AppHost should be disabled by default for macOS like it is for iOS / tvOS / Mac Catalyst / Android

[rolfbjarne]

Description

Xamarin.Mac for .NET (the net6.0-macos target framework) are like mobile platforms in that the app host should be disabled by default here:

https://github.com/dotnet/sdk/blob/c53c8ac81e1bcb8118c31bc4f5622396c72e9959/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.RuntimeIdentifierInference.targets#L118-L119

I'm not sure what's the best way to do it though, since the applicable RIDs (osx-x64/osx-arm64) are also used for other target frameworks where the app host shouldn't get the same behavior.

CC @akoeplinger

Tagging subscribers to this area: @vitek-karas, @agocke, @VSadov
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Issue Details

---

Description

Xamarin.Mac for .NET (the net6.0-macos target framework) are like mobile platforms in that the app host should be disabled by default here:

https://github.com/dotnet/sdk/blob/c53c8ac81e1bcb8118c31bc4f5622396c72e9959/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.RuntimeIdentifierInference.targets#L118-L119

I'm not sure what's the best way to do it though, since the applicable RIDs (osx-x64/osx-arm64) are also used for other target frameworks where the app host shouldn't get the same behavior.

CC @akoeplinger

Author:	rolfbjarne
Assignees:	-
Labels:	area-Host, untriaged
Milestone:	-

[agocke]

We're actually planning on enabling the apphost for Mac due to the x64/ARM64 split on Apple Si.

What's the reason why mobile platforms need to have the apphost disabled?

[rolfbjarne]

What's the reason why mobile platforms need to have the apphost disabled?

We don't use it, we host the runtime (either Mono or CoreCLR) ourselves.

[akoeplinger]

Hm as a workaround you can set _RuntimeIdentifierUsesAppHost=false and UseAppHost=false.

[agocke]

Yeah, I'm not sure that's bad as an actual solution -- it seems like we just need to decide on the correct properties to set in the Xamarin targets.

[rolfbjarne]

Hm as a workaround you can set _RuntimeIdentifierUsesAppHost=false and UseAppHost=false.

That can only be set in the csproj, because _RuntimeIdentifierUsesAppHost is evaluated before our WorkloadManifest.targets file is loaded (where we can set properties ourselves).

You can see the Import order here: https://gist.github.com/rolfbjarne/848f5c5fed4f3e1a5314232d269bb670

AutoImports.props is loaded at line 27: https://gist.github.com/rolfbjarne/848f5c5fed4f3e1a5314232d269bb670#file-gistfile1-txt-L27 - this is the first time our code is loaded, and at this point we can't set properties (https://github.com/xamarin/xamarin-macios/blob/85ce924296eb17b4a3860b32cc94d8b4c1bfae00/dotnet/targets/Microsoft.Sdk.DefaultItems.template.props#L5-L16)

Microsoft.NET.RuntimeIdentifierInference.targets is loaded at line 52: https://gist.github.com/rolfbjarne/848f5c5fed4f3e1a5314232d269bb670#file-gistfile1-txt-L52

Our WorkloadManifest.targets is loaded at line 65: https://gist.github.com/rolfbjarne/848f5c5fed4f3e1a5314232d269bb670#file-gistfile1-txt-L65 - this is where we can set properties, but it's too late.

[agocke]

As we're enabling the AppHost for Mac we may be removing some usages of those properties, so I would be careful about dependencies here. Clearly UseAppHost is public, so there's no problem there, but I'm not sure what will change in our usage of _RuntimeIdentifierUsesAppHost

[steveisok]

@akoeplinger what do you think the best solution is?

[vitek-karas]

I think this should be solved in the SDK specific to Xamarin.Mac - I assume there's such a thing as the core SDK will not produce apps for it. Should we maybe move the issue to the repo which track the work on that SDK?

[akoeplinger]

With dotnet/sdk#18639 the RuntimeIdentifierInference.targets is now imported after the workload targets so setting _RuntimeIdentifierUsesAppHost=false and UseAppHost=false should work now as a workaround.

Ideally we shouldn't need to rely on a "private" msbuild property though, an explicit UseAppHost=false setting should be enough to disable the apphost completely.

We only need the _RuntimeIdentifierUsesAppHost=false to disable this error check here: https://github.com/dotnet/sdk/blob/e2687a3e6e5259d2167173977e64f1e9ab91f51b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.RuntimeIdentifierInference.targets#L148-L149

@agocke sounds like if you touch this code anyway, can we just relax that check?