bpo-40637: Don't test builtin PBKDF2 without builtin hashes

Skip testing of pure Python PBKDF2 when one or more builtin hash module
is not available. Otherwise the import of hashlib prints noise on
stderr.

Signed-off-by: Christian Heimes <[email protected]>

Author: tiran

Lib/test/test_hashlib.py

@@ -25,17 +25,26 @@
 # Were we compiled --with-pydebug or with #define Py_DEBUG?
 COMPILED_WITH_PYDEBUG = hasattr(sys, 'gettotalrefcount')
 
-c_hashlib = import_fresh_module('hashlib', fresh=['_hashlib'])
-py_hashlib = import_fresh_module('hashlib', blocked=['_hashlib'])
-
+# default builtin hash module
+default_builtin_hashes = {'md5', 'sha1', 'sha256', 'sha512', 'sha3', 'blake2'}
+# --with-builtin-hashlib-hashes override
 builtin_hashes = sysconfig.get_config_var("PY_BUILTIN_HASHLIB_HASHES")
 if builtin_hashes is None:
-    builtin_hashes = {'md5', 'sha1', 'sha256', 'sha512', 'sha3', 'blake2'}
+    builtin_hashes = default_builtin_hashes
 else:
     builtin_hashes = {
         m.strip() for m in builtin_hashes.strip('"').lower().split(",")
     }
 
+# hashlib with and without OpenSSL backend for PBKDF2
+# only import builtin_hashlib when all builtin hashes are available.
+# Otherwise import prints noise on stderr
+openssl_hashlib = import_fresh_module('hashlib', fresh=['_hashlib'])
+if builtin_hashes == default_builtin_hashes:
+    builtin_hashlib = import_fresh_module('hashlib', blocked=['_hashlib'])
+else:
+    builtin_hashlib = None
+
 try:
     from _hashlib import HASH, HASHXOF, openssl_md_meth_names
 except ImportError:
@@ -1031,16 +1040,16 @@ def _test_pbkdf2_hmac(self, pbkdf2, supported):
                 iterations=1, dklen=None)
             self.assertEqual(out, self.pbkdf2_results['sha1'][0][0])
 
+    @unittest.skipIf(builtin_hashlib is None, "test requires builtin_hashlib")
     def test_pbkdf2_hmac_py(self):
-        self._test_pbkdf2_hmac(py_hashlib.pbkdf2_hmac, builtin_hashes)
+        self._test_pbkdf2_hmac(builtin_hashlib.pbkdf2_hmac, builtin_hashes)
 
-    @unittest.skipUnless(hasattr(c_hashlib, 'pbkdf2_hmac'),
+    @unittest.skipUnless(hasattr(openssl_hashlib, 'pbkdf2_hmac'),
                      '   test requires OpenSSL > 1.0')
     def test_pbkdf2_hmac_c(self):
-        self._test_pbkdf2_hmac(c_hashlib.pbkdf2_hmac, openssl_md_meth_names)
-
+        self._test_pbkdf2_hmac(openssl_hashlib.pbkdf2_hmac, openssl_md_meth_names)
 
-    @unittest.skipUnless(hasattr(c_hashlib, 'scrypt'),
+    @unittest.skipUnless(hasattr(hashlib, 'scrypt'),
                      '   test requires OpenSSL > 1.1')
     def test_scrypt(self):
         for password, salt, n, r, p, expected in self.scrypt_test_vectors: