[generator] Teach generator about WrapAttribute on Getters and Setters (#3388)

* [generator] Teach generator about WrapAttribute on Getters and Setters

https://bugzilla.xamarin.com/show_bug.cgi?id=57870

`WrapAttribute` can now be used in property getters and setters,
this allows to Wrap virtually anything the way you need, for example
smart enums, consider the following API definition:

```csharp
// Smart enum.
enum PersonRelationship {
	[Field (null)]
	None,

	[Field ("FMFather", "__Internal")]
	Father,

	[Field ("FMMother", "__Internal")]
	Mother
}
```

```csharp
// Property definition.

[Export ("presenceType")]
NSString _PresenceType { get; set; }

PersonRelationship PresenceType {
	[Wrap ("PersonRelationshipExtensions.GetValue (_PresenceType)")]
	get;
	[Wrap ("_PresenceType = value.GetConstant ()")]
	set;
}
```

* Fix Feedback

* Fix doc error

* Update error message

docs/website/binding_types_reference_guide.md

@@ -1900,8 +1900,6 @@ var strongDemo = new Demo ();
 demo.Delegate = new MyDelegate ();
 ```
 
- <a name="Parameter_Attributes" />
-
 Another use of the `Wrap` attribute is to support strongly typed version
 of methods.   For example:
 
@@ -1937,6 +1935,42 @@ interface FooExplorer {
 }
 ```
 
+`[Wrap]` can also be used directly in property getters and setters,
+this allows to have full control on them and adjust the code the way you need,
+for example using smart enums, consider the following API definition:
+
+```csharp
+// Smart enum.
+enum PersonRelationship {
+        [Field (null)]
+        None,
+
+        [Field ("FMFather", "__Internal")]
+        Father,
+
+        [Field ("FMMother", "__Internal")]
+        Mother
+}
+```
+
+Interface definition:
+
+```
+// Property definition.
+
+    [Export ("presenceType")]
+    NSString _PresenceType { get; set; }
+
+    PersonRelationship PresenceType {
+            [Wrap ("PersonRelationshipExtensions.GetValue (_PresenceType)")]
+            get;
+            [Wrap ("_PresenceType = value.GetConstant ()")]
+            set;
+    }
+```
+
+ <a name="Parameter_Attributes" />
+
 # Parameter Attributes
 
 This section describes the attributes that you can apply to the parameters in

docs/website/generator-errors.md

@@ -176,6 +176,8 @@ This usually indicates a bug in Xamarin.iOS/Xamarin.Mac; please [file a bug repo
 
 ### <a name='BI1062'/>BI1062: The member '*' contains ref/out parameters and must not be decorated with [Async].
 
+### <a name='BI1063'/>BI1063: The 'WrapAttribute' can only be used at the property or at getter/setter level at a given time. Property: '*'.
+
 # BI11xx: warnings
 
 <!-- 11xx: warnings -->

src/generator-attribute-manager.cs

@@ -283,6 +283,8 @@ public static class AttributeManager
 
 	public static T GetCustomAttribute<T> (ICustomAttributeProvider provider) where T : System.Attribute
 	{
+		if (provider is null)
+			return null;
 		var rv = GetCustomAttributes<T> (provider);
 		if (rv == null || rv.Length == 0)
 			return null;

src/generator.cs

@@ -426,13 +426,30 @@ public interface IMemberGatherer {
 	IEnumerable<MethodInfo> GetTypeContractMethods (Type source);
 }
 
+class WrapPropMemberInformation
+{
+	public bool HasWrapOnGetter { get => WrapGetter != null; }
+	public bool HasWrapOnSetter { get => WrapSetter != null; }
+	public string WrapGetter { get; private set; }
+	public string WrapSetter { get; private set; }
+
+	public WrapPropMemberInformation (PropertyInfo pi)
+	{
+		WrapGetter = AttributeManager.GetCustomAttribute<WrapAttribute> (pi?.GetMethod)?.MethodName;
+		WrapSetter = AttributeManager.GetCustomAttribute<WrapAttribute> (pi?.SetMethod)?.MethodName;
+	}
+}
+
+
 public class MemberInformation
 {
 	public readonly MemberInfo mi;
 	public readonly Type type;
 	public readonly Type category_extension_type;
+	internal readonly WrapPropMemberInformation wpmi;
 	public readonly bool is_abstract, is_protected, is_internal, is_unified_internal, is_override, is_new, is_sealed, is_static, is_thread_static, is_autorelease, is_wrapper, is_forced;
 	public readonly bool is_type_sealed, ignore_category_static_warnings, is_basewrapper_protocol_method;
+	public readonly bool has_inner_wrap_attribute;
 	public readonly Generator.ThreadCheck threadCheck;
 	public bool is_unsafe, is_virtual_method, is_export, is_category_extension, is_variadic, is_interface_impl, is_extension_method, is_appearance, is_model, is_ctor;
 	public bool is_return_release;
@@ -572,6 +589,17 @@ public class MemberInformation
 			is_virtual_method = false;
 		else
 			is_virtual_method = !is_static;
+
+		// Properties can have WrapAttribute on getter/setter so we need to check for this
+		// but only if no Export is already found on property level.
+		if (export is null) {
+			wpmi = new WrapPropMemberInformation (pi);
+			has_inner_wrap_attribute = wpmi.HasWrapOnGetter || wpmi.HasWrapOnSetter;
+
+			// Wrap can only be used either at property level or getter/setter level at a given time.
+			if (wrap_method != null && has_inner_wrap_attribute)
+				throw new BindingException (1063, true, $"The 'WrapAttribute' can only be used at the property or at getter/setter level at a given time. Property: '{pi.DeclaringType}.{pi.Name}'");
+		}
 	}
 
 	public string GetVisibility ()
@@ -2264,7 +2292,10 @@ public partial class Generator : IMemberGatherer {
 
 					if (AttributeManager.HasAttribute<CoreImageFilterPropertyAttribute> (pi))
 						continue;
-					
+
+					if (AttributeManager.HasAttribute<WrapAttribute> (pi.GetGetMethod ()) || AttributeManager.HasAttribute<WrapAttribute> (pi.GetSetMethod ()))
+						continue;
+
 					throw new BindingException (1018, true, "No [Export] attribute on property {0}.{1}", t.FullName, pi.Name);
 				}
 				if (AttributeManager.HasAttribute<StaticAttribute> (pi))
@@ -4653,6 +4684,39 @@ public partial class Generator : IMemberGatherer {
 			indent--;
 			print ("}\n");
 			return;			
+		} else if (minfo.has_inner_wrap_attribute) {
+			// If property getter or setter has its own WrapAttribute we let the user do whatever their heart desires
+			if (pi.CanRead) {
+				PrintAttributes (pi, platform: true);
+				PrintAttributes (pi.GetGetMethod (), platform: true, preserve: true, advice: true);
+				print ("get {");
+				indent++;
+
+				print ($"return {minfo.wpmi.WrapGetter};");
+
+				indent--;
+				print ("}");
+			}
+			if (pi.CanWrite) {
+				var setter = pi.GetSetMethod ();
+				var not_implemented_attr = AttributeManager.GetCustomAttribute<NotImplementedAttribute> (setter);
+
+				PrintAttributes (pi, platform: true);
+				PrintAttributes (setter, platform: true, preserve: true, advice: true, notImplemented: true);
+				print ("set {");
+				indent++;
+
+				if (not_implemented_attr != null)
+					print ("throw new NotImplementedException ({0});", not_implemented_attr.Message == null ? "" : $@"""{not_implemented_attr.Message}""");
+				else
+					print ($"{minfo.wpmi.WrapSetter};");
+
+				indent--;
+				print ("}");
+			}
+			indent--;
+			print ("}\n");
+			return;
 		}
 
 		if (pi.CanRead){

tests/generator/BGenTests.cs

@@ -522,15 +522,24 @@ namespace GeneratorTests
 		[Test]
 		public void Bug57531 () => BuildFile (Profile.iOS, "bug57531.cs");
 
+		[Test]
+		public void Bug57870 () => BuildFile (Profile.iOS, true, true, "bug57870.cs");
+
 		BGenTool BuildFile (Profile profile, params string [] filenames)
 		{
-			return BuildFile (profile, true, filenames);
+			return BuildFile (profile, true, false, filenames);
 		}
 
 		BGenTool BuildFile (Profile profile, bool nowarnings, params string [] filenames)
+		{
+			return BuildFile (profile, nowarnings, false, filenames);
+		}
+
+		BGenTool BuildFile (Profile profile, bool nowarnings, bool processEnums, params string [] filenames)
 		{
 			var bgen = new BGenTool ();
 			bgen.Profile = profile;
+			bgen.ProcessEnums = processEnums;
 			bgen.Defines = BGenTool.GetDefaultDefines (bgen.Profile);
 			bgen.CreateTemporaryBinding (filenames.Select ((filename) => File.ReadAllText (Path.Combine (Configuration.SourceRoot, "tests", "generator", filename))).ToArray ());
 			bgen.AssertExecute ("build");

tests/generator/ErrorTests.cs

@@ -535,6 +535,49 @@ namespace BI1062Tests {
 			bgen.AssertError (1062, "The member 'FooObject.FooMethod' contains ref/out parameters and must not be decorated with [Async].");
 		}
 
+		[Test]
+		public void BI1063_NoDoubleWrapTest ()
+		{
+			var bgen = new BGenTool {
+				Profile = Profile.iOS,
+				ProcessEnums = true
+			};
+			bgen.CreateTemporaryBinding (@"
+using System;
+using Foundation;
+
+namespace BI1063Tests {
+
+	enum PersonRelationship {
+		[Field (null)]
+		None,
+
+		[Field (""INPersonRelationshipFather"", ""__Internal"")]
+		Father,
+
+		[Field (""INPersonRelationshipMother"", ""__Internal"")]
+		Mother
+	}
+
+	[BaseType (typeof (NSObject))]
+	interface Wrappers {
+
+		// SmartEnum -- Normal Wrap getter Property
+
+		[Export (""presenceType"")]
+		NSString _PresenceType { get; }
+
+		[Wrap (""PersonRelationshipExtensions.GetValue (_PresenceType)"")]
+		PersonRelationship PresenceType {
+			[Wrap (""PersonRelationshipExtensions.GetValue (_PresenceType)"")]
+			get;
+		}
+	}
+}");
+			bgen.AssertExecuteError ("build");
+			bgen.AssertError (1063, "The 'WrapAttribute' can only be used at the property or at getter/setter level at a given time. Property: 'BI1063Tests.Wrappers.PresenceType'");
+		}
+
 		[Test]
 		[TestCase (Profile.iOS)]
 		[TestCase (Profile.macOSFull)]

tests/generator/bug57870.cs

@@ -0,0 +1,62 @@
+using System;
+using Foundation;
+
+namespace Bug57870 {
+
+	enum PersonRelationship {
+		[Field (null)]
+		None,
+
+		[Field ("INPersonRelationshipFather", "__Internal")]
+		Father,
+
+		[Field ("INPersonRelationshipMother", "__Internal")]
+		Mother
+	}
+
+	[BaseType (typeof (NSObject))]
+	interface Wrappers {
+
+		// SmartEnum -- Normal Wrap getter Property
+
+		[Export ("presenceType")]
+		NSString _PresenceType { get; }
+
+		[Wrap ("PersonRelationshipExtensions.GetValue (_PresenceType)")]
+		PersonRelationship PresenceType { get; }
+
+		// SmartEnum -- getter Wrap + NotImplemented setter
+
+		[Export ("presenceType2")]
+		NSString _PresenceType2 { get; [NotImplemented] set; }
+
+		PersonRelationship PresenceType2 {
+			[Wrap ("PersonRelationshipExtensions.GetValue (_PresenceType2)")]
+			get;
+			[NotImplemented ("Nope nope nope")]
+			set;
+		}
+
+		// SmartEnum -- getter Wrap Only
+
+		[Export ("presenceType3")]
+		NSString _PresenceType3 { get; }
+
+		PersonRelationship PresenceType3 {
+			[Wrap ("PersonRelationshipExtensions.GetValue (_PresenceType3)")]
+			get;
+		}
+
+		// SmartEnum -- Wrap getter and setter
+
+		[Export ("presenceType4")]
+		NSString _PresenceType4 { get; set; }
+
+		PersonRelationship PresenceType4 {
+			[Wrap ("PersonRelationshipExtensions.GetValue (_PresenceType4)")]
+			get;
+			[Wrap ("_PresenceType4 = value.GetConstant ()")]
+			set;
+		}
+	}
+}