gracefully handle invalid regexes

nomen/utils.py

@@ -4,6 +4,7 @@ from itertools import chain
 
 import re2 as re
 from disnake import ChannelType
+from disnake.ext.commands import BadArgument
 
 log = logging.getLogger("nomen.utils")
 
@@ -87,9 +88,14 @@ def compile_keyword(keyword, regex):
     if not regex:
         keyword = re.escape(keyword)
 
+    try:
         reg = re.compile(rf"(?i)\b{keyword}\b")
         regex_cache[(keyword, regex)] = reg
         return reg
+    except re._re2.Error:
+        raise BadArgument(
+            "Invalid regex. Nomen only supports regexes that [re2](<https://github.com/google/re2>) can parse."
+        )
 
 
 def contains(string, keyword, regex):