fix: enormously obscure bug in the typing module

Author: e3rd

docs/Changelog.md

@@ -1,6 +1,6 @@
 # Changelog
 
-## 1.1.0 (2025-09-11)
+## 1.1.0 (2025-09-12)
 * CHANGED – some [`run`][mininterface.run] arguments are no longer positional and can only be passed as keyword arguments
 * feat: interactive CLI (nested configuration missing fields dialogs)
 * feat: [`run`][mininterface.run] add_version, add_version_package, add_quiet flags

mininterface/__init__.py

@@ -1,4 +1,3 @@
-
 from ._lib.run import run
 from ._mininterface import Mininterface
 from .exceptions import Cancelled

mininterface/tag/flag.py

@@ -204,8 +204,6 @@ class Env:
 # for `Annotated[Blank4[int], Literal[fn()]]` for static literal values
 
 
-
-
 if not TYPE_CHECKING:
     # In runtime, flag must not be an Annotated but a full class.
     # When type checking, flag must not be a full class otherwise
@@ -283,4 +281,4 @@ def instance_from_str(args):
             instance_from_str=lambda args: instance_from_str(args),
             is_instance=lambda ins: ins is None or isinstance(ins, types),
             str_from_instance=lambda ins: [str(ins) + f" / or if left blank: {default_val}"],
-        )
+        )

mininterface/tag/tag_factory.py

@@ -4,7 +4,7 @@
 from pathlib import Path
 from typing import Any, Iterable, Literal, Type, get_origin, get_type_hints
 
-from annotated_types import BaseMetadata, GroupedMetadata
+from annotated_types import BaseMetadata, GroupedMetadata, Len
 
 from . import DatetimeTag, SelectTag, Tag
 from .callback_tag import CallbackTag
@@ -105,11 +105,48 @@ def tag_factory(
                                     new.annotation = annotation or field_type.__origin__
                                 # Annotated[date, Tag(name="hello")] = datetime.fromisoformat(...) -> DatetimeTag(date=True)
                                 tag = tag_assure_type(new._fetch_from(Tag(*args, **kwargs), include_ref=True))
-                            elif isinstance(metadata, (BaseMetadata, GroupedMetadata)):
+                            elif isinstance(metadata, (BaseMetadata, Len)):
+                                # Why not checking `GroupedMetadata` instead of `Len`? See below. You won't believe.
                                 validators.append(metadata)
     if not tag:
         tag = tag_assure_type(Tag(val, description, annotation, *args, **kwargs))
 
     if validators:  # we prepend annotated_types validators to the current validator
         tag._add_validation(validators)
     return tag
+
+# NOTE I'd like to check `GroupedMetadata` instead of the `Len` (the only currently supported GroupedMetadata).
+# However, that's not possible because a mere checking of some things from the typing module,
+# like `isinstance(Literal[2], GroupedMetadata)`, will add a trailing __annotations__ to some objects in the typing module.
+#
+# Once upon a day, I thought I debug a pretty obscure case from tyro, concerning global imports of a primitive specs registry
+# when doing tests in paralel. The bug appeared reliably but only on the server, never on the localhost, and for Python3.12+
+# only (which I am running to on localhost). I find out a test fails when another specific test is there. But it was not the end,
+# the problem lied not in tyro but deeper, some chances are there is a bug in the Python itself. It turned out
+# a mere presence of a Literal in an Annotated statement cause a bug in an independent test.
+#
+# The dark magic happens in typing._proto_hook at line
+# `getattr(base, '__annotations__', {})`
+# while `base = _LiteralSpecialForm)`
+#
+# This utterly obscure case will make tyro cycle when handling unions,
+# Union must not have trailing __annotations__
+# `runm([Subc1, Subc2])` # will cycle
+# So the code breaks up a different time on another place. Tremendous.
+#
+# https://github.com/annotated-types/annotated-types/issues/94
+#
+# ```python
+# from typing import Literal, Optional, Union
+# from annotated_types import GroupedMetadata, Len
+# print(hasattr(Union[1, 2],"__annotations__")) # False
+# print(hasattr(Optional,"__annotations__")) # False
+# print(hasattr(Literal,"__annotations__")) # False
+#
+# isinstance(Literal, GroupedMetadata)
+#
+# print(Union[1, 2].__annotations__) # {}
+# print(Optional.__annotations__) # {}
+# print(Literal.__annotations__) # {}
+# ````
+#