\Source\WebCore\svg/SVGComponentTransferFunctionElement.cpp(113): error C2440: 'return': cannot convert from 'initializer list' to 'WebCore::ComponentTransferFunction'
D:\WebKit\src\Source\WebCore\svg/SVGComponentTransferFunctionElement.cpp(121): note: No constructor could take the source type, or constructor overload resolution was ambiguous

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