[Generator] Ensure that selectors fields do not have overlapping names.

Fixes xamarin#18645

The way the generator names private fields for selectors results on not
compilable code when there are two selectoors A and B such that selector
B == AHandle.

That is, if selector A is "user", selector B will be
"userHandle". This happens because Handle is quite a common postfix in
security when working with user accounts (userHandler and others) and
we need to ensure that the Handle postfix added by the generator is unique.

As stated in the bug we could try to fix this by keeping track of the variables in the context
in wich the generator is creating code. The problem with such approach
is that it will make very hard to predict the name of the fields making
the manual code harder to write. The PR contains examples of such manual
code.

To fix the situation we have moved from using Handle to XHandle as a
postfix in the field names whihc reduces the chances of finding a
similar corner case in the future.

A test has been added to show the case in which we found the bug.

Fixes xamarin#18645

src/AppKit/Compat.cs

@@ -19,9 +19,9 @@ public virtual void SetTextBlocks (NSTextBlock [] array)
 				throw new ArgumentNullException (nameof (array));
 			var nsa_array = NSArray.FromNSObjects (array);
 			if (IsDirectBinding) {
-				global::ObjCRuntime.Messaging.void_objc_msgSend_IntPtr (this.Handle, selSetTextBlocks_Handle, nsa_array.Handle);
+				global::ObjCRuntime.Messaging.void_objc_msgSend_IntPtr (this.Handle, selSetTextBlocks_XHandle, nsa_array.Handle);
 			} else {
-				global::ObjCRuntime.Messaging.void_objc_msgSendSuper_IntPtr (this.SuperHandle, selSetTextBlocks_Handle, nsa_array.Handle);
+				global::ObjCRuntime.Messaging.void_objc_msgSendSuper_IntPtr (this.SuperHandle, selSetTextBlocks_XHandle, nsa_array.Handle);
 			}
 			nsa_array.Dispose ();
 		}
@@ -35,9 +35,9 @@ public virtual void SetTextLists (NSTextList [] array)
 				throw new ArgumentNullException (nameof (array));
 			var nsa_array = NSArray.FromNSObjects (array);
 			if (IsDirectBinding) {
-				global::ObjCRuntime.Messaging.void_objc_msgSend_IntPtr (this.Handle, selSetTextLists_Handle, nsa_array.Handle);
+				global::ObjCRuntime.Messaging.void_objc_msgSend_IntPtr (this.Handle, selSetTextLists_XHandle, nsa_array.Handle);
 			} else {
-				global::ObjCRuntime.Messaging.void_objc_msgSendSuper_IntPtr (this.SuperHandle, selSetTextLists_Handle, nsa_array.Handle);
+				global::ObjCRuntime.Messaging.void_objc_msgSendSuper_IntPtr (this.SuperHandle, selSetTextLists_XHandle, nsa_array.Handle);
 			}
 			nsa_array.Dispose ();
 		}

src/Foundation/NSArray.cs

@@ -247,7 +247,7 @@ static public NSArray FromIntPtrs (NativeHandle [] vals)
 		internal static nuint GetCount (IntPtr handle)
 		{
 #if MONOMAC
-			return (nuint) Messaging.UIntPtr_objc_msgSend (handle, selCountHandle);
+			return (nuint) Messaging.UIntPtr_objc_msgSend (handle, selCountXHandle);
 #else
 			return (nuint) Messaging.UIntPtr_objc_msgSend (handle, Selector.GetHandle ("count"));
 #endif
@@ -259,7 +259,7 @@ internal static NativeHandle GetAtIndex (NativeHandle handle, nuint i)
 			return Messaging.NativeHandle_objc_msgSend_UIntPtr (handle, Selector.GetHandle ("objectAtIndex:"), (UIntPtr) i);
 #else
 #if MONOMAC
-			return Messaging.IntPtr_objc_msgSend_UIntPtr (handle, selObjectAtIndex_Handle, (UIntPtr) i);
+			return Messaging.IntPtr_objc_msgSend_UIntPtr (handle, selObjectAtIndex_XHandle, (UIntPtr) i);
 #else
 			return Messaging.IntPtr_objc_msgSend_UIntPtr (handle, Selector.GetHandle ("objectAtIndex:"), (UIntPtr) i);
 #endif

src/Foundation/NSDictionary.cs

@@ -402,7 +402,7 @@ public IEnumerator<KeyValuePair<NSObject, NSObject>> GetEnumerator ()
 		public IntPtr LowlevelObjectForKey (IntPtr key)
 		{
 #if MONOMAC
-			return ObjCRuntime.Messaging.IntPtr_objc_msgSend_IntPtr (this.Handle, selObjectForKey_Handle, key);
+			return ObjCRuntime.Messaging.IntPtr_objc_msgSend_IntPtr (this.Handle, selObjectForKey_XHandle, key);
 #else
 			return ObjCRuntime.Messaging.IntPtr_objc_msgSend_IntPtr (this.Handle, Selector.GetHandle ("objectForKey:"), key);
 #endif

src/Foundation/NSMutableDictionary.cs

@@ -319,7 +319,7 @@ public IEnumerator<KeyValuePair<NSObject, NSObject>> GetEnumerator ()
 		public static NSMutableDictionary LowlevelFromObjectAndKey (IntPtr obj, IntPtr key)
 		{
 #if MONOMAC
-			return (NSMutableDictionary) Runtime.GetNSObject (ObjCRuntime.Messaging.IntPtr_objc_msgSend_IntPtr_IntPtr (class_ptr, selDictionaryWithObject_ForKey_Handle, obj, key));
+			return (NSMutableDictionary) Runtime.GetNSObject (ObjCRuntime.Messaging.IntPtr_objc_msgSend_IntPtr_IntPtr (class_ptr, selDictionaryWithObject_ForKey_XHandle, obj, key));
 #else
 			return (NSMutableDictionary) Runtime.GetNSObject (ObjCRuntime.Messaging.IntPtr_objc_msgSend_IntPtr_IntPtr (class_ptr, Selector.GetHandle ("dictionaryWithObject:forKey:"), obj, key));
 #endif
@@ -328,7 +328,7 @@ public static NSMutableDictionary LowlevelFromObjectAndKey (IntPtr obj, IntPtr k
 		public void LowlevelSetObject (IntPtr obj, IntPtr key)
 		{
 #if MONOMAC
-			ObjCRuntime.Messaging.void_objc_msgSend_IntPtr_IntPtr (this.Handle, selSetObject_ForKey_Handle, obj, key);
+			ObjCRuntime.Messaging.void_objc_msgSend_IntPtr_IntPtr (this.Handle, selSetObject_ForKey_XHandle, obj, key);
 #else
 			ObjCRuntime.Messaging.void_objc_msgSend_IntPtr_IntPtr (this.Handle, Selector.GetHandle ("setObject:forKey:"), obj, key);
 #endif

src/Foundation/NSObject2.cs

@@ -886,9 +886,9 @@ public void SetValueForKeyPath (NativeHandle handle, NSString keyPath)
 #else
 #if MONOMAC
 			if (IsDirectBinding) {
-				ObjCRuntime.Messaging.void_objc_msgSend_IntPtr_IntPtr (this.Handle, selSetValue_ForKeyPath_Handle, handle, keyPath.Handle);
+				ObjCRuntime.Messaging.void_objc_msgSend_IntPtr_IntPtr (this.Handle, selSetValue_ForKeyPath_XHandle, handle, keyPath.Handle);
 			} else {
-				ObjCRuntime.Messaging.void_objc_msgSendSuper_IntPtr_IntPtr (this.SuperHandle, selSetValue_ForKeyPath_Handle, handle, keyPath.Handle);
+				ObjCRuntime.Messaging.void_objc_msgSendSuper_IntPtr_IntPtr (this.SuperHandle, selSetValue_ForKeyPath_XHandle, handle, keyPath.Handle);
 			}
 #else
 			if (IsDirectBinding) {

src/Foundation/NSUrlProtocol.cs

@@ -47,9 +47,9 @@ public NSUrlProtocol (NSUrlRequest request, NSCachedUrlResponse cachedResponse,
 			if (client is null)
 				throw new ArgumentNullException ("client");
 			if (IsDirectBinding) {
-				InitializeHandle (IntPtr_objc_msgSend_IntPtr_IntPtr_IntPtr (this.Handle, selInitWithRequest_CachedResponse_Client_Handle, request.Handle, cachedResponse is null ? IntPtr.Zero : cachedResponse.Handle, client.Handle), "initWithRequest:cachedResponse:client:");
+				InitializeHandle (IntPtr_objc_msgSend_IntPtr_IntPtr_IntPtr (this.Handle, selInitWithRequest_CachedResponse_Client_XHandle, request.Handle, cachedResponse is null ? IntPtr.Zero : cachedResponse.Handle, client.Handle), "initWithRequest:cachedResponse:client:");
 			} else {
-				InitializeHandle (IntPtr_objc_msgSendSuper_IntPtr_IntPtr_IntPtr (this.SuperHandle, selInitWithRequest_CachedResponse_Client_Handle, request.Handle, cachedResponse is null ? IntPtr.Zero : cachedResponse.Handle, client.Handle), "initWithRequest:cachedResponse:client:");
+				InitializeHandle (IntPtr_objc_msgSendSuper_IntPtr_IntPtr_IntPtr (this.SuperHandle, selInitWithRequest_CachedResponse_Client_XHandle, request.Handle, cachedResponse is null ? IntPtr.Zero : cachedResponse.Handle, client.Handle), "initWithRequest:cachedResponse:client:");
 			}
 		}
 

src/bgen/Generator.cs

@@ -2669,8 +2669,8 @@ public string SelectorField (string s, bool ignore_inline_directive = false)
 			} else
 				sb.Append (c);
 		}
-		if (!InlineSelectors)
-			sb.Append ("Handle");
+		if (!InlineSelectors) 
+			sb.Append ("XHandle");
 		name = sb.ToString ();
 		selector_names [s] = name;
 		return name;

tests/generator/BGenTests.cs

@@ -824,6 +824,9 @@ public void DiamondProtocol ()
 		[Test]
 		public void GHIssue9065_Sealed () => BuildFile (Profile.iOS, nowarnings: true, "ghissue9065.cs");
 
+		[Test]
+		public void GHIssue18645_DuplicatedFiled() => BuildFile (Profile.iOS, nowarnings: true, "ghissue18645.cs");
+
 		// looking for [BindingImpl (BindingImplOptions.Optimizable)]
 		bool IsOptimizable (MethodDefinition method)
 		{

tests/generator/ghissue18645.cs

@@ -0,0 +1,44 @@
+using Foundation;
+using ObjCRuntime;
+
+namespace GHIssue18645{
+
+	[Protocol]
+	[BaseType (typeof(NSObject))]
+	interface ASCredentialIdentity {
+
+		[Abstract]
+		[Export ("user")]
+		string User { get; }
+
+		[Abstract]
+		[NullAllowed, Export ("recordIdentifier")]
+		string RecordIdentifier { get; }
+
+		[Abstract]
+		[Export ("rank")]
+		nint Rank { get; set; }
+	}
+
+	[BaseType (typeof (NSObject))]
+	interface ASPasskeyCredentialIdentity : ASCredentialIdentity {
+		[Export ("relyingPartyIdentifier")]
+		string RelyingPartyIdentifier { get; }
+
+		[Export ("userName")]
+		string UserName { get; }
+
+		[Export ("credentialID", ArgumentSemantic.Copy)]
+		NSData CredentialID { get; }
+
+		[Export ("userHandle", ArgumentSemantic.Copy)]
+		NSData UserHandle { get; }
+
+		[NullAllowed, Export ("recordIdentifier")]
+		new string RecordIdentifier { get; }
+
+		[Export ("rank")]
+		new nint Rank { get; set; }
+	}
+
+}