[Xamarin.Android.Build.Tasks] fix for .NET 6 targeting pack locations

[jonathanpeppers]

In .NET 6, we set a $(_XATargetFrameworkDirectories) MSBuild
property to be used throughout the legacy MSBuild targets:

_XATargetFrameworkDirectories =
    ...\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.2.21154.6\ref\net6.0\
    ...\dotnet\packs\Microsoft.Android.Ref\11.0.200-ci.main.148\ref\net6.0\

However, when testing a new workload for .NET Maui we hit the error:

error XARSD7004: System.ArgumentException: `...\dotnet\packs\Microsoft.Maui.Controls.Ref\0.0.1-alpha1\ref\net6.0` must be a directory! (Parameter 'frameworkDirectories')
error XARSD7004:    at Xamarin.Android.Tools.AndroidVersions..ctor(IEnumerable`1 frameworkDirectories) in /Users/builder/azdo/_work/1/s/xamarin-android/external/xamarin-android-tools/src/Xamarin.Android.Tools.AndroidSdk/AndroidVersions.cs:line 30
error XARSD7004:    at Xamarin.Android.Tasks.MonoAndroidHelper.RefreshSupportedVersions(String[] referenceAssemblyPaths)
error XARSD7004:    at Xamarin.Android.Tasks.ResolveSdks.RunTask()
error XARSD7004:    at Microsoft.Android.Build.Tasks.AndroidTask.Execute() in /Users/builder/azdo/_work/1/s/xamarin-android/external/xamarin-android-tools/src/Microsoft.Android.Build.BaseTasks/AndroidTask.cs:line 17

The net6.0 directory does not exist, because the assemblies are in
platform-specific directories such as net6.0-android30.0,
net6.0-ios13.6, net6.0-maccatalyst13.5, etc.

The problem with the current logic:

<_ResolveSdksFrameworkRefAssemblyPaths Include="@(ResolvedTargetingPack->'%(Path)\ref\%(TargetFramework)')" Condition=" '@(ResolvedTargetingPack)' == '@(FrameworkReference)' and '%(Identity)' != '' " />

The %(TargetFramework) item metadata is net6.0, but we somehow
need to use the net6.0-android30.0 directory.

The ResolvedTargetingPackAssets MSBuild target from the dotnet/sdk
sets @(Reference) for each assembly that comes from a "targeting
pack". The @(Reference) item group that contains item metadata such
as:

...\dotnet\packs\Microsoft.Maui.Controls.Ref\0.0.1-alpha1\ref\net6.0-android30.0\Microsoft.Maui.dll
    AssemblyVersion = 1.0.0.0
    ExternallyResolved = true
    FileVersion = 1.0.0.0
    FrameworkReferenceName = Microsoft.Maui.Controls
    FrameworkReferenceVersion = 0.0.1-alpha1
    NuGetPackageId = Microsoft.Maui.Controls.Ref
    NuGetPackageVersion = 0.0.1-alpha1
    Private = false
    PublicKeyToken =

If we grab directories of each item with %(FrameworkReferenceName)
filled out, which means they come from a "targeting pack":

<_ResolveSdksFrameworkRefAssemblyPaths Include="@(Reference->'%(RootDir)%(Directory)')" Condition=" '%(Reference.FrameworkReferenceName)' != '' " />

Then as long as we use ->Distinct(), we now get correct values for
$(_XATargetFrameworkDirectories):

_XATargetFrameworkDirectories =
    ...\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.2.21154.6\ref\net6.0\
    ...\dotnet\packs\Microsoft.Android.Ref\11.0.200-ci.main.148\ref\net6.0\
    ...\dotnet\packs\Microsoft.Maui.Controls.Ref\0.0.1-alpha1\ref\net6.0-android30.0\

After this change, I'm able to build projects with the .NET Maui
workload targeting Android. I think this logic should be correct going
forward in .NET 6.

[jonathanpeppers]

This is breaking, let me see what changed:

ILLink : error IL1019: Value used with '--custom-data' has to be in the KEY=VALUE format

Maybe we are picking up an extra directory now?

[jonathanpeppers]

The issue was the trailing \ was escaping the ":

XATargetFrameworkDirectories="C:\Users\AzDevOps\android-toolchain\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.3.21167.1\ref\net6.0\;C:\Users\AzDevOps\android-toolchain\dotnet\packs\Microsoft.Android.Ref\11.0.200-ci.pr.gh5767.171\ref\net6.0\"

While this one works:

XATargetFrameworkDirectories="C:\src\maui\bin\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.2.21154.6\ref\net6.0;C:\src\maui\bin\dotnet\packs\Microsoft.Android.Ref\11.0.200-ci.main.148\ref\net6.0"

I trimmed the trailing slash, which seems to fix it.