Fix compatibility with C++03 (#42)

* _Py_CAST() uses old-style cast on old Python versions to prevent
  C++ warnings.
* Fix _Py_NULL on C++ older than C++11: don't use nullptr.
* Test compatibility with C++03.
* Enable C tests on Python 3.11b1.
* runtests.py --verbose logs __cplusplus value.
* GitHub Actions: update Python 3.11 to 3.11b3.

Author: vstinner

.github/workflows/build.yml

@@ -22,7 +22,7 @@ jobs:
           - "3.8"
           - "3.9"
           - "3.10"
-          - "3.11.0-alpha.5"
+          - "3.11.0-beta.3"
           - "pypy2"
           - "pypy3"
         include:

README.rst

@@ -6,9 +6,10 @@ Python C API compatibility
    :alt: Build status of pythoncapi-compat on GitHub Actions
    :target: https://github.com/python/pythoncapi-compat/actions
 
-The ``pythoncapi-compat`` project can be used to write a C extension supporting
-a wide range of Python versions with a single code base. It is made of the
-``pythoncapi_compat.h`` header file and the ``upgrade_pythoncapi.py`` script.
+The ``pythoncapi-compat`` project can be used to write a C or C++ extension
+supporting a wide range of Python versions with a single code base.  It is made
+of the ``pythoncapi_compat.h`` header file and the ``upgrade_pythoncapi.py``
+script.
 
 ``upgrade_pythoncapi.py`` requires Python 3.6 or newer.
 

docs/api.rst

@@ -10,7 +10,7 @@ Supported Python versions:
 * Python 2.7, Python 3.4 - 3.11
 * PyPy 2.7, 3.6 and 3.7
 
-C++ is supported on Python 3.6 and newer.
+C++03 and C++11 are supported on Python 3.6 and newer.
 
 A C99 subset is required, like ``static inline`` functions: see `PEP 7
 <https://www.python.org/dev/peps/pep-0007/>`_.  ISO C90 is partially supported

docs/changelog.rst

@@ -1,6 +1,7 @@
 Changelog
 =========
 
+* 2022-06-14: Fix compatibility with C++ older than C++11.
 * 2022-05-03: Add ``PyCode_GetCode()`` function.
 * 2022-04-26: Rename the project from ``pythoncapi_compat`` to
   ``pythoncapi-compat``: replace the underscore separator with a dash.

docs/index.rst

@@ -2,9 +2,10 @@
 Python C API compatibility
 ++++++++++++++++++++++++++
 
-The ``pythoncapi-compat`` project can be used to write a C extension supporting
-a wide range of Python versions with a single code base. It is made of the
-``pythoncapi_compat.h`` header file and the ``upgrade_pythoncapi.py`` script.
+The ``pythoncapi-compat`` project can be used to write a C or C++ extension
+supporting a wide range of Python versions with a single code base.  It is made
+of the ``pythoncapi_compat.h`` header file and the ``upgrade_pythoncapi.py``
+script.
 
 * Homepage: `GitHub pythoncapi-compat project
   <https://github.com/python/pythoncapi-compat>`_.

pythoncapi_compat.h

@@ -32,39 +32,14 @@ extern "C" {
 #endif
 
 
-// C++ compatibility: _Py_CAST() and _Py_NULL
 #ifndef _Py_CAST
-#  ifdef __cplusplus
-extern "C++" {
-    namespace {
-        template <typename type, typename expr_type>
-            inline type _Py_CAST_impl(expr_type *expr) {
-                return reinterpret_cast<type>(expr);
-            }
-
-        template <typename type, typename expr_type>
-            inline type _Py_CAST_impl(expr_type const *expr) {
-                return reinterpret_cast<type>(const_cast<expr_type *>(expr));
-            }
-
-        template <typename type, typename expr_type>
-            inline type _Py_CAST_impl(expr_type &expr) {
-                return static_cast<type>(expr);
-            }
-
-        template <typename type, typename expr_type>
-            inline type _Py_CAST_impl(expr_type const &expr) {
-                return static_cast<type>(const_cast<expr_type &>(expr));
-            }
-    }
-}
-#    define _Py_CAST(type, expr) _Py_CAST_impl<type>(expr)
-#  else
-#    define _Py_CAST(type, expr) ((type)(expr))
-#  endif
+#  define _Py_CAST(type, expr) ((type)(expr))
 #endif
+
+// On C++11 and newer, _Py_NULL is defined as nullptr on C++11,
+// otherwise it is defined as NULL.
 #ifndef _Py_NULL
-#  ifdef __cplusplus
+#  if defined(__cplusplus) && __cplusplus >= 201103
 #    define _Py_NULL nullptr
 #  else
 #    define _Py_NULL NULL

tests/setup.py

@@ -3,9 +3,18 @@
 import sys
 
 
-TEST_CPP = False
+# C++ is only supported on Python 3.6 and newer
+TEST_CPP = (sys.version_info >= (3, 6))
+if 0x30b0000 <= sys.hexversion <= 0x30b00b3:
+    # Don't test C++ on Python 3.11b1 - 3.11b3: these versions have C++
+    # compatibility issues.
+    TEST_CPP = False
+
 SRC_DIR = os.path.normpath(os.path.join(os.path.dirname(__file__), '..'))
 
+# Windows uses MSVC compiler
+MSVC = (os.name == "nt")
+
 # C compiler flags for GCC and clang
 COMMON_FLAGS = [
     # Treat warnings as error
@@ -37,15 +46,9 @@ def main():
     except ImportError:
         from distutils.core import setup, Extension
 
-    if len(sys.argv) >= 3 and sys.argv[2] == '--build-cppext':
-        global TEST_CPP
-        TEST_CPP = True
-        del sys.argv[2]
-
     cflags = ['-I' + SRC_DIR]
     cppflags = list(cflags)
-    # Windows uses MSVC compiler
-    if os.name != "nt":
+    if not MSVC:
         cflags.extend(CFLAGS)
         cppflags.extend(CPPFLAGS)
 
@@ -58,12 +61,25 @@ def main():
 
     if TEST_CPP:
         # C++ extension
-        cpp_ext = Extension(
-            'test_pythoncapi_compat_cppext',
-            sources=['test_pythoncapi_compat_cppext.cpp'],
-            extra_compile_args=cppflags,
-            language='c++')
-        extensions.append(cpp_ext)
+
+        # MSVC has /std flag but doesn't support /std:c++11
+        if not MSVC:
+            versions = [
+                ('test_pythoncapi_compat_cpp03ext', '-std=c++03'),
+                ('test_pythoncapi_compat_cpp11ext', '-std=c++11'),
+            ]
+        else:
+            versions = [('test_pythoncapi_compat_cppext', None)]
+        for name, flag in versions:
+            flags = list(cppflags)
+            if flag is not None:
+                flags.append(flag)
+            cpp_ext = Extension(
+                name,
+                sources=['test_pythoncapi_compat_cppext.cpp'],
+                extra_compile_args=flags,
+                language='c++')
+            extensions.append(cpp_ext)
 
     setup(name="test_pythoncapi_compat",
           ext_modules=extensions)

tests/test_pythoncapi_compat.py

@@ -23,8 +23,13 @@
 from utils import run_command, command_stdout
 
 
-# C++ is only supported on Python 3.6 and newer
-TEST_CPP = (sys.version_info >= (3, 6))
+TESTS = [
+    ("test_pythoncapi_compat_cext", "C"),
+    ("test_pythoncapi_compat_cppext", "C++"),
+    ("test_pythoncapi_compat_cpp03ext", "C++03"),
+    ("test_pythoncapi_compat_cpp11ext", "C++11"),
+]
+
 VERBOSE = False
 
 
@@ -42,15 +47,10 @@ def display_title(title):
 
 
 def build_ext():
-    if TEST_CPP:
-        display_title("Build the C and C++ extensions")
-    else:
-        display_title("Build the C extension")
+    display_title("Build test extensions")
     if os.path.exists("build"):
         shutil.rmtree("build")
     cmd = [sys.executable, "setup.py", "build"]
-    if TEST_CPP:
-        cmd.append('--build-cppext')
     if VERBOSE:
         run_command(cmd)
         print()
@@ -98,15 +98,42 @@ def _check_refleak(test_func, verbose):
             raise AssertionError("refcnt leak, diff: %s" % diff)
 
 
-def run_tests(module_name):
-    if "cppext" in module_name:
-        lang = "C++"
+def python_version():
+    ver = sys.version_info
+    build = 'debug' if hasattr(sys, 'gettotalrefcount') else 'release'
+    if hasattr(sys, 'implementation'):
+        python_impl = sys.implementation.name
+        if python_impl == 'cpython':
+            python_impl = 'CPython'
+        elif python_impl == 'pypy':
+            python_impl = 'PyPy'
     else:
-        lang = "C"
+        if "PyPy" in sys.version:
+            python_impl = "PyPy"
+        else:
+            python_impl = 'Python'
+    return "%s %s.%s (%s build)" % (python_impl, ver.major, ver.minor, build)
+
+
+def run_tests(module_name, lang):
     title = "Test %s (%s)" % (module_name, lang)
     display_title(title)
 
-    testmod = import_tests(module_name)
+    try:
+        testmod = import_tests(module_name)
+    except ImportError:
+        # The C extension must always be available
+        if lang == "C":
+            raise
+
+        if VERBOSE:
+            print("%s: skip %s, missing %s extension"
+                  % (python_version(), lang, module_name))
+            print()
+        return
+
+    if VERBOSE and hasattr(testmod, "__cplusplus"):
+        print("__cplusplus: %s" % testmod.__cplusplus)
 
     check_refleak = hasattr(sys, 'gettotalrefcount')
 
@@ -125,21 +152,8 @@ def test_func():
     if VERBOSE:
         print()
 
-    ver = sys.version_info
-    build = 'debug' if hasattr(sys, 'gettotalrefcount') else 'release'
     msg = "%s %s tests succeeded!" % (len(tests), lang)
-    if hasattr(sys, 'implementation'):
-        python_impl = sys.implementation.name
-        if python_impl == 'cpython':
-            python_impl = 'CPython'
-        elif python_impl == 'pypy':
-            python_impl = 'PyPy'
-    else:
-        if "PyPy" in sys.version:
-            python_impl = "PyPy"
-        else:
-            python_impl = 'Python'
-    msg = "%s %s.%s (%s build): %s" % (python_impl, ver.major, ver.minor, build, msg)
+    msg = "%s: %s" % (python_version(), msg)
     if check_refleak:
         msg = "%s (no reference leak detected)" % msg
     print(msg)
@@ -150,9 +164,8 @@ def main():
     VERBOSE = ("-v" in sys.argv[1:] or "--verbose" in sys.argv[1:])
 
     # Implementing PyFrame_GetLocals() and PyCode_GetCode() require the
-    # internal C API in Python 3.11 alpha versions. Skip also Python 3.11b1
-    # which has issues with C++ casts: _Py_CAST() macro.
-    if 0x30b0000 <= sys.hexversion <= 0x30b00b1:
+    # internal C API in Python 3.11 alpha versions.
+    if 0x30b0000 <= sys.hexversion < 0x30b00b1:
         version = sys.version.split()[0]
         print("SKIP TESTS: Python %s is not supported" % version)
         return
@@ -166,9 +179,8 @@ def main():
 
     build_ext()
 
-    run_tests("test_pythoncapi_compat_cext")
-    if TEST_CPP:
-        run_tests("test_pythoncapi_compat_cppext")
+    for module_name, lang in TESTS:
+        run_tests(module_name, lang)
 
 
 if __name__ == "__main__":