[One .NET] fix 'dotnet publish' with no arguments

[jonathanpeppers]

Fixes: dotnet/maui#15696
Context: dotnet/sdk#30038

In .NET 8 Preview 5, there are various changes to default values:

• dotnet publish is now Release by default

• Builds that provide a $(RuntimeIdentifier) are no longer "self contained" by default.

The result of this change is the problem:

dotnet new android
dotnet publish
Microsoft.NET.RuntimeIdentifierInference.targets(212,5): error NETSDK1191: A runtime identifier for the property 'SelfContained' couldn't be inferred. Specify a rid explicitly.

While these commands all work:

dotnet build
dotnet build -c Release
dotnet publish -c Debug
dotnet publish -r android-arm64

Debug configurations work fine, because trimming is not involved. dotnet build works fine, because the offending default appears to be:

https://github.com/dotnet/sdk/blob/540b197311bc8d1c2a991fed1b935b094a4d7b2d/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.RuntimeIdentifierInference.targets#L64-L76

Microsoft.NET.RuntimeIdentifierInference.targets has a lot of MSBuild validation logic, that its main job is to emit nice error messages for incorrect combinations of MSBuild properties/settings.

Android is kind of the odd one out when you compare to .NET console apps, NativeAOT, etc.:

• We default to RuntimeIdentifiers=android-arm;android-arm64;android-x86;android-x64.

• We do our own "inner build" for each RuntimeIdentifier.

• Inside our build we force $(SelfContained) to true no matter what. As there is no such thing as a system-wide .NET on Android.

The fix appears to be to default PublishSelfContained=false and let our existing logic force SelfContained=true.

I added a new test for this scenario. Our existing test didn't catch this because it was passing a RuntimeIdentifier.

[pjcollins]

Makes sense to me, cc @rolfbjarne in case something similar should be done on the macios side.

[rolfbjarne]

Makes sense to me, cc @rolfbjarne in case something similar should be done on the macios side.

We only set SelfContained=true if we have a RuntimeIdentifier (either by default or set explicitly), so when RuntimeIdentifiers is set, we don't set SelfContained, and we don't seem to run into this problem:

https://github.com/xamarin/xamarin-macios/blob/6c32a1effcb3ea81618acaa5dc341b4428600179/dotnet/targets/Xamarin.Shared.Sdk.props#L90-L96

[jonathanpeppers]

I think we hit this, because we pass in RuntimeIdentifier for every build. Release builds use: RuntimeIdentifiers=android-arm;android-arm64;android-x86;android-x64

Debug builds, we detect the attached device and pick the appropriate one.