conflict fixes

discord/ext/commands/converter.py

@@ -263,7 +263,7 @@ class MessageConverter(Converter):
     3. Lookup by message URL
 
     .. versionchanged:: 1.5
-         Raise :exc:`.ChannelNotFound`, `MessageNotFound` or `ChannelNotReadable` instead of generic :exc:`.BadArgument`
+         Raise :exc:`.ChannelNotFound`, :exc:`.MessageNotFound` or :exc:`.ChannelNotReadable` instead of generic :exc:`.BadArgument`
     """
     async def convert(self, ctx, argument):
         id_regex = re.compile(r'(?:(?P<channel_id>[0-9]{15,21})-)?(?P<message_id>[0-9]{15,21})$')

discord/ext/commands/core.py

@@ -144,7 +144,7 @@ class Command(_BaseCommand):
         The long help text for the command.
     brief: Optional[:class:`str`]
         The short help text for the command.
-    usage: :class:`str`
+    usage: Optional[:class:`str`]
         A replacement for arguments in the default help text.
     aliases: Union[List[:class:`str`], Tuple[:class:`str`]]
         The list of aliases the command can be invoked under.
@@ -778,17 +778,22 @@ class Command(_BaseCommand):
         if not await self.can_run(ctx):
             raise CheckFailure('The check functions for command {0.qualified_name} failed.'.format(self))
 
-        if self.cooldown_after_parsing:
-            await self._parse_arguments(ctx)
-            self._prepare_cooldowns(ctx)
-        else:
-            self._prepare_cooldowns(ctx)
-            await self._parse_arguments(ctx)
-
         if self._max_concurrency is not None:
             await self._max_concurrency.acquire(ctx)
 
-        await self.call_before_hooks(ctx)
+        try:
+            if self.cooldown_after_parsing:
+                await self._parse_arguments(ctx)
+                self._prepare_cooldowns(ctx)
+            else:
+                self._prepare_cooldowns(ctx)
+                await self._parse_arguments(ctx)
+
+            await self.call_before_hooks(ctx)
+        except:
+            if self._max_concurrency is not None:
+                await self._max_concurrency.release(ctx)
+            raise
 
     def is_on_cooldown(self, ctx):
         """Checks whether the command is currently on cooldown.
@@ -1140,6 +1145,7 @@ class GroupMixin:
         self.all_commands[command.name] = command
         for alias in command.aliases:
             if alias in self.all_commands:
+                self.remove_command(command.name)
                 raise CommandRegistrationError(alias, alias_conflict=True)
             self.all_commands[alias] = command
 
@@ -1172,7 +1178,12 @@ class GroupMixin:
 
         # we're not removing the alias so let's delete the rest of them.
         for alias in command.aliases:
-            self.all_commands.pop(alias, None)
+            cmd = self.all_commands.pop(alias, None)
+            # in the case of a CommandRegistrationError, an alias might conflict
+            # with an already existing command. If this is the case, we want to
+            # make sure the pre-existing command is not removed.
+            if cmd not in (None, command):
+                self.all_commands[alias] = cmd
         return command
 
     def walk_commands(self):

discord/ext/commands/errors.py

@@ -289,7 +289,7 @@ class ChannelNotFound(BadArgument):
 
     Attributes
     -----------
-    channel: :class:`str`
+    argument: :class:`str`
         The channel supplied by the caller that was not found
     """
     def __init__(self, argument):