Annotate GetUninitializedObject (dotnet#37741)

We don't have a good annotation for this so going with a superset. We could choose to intrinsify it in the linker to restrict this if necessary.

src/coreclr/src/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.CoreCLR.cs

@@ -140,7 +140,14 @@ public static int OffsetToStringData
         public static extern bool TryEnsureSufficientExecutionStack();
 
         [MethodImpl(MethodImplOptions.InternalCall)]
-        private static extern object GetUninitializedObjectInternal(Type type);
+        private static extern object GetUninitializedObjectInternal(
+            // This API doesn't call any constructors, but the type needs to be seen as constructed.
+            // A type is seen as constructed if a constructor is kept.
+            // This obviously won't cover a type with no constructor. Reference types with no
+            // constructor are an academic problem. Valuetypes with no constructors are a problem,
+            // but IL Linker currently treats them as always implicitly boxed.
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
+            Type type);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         internal static extern object AllocateUninitializedClone(object obj);

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
 using System.Runtime.Serialization;
 using System.Reflection;
@@ -52,7 +53,14 @@ ref Unsafe.Add(ref MemoryMarshal.GetArrayDataReference(array), offset),
             }
         }
 
-        public static object GetUninitializedObject(Type type)
+        public static object GetUninitializedObject(
+            // This API doesn't call any constructors, but the type needs to be seen as constructed.
+            // A type is seen as constructed if a constructor is kept.
+            // This obviously won't cover a type with no constructor. Reference types with no
+            // constructor are an academic problem. Valuetypes with no constructors are a problem,
+            // but IL Linker currently treats them as always implicitly boxed.
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
+            Type type)
         {
             if (type is null)
             {

src/libraries/System.Runtime.Serialization.Formatters/src/System/Runtime/Serialization/FormatterServices.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Reflection;
@@ -180,7 +181,14 @@ public static void CheckTypeSecurity(Type t, TypeFilterLevel securityLevel)
             // nop
         }
 
-        public static object GetUninitializedObject(Type type) => RuntimeHelpers.GetUninitializedObject(type);
+        public static object GetUninitializedObject(
+            // This API doesn't call any constructors, but the type needs to be seen as constructed.
+            // A type is seen as constructed if a constructor is kept.
+            // This obviously won't cover a type with no constructor. Reference types with no
+            // constructor are an academic problem. Valuetypes with no constructors are a problem,
+            // but IL Linker currently treats them as always implicitly boxed.
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
+            Type type) => RuntimeHelpers.GetUninitializedObject(type);
 
         public static object GetSafeUninitializedObject(Type type) => RuntimeHelpers.GetUninitializedObject(type);