From 8d19e5a1c59ef9530fc0b3baf41013c6a6218b9b Mon Sep 17 00:00:00 2001
From: Rodrigo Kumpera <kumpera@users.noreply.github.com>
Date: Wed, 14 Feb 2018 11:58:15 -0500
Subject: [PATCH] [runtime] Unboxing of nullable enums should throw for boxed
 ints. (#6958)

* [runtime] Unboxing of nullable enums should throw for boxed ints. Fixes gh #6666.

For some reason, one can't unbox the underlying type of an enum into a nullable.

This is counter intuitive to the unboxing rules of enums, but it's what dotnet does.

* [interp] Unboxing of nullable enmus should throw for boxed ints

fixes https://github.com/mono/mono/issues/6666 for the interpreter
---
 mcs/class/corlib/LinkerDescriptor/mscorlib.xml |  3 +++
 mcs/class/corlib/System/Nullable.cs            | 11 +++++++++++
 mono/mini/interp/transform.c                   | 12 ++++++++++--
 mono/mini/method-to-ir.c                       |  7 ++++++-
 mono/mini/objects.cs                           | 25 +++++++++++++++++++++++++
 5 files changed, 55 insertions(+), 3 deletions(-)

diff --git a/mcs/class/corlib/LinkerDescriptor/mscorlib.xml b/mcs/class/corlib/LinkerDescriptor/mscorlib.xml
index 4d6b7cf095c..e879311ed1c 100644
--- a/mcs/class/corlib/LinkerDescriptor/mscorlib.xml
+++ b/mcs/class/corlib/LinkerDescriptor/mscorlib.xml
@@ -288,6 +288,9 @@
 			<method name="Box" />
 			<!-- method-to-ir.c (handle_unbox_nullable) -->
 			<method name="Unbox" />
+			<!-- method-to-ir.c (handle_unbox_nullable) -->
+			<method name="UnboxExact" />
+
 		</type>
 		
 		<!-- domain.c: mono_defaults.object_class -->
diff --git a/mcs/class/corlib/System/Nullable.cs b/mcs/class/corlib/System/Nullable.cs
index 32c4aa0885b..2d8a297e4ce 100644
--- a/mcs/class/corlib/System/Nullable.cs
+++ b/mcs/class/corlib/System/Nullable.cs
@@ -186,6 +186,17 @@ namespace System
 				return null;
 			return (T) o;
 		}
+
+		static T? UnboxExact (object o)
+		{
+			if (o == null)
+				return null;
+			if (o.GetType() != typeof (T))
+				throw new InvalidCastException();
+
+			return (T) o;
+		}
+
 #pragma warning restore 169
 	}
 }
diff --git a/mono/mini/interp/transform.c b/mono/mini/interp/transform.c
index d65cebb2f5b..5fb36c8080d 100644
--- a/mono/mini/interp/transform.c
+++ b/mono/mini/interp/transform.c
@@ -2936,7 +2936,11 @@ generate (MonoMethod *method, MonoMethodHeader *header, InterpMethod *rtm, unsig
 			}
 
 			if (mono_class_is_nullable (klass)) {
-				MonoMethod *target_method = mono_class_get_method_from_name (klass, "Unbox", 1);
+				MonoMethod *target_method;
+				if (mono_class_get_nullable_param (klass)->enumtype)
+					target_method = mono_class_get_method_from_name (klass, "UnboxExact", 1);
+				else
+					target_method = mono_class_get_method_from_name (klass, "Unbox", 1);
 				/* td->ip is incremented by interp_transform_call */
 				interp_transform_call (td, method, target_method, domain, generic_context, is_bb_start, body_start_offset, NULL, FALSE, error, FALSE);
 				goto_if_nok (error, exit);
@@ -2970,7 +2974,11 @@ generate (MonoMethod *method, MonoMethodHeader *header, InterpMethod *rtm, unsig
 				SET_TYPE (td->sp - 1, stack_type [mt], klass);
 				td->ip += 5;
 			} else if (mono_class_is_nullable (klass)) {
-				MonoMethod *target_method = mono_class_get_method_from_name (klass, "Unbox", 1);
+				MonoMethod *target_method;
+				if (mono_class_get_nullable_param (klass)->enumtype)
+					target_method = mono_class_get_method_from_name (klass, "UnboxExact", 1);
+				else
+					target_method = mono_class_get_method_from_name (klass, "Unbox", 1);
 				/* td->ip is incremented by interp_transform_call */
 				interp_transform_call (td, method, target_method, domain, generic_context, is_bb_start, body_start_offset, NULL, FALSE, error, FALSE);
 
diff --git a/mono/mini/method-to-ir.c b/mono/mini/method-to-ir.c
index c0f18d7105d..52526b8cac8 100644
--- a/mono/mini/method-to-ir.c
+++ b/mono/mini/method-to-ir.c
@@ -3453,7 +3453,12 @@ mini_emit_check_array_type (MonoCompile *cfg, MonoInst *obj, MonoClass *array_cl
 static MonoInst*
 handle_unbox_nullable (MonoCompile* cfg, MonoInst* val, MonoClass* klass, int context_used)
 {
-	MonoMethod* method = mono_class_get_method_from_name (klass, "Unbox", 1);
+	MonoMethod* method;
+
+	if (mono_class_get_nullable_param (klass)->enumtype)
+		method = mono_class_get_method_from_name (klass, "UnboxExact", 1);
+	else
+		method = mono_class_get_method_from_name (klass, "Unbox", 1);
 
 	if (context_used) {
 		MonoInst *rgctx, *addr;
diff --git a/mono/mini/objects.cs b/mono/mini/objects.cs
index e0cea4e8ba9..0663c9c1d35 100644
--- a/mono/mini/objects.cs
+++ b/mono/mini/objects.cs
@@ -1836,6 +1836,31 @@ ncells ) {
 		return 0;
 	}
 
+	enum FooEnum { Bar }
+	//https://github.com/mono/mono/issues/6666
+	public static int test_0_bad_unbox_nullable_of_enum () {
+		try {
+			var enumValue = FooEnum.Bar;
+			object value = (int)enumValue;
+			var res = (FooEnum?)value; // Should throw
+		} catch (InvalidCastException) {
+			return 0;
+		}
+		return 1;
+	}
+
+	//https://github.com/mono/mono/issues/6666
+	public static int test_0_unbox_nullable_of_enum () {
+		try {
+			var enumValue = FooEnum.Bar;
+			object value = (object)enumValue;
+			var res = (FooEnum?)value; // Should not throw
+		} catch (InvalidCastException) {
+			return 1;
+		}
+		return 0;
+	}
+
 	static void decode (out sbyte v) {
 		byte tmp = 134;
 		v = (sbyte)tmp;
-- 
2.11.4.GIT