gh-127405: Add ABIFLAGS to sysconfig.get_config_vars() on Windows

Lib/sysconfig/__init__.py

@@ -401,8 +401,12 @@ def _init_non_posix(vars):
     vars['BINLIBDEST'] = get_path('platstdlib')
     vars['INCLUDEPY'] = get_path('include')
 
-    # Add EXT_SUFFIX, SOABI, and Py_GIL_DISABLED
-    vars.update(_sysconfig.config_vars())
+    # Add EXT_SUFFIX, SOABI, ABIFLAGS, and Py_GIL_DISABLED
+    # NOTE: ABIFLAGS is only an emulated value. It is not present during build
+    #       on Windows. sys.abiflags is absent on Windows and `vars['abiflags']
+    #       is already widely used to calculate paths. vars['abiflags'] should
+    #       remain empty string.
+    vars.update(_sysconfig.config_vars())  # defined in Modules/_sysconfig.c
 
     vars['LIBDIR'] = _safe_realpath(os.path.join(get_config_var('installed_base'), 'libs'))
     if hasattr(sys, 'dllhandle'):

Lib/test/test_sysconfig.py

@@ -592,6 +592,10 @@ def test_osx_ext_suffix(self):
         suffix = sysconfig.get_config_var('EXT_SUFFIX')
         self.assertTrue(suffix.endswith('-darwin.so'), suffix)
 
+    def test_always_set_ABIFLAGS(self):
+        self.assertIn('ABIFLAGS', sysconfig.get_config_vars())
+        self.assertIsInstance(sysconfig.get_config_var('ABIFLAGS'), str)
+
     @requires_subprocess()
     def test_makefile_overwrites_config_vars(self):
         script = textwrap.dedent("""

Misc/ACKS

@@ -1402,6 +1402,7 @@ Todd R. Palmer
 Juan David Ibáñez Palomar
 Nicola Palumbo
 Jan Palus
+Xuehai Pan
 Yongzhi Pan
 Martin Panter
 Mathias Panzenböck

Misc/NEWS.d/next/Windows/2025-03-27-16-22-58.gh-issue-127405.aASs2Z.rst

@@ -0,0 +1 @@
+Add ``ABIFLAGS`` to :func:`sysconfig.get_config_vars` on Windows. Patch by Xuehai Pan.

Modules/_sysconfig.c

@@ -55,6 +55,23 @@ _sysconfig_config_vars_impl(PyObject *module)
         Py_DECREF(config);
         return NULL;
     }
+
+    // On Unix, the `ABIFLAGS` key is defined via a different logic.
+    //
+    // Emulate `sys.abiflags` value on Unix for Windows. ABIFLAGS here is only
+    // an emulated value. It is not present during build on Windows.
+    if (add_string_value(config, "ABIFLAGS",
+#  ifdef Py_GIL_DISABLED
+                         "t"
+#  endif
+#  ifdef _DEBUG
+                         "d"
+#  endif
+                         "")
+        < 0) {
+        Py_DECREF(config);
+        return NULL;
+    }
 #endif
 
 #ifdef Py_GIL_DISABLED