Bug 810742 - Handle callee thrown exceptions when invoking a mach command; r=jhammel

python/mach/mach/main.py

@@ -314,6 +314,18 @@ To see more help for a specific command, run:
             # The first frame is us and is never used.
             stack = traceback.extract_tb(exc_tb)[1:]
 
+            # If we have nothing on the stack, the exception was raised as part
+            # of calling the @Command method itself. This likely means a
+            # mismatch between @CommandArgument and arguments to the method.
+            # e.g. there exists a @CommandArgument without the corresponding
+            # argument on the method. We handle that here until the module
+            # loader grows the ability to validate better.
+            if not len(stack):
+                print(COMMAND_ERROR)
+                self._print_exception(sys.stdout, exc_type, exc_value,
+                    traceback.extract_tb(exc_tb))
+                return 1
+
             # Split the frames into those from the module containing the
             # command and everything else.
             command_frames = []