✅ add test cases

nonebot/params.py

@@ -1,5 +1,6 @@
 import asyncio
 import inspect
+from typing_extensions import Literal
 from typing import Any, Dict, List, Tuple, Callable, Optional, cast
 from contextlib import AsyncExitStack, contextmanager, asynccontextmanager
 
@@ -200,7 +201,7 @@ async def _event_message(event: Event) -> Message:
     return event.get_message()
 
 
-def EventMessage() -> Message:
+def EventMessage() -> Any:
     return Depends(_event_message)
 
 
@@ -260,7 +261,7 @@ def _command_arg(state=State()) -> Message:
     return state[PREFIX_KEY][CMD_ARG_KEY]
 
 
-def CommandArg() -> Message:
+def CommandArg() -> Any:
     return Depends(_command_arg, use_cache=False)
 
 
@@ -332,6 +333,44 @@ def LastReceived(default: Any = None) -> Any:
     return Depends(_last_received, use_cache=False)
 
 
+class ArgInner:
+    def __init__(
+        self, key: Optional[str], type: Literal["event", "message", "str"]
+    ) -> None:
+        self.key = key
+        self.type = type
+
+
+def Arg(key: Optional[str] = None) -> Any:
+    return ArgInner(key, "message")
+
+
+def ArgEvent(key: Optional[str] = None) -> Any:
+    return ArgInner(key, "event")
+
+
+def ArgStr(key: Optional[str] = None) -> Any:
+    return ArgInner(key, "str")
+
+
+class ArgParam(Param):
+    @classmethod
+    def _check_param(
+        cls, dependent: Dependent, name: str, param: inspect.Parameter
+    ) -> Optional["ArgParam"]:
+        if isinstance(param.default, ArgInner):
+            return cls(Required, key=param.default.key or name, type=param.default.type)
+
+    async def _solve(self, matcher: "Matcher", **kwargs: Any) -> Any:
+        event = matcher.get_arg(self.extra["key"])
+        if self.extra["type"] == "event":
+            return event
+        elif self.extra["type"] == "message":
+            return event.get_message()
+        else:
+            return matcher.get_arg_str(self.extra["key"])
+
+
 class ExceptionParam(Param):
     @classmethod
     def _check_param(