[generator] Handle Java class with base class set to itself. (#1032)

Fixes: #1031

There apparently exists a Java obfuscator that attempts to break
tools by setting the base class of a class to itself.

	public class c5<BaseHandler> extends c5<BaseHandler> {
	    // …
	}

This breaks `generator` with a `StackOverflowException`:

	Stack overflow: IP: 0x11ae88918, fault addr: 0x30d984fd8
	Stacktrace:
	   at Java.Interop.Tools.JavaTypeSystem.Models.JavaClassModel.PrepareGenericInheritanceMapping ()
	   <...>
	   at Java.Interop.Tools.JavaTypeSystem.Models.JavaClassModel.get_GenericInheritanceMapping ()
	   at Java.Interop.Tools.JavaTypeSystem.Models.JavaMethodModel/<>c__DisplayClass47_0.<FindBaseMethod>b__0 (Java.Interop.Tools.JavaTypeSystem.Models.JavaMethodModel)
	   at System.Linq.Enumerable.TryGetFirst<TSource_REF> (System.Collections.Generic.IEnumerable`1<TSource_REF>,System.Func`2<TSource_REF, bool>,bool&)
	   at System.Linq.Enumerable.FirstOrDefault<TSource_REF> (System.Collections.Generic.IEnumerable`1<TSource_REF>,System.Func`2<TSource_REF, bool>)
	   at Java.Interop.Tools.JavaTypeSystem.Models.JavaMethodModel.FindBaseMethod (Java.Interop.Tools.JavaTypeSystem.Models.JavaClassModel)
	   at Java.Interop.Tools.JavaTypeSystem.Models.JavaClassModel.ResolveBaseMembers ()k
	   at Java.Interop.Tools.JavaTypeSystem.Models.JavaTypeCollection.ResolveCollection (Java.Interop.Tools.JavaTypeSystem.TypeResolutionOptions)
	   at generator.JavaTypeResolutionFixups.Fixup (string,string,Java.Interop.Tools.Cecil.DirectoryAssemblyResolver,string[])
	   at Xamarin.Android.Binder.CodeGenerator.Run (Xamarin.Android.Binder.CodeGeneratorOptions,Java.Interop.Tools.Cecil.DirectoryAssemblyResolver)
	   at Xamarin.Android.Binder.CodeGenerator.Run (Xamarin.Android.Binder.CodeGeneratorOptions)
	   at Xamarin.Android.Binder.CodeGenerator.Main (string[])
	   at (wrapper runtime-invoke) <Module>.runtime_invoke_int_object (object,intptr,intptr,intptr)

Add a check for this scenario to `generator` to prevent the
`StackOverflowException` and instead remove the offending type.

This removal will be logged with other type removals in the
`java-resolution-report.log` (f658ab2):

	The class '[Class] my.namespace.c5' was removed because the base type 'my.namespace.c5' is invalid.

Author: jpobst

src/Java.Interop.Tools.JavaTypeSystem/JavaModels/JavaClassModel.cs

@@ -37,6 +37,13 @@ public override void Resolve (JavaTypeCollection types, ICollection<JavaUnresolv
 					throw;
 				}
 
+				// Apparently some Java obfuscator sets a class's base type to itself, which
+				// results in a stack overflow. Check for this case and remove the offending type.
+				if (BaseTypeReference.ReferencedType is JavaClassModel jcm && jcm == this) {
+					unresolvables.Add (new JavaUnresolvableModel (this, BaseTypeGeneric, UnresolvableType.InvalidBaseType));
+					throw new JavaTypeResolutionException (BaseTypeGeneric);
+				}
+
 				// We don't resolve reference-only types by default, so if our base class
 				// is a reference only type, we need to force it to resolve here. This will be
 				// needed later when we attempt to resolve base methods.

src/Java.Interop.Tools.JavaTypeSystem/Utilities/JavaUnresolvableModel.cs

@@ -25,6 +25,9 @@ public string GetDisplayMessage ()
 					$"The type '{member?.DeclaringType.FullName}' was removed because the required {GetUnresolvableType ()} '{GetUnresolvable ()}' was removed because its name contains a dollar sign." :
 					$"The {GetUnresolvableType ()} '{GetUnresolvable ()}' was removed because its name contains a dollar sign.";
 
+			if (Type == UnresolvableType.InvalidBaseType)
+				return $"The {GetUnresolvableType ()} '{GetUnresolvable ()}' was removed because the base type '{MissingType}' is invalid.";
+
 			if (Unresolvable is JavaTypeModel)
 				return $"The {GetUnresolvableType ()} '{GetUnresolvable ()}' was removed because the Java {GetReason ()} '{MissingType}' could not be found.";
 
@@ -77,6 +80,7 @@ public enum UnresolvableType
 		ReturnType,
 		ParameterType,
 		BaseType,
-		ImplementsType
+		ImplementsType,
+		InvalidBaseType,
 	}
 }

tests/Java.Interop.Tools.JavaTypeSystem-Tests/JavaTypeCollectionTests.cs

@@ -122,5 +122,30 @@ public void InheritedGenericTypeParameters ()
 			Assert.IsNotNull (t.Methods.SingleOrDefault (m => m.Name == "DoT"), "Method with generic T not found");
 			Assert.IsNotNull (t.Methods.SingleOrDefault (m => m.Name == "DoU"), "Method with generic U not found");
 		}
+
+		[Test]
+		public void InvalidBaseTypeResolution ()
+		{
+			var api = new JavaTypeCollection ();
+
+			// Create "my.ns" package
+			var my_ns = api.AddPackage ("my.ns", "my/ns");
+
+			// Create new "my.ns.MyObject" type with "my.ns.MyObject" as base type
+			var jlo = JavaApiTestHelper.CreateClass (my_ns, "MyObject", javaBaseType: "my.ns.MyObject", javaBaseTypeGeneric: "my.ns.MyObject");
+
+			api.AddType (jlo);
+
+			// Run the resolver
+			var results = api.ResolveCollection ();
+
+			// Ensure we marked it as unresolvable
+			Assert.AreEqual (1, results.Count);
+			Assert.AreEqual (1, results [0].Unresolvables.Count);
+			Assert.AreEqual ("The class '[Class] my.ns.MyObject' was removed because the base type 'my.ns.MyObject' is invalid.", results [0].Unresolvables [0].GetDisplayMessage ());
+
+			// Ensure we removed the type from the collection
+			Assert.AreEqual (0, api.TypesFlattened.Count);
+		}
 	}
 }