[RFC 6/8] mi/python: Handle python exception when executiong python-defined MI commands

[Jan Vrany <jan dot vrany at fit dot cvut dot cz>]

Respond with ^error,msg="..." when an unhandled python exception is thrown
while invoking python-defined MI command. The error message is taken from
python exception object.

gdb/Changelog:

	* python/py-micmd.c (py_mi_invoke): Handle exceptions thrown in Python
	code.
---
 gdb/ChangeLog         |  5 +++++
 gdb/python/py-micmd.c | 18 ++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 8bbaaba5ad..1fd49e703f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-12-10  Jan Vrany  <jan.vrany@fit.cvut.cz>
+
+	* python/py-micmd.c (py_mi_invoke): Handle exceptions thrown in Python
+	code. 
+
 2018-12-10  Jan Vrany  <jan.vrany@fit.cvut.cz>
 
 	* python/py-micmd.c (parse_mi_result): Polish to make the output
diff --git a/gdb/python/py-micmd.c b/gdb/python/py-micmd.c
index bbd746fa32..a099bb48cd 100644
--- a/gdb/python/py-micmd.c
+++ b/gdb/python/py-micmd.c
@@ -115,14 +115,28 @@ py_mi_invoke (void *py_obj, char **argv, int argc)
 	  error (_("Failed to create the python arguments list."));
 	}
     }
-
+  
+  gdb_assert (PyErr_Occurred () == NULL);
   gdbpy_ref<> result (PyObject_CallMethodObjArgs ((PyObject *) obj, invoke_cst, argobj.get (),
 				       NULL));
+  if (PyErr_Occurred () != NULL)
+    {
+      gdbpy_err_fetch ex;
+      gdb::unique_xmalloc_ptr<char> ex_msg (ex.to_string());
 
-  if (result != nullptr)
+      if (ex_msg == NULL || *ex_msg == '\0')
+        error (_("Failed to execute command"));
+      else
+        error (_(ex_msg.get ()));
+    }
+  else if (result != nullptr)
     {
       if (Py_None != result) parse_mi_result (result.get (), "result");
     }
+  else
+    {
+      error (_("Command invoke() method returned NULL but no python exception is set"));
+    }
 }
 
 /* Parse the name of the MI command to register.
-- 
2.20.1