gh-127906: Test the limited C API in test_cppext (#127916)

Lib/test/test_cppext/__init__.py

@@ -41,12 +41,17 @@ def test_build_cpp11(self):
     def test_build_cpp14(self):
         self.check_build('_testcpp14ext', std='c++14')
 
-    def check_build(self, extension_name, std=None):
+    @support.requires_gil_enabled('incompatible with Free Threading')
+    def test_build_limited(self):
+        self.check_build('_testcppext_limited', limited=True)
+
+    def check_build(self, extension_name, std=None, limited=False):
         venv_dir = 'env'
         with support.setup_venv_with_pip_setuptools_wheel(venv_dir) as python_exe:
-            self._check_build(extension_name, python_exe, std=std)
+            self._check_build(extension_name, python_exe,
+                              std=std, limited=limited)
 
-    def _check_build(self, extension_name, python_exe, std):
+    def _check_build(self, extension_name, python_exe, std, limited):
         pkg_dir = 'pkg'
         os.mkdir(pkg_dir)
         shutil.copy(SETUP, os.path.join(pkg_dir, os.path.basename(SETUP)))
@@ -56,6 +61,8 @@ def run_cmd(operation, cmd):
             env = os.environ.copy()
             if std:
                 env['CPYTHON_TEST_CPP_STD'] = std
+            if limited:
+                env['CPYTHON_TEST_LIMITED'] = '1'
             env['CPYTHON_TEST_EXT_NAME'] = extension_name
             if support.verbose:
                 print('Run:', ' '.join(map(shlex.quote, cmd)))

Lib/test/test_cppext/extension.cpp

@@ -62,6 +62,7 @@ test_api_casts(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
     Py_ssize_t refcnt = Py_REFCNT(obj);
     assert(refcnt >= 1);
 
+#ifndef Py_LIMITED_API
     // gh-92138: For backward compatibility, functions of Python C API accepts
     // "const PyObject*". Check that using it does not emit C++ compiler
     // warnings.
@@ -74,6 +75,7 @@ test_api_casts(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
     assert(PyTuple_GET_SIZE(const_obj) == 2);
     PyObject *one = PyTuple_GET_ITEM(const_obj, 0);
     assert(PyLong_AsLong(one) == 1);
+#endif
 
     // gh-92898: StrongRef doesn't inherit from PyObject but has an operator to
     // cast to PyObject*.
@@ -106,6 +108,12 @@ test_unicode(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
     }
 
     assert(PyUnicode_Check(str));
+
+    assert(PyUnicode_GetLength(str) == 3);
+    assert(PyUnicode_ReadChar(str, 0) == 'a');
+    assert(PyUnicode_ReadChar(str, 1) == 'b');
+
+#ifndef Py_LIMITED_API
     assert(PyUnicode_GET_LENGTH(str) == 3);
 
     // gh-92800: test PyUnicode_READ()
@@ -121,6 +129,7 @@ test_unicode(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
     assert(PyUnicode_READ(ukind, const_data, 2) == 'c');
 
     assert(PyUnicode_READ_CHAR(str, 1) == 'b');
+#endif
 
     Py_DECREF(str);
     Py_RETURN_NONE;

Lib/test/test_cppext/setup.py

@@ -33,6 +33,7 @@ def main():
     cppflags = list(CPPFLAGS)
     std = os.environ.get("CPYTHON_TEST_CPP_STD", "")
     module_name = os.environ["CPYTHON_TEST_EXT_NAME"]
+    limited = bool(os.environ.get("CPYTHON_TEST_LIMITED", ""))
 
     cppflags = list(CPPFLAGS)
     cppflags.append(f'-DMODULE_NAME={module_name}')
@@ -59,6 +60,11 @@ def main():
         # CC env var overrides sysconfig CC variable in setuptools
         os.environ['CC'] = cmd
 
+    # Define Py_LIMITED_API macro
+    if limited:
+        version = sys.hexversion
+        cppflags.append(f'-DPy_LIMITED_API={version:#x}')
+
     # On Windows, add PCbuild\amd64\ to include and library directories
     include_dirs = []
     library_dirs = []

Misc/NEWS.d/next/Tests/2024-12-13-13-41-34.gh-issue-127906.NuRHlB.rst

@@ -0,0 +1 @@
+Test the limited C API in test_cppext. Patch by Victor Stinner.