[v2,4/5] mi/python: Allow redefinition of python MI commands

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 4cbe97002b..0a5d95b4e3 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@ 
+2019-05-02  Jan Vrany  <jan.vrany@fit.cvut.cz>
+
+	* mi/mi-cmds.h (mi_command::can_be_redefined): New method.
+	* mi/mi-cmds.c: (mi_command::can_be_redefined): New method.
+	(insert_mi_cmd_entry): Allow redefinition of python-defined MI commands.
+	* python/py-micmd.h (mi_command_py::can_be_redefined): New method.
+	* python/py-micmd.c: (mi_command_py::can_be_redefined): New method.
+
 2019-05-02  Didier Nadeau  <didier.nadeau@gmail.com>
             Jan Vrany  <jan.vrany@fit.cvut.cz>
 
diff --git a/gdb/mi/mi-cmds.c b/gdb/mi/mi-cmds.c
index 7e1d2c3f2d..d7ac76d450 100644
--- a/gdb/mi/mi-cmds.c
+++ b/gdb/mi/mi-cmds.c
@@ -41,7 +41,8 @@  insert_mi_cmd_entry (mi_cmd_up command)
   const std::string &name = command->name ();
 
   if (mi_cmd_table.find (name) != mi_cmd_table.end ())
-    return false;
+    if (! mi_cmd_table[name]->can_be_redefined ())
+      return false;
 
   mi_cmd_table[name] = std::move (command);
 
@@ -80,6 +81,13 @@  mi_command::mi_command (const char *name, int *suppress_notification)
     m_suppress_notification (suppress_notification)
 {}
 
+bool
+mi_command::can_be_redefined()
+{
+  return false;
+}
+
+
 
 void
 mi_command::invoke (struct mi_parse *parse)
diff --git a/gdb/mi/mi-cmds.h b/gdb/mi/mi-cmds.h
index a2757bae20..dd2738f831 100644
--- a/gdb/mi/mi-cmds.h
+++ b/gdb/mi/mi-cmds.h
@@ -142,6 +142,9 @@  class mi_command
     /* Execute the MI command.  */
     void invoke (struct mi_parse *parse);
 
+    /* Return TRUE if command can be redefined, FALSE otherwise. */
+    virtual bool can_be_redefined();
+
   protected:
     gdb::optional<scoped_restore_tmpl<int>> do_suppress_notification ();
     virtual void do_invoke(struct mi_parse *parse) = 0;
diff --git a/gdb/python/py-micmd.c b/gdb/python/py-micmd.c
index c8d429bb4b..994d715d02 100644
--- a/gdb/python/py-micmd.c
+++ b/gdb/python/py-micmd.c
@@ -158,17 +158,22 @@  mi_command_py::mi_command_py (const char *name, int *suppress_notification,
 {
 }
 
-void
-mi_command_py::invoke (struct mi_parse *parse)
+bool
+mi_command_py::can_be_redefined()
 {
-  std::unique_ptr<scoped_restore_tmpl<int>> restore
-    = do_suppress_notification ();
+  return true;
+}
+
 
+void
+mi_command_py::do_invoke (struct mi_parse *parse)
+{
   mi_parse_argv (parse->args, parse);
 
   if (parse->argv == NULL)
     error (_("Problem parsing arguments: %s %s"), parse->command, parse->args);
 
+  std::string name (this->name ());
   PyObject *obj = this->pyobj.get ();
   int i;
 
@@ -176,20 +181,19 @@  mi_command_py::invoke (struct mi_parse *parse)
 
   if (!obj)
     error (_("-%s: invalid invocation of Python micommand object."),
-	   name ().c_str ());
+	   name.c_str ());
 
   if (!PyObject_HasAttr (obj, invoke_cst))
     {
       error (_("-%s: python command object missing 'invoke' method."),
-	     name ().c_str ());
+	     name.c_str ());
     }
-
   gdbpy_ref<> argobj (PyList_New (parse->argc));
   if (argobj == nullptr)
     {
       gdbpy_print_stack ();
       error (_("-%s: failed to create the python arguments list."),
-	     name ().c_str ());
+	     name.c_str ());
     }
 
   for (i = 0; i < parse->argc; ++i)
@@ -201,11 +205,16 @@  mi_command_py::invoke (struct mi_parse *parse)
       if (PyList_SetItem (argobj.get (), i, str) != 0)
 	{
 	  error (_("-%s: failed to create the python arguments list."),
-		 name ().c_str ());
+		 name.c_str ());
 	}
     }
 
   gdb_assert (PyErr_Occurred () == NULL);
+
+  /* From this point on, THIS must not be used since Python code may replace
+     the the very same command that is currently executing.  This in turn leads
+     to desctruction of THIS making it invalid.  See insert_mi_cmd_entry. */
+
   gdbpy_ref<> result (
     PyObject_CallMethodObjArgs (obj, invoke_cst, argobj.get (), NULL));
   if (PyErr_Occurred () != NULL)
@@ -214,9 +223,9 @@  mi_command_py::invoke (struct mi_parse *parse)
       gdb::unique_xmalloc_ptr<char> ex_msg (ex.to_string ());
 
       if (ex_msg == NULL || *ex_msg == '\0')
-	error (_("-%s: failed to execute command"), name ().c_str ());
+	error (_("-%s: failed to execute command"), name.c_str ());
       else
-	error (_("-%s: %s"), name ().c_str (), ex_msg.get ());
+	error (_("-%s: %s"), name.c_str (), ex_msg.get ());
     }
   else if (result != nullptr)
     {
@@ -228,7 +237,7 @@  mi_command_py::invoke (struct mi_parse *parse)
       error (
 	_("-%s: command invoke() method returned NULL but no python exception "
 	  "is set"),
-	name ().c_str ());
+	name.c_str ());
     }
 }
 
@@ -236,7 +245,6 @@  void mi_command_py::finalize ()
 {
   this->pyobj.reset (nullptr);
 }
-
 /* Initialize the MI command object.  */
 
 int
diff --git a/gdb/python/py-micmd.h b/gdb/python/py-micmd.h
index 418de41a10..eaa5a6c47c 100644
--- a/gdb/python/py-micmd.h
+++ b/gdb/python/py-micmd.h
@@ -38,7 +38,7 @@  class mi_command_py : public mi_command
 public:
   mi_command_py (const char *name, int *suppress_notification,
 		 gdbpy_ref<> object);
-  void invoke (struct mi_parse *parse) override;
+  bool can_be_redefined() override;
 
   /* This is called just before shutting down a Python interpreter
      to release python object implementing the command */
@@ -46,6 +46,7 @@  public:
 
 private:
   gdbpy_ref<> pyobj;
+  virtual void do_invoke(struct mi_parse *parse) override;
 };
 
 #endif