Incomplete System.Threading.Tasks.Extensions Facade in 15.9

[spouliot]

An incomplete facade assembly for System.Threading.Tasks.Extensions was included in d15.9. This breaks projects that were previously using the implementation provided by a nuget.

Workaround

On Windows delete the file
C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\Common7\IDE\ReferenceAssemblies\Microsoft\Framework\Xamarin.iOS\v1.0\Facades\System.Threading.Tasks.Extensions.dll

On macOS delete the files

/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib//mono/Xamarin.TVOS/Facades/System.Threading.Tasks.Extensions.dll
/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib//mono/2.1/Facades/System.Threading.Tasks.Extensions.dll
/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib//mono/Xamarin.WatchOS/Facades/System.Threading.Tasks.Extensions.dll
/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib//mono/Xamarin.iOS/Facades/System.Threading.Tasks.Extensions.dll
/Library/Frameworks/Xamarin.Mac.framework/Versions/Current/lib//mono/Xamarin.Mac/Facades/System.Threading.Tasks.Extensions.dll

This will fallback to using the nuget version, like the previous stable release was doing.

Issues

• Latest Xamarin.iOS's System.Threading.Tasks.Extensions facade causes build to fail mono/mono#11731
• After update today to VS 15.9 iOS not working aspnet/SignalR#3307
• Latest xamarin.ios and vs4mac cause build trouble #5135
• https://developercommunity.visualstudio.com/content/problem/383917/build-issue-when-updateing-to-xamarinios-122110.html
• MT3001 when attempting to build iOS Device project that uses Net Core SignalR with Linking off #5137
• Xamarin.iOS 12.2.1.10 breaks SignalR client start connection with exception. #5133

VS bug #732659, VS bug #732660

[xamarin-release-manager]

[VS sync] The field 'Milestone' contains the value '15.9' that is not in the list of supported values

[spouliot]

@dalexsoto please update the list of issues (with closed ones and new ones). thanks!

[spouliot]

Builds candidates (unverified at this time)

• https://bosstoragemirror.blob.core.windows.net/wrench/jenkins/d15-9/5ef73d34476630f441635d878360e94b95a048ee/45/package/xamarin.ios-12.2.1.11.pkg
• https://bosstoragemirror.blob.core.windows.net/wrench/jenkins/d15-9/5ef73d34476630f441635d878360e94b95a048ee/45/package/xamarin.mac-5.2.1.11.pkg

[CliffAgius]

This issue seems to have re-appeared in the VS19 Pre.1 release I have been playing with today. Running on Windows and the fix seems to have worked perfectly.