[generator] Allow identical (numeric) values in smart enums. Fixes #46285

src/error.cs

@@ -60,6 +60,7 @@
 //		BI1043 Repeated overload {mi.Name} and no [DelegateApiNameAttribute] provided to generate property name on host class.
 //		BI1044 Repeated name '{apiName.Name}' provided in [DelegateApiNameAttribute].
 //		BI1045 Only a single [DefaultEnumValue] attribute can be used inside enum {type.Name}.
+//		BI1046 The [Field] constant {fa.SymbolName} cannot only be used once inside enum {type.Name}.
 //	BI11xx	warnings
 //		BI1101 Trying to use a string as a [Target]
 //		BI1102 Using the deprecated EventArgs for a delegate signature in {0}.{1}, please use DelegateName instead

src/generator-enums.cs

@@ -71,10 +71,12 @@ void GenerateEnum (Type type)
 				print ("[Native (\"{0}\")]", native.NativeName);
 		}
 
+		var unique_constants = new HashSet<string> ();
 		var fields = new Dictionary<FieldInfo, FieldAttribute> ();
 		Tuple<FieldInfo, FieldAttribute> null_field = null;
 		Tuple<FieldInfo, FieldAttribute> default_symbol = null;
-		print ("public enum {0} : {1} {{", type.Name, GetCSharpTypeName (Enum.GetUnderlyingType (type)));
+		var underlying_type = GetCSharpTypeName (Enum.GetUnderlyingType (type));
+		print ("public enum {0} : {1} {{", type.Name, underlying_type);
 		indent++;
 		foreach (var f in type.GetFields ()) {
 			// skip value__ field 
@@ -89,8 +91,12 @@ void GenerateEnum (Type type)
 				continue;
 			if (fa.SymbolName == null)
 				null_field = new Tuple<FieldInfo, FieldAttribute> (f, fa);
-			else
+			else if (unique_constants.Contains (fa.SymbolName))
+				throw new BindingException (1046, true, $"The [Field] constant {fa.SymbolName} cannot only be used once inside enum {type.Name}.");
+			else {
 				fields.Add (f, fa);
+				unique_constants.Add (fa.SymbolName);
+			}
 			if (GetAttribute<DefaultEnumValueAttribute> (f) != null) {
 				if (default_symbol != null)
 					throw new BindingException (1045, true, $"Only a single [DefaultEnumValue] attribute can be used inside enum {type.Name}.");
@@ -99,6 +105,7 @@ void GenerateEnum (Type type)
 		}
 		indent--;
 		print ("}");
+		unique_constants.Clear ();
 
 		var library_name = type.Namespace;
 		var error = GetAttribute<ErrorDomainAttribute> (type);
@@ -164,10 +171,11 @@ void GenerateEnum (Type type)
 			print ("public static NSString GetConstant (this {0} self)", type.Name);
 			print ("{");
 			indent++;
-			print ("switch (self) {");
+			print ("switch (({0}) self) {{", underlying_type);
 			var default_symbol_name = default_symbol?.Item2.SymbolName;
+			// more than one enum member can share the same numeric value - ref: #46285
 			foreach (var kvp in fields) {
-				print ("case {0}.{1}:", type.Name, kvp.Key.Name);
+				print ("case {0}: // {1}.{2}", Convert.ToInt64 (kvp.Key.GetValue (null)), type.Name, kvp.Key.Name);
 				var sn = kvp.Value.SymbolName;
 				if (sn == default_symbol_name)
 					print ("default:");

tests/generator/Makefile

@@ -14,7 +14,7 @@ include $(TOP)/Make.config
 IOS_CURRENT_DIR=$(IOS_DESTDIR)/Library/Frameworks/Xamarin.iOS.framework/Versions/Current
 IOS_GENERATOR = $(IOS_CURRENT_DIR)/bin/btouch /baselib:$(IOS_CURRENT_DIR)/lib/mono/2.1/monotouch.dll /unsafe /compiler:$(IOS_CURRENT_DIR)/bin/smcs
 IOS_TESTS = bug15283 bug15307 bug15799 bug16036 sof20696157 bug23041 bug27430 bug27428 bug34042 btouch-with-hyphen-in-name property-redefination-ios arrayfromhandlebug bug36457 bug39614 bug40282 bug17232 bug24078-ignore-methods-events strong-dict-support-templated-dicts bug43579
-IOS_CUSTOM_TESTS = forum54078 desk63279 desk79124 multiple-api-definitions1 multiple-api-definitions2 bug29493 classNameCollision bi1036 bug37527 bug27986 bug35176
+IOS_CUSTOM_TESTS = forum54078 desk63279 desk79124 multiple-api-definitions1 multiple-api-definitions2 bug29493 classNameCollision bi1036 bug37527 bug27986 bug35176 bi1046
 
 MAC_CURRENT_DIR=$(MAC_DESTDIR)/Library/Frameworks/Xamarin.Mac.framework/Versions/Current
 MAC_GENERATOR = $(MAC_CURRENT_DIR)/bin/bmac
@@ -135,6 +135,9 @@ forcedtype:
 bi1036:
 	$(if $(V),,@echo "$@";) $(IOS_GENERATOR) $@.cs | grep BI1036 >/dev/null 2>&1
 
+bi1046:
+	$(if $(V),,@echo "$@";) $(IOS_GENERATOR) $@.cs --process-enums | grep BI1046 >/dev/null 2>&1
+
 clean-local::
 	rm -f *.dll *.source
 	rm -Rf *.tmpdir

tests/generator/bi1046.cs

@@ -0,0 +1,13 @@
+using System;
+using MonoTouch.Foundation;
+
+namespace BindingTests
+{
+	public enum HMAccessoryCategoryType {
+		[Field ("HMAccessoryCategoryTypeGarageDoorOpener")]
+		DoorOpener,
+
+		[Field ("HMAccessoryCategoryTypeGarageDoorOpener")]
+		GarageDoorOpener = DoorOpener,
+	}
+}