[registrar] Make the generated static registrar code implement protocols from [Adopts] attributes.

Make the generated static registrar code implement protocols from [Adopts]
attributes, so that we can just query the ObjC runtime to see if a type
implements a protocol instead of keeping this information around ourselves.

src/ObjCRuntime/DynamicRegistrar.cs

@@ -378,6 +378,11 @@ namespace Registrar {
 			return attr == null ? null : attr.WrapperType;
 		}
 
+		protected override IList<AdoptsAttribute> GetAdoptsAttributes (Type type)
+		{
+			return (AdoptsAttribute[]) type.GetCustomAttributes (typeof (AdoptsAttribute), false);
+		}
+
 		protected override string GetAssemblyName (Assembly assembly)
 		{
 			return assembly.GetName ().Name;

src/ObjCRuntime/Registrar.cs

@@ -135,6 +135,7 @@ namespace Registrar {
 			public TType Type;
 			public ObjCType BaseType;
 			public ObjCType [] Protocols;
+			public string [] AdoptedProtocols;
 			public bool IsModel;
 			// if this type represents an ObjC protocol (!= has the protocol attribute, since that can be applied to all kinds of things).
 			public bool IsProtocol;
@@ -1028,6 +1029,7 @@ namespace Registrar {
 		protected abstract TType GetProtocolAttributeWrapperType (TType type); // Return null if no attribute is found. Do not consider base types.
 		protected abstract BindAsAttribute GetBindAsAttribute (TMethod method, int parameter_index); // If parameter_index = -1 then get the attribute for the return type. Return null if no attribute is found. Must consider base method.
 		protected abstract BindAsAttribute GetBindAsAttribute (TProperty property);
+		protected abstract IList<AdoptsAttribute> GetAdoptsAttributes (TType type);
 		public abstract TType GetNullableType (TType type); // For T? returns T. For T returns null.
 		protected abstract bool HasReleaseAttribute (TMethod method); // Returns true of the method's return type/value has a [Release] attribute.
 		protected abstract bool IsINativeObject (TType type);
@@ -1640,6 +1642,17 @@ namespace Registrar {
 			return protocolList.ToArray ();
 		}
 
+		string [] GetAdoptedProtocols (ObjCType type)
+		{
+			var attribs = GetAdoptsAttributes (type.Type);
+			if (attribs == null || attribs.Count == 0)
+				return null;
+			var rv = new string [attribs.Count];
+			for (var i = 0; i < attribs.Count; i++)
+				rv [i] = attribs [i].ProtocolType;
+			return rv;
+		}
+
 		ObjCType RegisterCategory (TType type, CategoryAttribute attrib, ref List<Exception> exceptions)
 		{
 			if (IsINativeObject (type)) {
@@ -1823,6 +1836,7 @@ namespace Registrar {
 			};
 			objcType.VerifyRegisterAttribute (ref exceptions);
 			objcType.Protocols = GetProtocols (objcType, ref exceptions);
+			objcType.AdoptedProtocols = GetAdoptedProtocols (objcType);
 			objcType.BaseType = isProtocol ? null : (baseObjCType ?? objcType);
 			objcType.IsWrapper = (isProtocol && !isInformalProtocol) ? (GetProtocolAttributeWrapperType (objcType.Type) != null) : (objcType.RegisterAttribute != null && objcType.RegisterAttribute.IsWrapper);
 

tools/common/StaticRegistrar.cs

@@ -1602,6 +1602,28 @@ namespace Registrar {
 			return null;
 		}
 
+		protected override IList<AdoptsAttribute> GetAdoptsAttributes (TypeReference type)
+		{
+			var attributes = GetCustomAttributes (type.Resolve (), ObjCRuntime, "AdoptsAttribute");
+			if (attributes == null || !attributes.Any ())
+				return null;
+			
+			var rv = new List<AdoptsAttribute> ();
+			foreach (var ca in attributes) {
+				var attrib = new AdoptsAttribute ();
+				switch (ca.ConstructorArguments.Count) {
+				case 1:
+					attrib.ProtocolType = (string) ca.ConstructorArguments [0].Value;
+					break;
+				default:
+					throw ErrorHelper.CreateError (4124, "Invalid AdoptsAttribute found on '{0}': expected 1 constructor arguments, got {1}. Please file a bug report at https://bugzilla.xamarin.com", type.FullName, 1, ca.ConstructorArguments.Count);
+				}
+				rv.Add (attrib);
+			}
+
+			return rv;
+		}
+
 		protected override BindAsAttribute GetBindAsAttribute (PropertyDefinition property)
 		{
 			if (property == null)
@@ -2652,6 +2674,15 @@ namespace Registrar {
 							CheckNamespace (tp.Protocols [p], exceptions);
 						}
 					}
+					if (App.Optimizations.RegisterProtocols == true && tp.AdoptedProtocols != null) {
+						for (int p = 0; p < tp.AdoptedProtocols.Length; p++) {
+							if (tp.AdoptedProtocols [p] == "UIAppearance")
+								continue; // This is not a real protocol
+							iface.Append (any_protocols ? ", " : "<");
+							any_protocols = true;
+							iface.Append (tp.AdoptedProtocols [p]);
+						}
+					}
 					tp = tp.BaseType;
 				}
 				if (any_protocols)
@@ -4497,4 +4528,9 @@ namespace Registrar {
 		public bool IsWrapper { get; set; }
 		public bool SkipRegistration { get; set; }
 	}
+
+	class AdoptsAttribute : Attribute
+	{
+		public string ProtocolType { get; set; }
+	}
 }