[commands] Add Context.command_failed attribute.

discord/ext/commands/bot.py

@@ -627,6 +627,7 @@ class BotBase(GroupMixin):
             except CommandError as e:
                 yield from ctx.command.dispatch_error(e, ctx)
             else:
+                ctx.command_failed = False
                 self.dispatch('command_completion', ctx)
         elif ctx.invoked_with:
             exc = CommandNotFound('Command "{}" is not found'.format(ctx.invoked_with))

discord/ext/commands/context.py

@@ -67,6 +67,9 @@ class Context(discord.abc.Messageable):
         to point to a valid registered subcommand and could just point to a
         nonsense string. If nothing was passed to attempt a call to a
         subcommand then this is set to `None`.
+    command_failed: bool
+        A boolean that indicates if the command failed to be parsed, checked,
+        or invoked.
     """
 
     def __init__(self, **attrs):
@@ -80,6 +83,7 @@ class Context(discord.abc.Messageable):
         self.invoked_with = attrs.pop('invoked_with', None)
         self.invoked_subcommand = attrs.pop('invoked_subcommand', None)
         self.subcommand_passed = attrs.pop('subcommand_passed', None)
+        self.command_failed = attrs.pop('command_failed', True)
         self._state = self.message._state
 
     @asyncio.coroutine