Fix remaining ILLink warnings in System.Reflection (#45984)

* Add RequiresUnreferencedCode to Delegate constructors

Contributes to #45623

* Add RequiresUnreferencedCode to some internal Reflection methods to address ILLink warnings.

* Address remaining ILLink warnings in Reflection.Emit.

* Respond to PR feedback

Annotate Delegate.BindToMethod with DynamicallyAccessedMembers

Fix up requires unreferenced code comments

* Update API Compat txt for Delegate.CreateDelegate attribute removal

* Fix Mono ILLink warnings

src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs

@@ -33,6 +33,7 @@ public abstract partial class Delegate : ICloneable, ISerializable
 
         // This constructor is called from the class generated by the
         //  compiler generated code
+        [RequiresUnreferencedCode("The target method might be removed")]
         protected Delegate(object target, string method)
         {
             if (target == null)
@@ -56,7 +57,7 @@ protected Delegate(object target, string method)
         // This constructor is called from a class to generate a
         // delegate based upon a static method name and the Type object
         // for the class defining the method.
-        protected Delegate(Type target, string method)
+        protected Delegate([DynamicallyAccessedMembers(AllMethods)] Type target, string method)
         {
             if (target == null)
                 throw new ArgumentNullException(nameof(target));
@@ -257,8 +258,7 @@ protected virtual MethodInfo GetMethodImpl()
         }
 
         // V1 API.
-        [RequiresUnreferencedCode("The target method might be removed")]
-        public static Delegate? CreateDelegate(Type type, Type target, string method, bool ignoreCase, bool throwOnBindFailure)
+        public static Delegate? CreateDelegate(Type type, [DynamicallyAccessedMembers(AllMethods)] Type target, string method, bool ignoreCase, bool throwOnBindFailure)
         {
             if (type == null)
                 throw new ArgumentNullException(nameof(type));
@@ -417,10 +417,8 @@ internal static Delegate CreateDelegateNoSecurityCheck(Type type, object? target
         //
         // internal implementation details (FCALLS and utilities)
         //
-
-        [RequiresUnreferencedCode("The target method might be removed")]
         [MethodImpl(MethodImplOptions.InternalCall)]
-        private extern bool BindToMethodName(object? target, RuntimeType methodType, string method, DelegateBindingFlags flags);
+        private extern bool BindToMethodName(object? target, [DynamicallyAccessedMembers(AllMethods)] RuntimeType methodType, string method, DelegateBindingFlags flags);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         private extern bool BindToMethodInfo(object? target, IRuntimeMethodInfo method, RuntimeType methodType, DelegateBindingFlags flags);

src/coreclr/System.Private.CoreLib/src/System/MulticastDelegate.cs

@@ -25,14 +25,15 @@ public abstract class MulticastDelegate : Delegate
         // This constructor is called from the class generated by the
         //    compiler generated code (This must match the constructor
         //    in Delegate
+        [RequiresUnreferencedCode("The target method might be removed")]
         protected MulticastDelegate(object target, string method) : base(target, method)
         {
         }
 
         // This constructor is called from a class to generate a
         // delegate based upon a static method name and the Type object
         // for the class defining the method.
-        protected MulticastDelegate(Type target, string method) : base(target, method)
+        protected MulticastDelegate([DynamicallyAccessedMembers(AllMethods)] Type target, string method) : base(target, method)
         {
         }
 

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/ConstructorBuilder.cs

@@ -27,7 +27,7 @@ internal ConstructorBuilder(string name, MethodAttributes attributes, CallingCon
         }
 
         internal ConstructorBuilder(string name, MethodAttributes attributes, CallingConventions callingConvention,
-            Type[]? parameterTypes, ModuleBuilder mod, TypeBuilder type) :
+            Type[]? parameterTypes, ModuleBuilder mod, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] TypeBuilder type) :
             this(name, attributes, callingConvention, parameterTypes, null, null, mod, type)
         {
         }

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.cs

@@ -332,6 +332,8 @@ public override Type MakeArrayType(int rank)
 
         // Constructs a EnumBuilder.
         // EnumBuilder can only be a top-level (not nested) enum type.
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2064:UnrecognizedReflectionPattern",
+            Justification = "Reflection.Emit is not subject to trimming")]
         internal EnumBuilder(
             string name,                       // name of type
             Type underlyingType,             // underlying type for an Enum

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs

@@ -428,6 +428,11 @@ internal SignatureHelper GetMemberRefSignature(CallingConventions call, Type? re
             return sig;
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
+            Justification = "Module.ResolveMethod is marked as RequiresUnreferencedCode because it relies on tokens " +
+                            "which are not guaranteed to be stable across trimming. So if somebody hardcodes a token it could break. " +
+                            "The usage here is not like that as all these tokens come from existing metadata loaded from some IL " +
+                            "and so trimming has no effect (the tokens are read AFTER trimming occured).")]
         private static MethodBase GetGenericMethodBaseDefinition(MethodBase methodBase)
         {
             // methodInfo = G<Foo>.M<Bar> ==> methDef = G<T>.M<S>
@@ -601,6 +606,7 @@ internal Type[] GetTypesNoLock()
             }
         }
 
+        [RequiresUnreferencedCode("Types might be removed")]
         private Type? GetTypeNoLock(string className, bool throwOnError, bool ignoreCase)
         {
             // public API to to a type. The reason that we need this function override from module

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.cs

@@ -62,6 +62,8 @@ public void Bake(ModuleBuilder module, int token)
         #endregion
 
         #region Public Static Methods
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2055:UnrecognizedReflectionPattern",
+            Justification = "MakeGenericType is only called on a TypeBuilder which is not subject to trimming")]
         public static MethodInfo GetMethod(Type type, MethodInfo method)
         {
             if (!(type is TypeBuilder) && !(type is TypeBuilderInstantiation))
@@ -94,6 +96,9 @@ public static MethodInfo GetMethod(Type type, MethodInfo method)
 
             return MethodOnTypeBuilderInstantiation.GetMethod(method, (type as TypeBuilderInstantiation)!);
         }
+
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2055:UnrecognizedReflectionPattern",
+            Justification = "MakeGenericType is only called on a TypeBuilder which is not subject to trimming")]
         public static ConstructorInfo GetConstructor(Type type, ConstructorInfo constructor)
         {
             if (!(type is TypeBuilder) && !(type is TypeBuilderInstantiation))
@@ -114,6 +119,9 @@ public static ConstructorInfo GetConstructor(Type type, ConstructorInfo construc
 
             return ConstructorOnTypeBuilderInstantiation.GetConstructor(constructor, (type as TypeBuilderInstantiation)!);
         }
+
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2055:UnrecognizedReflectionPattern",
+            Justification = "MakeGenericType is only called on a TypeBuilder which is not subject to trimming")]
         public static FieldInfo GetField(Type type, FieldInfo field)
         {
             if (!(type is TypeBuilder) && !(type is TypeBuilderInstantiation))
@@ -1265,6 +1273,8 @@ public MethodBuilder DefineMethod(string name, MethodAttributes attributes, Call
             }
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2082:UnrecognizedReflectionPattern",
+            Justification = "Reflection.Emit is not subject to trimming")]
         private MethodBuilder DefineMethodNoLock(string name, MethodAttributes attributes, CallingConventions callingConvention,
             Type? returnType, Type[]? returnTypeRequiredCustomModifiers, Type[]? returnTypeOptionalCustomModifiers,
             Type[]? parameterTypes, Type[][]? parameterTypeRequiredCustomModifiers, Type[][]? parameterTypeOptionalCustomModifiers)
@@ -1344,6 +1354,8 @@ public MethodBuilder DefinePInvokeMethod(string name, string dllName, string ent
             return method;
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2082:UnrecognizedReflectionPattern",
+            Justification = "Reflection.Emit is not subject to trimming")]
         private MethodBuilder DefinePInvokeMethodHelper(
             string name, string dllName, string importName, MethodAttributes attributes, CallingConventions callingConvention,
             Type? returnType, Type[]? returnTypeRequiredCustomModifiers, Type[]? returnTypeOptionalCustomModifiers,
@@ -1459,6 +1471,8 @@ public ConstructorBuilder DefineTypeInitializer()
             }
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2082:UnrecognizedReflectionPattern",
+            Justification = "Reflection.Emit is not subject to trimming")]
         private ConstructorBuilder DefineTypeInitializerNoLock()
         {
             ThrowIfCreated();
@@ -1485,6 +1499,10 @@ public ConstructorBuilder DefineDefaultConstructor(MethodAttributes attributes)
             }
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2055:UnrecognizedReflectionPattern",
+            Justification = "MakeGenericType is only called on a TypeBuilderInstantiation which is not subject to trimming")]
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2075:UnrecognizedReflectionPattern",
+            Justification = "GetConstructor is only called on a TypeBuilderInstantiation which is not subject to trimming")]
         private ConstructorBuilder DefineDefaultConstructorNoLock(MethodAttributes attributes)
         {
             ConstructorBuilder constBuilder;
@@ -1558,6 +1576,8 @@ public ConstructorBuilder DefineConstructor(MethodAttributes attributes, Calling
             }
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2082:UnrecognizedReflectionPattern",
+            Justification = "Reflection.Emit is not subject to trimming")]
         private ConstructorBuilder DefineConstructorNoLock(MethodAttributes attributes, CallingConventions callingConvention,
             Type[]? parameterTypes, Type[][]? requiredCustomModifiers, Type[][]? optionalCustomModifiers)
         {

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs

@@ -691,6 +691,7 @@ public sealed override Type[] GetForwardedTypes()
             return types.ToArray();
         }
 
+        [RequiresUnreferencedCode("Types might be removed because recursive nested types can't currently be annotated for dynamic access.")]
         private static void AddPublicNestedTypes(Type type, List<Type> types, List<Exception> exceptions)
         {
             Type[] nestedTypes;

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeModule.cs

@@ -144,6 +144,7 @@ public override byte[] ResolveSignature(int metadataToken)
             }
         }
 
+        [RequiresUnreferencedCode("Trimming changes metadata tokens")]
         private FieldInfo? ResolveLiteralField(int metadataToken, Type[]? genericTypeArguments, Type[]? genericMethodArguments)
         {
             MetadataToken tk = new MetadataToken(metadataToken);
@@ -353,13 +354,14 @@ public override void GetPEKind(out PortableExecutableKinds peKind, out ImageFile
         #endregion
 
         #region Protected Virtuals
-        [RequiresUnreferencedCode("Methods might be removed")]
+        [RequiresUnreferencedCode("Methods might be removed because Module methods can't currently be annotated for dynamic access.")]
         protected override MethodInfo? GetMethodImpl(string name, BindingFlags bindingAttr, Binder? binder,
             CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {
             return GetMethodInternal(name, bindingAttr, binder, callConvention, types, modifiers);
         }
 
+        [RequiresUnreferencedCode("Methods might be removed because Module methods can't currently be annotated for dynamic access.")]
         internal MethodInfo? GetMethodInternal(string name, BindingFlags bindingAttr, Binder? binder,
             CallingConventions callConvention, Type[]? types, ParameterModifier[]? modifiers)
         {