[dotnet-linker] Use [DynamicDependency] attributes instead of manual marking when preserving block code.

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -549,6 +549,7 @@
 			<_UseDynamicDependenciesInsteadOfMarking Condition="'$(_UseDynamicDependenciesInsteadOfMarking)' == ''">true</_UseDynamicDependenciesInsteadOfMarking>
 			<_UseDynamicDependenciesForProtocolPreservation Condition="'$(_UseDynamicDependenciesForProtocolPreservation)' == ''">$(_UseDynamicDependenciesInsteadOfMarking)</_UseDynamicDependenciesForProtocolPreservation>
 			<_UseDynamicDependenciesForSmartEnumPreservation Condition="'$(_UseDynamicDependenciesForSmartEnumPreservation)' == ''">$(_UseDynamicDependenciesInsteadOfMarking)</_UseDynamicDependenciesForSmartEnumPreservation>
+			<_UseDynamicDependenciesForBlockCodePreservation Condition="'$(_UseDynamicDependenciesForBlockCodePreservation)' == ''">$(_UseDynamicDependenciesInsteadOfMarking)</_UseDynamicDependenciesForBlockCodePreservation>
 		</PropertyGroup>
 
 		<PropertyGroup>
@@ -752,6 +753,7 @@
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="MonoTouch.Tuner.ProcessExportedFields" />
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="Xamarin.Linker.PreserveProtocolsStep" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true' And '$(_UseDynamicDependenciesForProtocolPreservation)' == 'true'" />
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="Xamarin.Linker.Steps.PreserveSmartEnumConversionsStep" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true' And '$(_UseDynamicDependenciesForSmartEnumPreservation)' == 'true'" />
+			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="Xamarin.Linker.Steps.PreserveBlockCodeStep" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true' And '$(_UseDynamicDependenciesForBlockCodePreservation)' == 'true'" />
 			<!-- The final decision to remove/keep the dynamic registrar must be done before the linking step -->
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="MonoTouch.Tuner.RegistrarRemovalTrackingStep" />
 			<!-- TODO: these steps should probably run after mark. -->
@@ -761,7 +763,7 @@
 			<!--
 				IMarkHandlers which run during Mark
 			-->
-			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true'" Type="Xamarin.Linker.Steps.PreserveBlockCodeHandler" />
+			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true' And '$(_UseDynamicDependenciesForBlockCodePreservation)' != 'true'" Type="Xamarin.Linker.Steps.PreserveBlockCodeHandler" />
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true'" Type="Xamarin.Linker.OptimizeGeneratedCodeHandler" />
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true'" Type="Xamarin.Linker.BackingFieldDelayHandler" />
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true' And '$(_UseDynamicDependenciesForProtocolPreservation)' != 'true'" Type="Xamarin.Linker.MarkIProtocolHandler" />

tools/dotnet-linker/AppBundleRewriter.cs

@@ -1318,6 +1318,17 @@ public CustomAttribute CreateDynamicDependencyAttribute (DynamicallyAccessedMemb
 			return attribute;
 		}
 
+		/// <summary>
+		/// Preserve a method conditionally on another type
+		/// </summary>
+		/// <param name="onType">The type on which to add the dynamic dependency attribute.</param>
+		/// <param name="forMethod">The method that is the target of the dynamic dependency.</param>
+		public bool AddDynamicDependencyAttributeToStaticConstructor (TypeDefinition onType, MethodDefinition forMethod)
+		{
+			var attrib = CreateDynamicDependencyAttribute (DocumentationComments.GetSignature (forMethod), forMethod.DeclaringType, forMethod.Module.Assembly);
+			return AddAttributeToStaticConstructor (onType, attrib);
+		}
+
 		/// <summary>
 		/// Preserve a field conditionally on another type
 		/// </summary>

tools/dotnet-linker/Steps/PreserveBlockCodeHandler.cs

@@ -26,62 +26,11 @@ public override void Initialize (LinkContext context, MarkContext markContext)
 
 		protected override void Process (TypeDefinition type)
 		{
-			/* For the following class:
-
-			static internal class SDInnerBlock {
-				// this field is not preserved by other means, but it must not be linked away
-				static internal readonly DInnerBlock Handler = Invoke;
-
-				[MonoPInvokeCallback (typeof (DInnerBlock))]
-				static internal void Invoke (IntPtr block, int magic_number)
-				{
-				}
-			}
-
-			We need to make sure the linker doesn't remove the Handler field
-			and the Invoke method. 
-			*/
-
-			// First make sure we got the right class
-			// The type for the field we're looking for is abstract, sealed and nested and contains exactly 1 field.
-			if (!type.HasFields || !type.IsAbstract || !type.IsSealed || !type.IsNested)
-				return;
-			if (type.Fields.Count != 1)
-				return;
-
-			// The type is also nested inside ObjCRuntime.Trampolines class)
-			var nestingType = type.DeclaringType;
-			if (!nestingType.Is ("ObjCRuntime", "Trampolines"))
-				return;
-
-			// The class has a readonly field named 'Handler'
-			var field = type.Fields [0];
-			if (!field.IsInitOnly)
-				return;
-			if (field.Name != "Handler")
-				return;
-
-			// The class has a parameterless 'Invoke' method with a 'MonoPInvokeCallback' attribute
-			if (!type.HasMethods)
+			if (!PreserveBlockCodeStep.GetMembersToPreserve (type, out var field, out var method))
 				return;
-			var method = type.Methods.SingleOrDefault (v => {
-				if (v.Name != "Invoke")
-					return false;
-				if (!v.HasParameters)
-					return false;
-				if (!v.HasCustomAttributes)
-					return false;
-				if (!v.CustomAttributes.Any (v => v.AttributeType.Name == "MonoPInvokeCallbackAttribute"))
-					return false;
-				return true;
-			});
 
-			if (method is null)
-				return;
-
-			// The type was used, so preserve the method and field
-			Context.Annotations.Mark (method);
 			Context.Annotations.Mark (field);
+			Context.Annotations.Mark (method);
 		}
 	}
 }

tools/dotnet-linker/Steps/PreserveBlockCodeStep.cs

@@ -0,0 +1,107 @@
+using System;
+using System.Linq;
+
+using Mono.Cecil;
+
+using Mono.Linker;
+using Mono.Linker.Steps;
+using Mono.Tuner;
+
+using Xamarin.Bundler;
+
+#nullable enable
+
+namespace Xamarin.Linker.Steps {
+
+	public class PreserveBlockCodeStep : AssemblyModifierStep {
+
+		protected override string Name { get; } = "Preserve Block Code";
+		protected override int ErrorCode { get; } = 2240;
+
+		protected override bool IsActiveFor (AssemblyDefinition assembly)
+		{
+			// We only care about assemblies that are being linked.
+			if (Annotations.GetAction (assembly) != AssemblyAction.Link)
+				return false;
+
+			// Unless an assembly is or references our platform assembly, then it won't have anything we need to preserve
+			if (!Configuration.Profile.IsOrReferencesProductAssembly (assembly))
+				return false;
+
+			return true;
+		}
+
+		protected override bool ProcessType (TypeDefinition type)
+		{
+			if (!GetMembersToPreserve (type, out var field, out var method))
+				return false;
+
+			var modified = false;
+			modified |= abr.AddDynamicDependencyAttributeToStaticConstructor (type, field);
+			modified |= abr.AddDynamicDependencyAttributeToStaticConstructor (type, method);
+			return modified;
+		}
+
+		public static bool GetMembersToPreserve (TypeDefinition type, [NotNullWhen (true)] out FieldDefinition? field, [NotNullWhen (true)] out MethodDefinition? method)
+		{
+			field = null;
+			method = null;
+
+			/* For the following class:
+
+			static internal class SDInnerBlock {
+				// this field is not preserved by other means, but it must not be linked away
+				static internal readonly DInnerBlock Handler = Invoke;
+
+				[MonoPInvokeCallback (typeof (DInnerBlock))]
+				static internal void Invoke (IntPtr block, int magic_number)
+				{
+				}
+			}
+
+			* We need to make sure the linker doesn't remove the Handler field
+			* and the Invoke method.
+			*/
+
+			// First make sure we got the right class
+			// The type for the field we're looking for is abstract, sealed and nested and contains exactly 1 field.
+			if (!type.HasFields || !type.IsAbstract || !type.IsSealed || !type.IsNested)
+				return false;
+			if (type.Fields.Count != 1)
+				return false;
+
+			// The type is also nested inside ObjCRuntime.Trampolines class)
+			var nestingType = type.DeclaringType;
+			if (!nestingType.Is ("ObjCRuntime", "Trampolines"))
+				return false;
+
+			// The class has a readonly field named 'Handler'
+			field = type.Fields [0];
+			if (!field.IsInitOnly)
+				return false;
+			if (field.Name != "Handler")
+				return false;
+
+			// The class has a parameterless 'Invoke' method with a 'MonoPInvokeCallback' attribute
+			if (!type.HasMethods)
+				return false;
+			method = type.Methods.SingleOrDefault (v => {
+				if (v.Name != "Invoke")
+					return false;
+				if (!v.HasParameters)
+					return false;
+				if (!v.HasCustomAttributes)
+					return false;
+				if (!v.CustomAttributes.Any (v => v.AttributeType.Name == "MonoPInvokeCallbackAttribute"))
+					return false;
+				return true;
+			});
+
+			if (method is null)
+				return false;
+
+			// The type was used, so preserve the method and field
+			return true;
+		}
+	}
+}