Remove special handling of TypeDescriptionProviderAttribute and TypeConverterAttribute

[vitek-karas]

TypeDescriptionProviderAttribute - the .ctor parameter are now annotated with PublicParameterlessConstructor and so the intrinsic handling in linker is not necessary anymore (linker would preserve any parameterless .ctor on the type).

TypeConverterAttribute - the .ctor parameter is annotated with PublicConstructors

• Linker will mark any parameterless constructor on the type intrinsically
• Linker will also mark any method which has exactly one parameter with type System.Type. Since the type must be TypeConverter derived, that means methods CanConvertFrom and CanConvertTo.

The .ctor part is covered by the annotation. It's unclear why linker preserves the other methods though.

[vitek-karas]

@marek-safar the original logic was added by you in https://github.com/mono/linker/pull/778/files - do you remember why linker preserves any method with Type parameter on the target type?

@eerhardt since you did the annotation work on this - any idea why preserving methods with Type parameter would help? Is it needed (I assume not since the annotations would otherwise specify PublicMethods or something similar).

[marek-safar]

do you remember why linker preserves any method with Type parameter on the target type?

This looks like a bug. It should apply to constructors only.

[marek-safar]

I linked this with existing #1349

[eerhardt]

The System.ComponentModel.TypeConverter assembly is now fully annotated (sans one remaining warning about MaskedTextProvider which is not relevant here). None of the usages of the TypeDescriptionProviderAttribute needs PublicMethods.

https://github.com/dotnet/runtime/blob/52f986706dc96b4b146c6657e6bcce1f5d29cc55/src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs#L333-L339

Looking at the usages of TypeConverterAttribute, there are also some usages from WindowsBase and System.Xaml, and some other assemblies in full framework:

https://referencesource.microsoft.com/#System/compmod/system/componentmodel/TypeConverterAttribute.cs,70f7fb9a74c8db1f,references

• System.Activities.Presentation
• System.Configuration
• System.ServiceModel.Web
• System.Web
• System.Web.DataVisualization
• etc

Honestly, I can't think of any reason why that rule was added for TypeConverters.

[eerhardt]

Looking at the PR, I wonder if it was meant to handle this case:

https://github.com/mono/linker/pull/778/files#diff-85d907c0a93cce04b7e233874d9157a03e5950b94d565b90c3f2f3a136c85a3eR20-R22

		class Custom1 : TypeConverter
		{
			[Kept]			
			public Custom1 (Type type)
			{
			}

The case where the constructor took a single Type argument.

[eerhardt]

Note: I hit this issue in a dotnet new maui app today. The issue manifested itself in a strange way:

ILLink : Trim analysis warning IL2111: Microsoft.Maui.Controls.IVisual: Method 'Microsoft.Maui.Controls.VisualTypeConverter.CreateVisual(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [C:\DotNetTest\MauiTest\MauiTest.csproj]

	[System.ComponentModel.TypeConverter(typeof(VisualTypeConverter))]
	public interface IVisual
	{
	}

	public class VisualTypeConverter : TypeConverter
	{
		static IVisual CreateVisual(
			[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] Type visualType)
		{
...

We have that code in Maui. Since there is a method with a single parameter of type System.Type, this rule is firing:

linker/src/linker/Linker.Steps/MarkStep.cs

Lines 2057 to 2063 in 7079b34

	bool MarkSpecialCustomAttributeDependencies (CustomAttribute ca, ICustomAttributeProvider provider)
	{
	var dt = ca.Constructor.DeclaringType;
	if (dt.Name == "TypeConverterAttribute" && dt.Namespace == "System.ComponentModel") {
	MarkTypeConverterLikeDependency (ca, l =>
	l.IsDefaultConstructor () ||
	l.Parameters.Count == 1 && l.Parameters[0].ParameterType.IsTypeOf ("System", "Type"),

Since this method is a private static method, that is never used in Reflection, this is a bogus warning.

As above, we have annotated TypeConverterAttribute correctly with DynamicallyAccessedMembers. So the TypeConverter constructors will be preserved that way. We should be able to just delete all this special TypeConverter handling code in the linker.

[vitek-karas]

I think the agreement is that we should remove special handling of these types in the linker because the annotations already cover everything the runtime needs about them - which is also proved by the fact that the linker analysis of the callsites is clean.

The risk of breaking anything with this should be very low - and if it does break something, I'd like to know, because that would point to a bug in the analysis on the consumption side.

[eerhardt]

Re-opening to consider backporting this to .NET 6 for Maui.

I'm seeing the following warnings 330 times when trimming a Maui app, which is causing A LOT of noise.

ILLink : Trim analysis warning IL2111: Microsoft.Maui.Controls.VisualElement.Visual: Method 'Microsoft.Maui.Controls.VisualTypeConverter.CreateVisual(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [C:\git\WeatherTwentyOne\src\WeatherTwentyOne\WeatherTwentyOne.csproj]
ILLink : Trim analysis warning IL2111: Microsoft.Maui.Controls.VisualElement.Visual: Method 'Microsoft.Maui.Controls.VisualTypeConverter.CreateVisual(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [C:\git\WeatherTwentyOne\src\WeatherTwentyOne\WeatherTwentyOne.csproj]
ILLink : Trim analysis warning IL2111: Microsoft.Maui.Controls.VisualElement.Visual: Method 'Microsoft.Maui.Controls.VisualTypeConverter.CreateVisual(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [C:\git\WeatherTwentyOne\src\WeatherTwentyOne\WeatherTwentyOne.csproj]
ILLink : Trim analysis warning IL2111: Microsoft.Maui.Controls.VisualElement.Visual: Method 'Microsoft.Maui.Controls.VisualTypeConverter.CreateVisual(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [C:\git\WeatherTwentyOne\src\WeatherTwentyOne\WeatherTwentyOne.csproj]
ILLink : Trim analysis warning IL2111: Microsoft.Maui.Controls.VisualElement.Visual: Method 'Microsoft.Maui.Controls.VisualTypeConverter.CreateVisual(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [C:\git\WeatherTwentyOne\src\WeatherTwentyOne\WeatherTwentyOne.csproj]
ILLink : Trim analysis warning IL2111: Microsoft.Maui.Controls.VisualElement.Visual: Method 'Microsoft.Maui.Controls.VisualTypeConverter.CreateVisual(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [C:\git\WeatherTwentyOne\src\WeatherTwentyOne\WeatherTwentyOne.csproj]
ILLink : Trim analysis warning IL2111: Microsoft.Maui.Controls.VisualElement.Visual: Method 'Microsoft.Maui.Controls.VisualTypeConverter.CreateVisual(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [C:\git\WeatherTwentyOne\src\WeatherTwentyOne\WeatherTwentyOne.csproj]

cc @agocke