Refactor the special ErrorCode function into a static method.

I think this also fixes a bug.

Author: wyattscarpenter

mypy/errorcodes.py

@@ -34,8 +34,17 @@ def __init__(
             sub_code_map[sub_code_of.code].add(code)
         error_codes[code] = self
 
-    def is_import_related_code(self) -> bool:
-        return IMPORT in (self.code, self.sub_code_of)
+    @staticmethod
+    def is_code_or_sub_code_of(
+        possible_child_code: ErrorCode | None, possible_parent_code: ErrorCode
+    ) -> bool:
+        """Check if the first code ⊆ the second code, so to speak.
+        If None is supplied as the first argument, this is always false.
+        Again, to quote the assert in ErrorCode above, "Nested subcategories are not supported"."""
+        if possible_child_code is None:
+            return False
+        else:
+            return possible_parent_code in (possible_child_code, possible_child_code.sub_code_of)
 
     def __str__(self) -> str:
         return f"<ErrorCode {self.code}>"

mypy/errors.py

@@ -11,7 +11,7 @@
 
 from mypy import errorcodes as codes
 from mypy.error_formatter import ErrorFormatter
-from mypy.errorcodes import ErrorCode, mypy_error_codes
+from mypy.errorcodes import IMPORT, ErrorCode, mypy_error_codes
 from mypy.nodes import Context
 from mypy.options import Options
 from mypy.scope import Scope
@@ -583,7 +583,7 @@ def _add_error_info(self, file: str, info: ErrorInfo) -> None:
         self.error_info_map[file].append(info)
         if info.blocker:
             self.has_blockers.add(file)
-        if info.code is not None and info.code.is_import_related_code():
+        if ErrorCode.is_code_or_sub_code_of(info.code, IMPORT):
             self.seen_import_error = True
 
     def get_watchers(self) -> Iterator[ErrorWatcher]:
@@ -630,7 +630,7 @@ def add_error_info(self, info: ErrorInfo) -> None:
             self.only_once_messages.add(info.message)
         if (
             self.seen_import_error
-            and (info.code is None or (not info.code.is_import_related_code()))
+            and ErrorCode.is_code_or_sub_code_of(info.code, IMPORT)
             and self.has_many_errors()
         ):
             # Missing stubs can easily cause thousands of errors about