detect the implementation issue on IsAssignableFrom, and go the other…

… way around for ART. Also dont try to use ExceptionDescribe if there is no Exception throw, or we will get a bad bad native crash. Closes kivy#92

jnius/jnius_utils.pxi

@@ -44,8 +44,25 @@ cdef void check_exception(JNIEnv *j_env) except *:
 
 
 cdef dict assignable_from = {}
+cdef int assignable_from_order = 0
 cdef void check_assignable_from(JNIEnv *env, JavaClass jc, bytes signature) except *:
- cdef jclass cls
+ global assignable_from_order
+ cdef jclass cls, clsA, clsB
+ cdef jthrowable exc
+
+ # first call, we need to get over the libart issue, which implemented
+ # IsAssignableFrom the wrong way.
+ # Ref: https://github.com/kivy/pyjnius/issues/92
+ # Google Bug: https://android.googlesource.com/platform/art/+/1268b74%5E!/
+ if assignable_from_order == 0:
+ clsA = env[0].FindClass(env, "java/lang/String")
+ clsB = env[0].FindClass(env, "java/lang/Object")
+ if env[0].IsAssignableFrom(env, clsB, clsA):
+ # Bug triggered, IsAssignableFrom said we can do things like:
+ # String a = Object()
+ assignable_from_order = -1
+ else:
+ assignable_from_order = 1
 
  # if we have a JavaObject, it's always ok.
  if signature == 'java/lang/Object':
@@ -74,9 +91,16 @@ cdef void check_assignable_from(JNIEnv *env, JavaClass jc, bytes signature) exce
  raise JavaException('Unable to found the class for {0!r}'.format(
  signature))
 
- result = bool(env[0].IsAssignableFrom(env, jc.j_cls, cls))
- env[0].ExceptionDescribe(env)
- env[0].ExceptionClear(env)
+ if assignable_from_order == 1:
+ result = bool(env[0].IsAssignableFrom(env, jc.j_cls, cls))
+ else:
+ result = bool(env[0].IsAssignableFrom(env, cls, jc.j_cls))
+
+ exc = env[0].ExceptionOccurred(env)
+ if exc:
+ env[0].ExceptionDescribe(env)
+ env[0].ExceptionClear(env)
+
  assignable_from[(jc.__javaclass__, signature)] = bool(result)
 
  if result is False: