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openedon May 24, 2023
Using a recent .NET 8 SDK, build the following project
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net8.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
<PublishAot>true</PublishAot>
</PropertyGroup>
<ItemGroup>
<PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="8.0.0-preview.4.23259.5" />
</ItemGroup>
</Project>using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;
var services = new ServiceCollection();
services.AddService<MyService>();
record MyService;
static class Extensions
{
public static void AddService<TService>(this ServiceCollection services)
where TService : class
{
services.TryAddSingleton<TService>();
}
}You should get a warning from the trimming analyzer because AddService<TService> isn't annotated to preserve the constructors of TService, however it calls services.TryAddSingleton<TService>(); which IS annotated with a DynamicallyAccessedMembers attribute. So the analyzer should be able to give a warning here during build, but doesn't.
Now dotnet publish the app, and now you get the warning:
C:\Users\eerhardt\source\repos\ConsoleApp90\ConsoleApp90\Program.cs(16): Trim analysis warning IL2091: Extensions.AddService<TService>(ServiceCollection):
'TService' generic argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicConstructors' in 'Microsoft.Extensions.DependencyInjection.Extensions.
ServiceCollectionDescriptorExtensions.TryAddSingleton<TService>(IServiceCollection)'. The generic parameter 'TService' of 'Extensions.AddService<TService>
(ServiceCollection)' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target loca
tion it is assigned to. [C:\Users\eerhardt\source\repos\ConsoleApp90\ConsoleApp90\ConsoleApp90.csproj]
The analyzer needs to catch this warning so libraries that are depending on it for warnings know they have a trimming issue here.
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