Throw error if no permissions to post in log channel

If the bot has no permission to send messages to the log channel, we throw an error in DMs

src/pluralkit/bot/commands/mod_commands.py

@@ -17,5 +17,23 @@ async def set_log(ctx: CommandContext):
             raise CommandError("Channel not found.")
         channel_id = channel.id
 
-    await db.update_server(ctx.conn, server.id, logging_channel_id=channel_id)
-    await ctx.reply_ok("Updated logging channel." if channel_id else "Cleared logging channel.")
+    # Check if we can send messages in the log channel. If not, raise an error
+    # in the channel. If we don't have permission to do that, DM the user who sent
+    # the command and skip updating the log channel in the database
+    try:
+        # Send a message in the log channel to confirm and also to test permission.
+        if channel_id:
+            await channel.send("✅ PluralKit will now log proxied messages in this channel.")
+        await db.update_server(ctx.conn, server.id, logging_channel_id=channel_id)
+        await ctx.reply_ok("Updated logging channel." if channel_id else "Cleared logging channel.")
+    except discord.Forbidden:
+        # Try (heh) to let the user know we don't have permission to post there
+        error_msg = "PluralKit doesn't have permission to read and/or send messages in that channel! Please check my permissions then try again."
+        raise CommandError(error_msg)
+        # nested try asdhfakjd
+        try:
+            # Failing that, we DM the user who issued the command
+            await ctx.message.author.send(await CommandError(error_msg))
+        except discord.Forbidden:
+            # and if that fails, well... crap, nothing we can do
+            pass