[Bug][UWP] Loading wrong Xamarin.Forms.Core.dll

[kapsiR]

Description

It seems there is an issue with loading the wrong Xamarin.Forms.Core.dll on UWP which leads to a System.MissingMethodException or a compiler error Error CS0029 Cannot implicitly convert type 'Xamarin.Forms.Color' to 'System.Drawing.Color'.

This happens only on UWP.

Steps to Reproduce

1. Create a new Xamarin Forms project (Only UWP necessary to reproduce)
   • Target .NET Standard 2.0
   • UWP-Target 16299
2. Update to latest Xamarin Forms stable (4.4.0.991640)
3. Add an implicit Color conversion from System.Drawing.Color to Xamarin.Forms.Color or the other way around

Expected Behavior

No exception or compiler error

Actual Behavior

• When writing the Color conversion into the UWP-Project, then there is a compiler error.
• When writing the Color conversion into the Xamarin class library, then there is a runtime error.

Method not found: 'System.Drawing.Color Xamarin.Forms.Color.op_Implicit(Xamarin.Forms.Color)'.

at MethodNotFoundRepro.App.App.TestBug() in \MethodNotFoundRepro\MethodNotFoundRepro.App\MethodNotFoundRepro.App\App.xaml.cs:line 22
   at MethodNotFoundRepro.App.App.OnStart() in \MethodNotFoundRepro\MethodNotFoundRepro.App\MethodNotFoundRepro.App\App.xaml.cs:line 16
   at Xamarin.Forms.Platform.UWP.WindowsBasePage.LoadApplication(Application application)
   at MethodNotFoundRepro.App.UWP.MainPage..ctor() in \MethodNotFoundRepro\MethodNotFoundRepro.App\MethodNotFoundRepro.App.UWP\MainPage.xaml.cs:line 24
   at MethodNotFoundRepro.App.UWP.MethodNotFoundRepro_App_UWP_XamlTypeInfo.XamlTypeInfoProvider.Activate_4_MainPage() in \MethodNotFoundRepro\MethodNotFoundRepro.App\MethodNotFoundRepro.App.UWP\obj\x86\Debug\XamlTypeInfo.g.cs:line 311
   at MethodNotFoundRepro.App.UWP.MethodNotFoundRepro_App_UWP_XamlTypeInfo.XamlUserType.ActivateInstance() in \MethodNotFoundRepro\MethodNotFoundRepro.App\MethodNotFoundRepro.App.UWP\obj\x86\Debug\XamlTypeInfo.g.cs:line 1407

Basic Information

• Version with issue: 4.4.0.991220-pre3 (introduced with PR #7079)
• Last known good version: 4.4.0.991210-pre2 or stable 4.3.0.991250
• New known good version: 4.5.0.282-pre4 (working again with PR #9132)
• IDE: VS 2019
• Platform Target Frameworks:
  • UWP: >= 16299
• Nuget Packages: NETStandard.Library, Xamarin.Essentials, Xamarin.Forms

Reproduction Link

XamarinMethodNotFoundRepro

Workaround

Use latest Xamarin Forms 4.5.0.282-pre4 or 4.4.0.991210-pre2 or the stable 4.3.0.991250

[PureWeen]

We're close to releasing 4.5 stable so for now we aren't planning on backporting the fix to 4.4