[PATCH v3 4/5] mi/python: Allow redefinition of python MI commands

[Jan Vrany <jan.vrany@fit.cvut.cz>]

Redefining python MI commands is especially useful when developing
them.

gdb/Changelog:

	* 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.
---
 gdb/ChangeLog         |  8 ++++++++
 gdb/mi/mi-cmds.c      | 10 +++++++++-
 gdb/mi/mi-cmds.h      |  3 +++
 gdb/python/py-micmd.c | 24 +++++++++++++++++-------
 gdb/python/py-micmd.h |  2 +-
 5 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 241e5da68f..1d264c44f7 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 0aead954f9..e280e51daf 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 5ca7232fca..331b1349df 100644
--- a/gdb/mi/mi-cmds.h
+++ b/gdb/mi/mi-cmds.h
@@ -143,6 +143,9 @@ public:
   /* 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 e99632c97a..4f2b13f3c7 100644
--- a/gdb/python/py-micmd.c
+++ b/gdb/python/py-micmd.c
@@ -171,6 +171,12 @@ mi_command_py::mi_command_py (const char *name, gdbpy_ref<> object)
 {
 }
 
+bool
+mi_command_py::can_be_redefined()
+{
+  return true;
+}
+
 void
 mi_command_py::do_invoke (struct mi_parse *parse)
 {
@@ -179,6 +185,7 @@ mi_command_py::do_invoke (struct mi_parse *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 ();
 
   gdbpy_enter enter_py (get_current_arch (), current_language);
@@ -187,15 +194,14 @@ mi_command_py::do_invoke (struct mi_parse *parse)
 
   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 (int i = 0; i < parse->argc; ++i)
@@ -205,11 +211,16 @@ mi_command_py::do_invoke (struct mi_parse *parse)
       if (PyList_SetItem (argobj.get (), i, str.release ()) != 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)
@@ -218,9 +229,9 @@ mi_command_py::do_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
     {
@@ -233,7 +244,6 @@ 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 deadc0116b..0d61069ca5 100644
--- a/gdb/python/py-micmd.h
+++ b/gdb/python/py-micmd.h
@@ -44,7 +44,7 @@ class mi_command_py : public mi_command
 
     mi_command_py (const char *name, gdbpy_ref<> object);
 
-
+    bool can_be_redefined() override;
     /* This is called just before shutting down a Python interpreter
        to release python object implementing the command. */
 
-- 
2.20.1