[commands] Get guild_id from message link for message converters

discord/ext/commands/converter.py

@@ -326,22 +326,42 @@ class PartialMessageConverter(Converter[discord.PartialMessage]):
     """
 
     @staticmethod
-    def _get_id_matches(argument):
+    def _get_id_matches(ctx, argument):
         id_regex = re.compile(r'(?:(?P<channel_id>[0-9]{15,20})-)?(?P<message_id>[0-9]{15,20})$')
         link_regex = re.compile(
             r'https?://(?:(ptb|canary|www)\.)?discord(?:app)?\.com/channels/'
-            r'(?:[0-9]{15,20}|@me)'
+            r'(?P<guild_id>[0-9]{15,20}|@me)'
             r'/(?P<channel_id>[0-9]{15,20})/(?P<message_id>[0-9]{15,20})/?$'
         )
         match = id_regex.match(argument) or link_regex.match(argument)
         if not match:
             raise MessageNotFound(argument)
-        channel_id = match.group('channel_id')
-        return int(match.group('message_id')), int(channel_id) if channel_id else None
+        data = match.groupdict()
+        channel_id = discord.utils._get_as_snowflake(data, 'channel_id')
+        message_id = int(data['message_id'])
+        guild_id = data.get('guild_id')
+        if guild_id is None:
+            guild_id = ctx.guild and ctx.guild.id
+        elif guild_id == '@me':
+            guild_id = None
+        else:
+            guild_id = int(guild_id)
+        return guild_id, message_id, channel_id
+
+    @staticmethod
+    def _resolve_channel(ctx, guild_id, channel_id):
+        if guild_id is not None:
+            guild = ctx.bot.get_guild(guild_id)
+            if guild is not None and channel_id is not None:
+                return guild.get_channel(channel_id)
+            else:
+                return None
+        else:
+            return ctx.bot.get_channel(channel_id) if channel_id else ctx.channel
 
     async def convert(self, ctx: Context, argument: str) -> discord.PartialMessage:
-        message_id, channel_id = self._get_id_matches(argument)
-        channel = ctx.bot.get_channel(channel_id) if channel_id else ctx.channel
+        guild_id, message_id, channel_id = self._get_id_matches(ctx, argument)
+        channel = self._resolve_channel(ctx, guild_id, channel_id)
         if not channel:
             raise ChannelNotFound(channel_id)
         return discord.PartialMessage(channel=channel, id=message_id)
@@ -363,11 +383,11 @@ class MessageConverter(IDConverter[discord.Message]):
     """
 
     async def convert(self, ctx: Context, argument: str) -> discord.Message:
-        message_id, channel_id = PartialMessageConverter._get_id_matches(argument)
+        guild_id, message_id, channel_id = PartialMessageConverter._get_id_matches(ctx, argument)
         message = ctx.bot._connection._get_message(message_id)
         if message:
             return message
-        channel = ctx.bot.get_channel(channel_id) if channel_id else ctx.channel
+        channel = PartialMessageConverter._resolve_channel(ctx, guild_id, channel_id)
         if not channel:
             raise ChannelNotFound(channel_id)
         try: