gh-95991: Add some infrastructure for testing Limited API in _testcapi

Doc/library/test.rst

@@ -794,6 +794,12 @@ The :mod:`test.support` module defines the following functions:
  Decorator for only running the test if :data:`HAVE_DOCSTRINGS`.
 
 
+.. decorator:: requires_limited_api
+
+ Decorator for only running the test if :ref:`Limited C API <stable>`
+ is available.
+
+
 .. decorator:: cpython_only
 
  Decorator for tests only applicable to CPython.

Lib/test/support/__init__.py

@@ -46,6 +46,7 @@
  "anticipate_failure", "load_package_tests", "detect_api_mismatch",
  "check__all__", "skip_if_buggy_ucrt_strfptime",
  "check_disallow_instantiation", "check_sanitizer", "skip_if_sanitizer",
+ "requires_limited_api",
  # sys
  "is_jython", "is_android", "is_emscripten", "is_wasi",
  "check_impl_detail", "unix_shell", "setswitchinterval",
@@ -1069,6 +1070,15 @@ def refcount_test(test):
  return no_tracing(cpython_only(test))
 
 
+def requires_limited_api(test):
+ try:
+ import _testcapi
+ except ImportError:
+ return unittest.skip('needs _testcapi module')(test)
+ return unittest.skipUnless(
+ _testcapi.LIMITED_API_AVAILABLE, 'needs Limited API support')(test)
+
+
 def _filter_suite(suite, pred):
  """Recursively filter test cases in a suite based on a predicate."""
  newtests = []

Lib/test/test_call.py

@@ -1,5 +1,5 @@
 import unittest
-from test.support import cpython_only
+from test.support import cpython_only, requires_limited_api
 try:
  import _testcapi
 except ImportError:
@@ -760,9 +760,7 @@ def __call__(self, *args):
  self.assertEqual(expected, meth(*args1, **kwargs))
  self.assertEqual(expected, wrapped(*args, **kwargs))
 
- @unittest.skipIf(
- hasattr(sys, 'getobjects'),
- "Limited API is not compatible with Py_TRACE_REFS")
+ @requires_limited_api
  def test_vectorcall_limited(self):
  from _testcapi import pyobject_vectorcall
  obj = _testcapi.LimitedVectorCallClass()

Modules/_testcapi/parts.h

@@ -1,9 +1,36 @@
-#include "Python.h"
+#ifndef Py_TESTCAPI_PARTS_H
+#define Py_TESTCAPI_PARTS_H
+
+#include "pyconfig.h" // for Py_TRACE_REFS
+
+// Figure out if Limited API is available for this build. If it isn't we won't
+// build tests for it.
+// Currently, only Py_TRACE_REFS disables Limited API.
+#ifdef Py_TRACE_REFS
+#undef LIMITED_API_AVAILABLE
+#else
+#define LIMITED_API_AVAILABLE 1
+#endif
 
-/* Always enable assertions */
+// Always enable assertions
 #undef NDEBUG
 
+#if !defined(LIMITED_API_AVAILABLE) && defined(Py_LIMITED_API)
+// Limited API being unavailable means that with Py_LIMITED_API defined
+// we can't even include Python.h.
+// Do nothing; the .c file that defined Py_LIMITED_API should also do nothing.
+
+#else
+
+#include "Python.h"
+
 int _PyTestCapi_Init_Vectorcall(PyObject *module);
-int _PyTestCapi_Init_VectorcallLimited(PyObject *module);
 int _PyTestCapi_Init_Heaptype(PyObject *module);
 int _PyTestCapi_Init_Unicode(PyObject *module);
+
+#ifdef LIMITED_API_AVAILABLE
+int _PyTestCapi_Init_VectorcallLimited(PyObject *module);
+#endif // LIMITED_API_AVAILABLE
+
+#endif
+#endif // Py_TESTCAPI_PARTS_H

Modules/_testcapi/vectorcall_limited.c

@@ -1,18 +1,8 @@
-#include "pyconfig.h" // Py_TRACE_REFS
-
-#ifdef Py_TRACE_REFS
-
-// Py_TRACE_REFS is incompatible with Limited API
+#define Py_LIMITED_API 0x030c0000 // 3.12
 #include "parts.h"
-int
-_PyTestCapi_Init_VectorcallLimited(PyObject *m) {
- return 0;
-}
 
-#else
+#ifdef LIMITED_API_AVAILABLE
 
-#define Py_LIMITED_API 0x030c0000 // 3.12
-#include "parts.h"
 #include "structmember.h" // PyMemberDef
 
 /* Test Vectorcall in the limited API */
@@ -89,4 +79,4 @@ _PyTestCapi_Init_VectorcallLimited(PyObject *m) {
  return 0;
 }
 
-#endif // Py_TRACE_REFS
+#endif // LIMITED_API_AVAILABLE

Modules/_testcapimodule.c

@@ -6544,16 +6544,22 @@ PyInit__testcapi(void)
  if (_PyTestCapi_Init_Vectorcall(m) < 0) {
  return NULL;
  }
- if (_PyTestCapi_Init_VectorcallLimited(m) < 0) {
- return NULL;
- }
  if (_PyTestCapi_Init_Heaptype(m) < 0) {
  return NULL;
  }
  if (_PyTestCapi_Init_Unicode(m) < 0) {
  return NULL;
  }
 
+#ifndef LIMITED_API_AVAILABLE
+ PyModule_AddObjectRef(m, "LIMITED_API_AVAILABLE", Py_False);
+#else
+ PyModule_AddObjectRef(m, "LIMITED_API_AVAILABLE", Py_True);
+ if (_PyTestCapi_Init_VectorcallLimited(m) < 0) {
+ return NULL;
+ }
+#endif
+
  PyState_AddModule(m, &_testcapimodule);
  return m;
 }

PCbuild/_testcapi.vcxproj

@@ -107,6 +107,10 @@
  <Project>{cf7ac3d1-e2df-41d2-bea6-1e2556cdea26}</Project>
  <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
  </ProjectReference>
+ <ProjectReference Include="python3dll.vcxproj">
+ <Project>{885d4898-d08d-4091-9c40-c700cfe3fc5a}</Project>
+ <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
+ </ProjectReference>
  </ItemGroup>
  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
  <ImportGroup Label="ExtensionTargets">