gdb/python: implement support for sending custom MI async notifications

This commit adds a new Python function, gdb.notify_mi, that can be used
to emit custom async notification to MI channel.  This can be used, among
other things, to implement notifications about events MI does not support,
such as remote connection closed or register change.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-By: Andrew Burgess <aburgess@redhat.com>

gdb/NEWS

@@ -6,6 +6,11 @@
 * GDB index now contains information about the main function. This speeds up
   startup when it is being used for some large binaries.
 
+* Python API
+
+  ** New function gdb.notify_mi(NAME, DATA), that emits custom
+     GDB/MI async notification.
+
 *** Changes in GDB 14
 
 * GDB now supports the AArch64 Scalable Matrix Extension 2 (SME2), which

gdb/doc/python.texi

@@ -211,6 +211,7 @@ optional arguments while skipping others.  Example:
 * Recordings In Python::        Accessing recordings from Python.
 * CLI Commands In Python::      Implementing new CLI commands in Python.
 * GDB/MI Commands In Python::   Implementing new @sc{gdb/mi} commands in Python.
+* GDB/MI Notifications In Python:: Implementing new @sc{gdb/mi} notifications in Python.
 * Parameters In Python::        Adding new @value{GDBN} parameters.
 * Functions In Python::         Writing new convenience functions.
 * Progspaces In Python::        Program spaces.
@@ -4804,6 +4805,50 @@ Here is how this works using the commands from the example above:
 @{'string': 'abc, def, ghi'@}
 @end smallexample
 
+@node GDB/MI Notifications In Python
+@subsubsection @sc{gdb/mi} Notifications In Python
+
+@cindex MI notifications in python
+@cindex notifications in python, GDB/MI
+@cindex python notifications, GDB/MI
+
+It is possible to emit @sc{gdb/mi} notifications from
+Python.  Use the @code{gdb.notify_mi} function to do that.
+
+@defun gdb.notify_mi (name @r{[}, data@r{]})
+Emit a @sc{gdb/mi} asynchronous notification.  @var{name} is the name of the
+notification, consisting of alphanumeric characters and a hyphen (@code{-}).
+@var{data} is any additional data to be emitted with the notification, passed
+as a Python dictionary. This argument is optional. The dictionary is converted
+to a @sc{gdb/mi} @var{result} records (@pxref{GDB/MI Output Syntax}) the same way
+as result of Python MI command (@pxref{GDB/MI Commands In Python}).
+
+If @var{data} is @code{None} then no additional values are emitted.
+@end defun
+
+While using existing notification names (@pxref{GDB/MI Async Records}) with
+@code{gdb.notify_mi} is allowed, users are encouraged to prefix user-defined
+notification with a hyphen (@code{-}) to avoid possible conflict.
+@value{GDBN} will never introduce notification starting with hyphen.
+
+Here is how to emit @code{=-connection-removed} whenever a connection to remote
+GDB server is closed (@pxref{Connections In Python}):
+
+@smallexample
+def notify_connection_removed(event):
+    data = @{"id": event.connection.num, "type": event.connection.type@}
+    gdb.notify_mi("-connection-removed", data)
+
+
+gdb.events.connection_removed.connect(notify_connection_removed)
+@end smallexample
+
+Then, each time a connection is closed, there will be a notification on MI channel:
+
+@smallexample
+=-connection-removed,id="1",type="remote"
+@end smallexample
+
 @node Parameters In Python
 @subsubsection Parameters In Python
 

gdb/python/py-mi.c

@@ -19,8 +19,14 @@
 
 #include "defs.h"
 #include "python-internal.h"
+#include "utils.h"
+#include "ui.h"
 #include "ui-out.h"
+#include "interps.h"
+#include "target.h"
 #include "mi/mi-parse.h"
+#include "mi/mi-console.h"
+#include "mi/mi-interp.h"
 
 /* A ui_out subclass that creates a Python object based on the data
    that is passed in.  */
@@ -455,3 +461,71 @@ serialize_mi_results (PyObject *results)
       serialize_mi_result_1 (value, key_string.get ());
     }
 }
+
+/* See python-internal.h.  */
+
+PyObject *
+gdbpy_notify_mi (PyObject *self, PyObject *args, PyObject *kwargs)
+{
+  static const char *keywords[] = { "name", "data", nullptr };
+  char *name = nullptr;
+  PyObject *data = Py_None;
+
+  if (!gdb_PyArg_ParseTupleAndKeywords (args, kwargs, "s|O", keywords,
+					&name, &data))
+    return nullptr;
+
+  /* Validate notification name.  */
+  const int name_len = strlen (name);
+  if (name_len == 0)
+    {
+      PyErr_SetString (PyExc_ValueError, _("MI notification name is empty."));
+      return nullptr;
+    }
+  for (int i = 0; i < name_len; i++)
+    {
+      if (!isalnum (name[i]) && name[i] != '-')
+	{
+	  PyErr_Format
+	    (PyExc_ValueError,
+	     _("MI notification name contains invalid character: %c."),
+	     name[i]);
+	  return nullptr;
+	}
+    }
+
+  /* Validate additional data.  */
+  if (!(data == Py_None || PyDict_Check (data)))
+    {
+      PyErr_Format
+	(PyExc_ValueError,
+	 _("MI notification data must be either None or a dictionary, not %s"),
+	 Py_TYPE (data)->tp_name);
+      return nullptr;
+    }
+
+  SWITCH_THRU_ALL_UIS ()
+    {
+      struct mi_interp *mi = as_mi_interp (top_level_interpreter ());
+
+      if (mi == nullptr)
+	continue;
+
+      target_terminal::scoped_restore_terminal_state term_state;
+      target_terminal::ours_for_output ();
+
+      gdb_printf (mi->event_channel, "%s", name);
+      if (data != Py_None)
+	{
+	  ui_out *mi_uiout = mi->interp_ui_out ();
+	  ui_out_redirect_pop redir (mi_uiout, mi->event_channel);
+	  scoped_restore restore_uiout
+	    = make_scoped_restore (&current_uiout, mi_uiout);
+
+	  serialize_mi_results (data);
+	}
+      gdb_flush (mi->event_channel);
+    }
+
+  Py_RETURN_NONE;
+}

gdb/python/python-internal.h

@@ -499,6 +499,11 @@ extern PyObject *gdbpy_execute_mi_command (PyObject *self, PyObject *args,
 
 extern void serialize_mi_results (PyObject *results);
 
+/* Implementation of the gdb.notify_mi function.  */
+
+extern PyObject *gdbpy_notify_mi (PyObject *self, PyObject *args,
+				  PyObject *kw);
+
 /* Convert Python object OBJ to a program_space pointer.  OBJ must be a
    gdb.Progspace reference.  Return nullptr if the gdb.Progspace is not
    valid (see gdb.Progspace.is_valid), otherwise return the program_space

gdb/python/python.c

@@ -2669,6 +2669,10 @@ Return the name of the currently selected language." },
     "print_options () -> dict\n\
 Return the current print options." },
 
+  { "notify_mi", (PyCFunction) gdbpy_notify_mi,
+    METH_VARARGS | METH_KEYWORDS,
+    "notify_mi (name, data) -> None\n\
+Output async record to MI channels if any." },
   {NULL, NULL, 0, NULL}
 };
 

gdb/testsuite/gdb.python/py-mi-notify.exp

@@ -0,0 +1,71 @@
+# Copyright (C) 2023 Free Software Foundation, Inc.
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test custom MI notifications implemented in Python.
+
+load_lib gdb-python.exp
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+gdb_exit
+if {[mi_gdb_start]} {
+    return
+}
+
+if {[lsearch -exact [mi_get_features] python] < 0} {
+    unsupported "python support is disabled"
+    return -1
+}
+
+standard_testfile
+
+mi_gdb_test "set python print-stack full" \
+    ".*\\^done" \
+    "set python print-stack full"
+
+mi_gdb_test "python gdb.notify_mi('-test-notification')" \
+    ".*=-test-notification\r\n\\^done" \
+    "python notification, no additional data parameter"
+
+mi_gdb_test "python gdb.notify_mi('-test-notification', None)" \
+    ".*=-test-notification\r\n\\^done" \
+    "python notification, no additional data"
+
+mi_gdb_test "python gdb.notify_mi('-test-notification', \{ 'data1' : 1 , 'data2' : 2 })" \
+    ".*=-test-notification,data1=\"1\",data2=\"2\"\r\n\\^done" \
+    "python notification, with additional data"
+
+mi_gdb_test "python gdb.notify_mi('-test-notification', 1)" \
+    ".*\\^error,msg=\".*\"" \
+    "python notification, invalid additional data"
+
+mi_gdb_test "python gdb.notify_mi('', None)" \
+    ".*\\^error,msg=\".*\"" \
+    "python notification, empty notification name"
+
+mi_gdb_test "python gdb.notify_mi('**invalid**', None)" \
+    ".*\\^error,msg=\".*\"" \
+    "python notification, invalid notification name"
+
+mi_gdb_test "python gdb.notify_mi(\[1,2,3\], None)" \
+    ".*\\^error,msg=\".*\"" \
+    "python notification, non-string notification name"
+
+mi_gdb_test "python gdb.notify_mi()" \
+    ".*\\^error,msg=\".*\"" \
+    "python notification, no arguments passed"
+
+mi_gdb_test "python gdb.notify_mi('thread-group-added', \{'id' : 'i2'\})" \
+    ".*=thread-group-added,id=\"i2\"\r\n\\^done" \
+    "python notification, using existing internal notification name"