IL2077/IL2080/IL2075 when trimming application using System.CommandLine.Hosting

[azchohfi]

Similar to #1465

/_/src/System.CommandLine.Hosting/HostingExtensions.cs(113,21): Trim analysis error IL2077: System.CommandLine.Hosting.HostingExtensions.<>c__DisplayClass6_0.<UseCommandHandler>b__1(IServiceCollection): 'serviceType' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicConstructors' in call to 'Microsoft.Extensions.DependencyInjection.ServiceCollectionServiceExtensions.AddTransient(IServiceCollection,Type)'. The field 'System.CommandLine.Hosting.HostingExtensions.<>c__DisplayClass6_0.handlerType' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.
/_/src/System.CommandLine.Hosting/HostingExtensions.cs(116,17): Trim analysis error IL2080: System.CommandLine.Hosting.HostingExtensions.UseCommandHandler(IHostBuilder,Type,Type): 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicMethods' in call to 'System.Type.GetMethod(String)'. The field 'System.CommandLine.Hosting.HostingExtensions.<>c__DisplayClass6_0.handlerType' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.
/_/src/System.CommandLine.NamingConventionBinder/ModelDescriptor.cs(38,9): Trim analysis error IL2075: System.CommandLine.NamingConventionBinder.ModelDescriptor.ConstructorDescriptors.get: 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicConstructors', 'DynamicallyAccessedMemberTypes.NonPublicConstructors' in call to 'System.Type.GetConstructors(BindingFlags)'. The return value of method 'System.CommandLine.NamingConventionBinder.ModelDescriptor.ModelType.get' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.
/_/src/System.CommandLine.NamingConventionBinder/ModelDescriptor.cs(47,9): Trim analysis error IL2075: System.CommandLine.NamingConventionBinder.ModelDescriptor.PropertyDescriptors.get: 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicProperties', 'DynamicallyAccessedMemberTypes.NonPublicProperties' in call to 'System.Type.GetProperties(BindingFlags)'. The return value of method 'System.CommandLine.NamingConventionBinder.ModelDescriptor.ModelType.get' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.

I worked around this by adding one entry like this:

[DynamicDependency(DynamicallyAccessedMemberTypes.All, typeof(MyCommand.Handler))]

for each of my command handlers, and ignoring the 3 warnings, but this will blow in my face in the future, so proper support for ILTrimming is preferred.

[azchohfi]

I'm working on this. Not that complicated for System.CommandLine and System.CommandLine.Hosting.

[perlun]

For the reference, I am also seeing linking errors from System.CommandLine.NamingConventionBinder in my app:

.../system.commandline.namingconventionbinder/2.0.0-beta4.22272.1/lib/netstandard2.0/System.CommandLine.NamingConventionBinder.dll : error IL2104: Assembly 'System.CommandLine.NamingConventionBinder' produced trim warnings. For more information see https://aka.ms/dotnet-illink/libraries [/home/per/git/perlang/src/Perlang.ConsoleApp/Perlang.ConsoleApp.csproj]

[jonsequitur]

System.CommandLine.NamingConventionBinder is heavily reliant on reflection and would need an almost complete rewrite in order to become trimmable.

[perlun]

Thanks for the feedback @jonsequitur. Are there any known workarounds to this apart from keeping <SuppressTrimAnalysisWarnings>true</SuppressTrimAnalysisWarnings> in my app? I'd rather be able to disable it, since there is a risk that it hides other real trimming-related problems in the app. (https://github.com/perlang-org/perlang/pull/347#issuecomment-1267420299)

[jonsequitur]

I'm not aware of any.

We're planning to create a source generator that will replace System.CommandLine.NamingConventionBinder with something as concise but with all of the trimmability of the core System.CommandLine, but for that to be source code-compatible with the System.CommandLine.NamingConventionBinder API doesn't look feasible.