Support providing OS APIs from targeted platform

[dsplaisted]

When a project targets iOS or Android, the operating system API projections should be available to the project at compile time.

This should be via an implicit FrameworkReference added by the corresponding SDK workload. The workload should also probably be in charge of carrying the corresponding KnownFrameworkReference information.

In the .NET SDK, we will probably have to update the framework reference resolution to understand the target platform information. IE a KnownFrameworkReference for net5.0 should be available in a project targeting net5.0-ios, but not vice versa.

Additionally, we need to update the SDK to download runtime packs based on the RuntimeIdentifiers property (plural). This is so that a device app can specify multiple architectures that the produced package should support. (EDIT: Turns out this is already supported. See #11637)

[wli3]

blocked by ios and android provide a work in progress workload -- we need to sync with Xamiarn for when we can have a "good enough" implementation to try. And how to try -- just dropping file might be good enough

[wli3]

This works is mostly on workload owner right?

[steveisok]

@dsplaisted To make sure I understand, you're suggesting that, for example, the iOS SDK (the optional workload) would be responsible for including both its KnownFrameworkReference for Xamarin.iOS.Sdk AND the one for the underlying mono runtime?

[dsplaisted]

@steveisok Based on dotnet/installer#7034, it sounds like the Mono runtime for the base framework might be defined in the core SDK, not in the workloads. I think it would work either way though.

[steveisok]

Yes, it's defined in the core SDK right now. I wasn't sure as a result of this issue that would shift. And if it's still in the core sdk, then there would need to be a way to pluck the right runtime pack where there's > 1 for the rid.

For example: A project with net5.0-macos would need to ultimately load the Microsoft.NETCore.App.Runtime.Mono.osx-x64 runtime pack.

[pjcollins]

Here's some additional context on the Xamarin SDK side if it's at all helpful/relevant -- The Android SDK is currently defining its own FrameworkReference here: https://github.com/xamarin/xamarin-android/blob/fcdf728ca45c3174bd69458f4b7aba1bfa3b352e/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultItems.props#L24

We're also declaring a KnownFrameworkReference in our own BundledVersions file that we are generating in our SDK: https://github.com/xamarin/xamarin-android/blob/fcdf728ca45c3174bd69458f4b7aba1bfa3b352e/build-tools/create-packs/Microsoft.Android.Sdk.proj#L114

[wli3]

For 5.0 we will only do that for windows

[wli3]

And windows part is done. We should move this to 6.0. Although pending #12202 to get net5.0-windows working

[marcpopMSFT]

There may be additional needed .net 6 when we integrate with Xamarin.