NameGenerator now honors the RegisterAttribute

docs/errors.md

@@ -217,6 +217,53 @@ Selectors on the [NSObjectProtocol](https://developer.apple.com/reference/object
 
 Note: The list of reserved selectors will evolve with new versions of the tool.
 
+<h3><a name="EM1060"/>Invalid `RegisterAttribute` found on class `T`. Expected the first constructor parameter to be of type `string` but found type `U` instead.</h3>
+
+This is a **warning** that the class `T` was decorated with a `RegisterAttribute`, indicating the author wishes to rename the name of generated objective-c class.
+
+When either one or two arguments are passed into the constructor, the first must be of type `System.String` but in this case, some other type was provided instead. For this to happen, the `RegisterAttribute` did not come from Xamarin.iOS or Xamarin.Mac.
+
+If an argument was not also passed for named parameter "Name" then the class will be named according to the default convention.
+
+<h3><a name="EM1061"/>Invalid `RegisterAttribute` found on class `T`. Expected a constructor with either 1 or 2 parameters but found {argsCount} instead..</h3>
+
+This is a **warning** that the class `T` was decorated with a `RegisterAttribute`, indicating the author wishes to rename the name of generated objective-c class.
+
+Either one or two arguments are passed into the constructor, the first must be of type `System.String`. In this case, {argsCount} were found instead. For this to happen, the `RegisterAttribute` did not come from Xamarin.iOS or Xamarin.Mac.
+
+If an argument was not also passed for named parameter "Name" then the class will be named according to the default convention.
+
+<h3><a name="EM1062"/>Invalid `RegisterAttribute` found on class `T`. Conflicting values specified for `Name`, using value of named parameter: '{propVal}' instead of constructor parameter: '{name}'.</h3>
+
+This is a **warning** that the class `T` was decorated with a `RegisterAttribute`, indicating the author wishes to rename the name of generated objective-c class.
+
+However, two conflicting values were given for 'Name': one as a positional argument, the other as a named parameter. For example, consider: `[Register("myFoo", Name = "foo")]`.
+
+The value of the named parameter, 'foo' will be used instead of value provided to the positional parameter: 'myFoo'. If that is not the value intended, remove the named argument.
+
+<h3><a name="EM1063"/>Invalid `RegisterAttribute` found on class `T`. Named parameter `SkipRegistration` is not supported and will be ignored.</h3>
+
+This is a **warning** that the class `T` was decorated with a `RegisterAttribute`, indicating the author wishes to rename the name of generated objective-c class.
+
+Users already familiar with the `RegisterAttribute` might expect `SkipRegistration` to function is it does in Xamarin.iOS or Xamarin.Android. However, this is unsupported and the value of `SkipRegistration` will be ignored.
+
+This warning is informational only. If a custom class name was also passed either via positional argument or a named argument, then the value provided will still be used.
+
+<h3><a name="EM1064"/>Invalid `RegisterAttribute` found on class `T`. Named parameter {propName} is not supported and will be ignored.</h3>
+
+This is a **warning** that the class `T` was decorated with a `RegisterAttribute`, indicating the author wishes to rename the name of generated objective-c class.
+
+The `RegisterAttribute` decorating class `T` included named parameters which were unexpected and unsupported. For this to happen, the `RegisterAttribute` did not come from Xamarin.iOS or Xamarin.Mac.
+
+This warning is informational only. If a custom class name was also passed either via positional argument or a named argument, then the provided value will still be used.
+
+<h3><a name="EM1065"/>Invalid `RegisterAttribute` found on class `T`. No name argument for was provided to the constructor via positional or named parameters. Will use the default class naming convention instead.</h3>
+
+This is a **warning** that the class `T` was decorated with a `RegisterAttribute`, indicating the author wishes to rename the name of generated objective-c class.
+
+However, no value was actually provided to the attribute. This can happen when an attribute is provided without any arguments (`[Register]`).
+
+The class will be named as if it had not been decorated with `RegisterAttribute` to begin with.
 
 <!-- 2xxx: code generation -->
 

objcgen/NameGenerator.cs

@@ -53,6 +53,71 @@ public static class NameGenerator {
 
 		public static string GetObjCName (Type t)
 		{
+			if (t.IsClass) {
+				string name = null;
+				var delayed = new List<Exception> ();
+
+				var attrib = t.GetCustomAttributesData ().SingleOrDefault (a => a.AttributeType.Name.Equals ("RegisterAttribute"));
+				if (attrib != null) {
+					var argsCount = attrib.ConstructorArguments.Count;
+					switch (argsCount) {
+					// case 0 is considered invalid for use here, so handle it the same as the default case.
+					case 1:
+					case 2: {
+							// Since we aren't enforcing RegisterAttribute come from 
+							// a Xamarin-provided assembly, check to ensure the RA we
+							// found conforms to our expectations.
+							var arg = attrib.ConstructorArguments [0].ArgumentType;
+							if (Type.GetTypeCode (arg) == TypeCode.String) {
+								name = (string)attrib.ConstructorArguments [0].Value;
+							} else {
+								delayed.Add (ErrorHelper.CreateWarning (1060, $"Invalid RegisterAttribute found on class '{t.FullName}'. Expected the first constructor parameter to be of type `string` but found type `{arg.FullName}` instead."));
+							}
+							break;
+						}
+					default:
+						delayed.Add (ErrorHelper.CreateWarning (1061, $"Invalid RegisterAttribute found on class '{t.FullName}'. Expected a constructor with either 1 or 2 parameters but found {argsCount} instead."));
+						break;
+					}
+					// Handle cases where some used named properties.
+					// If they mixed both positional and named params,
+					// then assume the more specific one (the named)
+					// parameter is correct, and issue a warning.
+					if (attrib.NamedArguments.Any (a => !a.IsField)) {
+						foreach (var prop in attrib.NamedArguments) {
+							var propName = prop.MemberName;
+							switch (propName) {
+							case "IsWrapper":
+								continue; // Intentionally ignore.
+							case "Name":
+								if (string.IsNullOrWhiteSpace (name)) {
+									name = (string)prop.TypedValue.Value;
+								} else {
+									var propVal = (string)prop.TypedValue.Value;
+									if (!name.Equals (propVal)) {
+										delayed.Add (ErrorHelper.CreateWarning (1062, $"Invalid RegisterAttribute found on class '{t.FullName}'. Conflicting values specified for 'Name', using value of named parameter: '{propVal}' instead of constructor parameter: '{name}'."));
+									}
+									name = propVal;
+								}
+								break;
+							case "SkipRegistration":
+								delayed.Add (ErrorHelper.CreateWarning (1063, $"Invalid RegisterAttribute found on class '{t.FullName}'. SkipRegistration is not supported, and will be ignored."));
+								break;
+							default:
+								delayed.Add (ErrorHelper.CreateWarning (1064, $"Invalid RegisterAttribute found on class '{t.FullName}'. Named parameter {propName} is not supported and will be ignored."));
+								break;
+							}
+						}
+					}
+					if (!string.IsNullOrWhiteSpace (name)) {
+						ErrorHelper.Show (delayed);
+						return name;
+					}
+					// Fall back to the default strategy.
+					delayed.Add (ErrorHelper.CreateWarning (1065, $"Invalid RegisterAttribute found on class '{t.FullName}'. No name argument for was provided to the constructor via either position or named parameter. Will use the default class naming convention instead."));
+					ErrorHelper.Show (delayed);
+				}
+			}
 			return t.FullName.Replace ('.', '_').Replace ("+", "_");
 		}