Trimming unused code from libraries used in an application is crucial to minimize deployment size. One of our goals for .NET 9 is to make MAUI trimming-friendly (#18658).

Publishing the base MAUI app dotnet new maui for iOS with NativeAOT currently emits 69 warnings (64 Trim analysis warnings + 5 AOT analysis warnings). Our first goal is to make the codepaths used in the base MAUI app trimming and AOT friendly (0 warnings).

Once the template MAUI app is warning-free, we will move onto more complex scenarios (possibly WeatherTwentyOne or eShop ClientApp).

Build steps

1. create new MAUI project

./bin/dotnet/dotnet new maui -o TestApp && cd TestApp && dotnet restore

2. build for iOS with NativeAOT

./bin/dotnet/dotnet publish \
  -f net8.0-ios \
  -r ios-arm64 \
  -p:PublishAot=true \
  -p:PublishAotUsingRuntimePack=true \
  -p:_RequireCodeSigning=false \
  -p:EnableTrimAnalyzer=true \
  -p:TrimmerSingleWarn=false | tee TestApp.log

3. count warnings

grep -c 'Trim analysis warning\|AOT analysis warning' TestApp.log

Warnings (grouped by class or namespace)

• Microsoft.Maui.Controls.BindableProperty - 1
  • fixed in [Trimming] Fix several trimming warnings #19402
  • Invokes System.Activator.CreateInstance(Type) without a DynamicallyAccessedMemberTypes.PublicParameterlessConstructor type.
• Microsoft.Maui.Controls.BindablePropertyConverter - 1
  • addressed in [Trimming] Fix remaining trimming warnings related to XAML parsing #20474
  • Invokes Type.GetType(String) to grab a Microsoft.Maui.Controls.* type.
• Microsoft.Maui.HotReload.MauiHotReloadHelper - 2
  • fixed in [Trimming] Fix several trimming warnings #19402
  • Invokes System.Activator.CreateInstance(Type,Object[]) without a DynamicallyAccessedMemberTypes.PublicConstructors type
  • Invokes System.Activator.CreateInstance(Type) without a DynamicallyAccessedMemberTypes.PublicParameterlessConstructor type
• Microsoft.Maui.Controls.DependencyService - 1
  • fixed in [Trimming] Fix several trimming warnings #19402
  • List<Types> DependencyTypes's elements aren't DynamicallyAccessedMembers Types
• Microsoft.Maui.Controls.ResourceDictionary - 1
  • fixed in [Trimming] Fix several trimming warnings #19402
  • Invokes System.Activator.CreateInstance(Type) without a DynamicallyAccessedMemberTypes.PublicParameterlessConstructor type.
• Microsoft.Maui.Controls.Routing - 1
  • fixed in [Trimming] Fix several trimming warnings #19402
  • RegisterRoute(string, [DynamicallyAccessedMembers...] Type) is accessed through reflection.
• Microsoft.Maui.Controls.ShellContent - 2
  • trimming-unsafe code disabled with a feature switch in [Trimming] Disable query property assignment via reflection on NativeAOT #20731
  • solution proposed in [Proposal] Source generator for [QueryProperty] #20466
  • System.Object.GetType() does not return [DynamicallyAccessedMembers] Type required by System.Reflection.RuntimeReflectionExtensions.GetRuntimeProperty(Type,String)
• Microsoft.Maui.Controls.VisualTypeConverter - 2
  • fixed in [Trimming] Disable assembly scanning for types implementing IVisual #20417
  • Invokes System.Reflection.Assembly.GetExportedTypes() from an overridden ConvertFrom(ITypeDescriptorContext,CultureInfo,object) and ConvertTo(ITypeDescriptorContext,CultureInfo,object,Type) which aren't decorated with RequiresUnreferencedCodeAttribute
  • Type from System.Reflection.Assembly.GetExportedTypes() is not decorated with DynamicallAccessedMemberTypes.PublicParameterlessConstructor
• Microsoft.Maui.Controls.Xaml.TypeConversionExtensions - 2
  • discussed in [Trimming] Fix trimming unfriendly usage of implicit operators through reflection #19922
  • Uses trimming-unsafe Microsoft.Maui.Controls.Xaml.TypeConversionExtensions.GetImplicitConversionOperator(Type,Type,Type)
• Microsoft.Maui.Controls.Xaml.TypeConversionExtensions - 4
  • fixed in [Trimming] Fix several trimming warnings #19402
  • Unrecognized value passed to the parameter typeName of method System.Type.GetType(String)
  • Invokes System.Activator.CreateInstance(Type) without a DynamicallyAccessedMemberTypes.PublicParameterlessConstructor type.
• Microsoft.Maui.Controls.Xaml.ApplyPropertiesVisitor - 18
  • fixed in [Trimming] Add a feature flag to disable XAML loading at runtime #19310
  • Invokes System.Reflection.RuntimeReflectionExtensions.GetRuntimeEvents(Type) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents
  • Invokes System.Reflection.RuntimeReflectionExtensions.GetRuntimeEvent(Type,String) with a String not decorated with DynamicallyAccessedMemberTypes.PublicEvents
  • Invokes System.Reflection.RuntimeReflectionExtensions.GetRuntimeMethods(Type) for a type not decorated with DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods
  • Invokes System.Reflection.RuntimeReflectionExtensions.GetRuntimeProperties(Type) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties
  • Invokes System.Type.GetFields(BindingFlags) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFieldsInvokes
  • Invokes System.Type.GetInterfaces() with a Type not decorated with DynamicallyAccessedMemberTypes.Interfaces
  • Invokes System.Type.GetMethod(String,BindingFlags) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods
  • Invokes System.Type.GetProperty(String,BindingFlags) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicProperties
• Microsoft.Maui.Controls.Xaml.CreateValuesVisitor - 8
  • fixed in [Trimming] Add a feature flag to disable XAML loading at runtime #19310
  • Invokes System.Activator.CreateInstance(Type) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicParameterlessConstructor
  • Invokes System.Activator.CreateInstance(Type,Object[]) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicConstructors
  • Invokes System.Reflection.TypeInfo.DeclaredConstructors.get with a TypeInfo not decorated with DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors
  • Invokes System.Reflection.RuntimeReflectionExtensions.GetRuntimeMethods(Type) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods
• Microsoft.Maui.Controls.Xaml.MarkupExpressionParser - 1
  • fixed in [Trimming] Add a feature flag to disable XAML loading at runtime #19310
  • Invokes System.Activator.CreateInstance(Type) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicParameterlessConstructor
• Microsoft.Maui.Controls.Xaml.XamlParser - 3
  • addressed in [Trimming] Fix remaining trimming warnings related to XAML parsing #20474
  • Unrecognized interpolated string composed of typeInfofields passed to System.Type.GetType(String)
  • Invokes System.Type.MakeGenericType(Type[])
• Microsoft.Maui.Hosting.ImageSourceServiceProvider - 7
  • addressed in [Trimming] Fix trimming warnings related to image source service provider #20058
  • Invokes System.Type.MakeGenericType(Type[])
  • Invokes System.Type.GetInterfaces() with a Type not decorated with DynamicallyAccessedMemberTypes.Interfaces
  • Invokes System.Type.GetInterfaces(String) with a Type not decorated with DynamicallyAccessedMemberTypes.Interfaces
• Microsoft.Maui.Hosting.Internal.MauiFactory - 4
  • addressed in [Core][Hosting] Resolve handler services through registered service types #20298
  • Invokes System.Type.MakeGenericType(Type[])
  • Invokes System.Type.GetInterfaces() with a Type not decorated with DynamicallyAccessedMemberTypes.Interfaces
  • Invokes System.Activator.CreateInstance(Type) with a Type not decorated with DynamicallyAccessedMemberTypes.PublicParameterlessConstructor
• Microsoft.Maui.Platform.ReflectionExtensions - 1
  • addressed in [Trimming] Fix remaining trimming warnings related to XAML parsing #20474
  • Invokes System.Reflection.TypeInfo.DeclaredFields.get with a TypeInfo not decorated with DynamicallyAccessedMemberTypes.PublicFields | DynamicallyAccessedMemberTypes.NonPublicFields
• Microsoft.Maui.Controls.BindingExpression - 9
  • solution proposed in [Trimming] Use typed bindings internally #20567
  • Invokes System.Reflection APIs (DeclaredProperties.get, ImplementedInterfaces.get, GetDeclaredMethod(String), GetDeclaredProperty(String) GetDeclaredField(String)) with a TypeInfo not decorated with DynamicallyAccessedMemberTypes
• <Module>..cctor() - 1
  • fixed in [NativeAOT] Improve the transformation of [Preserve(AllMembers = true)] macios#19516
  • Invokes System.Enum.GetValues(Type)

Automated testing

There is a test that counts the warnings in the MAUI app (introduced in #19194). PRs which fix any of the warnings should update the list of expected warnings.

/cc @jonathanpeppers @mdh1418 @ivanpovazan