Nullable annotations metadata on non-public members

[JamesNK]

Description

In ASP.NET Core we want to use nullable annotations metadata to make decisions about how to call user-defined methods and local-methods/delegates. For more information, see #32375

Today that metadata is removed from private members and compiler-generated methods: dotnet/runtime#29723 (comment)

Also we set the flag for the compiler to not emit nullable metadata for non visible outside the assembly APIs; I don't know how interesting it would be for apps to figure out nullability for internal/private APIs of the framework, I guess that is a non-goal for this API but something to add on the docs?

I'm guessing this was done to reduce metadata in assemblies.

Unfortunately, it means that today we can't use that information when calling compiler-generated methods and private methods.

// Nullable IService means if IService is not resolved from DI
// then the method will be called will a null value instead of throwing an error
app.MapPost("/todos", (IService? service) => {
    // stuff
});

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[JamesNK]

@halter73 @davidfowl

[jkotas]

This option is called nullablePublicOnly and it is set here: https://github.com/dotnet/runtime/blob/main/Directory.Build.props#L268

This option is right for dotnet/runtime since we generally try to avoid reflection and we do not support 3rd party code using reflection against internal implementation details.

If you would like to not set this for ASP.NET and take the size hit, that's your call to make on whether it is the right tradeoff.

[JamesNK]

The private and compiler-generated methods in this situation aren't written by us. They're from user's applications and we're reflecting on them.

Would that mean the nullablePublicOnly setting must be not set in the ASP.NET Core SDK?

[jkotas]

I do not see anyting setting nullablePublicOnly in any SDK. Do you have a repro for the problem that you are trying to solve? Maybe you are getting confused by nullablePublicOnly being set for ASP.NET Core repo here

aspnetcore/eng/targets/CSharp.Common.props

Line 7 in 52eff90

<Features>strict;nullablePublicOnly</Features>

?

[JamesNK]

Ahh, I get what is going on now. This is something that we've opted into for assemblies produced by runtime and aspnetcore.

In user app assemblies this flag isn't on so the nullable metadata will always be available.

My confusion was because I was testing this in an aspnetcore test assembly, which has the nullablePublicOnly flag applied to it.

I think the only change here will be to turn nullablePublicOnly on in just the assemblies that are deployed in the SDK, and leave it off in test assemblies. That will allow test assemblies to simulate user's apps more closely.

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[halter73]

Closing but the context might be relevant for #32375