fail an alias when an ${} var isn't found

src/core_modules/aliases.py

@@ -3,6 +3,8 @@ from src import EventManager, ModuleManager, utils
 
 SETTING_PREFIX = "command-alias-"
 
+class VariableKeyError(KeyError):
+    pass
 class Module(ModuleManager.BaseModule):
     def _arg_replace(self, s, args_split, kwargs):
         vars = {}
@@ -11,7 +13,11 @@ class Module(ModuleManager.BaseModule):
             vars["%d-" % i] = " ".join(args_split[i:])
         vars["-"] = " ".join(args_split)
         vars.update(kwargs)
-        return utils.parse.format_token_replace(s, vars)
+
+        not_found, new_s = utils.parse.format_token_replace(s, vars)
+        if not_found:
+            raise VariableKeyError(f"not found: {not_found!r}")
+        return new_s
 
     def _get_alias(self, server, target, command):
         setting = "%s%s" % (SETTING_PREFIX, command)
@@ -45,9 +51,14 @@ class Module(ModuleManager.BaseModule):
             if event["command"].args:
                 given_args = event["command"].args.split(" ")
 
-            event["command"].command = alias
-            event["command"].args = self._arg_replace(alias_args, given_args,
-                event["kwargs"])
+            try:
+                event["command"].args = self._arg_replace(alias_args,
+                    given_args, event["kwargs"])
+            except VariableKeyError:
+                pass
+            else:
+                event["command"].command = alias
+
 
     @utils.hook("received.command.alias",
         permission="alias")

src/utils/parse/__init__.py

@@ -131,7 +131,7 @@ def format_tokens(s: str, sigil: str="$"
     return tokens
 
 def format_token_replace(s: str, vars: typing.Dict[str, str],
-        sigil: str="$") -> str:
+        sigil: str="$") -> typing.Tuple[typing.List[str], str]:
     vars = vars.copy()
     vars.update({sigil: sigil})
 
@@ -140,7 +140,10 @@ def format_token_replace(s: str, vars: typing.Dict[str, str],
     tokens.sort(key=lambda x: x[0])
     tokens.reverse()
 
+    not_found: typing.List[str] = []
     for start, end, token in tokens:
         if token in vars:
             s = s[:start] + vars[token] + s[end+1:]
-    return s
+        else:
+            not_found += token
+    return not_found, s