[generator] Do not generate PlatformNotSupportedException in chaining…

… .ctor

Types that are new in 64bits only OS are generated differently on 32bits
bindings. They mainly throw a `PlatformNotSupportedException` so it's
easier to diagnose (than a crash) what's happening at runtime.

This works well in all cases except one. When a new type, let's say
`UIMenuElement` is added **and** serves as a new base type for existing
types.

`UIKeyCommand` (iOS 7) -> `UICommand` (iOS 13)-> `UIMenuElement` (iOS 13)

This is _correct_ as new base types can be added (in ObjC and C#).
However the generated code for the constructors of `UICommand` and
`UIMenuElement` would be throwing a `PlatformNotSupportedException`
which breaks the `UIKeyCommand` on 32 bits devices.

We fixed this in a few places by tweaking the availability attribute
but that requires spotting the new base type while doing bindings and
that is error prone [1][2].

This PR simply does let the `protected` constructor, using when chaining,
be generated normally. It's simpler and will cover all the cases (without
requiring hacks in the availability of those types)

[1] xamarin#7083
[2] xamarin#7084

src/generator.cs

@@ -6479,32 +6479,18 @@ public void Generate (Type type)
 						sw.WriteLine ("\t\t[EditorBrowsable (EditorBrowsableState.Advanced)]");
 						sw.WriteLine ("\t\tprotected {0} (NSObjectFlag t) : base (t)", TypeName);
 						sw.WriteLine ("\t\t{");
-						if (is32BitNotSupported) {
-							sw.WriteLine ("\t\t#if ARCH_32");
-							sw.WriteLine ("\t\t\tthrow new PlatformNotSupportedException (\"This API is not supported on this version of iOS\");");
-							sw.WriteLine ("\t\t#else");
-						}
 						if (is_direct_binding_value != null)
 							sw.WriteLine ("\t\t\tIsDirectBinding = {0};", is_direct_binding_value);
 						WriteMarkDirtyIfDerived (sw, type);
-						if (is32BitNotSupported)
-							sw.WriteLine ("\t\t#endif");
 						sw.WriteLine ("\t\t}");
 						sw.WriteLine ();
 					}
 					GeneratedCode (sw, 2);
 					sw.WriteLine ("\t\t[EditorBrowsable (EditorBrowsableState.Advanced)]");
 					sw.WriteLine ("\t\tprotected internal {0} (IntPtr handle) : base (handle)", TypeName);
 					sw.WriteLine ("\t\t{");
-					if (is32BitNotSupported) {
-						sw.WriteLine ("\t\t#if ARCH_32");
-						sw.WriteLine ("\t\t\tthrow new PlatformNotSupportedException (\"This API is not supported on this version of iOS\");");
-						sw.WriteLine ("\t\t#else");
-					}
 					if (is_direct_binding_value != null)
 						sw.WriteLine ("\t\t\tIsDirectBinding = {0};", is_direct_binding_value);
-					if (is32BitNotSupported)
-						sw.WriteLine ("\t\t#endif");
 					WriteMarkDirtyIfDerived (sw, type);
 					sw.WriteLine ("\t\t}");
 					sw.WriteLine ();

tests/monotouch-test/UIKit/KeyCommandTest.cs

@@ -0,0 +1,23 @@
+using System;
+
+using Foundation;
+using ObjCRuntime;
+using UIKit;
+
+using NUnit.Framework;
+
+namespace MonoTouchFixtures.UIKit {
+
+	[TestFixture]
+	[Preserve (AllMembers = true)]
+	public class KeyCommandTest {
+
+		[Test]
+		public void Create ()
+		{
+			using (var key = new NSString ("a")) {
+				Assert.NotNull (UIKeyCommand.Create (key, UIKeyModifierFlags.Command, new Selector ("foo")), "Create");
+			}
+		}
+	}
+}