Add --strict-type-check-only flag

Author: brianschubert

docs/source/stubtest.rst

@@ -183,6 +183,11 @@ The rest of this section documents the command line interface of stubtest.
 
     Ignore errors for whether an argument should or shouldn't be positional-only
 
+.. option:: --strict-type-check-only
+
+    Require :py:func:`@type_check_only <typing.type_check_only>` on private types
+    that are not present at runtime.
+
 .. option:: --allowlist FILE
 
     Use file as an allowlist. Can be passed multiple times to combine multiple

mypy/stubtest.py

@@ -146,6 +146,11 @@ def is_disjoint_base_related(self) -> bool:
         # TODO: This is hacky, use error codes or something more resilient
         return "@disjoint_base" in self.message
 
+    def is_private_type_check_only_related(self) -> bool:
+        """Whether or not the error is related to @type_check_only on private types."""
+        # TODO: This is hacky, use error codes or something more resilient
+        return self.message.endswith('Maybe mark it as "@type_check_only"?')
+
     def get_description(self, concise: bool = False) -> str:
         """Returns a description of the error.
 
@@ -2330,6 +2335,7 @@ class _Arguments:
     ignore_missing_stub: bool
     ignore_positional_only: bool
     ignore_disjoint_bases: bool
+    strict_type_check_only: bool
     allowlist: list[str]
     generate_allowlist: bool
     ignore_unused_allowlist: bool
@@ -2429,6 +2435,8 @@ def warning_callback(msg: str) -> None:
             if error.object_desc in allowlist:
                 allowlist[error.object_desc] = True
                 continue
+            if not args.strict_type_check_only and error.is_private_type_check_only_related():
+                continue
             is_allowlisted = False
             for w in allowlist:
                 if allowlist_regexes[w].fullmatch(error.object_desc):
@@ -2522,6 +2530,11 @@ def parse_options(args: list[str]) -> _Arguments:
         action="store_true",
         help="Disable checks for PEP 800 @disjoint_base classes",
     )
+    parser.add_argument(
+        "--strict-type-check-only",
+        action="store_true",
+        help="Require @type_check_only on private types that are not present at runtime",
+    )
     parser.add_argument(
         "--allowlist",
         "--whitelist",