Fix infinite recursion when resolving the base type of "class Test : Test.Base { public class Base {} }"

ICSharpCode.NRefactory.CSharp/Resolver/MemberTypeOrNamespaceReference.cs

@@ -91,7 +91,15 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 			for (int i = 0; i < typeArgs.Length; i++) {
 				typeArgs[i] = typeArguments[i].Resolve(context);
 			}
-			ResolveResult rr = r.ResolveMemberType(targetRR, identifier, typeArgs);
+			ResolveResult rr;
+			using (var busyLock = BusyManager.Enter(this)) {
+				if (busyLock.Success) {
+					rr = r.ResolveMemberType(targetRR, identifier, typeArgs);
+				} else {
+					// This can happen for "class Test : $Test.Base$ { public class Base {} }":
+					return ErrorResolveResult.UnknownError; // don't cache this error
+				}
+			}
 			if (cacheManager != null)
 				cacheManager.SetShared(this, rr);
 			return rr;

ICSharpCode.NRefactory.Tests/CSharp/Resolver/NameLookupTests.cs

@@ -860,5 +860,13 @@ class B
 			Assert.AreEqual("T", m.Parameters[0].Type.Resolve(context).Name);
 			Assert.AreEqual("X", m.Parameters[1].Type.Resolve(context).Name);
 		}
+		
+		[Test]
+		public void InheritingInnerClassShouldNotCauseStackOverflow() 
+		{
+			string program = @"class Test : $Test.Base$, Test.ITest { public class Base {} interface ITest {} }";
+			var result = Resolve<TypeResolveResult>(program);
+			Assert.AreEqual("Test.Base", result.Type.FullName);
+		}
 	}
 }

ICSharpCode.NRefactory/Utils/BusyManager.cs

@@ -27,7 +27,7 @@ namespace ICSharpCode.NRefactory.Utils
 	/// However, using a simple 'bool busy' is not thread-safe, so we use a
 	/// thread-static BusyManager.
 	/// </summary>
-	static class BusyManager
+	public static class BusyManager
 	{
 		public struct BusyLock : IDisposable
 		{