use before_prompt hook to notify the frame_changed event

gui/__init__.py

@@ -1,4 +1,4 @@
-# Copyright (C) 2013 Tom Tromey <tom@tromey.com>
+# Copyright (C) 2013, 2015 Tom Tromey <tom@tromey.com>
 
 # 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
@@ -20,3 +20,4 @@ self_dir = os.path.abspath(os.path.dirname(__file__))
 # Import anything that defines a command or parameter.
 import gui.commands
 import gui.toplevel
+import gui.framecache

gui/commands.py

@@ -1,4 +1,4 @@
-# Copyright (C) 2012, 2013 Tom Tromey <tom@tromey.com>
+# Copyright (C) 2012, 2013, 2015 Tom Tromey <tom@tromey.com>
 
 # 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
@@ -206,7 +206,10 @@ class TestCommand(gdb.Command):
 TestCommand(True)
 TestCommand(False).invoke('', 0)
 
-if _can_override:
+# See framecache.py - we prefer the before_prompt event if it exists;
+# but otherwise try the overriding approach.  Both of these rely on a
+# hacked gdb :-(
+if _can_override and not hasattr(gdb.events, 'before_prompt'):
     class Overrider(gdb.Command):
         def __init__(self, name, event):
             super(Overrider, self).__init__(name, gdb.COMMAND_DATA)

gui/framecache.py

@@ -0,0 +1,34 @@
+# Copyright (C) 2015 Tom Tromey <tom@trolley.com>
+
+# 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/>.
+
+import gdb
+import gui.events
+
+_last_selected_frame = None
+
+def check_frame():
+    global _last_selected_frame
+    sel = None
+    try:
+        sel = gdb.selected_frame()
+    except:
+        pass
+    if _last_selected_frame is not sel:
+        _last_selected_frame = sel
+        gui.events.frame_changed.post()
+
+# See my gdb branch on github.
+if hasattr(gdb.events, 'before_prompt'):
+    gdb.events.before_prompt.connect(check_frame)