Parameter name: The language 'F#' is not supported

Description

When trying to compile the FSharp.Mobile.Templates’s MAUI template, compilation with Visual Studio on Windows fails with the error:

Xaml Internal Error error WMC9999: Specified argument was out of the range of valid values.
Xaml Internal Error error WMC9999: Parameter name: The language 'F#' is not supported

According to macOS users, it compiles on macOS normally though. Therefore, it seems to be a bug within MAUI itself.

Steps to Reproduce

1. Make sure Visual Studio 2022 with update 17.3.0 or higher is installed
2. Install the required workloads via

dotnet workload install android
dotnet workload install ios
dotnet workload install maccatalyst
dotnet workload install maui

and project templates via via

dotnet new -i FSharp.Mobile.Templates

(See FSharp.Mobile.Templates for more details) 3. Create a project via dotnet new maui-fsharp -n MyMauiFsharp 4. Build via

cd MyMauiFsharp
dotnet build MyMauiFsharp.sln

1. Notice the error messages

Version with bug

6.0.400

Last version that worked well

Unknown/Other

Affected platforms

Windows

Affected platform versions

Windows SDK 10.0.19041.0

Did you find any workaround?

Compiling on macOS works according to this comment.

Relevant log output

dotnet build MyMauiFsharp.sln
MSBuild version 17.3.0+92e077650 for .NET
  Determining projects to restore...
  Restored d:\Softdev\Test\MyMauiFsharp\MyMauiFsharp.fsproj (in 777 ms).
EXEC : Xaml Internal error : Specified argument was out of the range of valid values. [d:\Softdev\Test\MyMauiFsharp\MyM
auiFsharp.fsproj]
  Parameter name: The language 'F#' is not supported
C:\Users\Win11\.nuget\packages\microsoft.windowsappsdk\1.1.3\buildTransitive\Microsoft.UI.Xaml.Markup.Compiler.interop.
targets(559,9): error MSB3073: The command ""C:\Users\Win11\.nuget\packages\microsoft.windowsappsdk\1.1.3\buildTransiti
ve\..\tools\net5.0\..\net472\XamlCompiler.exe" "obj\Debug\net6.0-windows10.0.19041.0\win10-x64\\input.json" "obj\Debug\
net6.0-windows10.0.19041.0\win10-x64\\output.json"" exited with code 1. [d:\Softdev\Test\MyMauiFsharp\MyMauiFsharp.fspr
oj]
  MyMauiFsharp -> d:\Softdev\Test\MyMauiFsharp\bin\Debug\net6.0-maccatalyst\maccatalyst-x64\MyMauiFsharp.dll
  MyMauiFsharp -> d:\Softdev\Test\MyMauiFsharp\bin\Debug\net6.0-ios\iossimulator-x64\MyMauiFsharp.dll
d:\Softdev\Test\MyMauiFsharp\Platforms\Android\MainApplication.fs(10,21): error FS0039: The value, constructor, namespa
ce or type 'Resource' is not defined. [d:\Softdev\Test\MyMauiFsharp\MyMauiFsharp.fsproj]

Build FAILED.

EXEC : Xaml Internal error : Specified argument was out of the range of valid values. [d:\Softdev\Test\MyMauiFsharp\MyM
auiFsharp.fsproj]
C:\Users\Win11\.nuget\packages\microsoft.windowsappsdk\1.1.3\buildTransitive\Microsoft.UI.Xaml.Markup.Compiler.interop.
targets(559,9): error MSB3073: The command ""C:\Users\Win11\.nuget\packages\microsoft.windowsappsdk\1.1.3\buildTransiti
ve\..\tools\net5.0\..\net472\XamlCompiler.exe" "obj\Debug\net6.0-windows10.0.19041.0\win10-x64\\input.json" "obj\Debug\
net6.0-windows10.0.19041.0\win10-x64\\output.json"" exited with code 1. [d:\Softdev\Test\MyMauiFsharp\MyMauiFsharp.fspr
oj]
d:\Softdev\Test\MyMauiFsharp\Platforms\Android\MainApplication.fs(10,21): error FS0039: The value, constructor, namespa
ce or type 'Resource' is not defined. [d:\Softdev\Test\MyMauiFsharp\MyMauiFsharp.fsproj]
    0 Warning(s)
    3 Error(s)

[WillEhrendreich]

Where can I find out what the plan is for enabling fsharp with MAUI on windows? I can’t find a roadmap with this, and I can’t be the only one interested haha.

[TimLariviere]

Forgot to post it here, but with the help of @PureWeen, we found a workaround to allow building Maui WinUI apps with F#. More informations at https://github.com/fabulous-dev/FSharp.Maui.WinUICompat

Both FSharp.Mobile.Templates and Fabulous.MauiControls.Templates have been updated with this fix.