Fixing issue #176

Special case interfaces documented at
https://docs.microsoft.com/en-us/dotnet/api/system.array?view=netframework-4.7.2

src/Boo.Lang.Compiler/TypeSystem/Core/ArrayType.cs

@@ -144,16 +144,25 @@ public virtual bool IsSubclassOf(IType other)
 			TypeSystemServices services = My<TypeSystemServices>.Instance;
 			if (other == services.ArrayType || services.ArrayType.IsSubclassOf(other))
 				return true;
-			
-			// Arrays also implement generic IEnumerable of their element type 
-			if (other.ConstructedInfo != null && 
-			    other.ConstructedInfo.GenericDefinition == services.IEnumerableGenericType &&
+
+			// Arrays also implement several generic collection interfaces of their element type 
+			if (other.ConstructedInfo != null && other.IsInterface &&
+			    IsSupportedInterfaceType(services, other.ConstructedInfo.GenericDefinition) &&
 			    IsSubclassOfGenericEnumerable(other))
 				return true;
 
 			return false;
 		}
 
+		protected bool IsSupportedInterfaceType(TypeSystemServices services, IType definition)
+		{
+			return definition == services.IEnumerableGenericType
+			       || definition == services.IListGenericType
+			       || definition == services.ICollectionGenericType
+			       || definition == services.IReadOnlyListGenericType
+			       || definition == services.IReadOnlyCollectionGenericType;
+		}
+
 		protected virtual bool IsSubclassOfGenericEnumerable(IType enumerableType)
 		{
 			return IsAssignableFrom(enumerableType.ConstructedInfo.GenericArguments[0], _elementType);

src/Boo.Lang.Compiler/TypeSystem/Services/TypeSystemServices.cs

@@ -73,13 +73,15 @@ public class TypeSystemServices
 
 		public IType ICallableType;
 		public IType ICollectionGenericType;
+		public IType IReadOnlyCollectionGenericType;
 		public IType ICollectionType;
 		public IType IDisposableType;
 
 		public IType IEnumerableGenericType;
 		public IType IEnumerableType;
 
 		public IType IListGenericType;
+		public IType IReadOnlyListGenericType;
 		public IType IListType;
 
 		public IType NullableGenericType;
@@ -196,7 +198,9 @@ public TypeSystemServices(CompilerContext context)
 			IEnumerableGenericType = Map(Types.IEnumerableGeneric);
 			IEnumeratorGenericType = Map(typeof(IEnumerator<>));
 			ICollectionGenericType = Map(typeof(ICollection<>));
+			IReadOnlyCollectionGenericType = Map(typeof(IReadOnlyCollection<>));
 			IListGenericType = Map(typeof (IList<>));
+			IReadOnlyListGenericType = Map(typeof(IReadOnlyList<>));
 			IListType = Map(typeof (IList));
 			NullableGenericType = Map(Types.Nullable);
 			IAstMacroType = Map(typeof(IAstMacro));