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:/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

[ghost]

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:/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:/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:/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?

[agocke]

I think the right approach for now is to use _RuntimeIdentifierUsesAppHost. I don't think disabling that check is the right thing -- it's an important safe guard for later passes that may require the apphost.

It seems better to make _RuntimeIdentifierUsesAppHost a public property, since it's being used like one. I'm going to close this issue for now since it's been resolved (at least temporarily). If we want to come back to this, the SDK is the right repo for a new issue.