File feature-detection.patch of Package python-zstandard

---
 c-ext/backend_c.c               |   14 ++++++++++++++
 setup_zstd.py                   |    1 +
 tests/test_module_attributes.py |   10 +++++++++-
 3 files changed, 24 insertions(+), 1 deletion(-)

Index: zstandard-0.24.0/c-ext/backend_c.c
===================================================================
--- zstandard-0.24.0.orig/c-ext/backend_c.c	2025-08-17 01:50:50.000000000 +0200
+++ zstandard-0.24.0/c-ext/backend_c.c	2025-09-16 16:15:10.125710215 +0200
@@ -210,6 +210,20 @@
     Py_DECREF(feature);
 #endif
 
+#ifdef SYSTEM_ZSTD
+    feature = PyUnicode_FromString("system_zstd");
+    if (NULL == feature) {
+        PyErr_SetString(PyExc_ImportError, "could not create feature string");
+        return;
+    }
+
+    if (PySet_Add(features, feature) == -1) {
+        return;
+    }
+
+    Py_DECREF(feature);
+#endif
+
     if (PyObject_SetAttrString(m, "backend_features", features) == -1) {
         return;
     }
Index: zstandard-0.24.0/setup_zstd.py
===================================================================
--- zstandard-0.24.0.orig/setup_zstd.py	2025-08-17 02:20:18.000000000 +0200
+++ zstandard-0.24.0/setup_zstd.py	2025-09-16 16:15:10.125758965 +0200
@@ -79,6 +79,7 @@
 
     if system_zstd:
         extra_args.append("-DZSTD_MULTITHREAD")
+        extra_args.append("-DSYSTEM_ZSTD")
     else:
         extra_args.append("-DZSTD_SINGLE_FILE")
         extra_args.append("-DZSTDLIB_VISIBLE=")
Index: zstandard-0.24.0/tests/test_module_attributes.py
===================================================================
--- zstandard-0.24.0.orig/tests/test_module_attributes.py	2025-08-17 19:03:17.000000000 +0200
+++ zstandard-0.24.0/tests/test_module_attributes.py	2025-09-16 16:15:10.125970238 +0200
@@ -26,7 +26,15 @@
             },
         }[zstd.backend]
 
-        self.assertEqual(zstd.backend_features, expected)
+        # The following features are available only with
+        # statically linked version of the module.
+        available_features = set(zstd.backend_features)
+        if 'system_zstd' in available_features:
+            available_features.remove('system_zstd')
+            expected.discard('multi_compress_to_buffer')
+            expected.discard('multi_decompress_to_buffer')
+
+        self.assertEqual(available_features, expected)
 
     def test_constants(self):
         self.assertEqual(zstd.MAX_COMPRESSION_LEVEL, 22)