Prohibit zero-length prefixes in [p]set [server]prefix (#6013)

Co-authored-by: Kreusada Ignad Amredes <67752638+Kreusada@users.noreply.github.com>

redbot/core/core_commands.py

@@ -117,6 +117,7 @@ _ = i18n.Translator("Core", __file__)
 TokenConverter = commands.get_dict_converter(delims=[" ", ",", ";"])
 
 MAX_PREFIX_LENGTH = 25
+MINIMUM_PREFIX_LENGTH = 1
 
 
 class CoreLogic:
@@ -4052,6 +4053,24 @@ class Core(commands.commands._RuleDropper, commands.Cog, CoreLogic):
                 _("Prefixes cannot start with '/', as it conflicts with Discord's slash commands.")
             )
             return
+        if any(len(x) < MINIMUM_PREFIX_LENGTH for x in prefixes):
+            await ctx.send(
+                _(
+                    "Warning: A prefix is below the recommended length (1 character).\n"
+                    "Do you want to continue?"
+                )
+                + " (yes/no)"
+            )
+            pred = MessagePredicate.yes_or_no(ctx)
+            try:
+                await self.bot.wait_for("message", check=pred, timeout=30)
+            except asyncio.TimeoutError:
+                await ctx.send(_("Response timed out."))
+                return
+            else:
+                if pred.result is False:
+                    await ctx.send(_("Cancelled."))
+                    return
         if any(len(x) > MAX_PREFIX_LENGTH for x in prefixes):
             await ctx.send(
                 _(
@@ -4111,6 +4130,9 @@ class Core(commands.commands._RuleDropper, commands.Cog, CoreLogic):
                 _("Prefixes cannot start with '/', as it conflicts with Discord's slash commands.")
             )
             return
+        if any(len(x) < MINIMUM_PREFIX_LENGTH for x in prefixes):
+            await ctx.send(_("You cannot have a prefix shorter than 1 character."))
+            return
         if any(len(x) > MAX_PREFIX_LENGTH for x in prefixes):
             await ctx.send(_("You cannot have a prefix longer than 25 characters."))
             return