[dotnet-linker] Create an xml descriptor instead of manual marking when applying the [Preserve] attribute.

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -551,6 +551,8 @@
 			<_UseDynamicDependenciesForSmartEnumPreservation Condition="'$(_UseDynamicDependenciesForSmartEnumPreservation)' == ''">$(_UseDynamicDependenciesInsteadOfMarking)</_UseDynamicDependenciesForSmartEnumPreservation>
 			<_UseDynamicDependenciesForBlockCodePreservation Condition="'$(_UseDynamicDependenciesForBlockCodePreservation)' == ''">$(_UseDynamicDependenciesInsteadOfMarking)</_UseDynamicDependenciesForBlockCodePreservation>
 			<_UseDynamicDependenciesForGeneratedCodeOptimizations Condition="'$(_UseDynamicDependenciesForGeneratedCodeOptimizations)' == ''">$(_UseDynamicDependenciesInsteadOfMarking)</_UseDynamicDependenciesForGeneratedCodeOptimizations>
+			<_UseLinkDescriptionForApplyPreserveAttribute Condition="'$(_UseLinkDescriptionForApplyPreserveAttribute)' == '' And '$(_XamarinRuntime)' == 'NativeAOT'">true</_UseLinkDescriptionForApplyPreserveAttribute>
+			<_UseLinkDescriptionForApplyPreserveAttribute Condition="'$(_UseLinkDescriptionForApplyPreserveAttribute)' == ''">$(_UseDynamicDependenciesInsteadOfMarking)</_UseLinkDescriptionForApplyPreserveAttribute>
 		</PropertyGroup>
 
 		<PropertyGroup>
@@ -756,6 +758,7 @@
 			<_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'" />
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="Xamarin.Linker.Steps.OptimizeGeneratedCodeStep" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true' And '$(_UseDynamicDependenciesForGeneratedCodeOptimizations)' == 'true'" />
+			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="Xamarin.Linker.Steps.ApplyPreserveAttributeStep" Condition="'$(_AreAnyAssembliesTrimmed)' == 'true' And '$(_UseLinkDescriptionForApplyPreserveAttribute)' == 'true'" />
 			<!-- The final decision to remove/keep the dynamic registrar must be done before the linking step -->
 			<_TrimmerCustomSteps Include="$(_AdditionalTaskAssembly)" BeforeStep="MarkStep" Type="MonoTouch.Tuner.RegistrarRemovalTrackingStep" />
 			<!-- TODO: these steps should probably run after mark. -->
@@ -1084,6 +1087,7 @@
 			<_LinkerItemFiles Include="$(_LinkerItemsDirectory)/_AssembliesToAOT.items" />
 			<_LinkerItemFiles Include="$(_LinkerItemsDirectory)/_FrameworkToPublish.items" />
 			<_LinkerItemFiles Include="$(_LinkerItemsDirectory)/_DynamicLibraryToPublish.items" />
+			<_LinkerItemFiles Include="$(_LinkerItemsDirectory)/TrimmerRootDescriptor.items" />
 		</ItemGroup>
 
 		<ItemGroup>
@@ -1108,7 +1112,17 @@
 			<_AssembliesToAOT Include="@(_AllLinkerItems)" Condition="'%(_AllLinkerItems.SourceFile)' == '_AssembliesToAOT.items'" />
 			<_FrameworkToPublish Include="@(_AllLinkerItems)" Condition="'%(_AllLinkerItems.SourceFile)' == '_FrameworkToPublish.items'" />
 			<_DynamicLibraryToPublish Include="@(_AllLinkerItems)" Condition="'%(_AllLinkerItems.SourceFile)' == '_DynamicLibraryToPublish.items'" />
+			<_TrimmerRootDescriptorFromCustomLinkerSteps Include="@(_AllLinkerItems)" Condition="'%(_AllLinkerItems.SourceFile)' == 'TrimmerRootDescriptor.items'" />
+
+			<TrimmerRootDescriptor Include="@(_TrimmerRootDescriptorFromCustomLinkerSteps)" />
 		</ItemGroup>
+		<PropertyGroup Condition="'$(RunILLink)' == 'true' And '$(_UseNativeAot)' == 'true' And @(_TrimmerRootDescriptorFromCustomLinkerSteps->Count()) &gt; 0">
+			<!-- When the custom linker steps produce xml root descriptors, those xml root descriptors may refer to types and members that are removed
+			     during linking (for members that are conditionally preserved). If we then pass those xml root descriptors to ilc, ilc will show
+			     a IL2008 warning about those members that have been trimmed away. So ignore any IL2008 warnings when we add trimmer root descriptors
+			     from a custom linker step. This will become unnecessary when we stop using custom linker steps. -->
+			<NoWarn>$(NoWarn);IL2008</NoWarn> <!-- Could not resolve type '...' -->
+		</PropertyGroup>
 	</Target>
 
 	<!-- Native code -->

tests/dotnet/UnitTests/expected/MacCatalyst-NativeAOT-size.txt

@@ -1,7 +1,7 @@
-AppBundleSize: 2,450,516 bytes (2,393.1 KB = 2.3 MB)
+AppBundleSize: 2,599,110 bytes (2,538.2 KB = 2.5 MB)
 # The following list of files and their sizes is just informational / for review, and isn't used in the test:
 Contents/_CodeSignature/CodeResources: 2,358 bytes (2.3 KB = 0.0 MB)
-Contents/Info.plist: 1,094 bytes (1.1 KB = 0.0 MB)
-Contents/MacOS/SizeTestApp: 2,445,248 bytes (2,387.9 KB = 2.3 MB)
+Contents/Info.plist: 1,128 bytes (1.1 KB = 0.0 MB)
+Contents/MacOS/SizeTestApp: 2,593,808 bytes (2,533.0 KB = 2.5 MB)
 Contents/MonoBundle/runtimeconfig.bin: 1,808 bytes (1.8 KB = 0.0 MB)
 Contents/PkgInfo: 8 bytes (0.0 KB = 0.0 MB)

tests/dotnet/UnitTests/expected/MacOSX-NativeAOT-size.txt

@@ -1,8 +1,8 @@
-AppBundleSize: 8,094,981 bytes (7,905.3 KB = 7.7 MB)
+AppBundleSize: 8,440,007 bytes (8,242.2 KB = 8.0 MB)
 # The following list of files and their sizes is just informational / for review, and isn't used in the test:
 Contents/_CodeSignature/CodeResources: 3,489 bytes (3.4 KB = 0.0 MB)
-Contents/Info.plist: 725 bytes (0.7 KB = 0.0 MB)
-Contents/MacOS/SizeTestApp: 5,101,408 bytes (4,981.8 KB = 4.9 MB)
+Contents/Info.plist: 759 bytes (0.7 KB = 0.0 MB)
+Contents/MacOS/SizeTestApp: 5,446,400 bytes (5,318.8 KB = 5.2 MB)
 Contents/MonoBundle/libSystem.Globalization.Native.dylib: 252,176 bytes (246.3 KB = 0.2 MB)
 Contents/MonoBundle/libSystem.IO.Compression.Native.dylib: 2,005,440 bytes (1,958.4 KB = 1.9 MB)
 Contents/MonoBundle/libSystem.Native.dylib: 292,176 bytes (285.3 KB = 0.3 MB)

tests/dotnet/UnitTests/expected/TVOS-NativeAOT-size.txt

@@ -1,8 +1,8 @@
-AppBundleSize: 2,450,669 bytes (2,393.2 KB = 2.3 MB)
+AppBundleSize: 2,616,495 bytes (2,555.2 KB = 2.5 MB)
 # The following list of files and their sizes is just informational / for review, and isn't used in the test:
 _CodeSignature/CodeResources: 2,589 bytes (2.5 KB = 0.0 MB)
 archived-expanded-entitlements.xcent: 384 bytes (0.4 KB = 0.0 MB)
-Info.plist: 1,112 bytes (1.1 KB = 0.0 MB)
+Info.plist: 1,146 bytes (1.1 KB = 0.0 MB)
 PkgInfo: 8 bytes (0.0 KB = 0.0 MB)
 runtimeconfig.bin: 1,808 bytes (1.8 KB = 0.0 MB)
-SizeTestApp: 2,444,768 bytes (2,387.5 KB = 2.3 MB)
+SizeTestApp: 2,610,560 bytes (2,549.4 KB = 2.5 MB)

tests/dotnet/UnitTests/expected/iOS-NativeAOT-size.txt

@@ -1,8 +1,8 @@
-AppBundleSize: 2,437,189 bytes (2,380.1 KB = 2.3 MB)
+AppBundleSize: 2,602,055 bytes (2,541.1 KB = 2.5 MB)
 # The following list of files and their sizes is just informational / for review, and isn't used in the test:
 _CodeSignature/CodeResources: 2,589 bytes (2.5 KB = 0.0 MB)
 archived-expanded-entitlements.xcent: 384 bytes (0.4 KB = 0.0 MB)
-Info.plist: 1,136 bytes (1.1 KB = 0.0 MB)
+Info.plist: 1,170 bytes (1.1 KB = 0.0 MB)
 PkgInfo: 8 bytes (0.0 KB = 0.0 MB)
 runtimeconfig.bin: 1,808 bytes (1.8 KB = 0.0 MB)
-SizeTestApp: 2,431,264 bytes (2,374.3 KB = 2.3 MB)
+SizeTestApp: 2,596,096 bytes (2,535.2 KB = 2.5 MB)

tools/common/DerivedLinkContext.cs

@@ -48,6 +48,8 @@ public class DerivedLinkContext : LinkContext {
 		// so we need a second dictionary
 		Dictionary<TypeDefinition, LinkedAwayTypeReference> LinkedAwayTypeMap = new Dictionary<TypeDefinition, LinkedAwayTypeReference> ();
 
+		public bool DidRunApplyPreserveAttributeStep { get; set; }
+
 		public DerivedLinkContext (LinkerConfiguration configuration, Application app)
 #if !LEGACY_TOOLS
 			: base (configuration)

tools/dotnet-linker/AppBundleRewriter.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
+using System.Text;
 
 using Mono.Cecil;
 using Mono.Cecil.Cil;
@@ -1384,7 +1385,7 @@ public bool AddAttributeToStaticConstructor (TypeDefinition onType, CustomAttrib
 			return modified;
 		}
 
-		MethodDefinition GetOrCreateStaticConstructor (TypeDefinition type, out bool modified)
+		public MethodDefinition GetOrCreateStaticConstructor (TypeDefinition type, out bool modified)
 		{
 			modified = false;
 
@@ -1408,7 +1409,7 @@ MethodDefinition GetOrCreateStaticConstructor (TypeDefinition type, out bool mod
 		/// <param name="provider">The provider to which the attribute should be added.</param>
 		/// <param name="attribute">The attribute to add.</param>
 		/// <returns>Whether the attribute was added or not.</returns>
-		bool AddAttributeOnlyOnce (ICustomAttributeProvider provider, CustomAttribute attribute)
+		public bool AddAttributeOnlyOnce (ICustomAttributeProvider provider, CustomAttribute attribute)
 		{
 			if (provider.HasCustomAttributes) {
 				foreach (var ca in provider.CustomAttributes) {
@@ -1460,7 +1461,18 @@ bool AddAttributeOnlyOnce (ICustomAttributeProvider provider, CustomAttribute at
 				}
 			}
 			provider.CustomAttributes.Add (attribute);
+			if (DebugAttributes)
+				Console.WriteLine ($"Added {attribute.RenderAttribute ()} to {provider}");
 			return true;
 		}
+
+		static bool? debug_attributes;
+		static bool DebugAttributes {
+			get {
+				if (!debug_attributes.HasValue)
+					debug_attributes = !string.IsNullOrEmpty (Environment.GetEnvironmentVariable ("PRINT_ATTRIBUTES"));
+				return debug_attributes.Value;
+			}
+		}
 	}
 }