IL2026/IL3050 Warnings only visible via dotnet format, neither in Visual Studio 2026 nor via dotnet build /publish

[ene-one]

After installing Visual Studio 2026 and .NET10 I noticed the following behavior:

I’m building an AOT project that uses DI. When I build and publish the project, the IL trimming/AOT warnings are not shown in Visual Studio — neither in the Build Output nor in the Error List (Build + IntelliSense).
Code snippet:

 LogManager.Setup().SetupExtensions(e => e.RegisterTarget<EventLogTarget>());
        var config = new ConfigurationBuilder()
            .SetBasePath(AppContext.BaseDirectory)
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .Build() ??
                throw new InvalidOperationException("Cannot get configuration.");

        var services = new ServiceCollection();
        services.AddSingleton<IConfiguration>(config);
        services.Configure<LicensingOptions>(config.GetSection(nameof(LicensingOptions)));
        services.Configure<SettingsServiceOptions>(config.GetSection(nameof(SettingsServiceOptions)));

However, when I run dotnet format, those warnings do appear:

...\Program.cs(29,9): warning IL2026: Using member 'Microsoft.Extensions.DependencyInjection.OptionsConfigurationServiceCollectionExtensions.Configure<TOptions>(IServiceCollection, IConfiguration)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. TOptions's dependent types may have their members trimmed. Ensure all required members are preserved.
...\Program.cs(29,9): warning IL3050: Using member 'Microsoft.Extensions.DependencyInjection.OptionsConfigurationServiceCollectionExtensions.Configure<TOptions>(IServiceCollection, IConfiguration)' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. Binding strongly typed objects to configuration values may require generating dynamic code at runtime.

Before upgrading from .NET 8 to .NET 10 and from VS 2022 to VS 2026, these warnings were displayed both during the build / publish and inside the Visual Studio Error List.

I think that in this specific case I can ignore the warnings, because I use my own classes in this project for Configure(). I’m mainly curious whether anyone else has seen this behavior and whether this might be a Visual Studio or SDK bug.

[huoyaoyuan]

The trimming warnings should only be enabled when IsTrimmable or PublishTrimmed is set. Are you enabling these options? If not, it should be better to ask at dotnet/format repo.

[ene-one]

No, I am not explicitly setting PublishTrimmed or IsTrimmable. I am only using <PublishAot>true</PublishAot>.
Thanks for the tip.

[huoyaoyuan]

I am only using <PublishAot>true</PublishAot>.

PublishAot also implies the trimming warning. You may need to use the source generator for the configurations.

[ene-one]

Ok, but the core problem still remains: why do these warnings only appear during format and not during build or publish? That's what I do not unterstand.”

[huoyaoyuan]

You can try to collect binlog for each operation by adding -bl switch to the command, and try to see what's different.