wip

.github/workflows/check.yaml

@@ -26,7 +26,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - run: ./pw poetry config virtualenvs.in-project true
       - name: Set up cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         id: cache
         with:
           path: .venv
@@ -47,7 +47,7 @@ jobs:
           python-version: "3.9"
       - run: ./pw poetry config virtualenvs.in-project true
       - name: Set up cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         id: cache
         with:
           path: .venv

src/basedtyping/__init__.py

@@ -23,7 +23,6 @@
     _remove_dups_flatten,
     _SpecialForm,
     _tp_cache,
-    _type_check,
     cast,
 )
 
@@ -33,6 +32,7 @@
 from basedtyping import transformer
 from basedtyping.runtime_only import OldUnionType
 
+BASEDMYPY_TYPE_CHECKING = False
 if not TYPE_CHECKING:
     if sys.version_info >= (3, 11):
         from typing import _collect_parameters
@@ -57,6 +57,7 @@
     "TypeForm",
     "as_functiontype",
     "ForwardRef",
+    "BASEDMYPY_TYPE_CHECKING",
 )
 
 if TYPE_CHECKING:
@@ -453,11 +454,7 @@ def issubform(form: _Forms, forminfo: _Forms) -> bool:
     return issubclass(form, forminfo)  # type: ignore[arg-type]
 
 
-if TYPE_CHECKING:
-    # We pretend that it's an alias to Any so that it's slightly more compatible with
-    #  other tools, basedmypy will still utilize the SpecialForm over the TypeAlias.
-    Untyped: TypeAlias = Any  # type: ignore[no-any-explicit]
-else:
+if BASEDMYPY_TYPE_CHECKING or not TYPE_CHECKING:
 
     @_BasedSpecialForm
     def Untyped(  # noqa: N802
@@ -469,6 +466,10 @@ def Untyped(  # noqa: N802
         This is more specialized than ``Any`` and can help with gradually typing modules.
         """
         raise TypeError(f"{self} is not subscriptable")
+else:
+    # We pretend that it's an alias to Any so that it's slightly more compatible with
+    #  other tools
+    Untyped: TypeAlias = Any  # type: ignore[no-any-explicit]
 
 
 class _IntersectionGenericAlias(_BasedGenericAlias, _root=True):
@@ -529,7 +530,7 @@ def Intersection(self: _BasedSpecialForm, parameters: object) -> object:  # noqa
     if not isinstance(parameters, tuple):
         parameters = (parameters,)
     msg = "Intersection[arg, ...]: each arg must be a type."
-    parameters = tuple(_type_check(p, msg) for p in parameters)  # type: ignore[no-any-expr]
+    parameters = tuple(_type_check(p, msg) for p in parameters)
     parameters = _remove_dups_flatten(parameters)  # type: ignore[no-any-expr]
     if len(parameters) == 1:  # type: ignore[no-any-expr]
         return parameters[0]  # type: ignore[no-any-expr]
@@ -660,3 +661,31 @@ def _evaluate(
             recursive_guard: frozenset[str],  # noqa: ARG002
         ) -> object | None:
             return transformer._eval_direct(self, globalns, localns)
+
+
+def _type_check(arg: object, msg: str) -> object:
+    """Check that the argument is a type, and return it (internal helper).
+
+    As a special case, accept None and return type(None) instead. Also wrap strings
+    into ForwardRef instances. Consider several corner cases, for example plain
+    special forms like Union are not valid, while Union[int, str] is OK, etc.
+    The msg argument is a human-readable error message, e.g::
+
+        "Union[arg, ...]: arg should be a type."
+
+    We append the repr() of the actual value (truncated to 100 chars).
+    """
+    invalid_generic_forms = (Generic, typing.Protocol)
+
+    arg = _type_convert(arg)
+    if isinstance(arg, _GenericAlias) and arg.__origin__ in invalid_generic_forms:  # type: ignore[comparison-overlap]
+        raise TypeError(f"{arg} is not valid as type argument")
+    if arg in (Any, NoReturn, typing.Final, Untyped):
+        return arg
+    if isinstance(arg, _SpecialForm) or arg in (Generic, typing.Protocol):
+        raise TypeError(f"Plain {arg} is not valid as type argument")
+    if isinstance(arg, (type, TypeVar, ForwardRef)):
+        return arg
+    if not callable(arg):
+        raise TypeError(f"{msg} Got {arg!r:.100}.")
+    return arg

tests/test_basedspecialform.py

@@ -1,8 +1,5 @@
 from __future__ import annotations
 
-import sys
-
-import pytest
 from basedtyping import Intersection, TypeForm, Untyped
 
 
@@ -11,15 +8,6 @@ def test_basedgenericalias_intersection():
     assert None & TypeForm[int] == Intersection[None, TypeForm[int]]
 
 
-@pytest.mark.xfail(
-    sys.version_info >= (3, 9),
-    reason="""
-`typing._type_check` says:
-
-    if arg in (Any, LiteralString, NoReturn, Never, Self, TypeAlias):
-        return arg
-""",
-)
 def test_basedspecialform_intersection():
-    assert Untyped & None == Intersection[Untyped, None]  # type: ignore[no-any-expr]
-    assert None & Untyped == Intersection[Untyped, None]  # type: ignore[no-any-expr]
+    assert Untyped & None == Intersection[Untyped, None]
+    assert None & Untyped == Intersection[Untyped, None]