swig: fix Py_NewRef compatibility with Python < 3.10

SWIG >= 4.1 generates calls to Py_NewRef() in its runtime boilerplate.
Py_NewRef was introduced in Python 3.10, causing an undefined symbol
error on older distributions (e.g. SLES 15.6/15.7 with Python 3.6).

Add a static inline shim inside the %begin block, guarded by
PY_VERSION_HEX, so it precedes SWIG's own runtime in the generated C
file. Python.h is included explicitly at that point to make PyObject
available. A meson warning is emitted at configure time when the older
Python is detected.

Signed-off-by: Martin Belanger <[email protected]>
Assisted-by: Claude Sonnet 4.6 <[email protected]>

Author: Martin Belanger

libnvme/libnvme/meson.build

@@ -6,6 +6,10 @@
 # Authors: Martin Belanger <[email protected]>
 #
 if want_python
+    if not cc.has_header_symbol('Python.h', 'Py_NewRef', dependencies: py3_dep)
+        warning('Python < 3.10 detected: Py_NewRef compatibility shim will be used')
+    endif
+
     r = run_command(swig, ['-version'], check: true)  # Returns: "\nSWIG Version 4.1.1\n\nCompiled with ..."
     swig_version = r.stdout().split('\n')[1].split()[2].strip()
     if swig_version.version_compare('<4.1.0')

libnvme/libnvme/nvme.i

@@ -10,6 +10,20 @@
                clashes with the same macro defined in Python.h.
  */
 #undef fallthrough
+
+#include <Python.h>
+
+/* WORKAROUND: Py_NewRef() was introduced in Python 3.10. SWIG >= 4.1 generates
+               calls to it in its runtime boilerplate, which breaks older
+               distributions (e.g. SLES 15.6/15.7 with Python 3.6).
+ */
+#if PY_VERSION_HEX < 0x030a0000
+static inline PyObject *Py_NewRef(PyObject *obj)
+{
+	Py_INCREF(obj);
+	return obj;
+}
+#endif
 %}
 
 %module(docstring="Python bindings for libnvme") nvme