Fix __post_init__() internal error

Author: ikonst

mypy/checker.py

@@ -1076,6 +1076,8 @@ def check_func_item(
 
         if name == "__exit__":
             self.check__exit__return_type(defn)
+        # TODO: the following logic should move to the dataclasses plugin
+        #  https://github.com/python/mypy/issues/15515
         if name == "__post_init__":
             if dataclasses_plugin.is_processed_dataclass(defn.info):
                 dataclasses_plugin.check_post_init(self, defn, defn.info)

mypy/nodes.py

@@ -515,7 +515,6 @@ def __init__(self) -> None:
         # Original, not semantically analyzed type (used for reprocessing)
         self.unanalyzed_type: mypy.types.ProperType | None = None
         # If method, reference to TypeInfo
-        # TODO: Type should be Optional[TypeInfo]
         self.info = FUNC_NO_INFO
         self.is_property = False
         self.is_class = False

mypy/plugins/dataclasses.py

@@ -1070,8 +1070,8 @@ def replace_function_sig_callback(ctx: FunctionSigContext) -> CallableType:
     )
 
 
-def is_processed_dataclass(info: TypeInfo | None) -> bool:
-    return info is not None and "dataclass" in info.metadata
+def is_processed_dataclass(info: TypeInfo) -> bool:
+    return info and "dataclass" in info.metadata
 
 
 def check_post_init(api: TypeChecker, defn: FuncItem, info: TypeInfo) -> None: