🐛 Fix MessageTemplate improper behavior when no format spec (#947)

* 🧪 Add a test to figure out bug in #938

* ♻️ 🐛 Refactor rich message template formatting, fix #938

nonebot/internal/adapter/template.py

@@ -49,7 +49,9 @@ class MessageTemplate(Formatter, Generic[TF]):
     ) -> None:
         ...
 
-    def __init__(self, template, factory=str) -> None:
+    def __init__(  # type:ignore
+        self, template, factory=str
+    ) -> None:  # TODO: fix type hint here
         self.template: TF = template
         self.factory: Type[TF] = factory
         self.format_specs: Dict[str, FormatSpecFunc] = {}
@@ -72,25 +74,37 @@ class MessageTemplate(Formatter, Generic[TF]):
         return self._format([], mapping)
 
     def _format(self, args: Sequence[Any], kwargs: Mapping[str, Any]) -> TF:
-        msg = self.factory()
+        full_message = self.factory()
+        used_args, arg_index = set(), 0
+
         if isinstance(self.template, str):
-            msg += self.vformat(self.template, args, kwargs)
+            msg, arg_index = self._vformat(
+                self.template, args, kwargs, used_args, arg_index
+            )
+            full_message += msg
         elif isinstance(self.template, self.factory):
             template = cast("Message[MessageSegment]", self.template)
             for seg in template:
-                msg += self.vformat(str(seg), args, kwargs) if seg.is_text() else seg
+                if not seg.is_text():
+                    full_message += seg
+                else:
+                    msg, arg_index = self._vformat(
+                        str(seg), args, kwargs, used_args, arg_index
+                    )
+                    full_message += msg
         else:
             raise TypeError("template must be a string or instance of Message!")
 
-        return msg  # type:ignore
+        self.check_unused_args(list(used_args), args, kwargs)
+        return cast(TF, full_message)
 
     def vformat(
-        self, format_string: str, args: Sequence[Any], kwargs: Mapping[str, Any]
+        self,
+        format_string: str,
+        args: Sequence[Any],
+        kwargs: Mapping[str, Any],
     ) -> TF:
-        used_args = set()
-        result, _ = self._vformat(format_string, args, kwargs, used_args, 2)
-        self.check_unused_args(list(used_args), args, kwargs)
-        return result
+        raise NotImplementedError("`vformat` has merged into `_format`")
 
     def _vformat(
         self,
@@ -98,12 +112,8 @@ class MessageTemplate(Formatter, Generic[TF]):
         args: Sequence[Any],
         kwargs: Mapping[str, Any],
         used_args: Set[Union[int, str]],
-        recursion_depth: int,
         auto_arg_index: int = 0,
     ) -> Tuple[TF, int]:
-        if recursion_depth < 0:
-            raise ValueError("Max string recursion exceeded")
-
         results: List[Any] = [self.factory()]
 
         for (literal_text, field_name, format_spec, conversion) in self.parse(
@@ -143,23 +153,13 @@ class MessageTemplate(Formatter, Generic[TF]):
                 obj, arg_used = self.get_field(field_name, args, kwargs)
                 used_args.add(arg_used)
 
-                assert format_spec is not None
-
                 # do any conversion on the resulting object
                 obj = self.convert_field(obj, conversion) if conversion else obj
 
-                # expand the format spec, if needed
-                format_control, auto_arg_index = self._vformat(
-                    format_spec,
-                    args,
-                    kwargs,
-                    used_args,
-                    recursion_depth - 1,
-                    auto_arg_index,
-                )
-
                 # format the object and append to the result
-                formatted_text = self.format_field(obj, str(format_control))
+                formatted_text = (
+                    self.format_field(obj, format_spec) if format_spec else obj
+                )
                 results.append(formatted_text)
 
         return functools.reduce(self._add, results), auto_arg_index