[net10.0] Aggressive attribute trimming breaks NativeAOT builds

[simonrozsival]

Apple platform

Mac Catalyst, iOS

Framework version

net10.0-*

Affected platform version

.NET 10 P1

Description

The recent addition of the switch/build property MobileAggressiveAttributeTrimming which enables aggressive attribute trimming in .NET 10 (#21314) causes problems with NativeAOT builds. This problem surfaced in dotnet/maui#27103

When the feature switch is enabled (the default behavior), ILLink removes all [DynamicallyAccessedMembers] and when ILC builds a NativeAOT binary, it cannot see these annotations anymore and it produces trim warnings and the final binary most likely won't work as expected.

I see two possible fixes:

• Disable MobileAggressiveAttributeTrimming for NativeAOT builds and let ILC trim unnecessary attributes
• Remove DynamicallyAccessedMembersAttribute from TrimAttributes.LinkDescription.xml.
  • My hunch is that this will reveal other problems, because the NativeAOT compiler uses other attributes from the System.Diagnostics.CodeAnalysis namespace for static analysis of the program, such as the FeatureGuardAttribute.

/cc @rolfbjarne @jonathanpeppers @sbomer

Steps to Reproduce

1. Create a new MAUI project
2. Add <PublishAot Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'maccatalyst'">true</PublishAot> to the project file
3. Build the project with a local build of .NET MAUI from the net10.0 branch with this command:
   $(MAUI_DIR)/dotnet-local.sh publish -f net10.0-maccatalyst -r maccatalyst-arm64 -p:TrimmerSingleWarn=false

Did you find any workaround?

Set $(MobileAggressiveAttributeTrimming)=false in the MAUI project.

Build logs

 TestApp net10.0-maccatalyst succeeded with 18 warning(s) (37.4s) → bin/Release/net10.0-maccatalyst/maccatalyst-arm64/TestApp.dll
    /.../Projects/dotnet/maui/src/Controls/src/Core/BindableProperty.cs(93): Trim analysis warning IL2067: Microsoft.Maui.Controls.BindableProperty.BindableProperty(String,Type,Type,Object,BindingMode,BindableProperty.ValidateValueDelegate,BindableProperty.BindingPropertyChangedDelegate,BindableProperty.BindingPropertyChangingDelegate,BindableProperty.CoerceValueDelegate,BindableProperty.BindablePropertyBindingChanging,Boolean,BindableProperty.CreateDefaultValueDelegate): 'type' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicParameterlessConstructor' in call to 'System.Activator.CreateInstance(Type)'. The parameter '#1' of method 'Microsoft.Maui.Controls.BindableProperty.BindableProperty(String,Type,Type,Object,BindingMode,BindableProperty.ValidateValueDelegate,BindableProperty.BindingPropertyChangedDelegate,BindableProperty.BindingPropertyChangingDelegate,BindableProperty.CoerceValueDelegate,BindableProperty.BindablePropertyBindingChanging,Boolean,BindableProperty.CreateDefaultValueDelegate)' 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.
    ILC : Trim analysis warning IL2070: Microsoft.Extensions.DependencyInjection.ActivatorUtilities.TryFindMatchingConstructor(Type,Type[],ConstructorInfo&,Nullable`1<Int32>[]&): 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicConstructors' in call to 'System.Type.GetConstructors()'. The parameter '#0' of method 'Microsoft.Extensions.DependencyInjection.ActivatorUtilities.TryFindMatchingConstructor(Type,Type[],ConstructorInfo&,Nullable`1<Int32>[]&)' 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.
    ILC : Trim analysis warning IL2067: Microsoft.Extensions.Internal.ParameterDefaultValue.<TryGetDefaultValue>g__CreateValueType|0_0(Type): 'type' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicConstructors', 'DynamicallyAccessedMemberTypes.NonPublicConstructors' in call to 'System.Runtime.CompilerServices.RuntimeHelpers.GetUninitializedObject(Type)'. The parameter '#0' of method 'Microsoft.Extensions.Internal.ParameterDefaultValue.<TryGetDefaultValue>g__CreateValueType|0_0(Type)' 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.
 ...

Build succeeded with 18 warning(s) in 29.0s

[ivanpovazan]

@simonrozsival

Set $(MobileAggressiveAttributeTrimming)=true in the MAUI project.

Isn't the workaround setting the feature to false?

[vitek-karas]

If we really need this (personally I would prefer slightly bigger apps which work more often, over slightly smaller apps which break more often, but this is up to the iOS team to decide) I think we should make two changes to this:

• Only enable it if TrimMode=partial, if we turn on full trimming which also enables all the trim analysis warnings, we should "play by the book" and keep attributes which trimmer can't remove. The promise of TrimMode=full and no warnings is that the app never breaks, we should keep that promise.
• Not enable it for NativeAOT (which would happen from the above as well, since NativeAOT requires TrimMode=full) - the size impact of keeping attributes in NativeAOT is smaller than in IL apps, and again, NativeAOT should have a predictable behavior.

[rolfbjarne]

• Only enable it if TrimMode=partial, if we turn on full trimming which also enables all the trim analysis warnings, we should "play by the book" and keep attributes which trimmer can't remove. The promise of TrimMode=full and no warnings is that the app never breaks, we should keep that promise.

This might result in a rather unintuitive result: TrimMode=full apps can end up bigger than TrimMode=partial apps.

• Not enable it for NativeAOT

I've created a PR with this change. We have fewer compatibility concerns with NativeAOT, while at the same time we have a bigger correctness promise, so this seemed like the best way forward.

[vitek-karas]

This might result in a rather unintuitive result: TrimMode=full apps can end up bigger than TrimMode=partial apps.

I think the same thing you mentioned for NativeAOT applies to TrimMode=full: "We have fewer compatibility concerns with NativeAOT, while at the same time we have a bigger correctness promise".
Yes - in theory it might make the app bigger, but in this mode we show trim warnings, and thus the expected behavior is that if there are now warnings, the app will work - removing attributes may break some apps without trim warnings.