[bgen] Fix using types that are in multiple namespaces. (#21182)

There's both a Network.NWEndpoint and a NetworkExtension.NWEndpoint, and the
generator generates ambiguous code in certain cases.

Fix the generator to use the full type reference for such types.

src/bgen/Caches/NamespaceCache.cs

@@ -17,6 +17,7 @@ public class NamespaceCache {
 	public ICollection<string> UINamespaces { get; private set; }
 	public ICollection<string> ImplicitNamespaces { get; private set; }
 	public ICollection<string> NamespacesThatConflictWithTypes { get; private set; }
+	public ICollection<string> TypesInMultipleNamespaces { get; private set; }
 
 	public NamespaceCache (PlatformName currentPlatform, string customObjCRuntimeNS, bool skipSystemDrawing)
 	{
@@ -154,6 +155,10 @@ public NamespaceCache (PlatformName currentPlatform, string customObjCRuntimeNS,
 			"AudioUnit",
 		};
 
+		TypesInMultipleNamespaces = new HashSet<string> {
+			"NWEndpoint", // Both in Network and NetworkExtension
+		};
+
 		if (!skipSystemDrawing)
 			ImplicitNamespaces.Add ("System.Drawing");
 	}

src/bgen/Generator.cs

@@ -894,6 +894,9 @@ public string MarshalParameter (MethodInfo mi, ParameterInfo pi, bool null_allow
 			return safe_name + ".Handle";
 		}
 
+		if (TypeCache.INativeObject.IsAssignableFrom (pi.ParameterType))
+			return $"{safe_name}.GetHandle ()";
+
 		// This means you need to add a new MarshalType in the method "Go"
 		throw new BindingException (1002, true, pi.ParameterType.FullName, mi.DeclaringType.FullName, mi.Name.GetSafeParamName ());
 	}

src/bgen/TypeManager.cs

@@ -300,12 +300,17 @@ public string FormatTypeUsedIn (string? usedInNamespace, Type? type)
 
 		if (t.Namespace is not null) {
 			string ns = t.Namespace;
-			if (NamespaceCache.ImplicitNamespaces.Contains (ns) || t.IsGenericType) {
+			var isImplicitNamespace = NamespaceCache.ImplicitNamespaces.Contains (ns);
+			var isInMultipleNamespaces = IsInMultipleNamespaces (t);
+			var nonGlobalCandidate = isImplicitNamespace && !isInMultipleNamespaces;
+			if (nonGlobalCandidate || t.IsGenericType) {
 				var targs = t.GetGenericArguments ();
 				if (targs.Length == 0)
 					return t.Name + nullable;
 				return $"global::{t.Namespace}." + t.Name.RemoveArity () + "<" + string.Join (", ", targs.Select (l => FormatTypeUsedIn (null, l)).ToArray ()) + ">" + nullable;
 			}
+			if (isInMultipleNamespaces)
+				return "global::" + t.FullName + nullable;
 			if (NamespaceCache.NamespacesThatConflictWithTypes.Contains (ns))
 				return "global::" + t.FullName + nullable;
 			if (t.Name == t.Namespace)
@@ -317,6 +322,17 @@ public string FormatTypeUsedIn (string? usedInNamespace, Type? type)
 		return t.FullName + nullable;
 	}
 
+	bool IsInMultipleNamespaces (Type? type)
+	{
+		if (type is null)
+			return false;
+
+		if (NamespaceCache.TypesInMultipleNamespaces.Contains (type.Name))
+			return true;
+
+		return IsInMultipleNamespaces (type.GetElementType ());
+	}
+
 	// TODO: If we ever have an API with nested properties of the same name more than
 	// 2 deep, we'll need to have this return a list of PropertyInfo and comb through them all.
 	public PropertyInfo? GetParentTypeWithSameNamedProperty (BaseTypeAttribute bta, string propertyName)

tests/generator/BGenTests.cs

@@ -526,6 +526,13 @@ public void StackOverflow20696157 ()
 			BuildFile (Profile.iOS, "sof20696157.cs");
 		}
 
+		[Test]
+		[TestCase (Profile.iOS)]
+		public void TypesInMultipleNamespaces (Profile profile)
+		{
+			BuildFile (profile, "tests/types-in-multiple-namespaces.cs");
+		}
+
 		[Test]
 		public void HyphenInName ()
 		{

tests/generator/tests/types-in-multiple-namespaces.cs

@@ -0,0 +1,15 @@
+using System;
+
+using CoreFoundation;
+using Foundation;
+using ObjCRuntime;
+
+namespace NS {
+	delegate void D1 ([NullAllowed] Network.NWEndpoint remoteEndpoints);
+
+	[BaseType (typeof (NSObject))]
+	interface TypesInMultipleNamespaces {
+		[Export ("someProperty")]
+		D1 SomeProperty { get; set; }
+	}
+}