Add default validation failure expression config

nonebot/command/argfilter/__init__.py

@@ -1,4 +1,9 @@
-from typing import Callable, Any, Awaitable, Union
+from typing import Callable, Any, Awaitable, Union, List, TYPE_CHECKING
+
+from nonebot.helpers import render_expression
+
+if TYPE_CHECKING:
+    from nonebot.command import CommandSession
 
 ArgFilter_T = Callable[[Any], Union[Any, Awaitable[Any]]]
 
@@ -6,3 +11,25 @@ ArgFilter_T = Callable[[Any], Union[Any, Awaitable[Any]]]
 class ValidateError(ValueError):
     def __init__(self, message=None):
         self.message = message
+
+
+async def run_arg_filters(session: 'CommandSession',
+                          arg_filters: List[ArgFilter_T]) -> None:
+    arg = session.current_arg
+    for f in arg_filters:
+        try:
+            res = f(arg)
+            if isinstance(res, Awaitable):
+                res = await res
+            arg = res
+        except ValidateError as e:
+            # validation failed
+            failure_message = e.message
+            if failure_message is None:
+                failure_message = render_expression(
+                    session.bot.config.DEFAULT_VALIDATION_FAILURE_EXPRESSION
+                )
+            session.pause(failure_message)
+
+    # passed all filters
+    session.state[session.current_key] = arg