Fix infinite loop when diffing non-equatable recursive objects

Fixes #136.

Author: stephencelis

Sources/CustomDump/Internal/Mirror.swift

@@ -27,6 +27,10 @@ extension Mirror {
 }
 
 func isMirrorEqual(_ lhs: Any, _ rhs: Any) -> Bool {
+  let lhsType = type(of: lhs)
+  if lhsType is AnyClass, lhsType == type(of: rhs), lhs as AnyObject === rhs as AnyObject {
+    return true
+  }
   guard let lhs = lhs as? any Equatable else {
     let lhsMirror = Mirror(customDumpReflecting: lhs)
     let rhsMirror = Mirror(customDumpReflecting: rhs)

Tests/CustomDumpTests/DiffTests.swift

@@ -1290,6 +1290,19 @@ final class DiffTests: XCTestCase {
       """
     )
   }
+
+  func testRecursion() {
+    class Object {
+      var child: Object?
+    }
+    let object = Object()
+    object.child = object
+    expectNoDifference(
+      diff(object, object),
+      """
+      """
+    )
+  }
 }
 
 private class Shared: _CustomDiffObject, Equatable {