Implement command for confirming command sequences.

First attempt at implementing a confirmation command intended for use in
command sequences.

When called (optionally with a free-form string message), prompts the
user for confirmation. If the user declines, a SequenceCanceled
exception is raised, which trickles up the error handling into
apply_commandline where it is explicitly caught outside the common error
handler. This aborts the execution of subsequent commands in the
commandline, but does not show up as an error in the log.

Closes #1368

alot/commands/__init__.py

@@ -33,6 +33,13 @@ class CommandCanceled(Exception):
     pass
 
 
+class SequenceCanceled(Exception):
+    """ Exception triggered when a command sequence has been cancelled by the
+    confirmsequence command
+    """
+    pass
+
+
 COMMANDS = {
     'search': {},
     'envelope': {},

alot/commands/globals.py

@@ -17,7 +17,7 @@
 import urwid
 
 from . import Command, registerCommand
-from . import CommandCanceled
+from . import CommandCanceled, SequenceCanceled
 from .utils import update_keys
 from .. import commands
 
@@ -1178,3 +1178,30 @@ def apply(self, ui):
         # flush index
         if self.flush:
             ui.apply_command(commands.globals.FlushCommand())
+
+
+@registerCommand(
+    MODE, 'confirmsequence',
+    arguments=[
+        (['msg'], {'help': 'Additional message to prompt',
+                   'nargs': '*'})
+    ],
+    help="prompt to confirm a sequence of commands")
+class ConfirmCommand(Command):
+    """Prompt user to confirm a sequence of commands."""
+
+    def __init__(self, msg=None, **kwargs):
+        """
+        :param msg: Additional message to prompt the user with
+        :type msg: List[str]
+        """
+        super(ConfirmCommand, self).__init__(**kwargs)
+        if not msg:
+            self.msg = "Confirm sequence?"
+        else:
+            self.msg = "Confirm sequence: {}?".format(" ".join(msg))
+
+    async def apply(self, ui):
+        if (await ui.choice(self.msg, select='yes', cancel='no',
+                            msg_position='left')) == 'no':
+            raise SequenceCanceled()

alot/ui.py

@@ -16,7 +16,7 @@
 from .buffers import SearchBuffer
 from .commands import globals
 from .commands import commandfactory
-from .commands import CommandCanceled
+from .commands import CommandCanceled, SequenceCanceled
 from .commands import CommandParseError
 from .helper import split_commandline
 from .helper import string_decode
@@ -145,6 +145,10 @@ def _error_handler(self, exception):
             self.notify(str(exception), priority='error')
         elif isinstance(exception, CommandCanceled):
             self.notify("operation cancelled", priority='error')
+        elif isinstance(exception, SequenceCanceled):
+            # This exception needs to trickle up to apply_commandline,
+            # then be handled explicitly.
+            raise exception
         else:
             logging.error(traceback.format_exc())
             msg = "{}\n(check the log for details)".format(exception)
@@ -267,7 +271,11 @@ def apply_this_command(cmdstring):
             for c in split_commandline(cmdline):
                 await apply_this_command(c)
         except Exception as e:
-            self._error_handler(e)
+            if isinstance(e, SequenceCanceled):
+                self.notify("sequence of operations cancelled",
+                            priority='error')
+            else:
+                self._error_handler(e)
 
     @staticmethod
     def _unhandled_input(key):

docs/source/usage/modes/global.rst

@@ -77,6 +77,16 @@ The following commands are available globally:
         :---omit_signature: do not add signature
         :---spawn: spawn editor in new terminal
 
+.. _cmd.global.confirmsequence:
+
+.. describe:: confirmsequence
+
+    prompt to confirm a sequence of commands
+
+    argument
+        Additional message to prompt
+
+
 .. _cmd.global.exit:
 
 .. describe:: exit