python37Packages.cryptography: Improve the test vectors integration

This should make the management easier. The package cryptography_vectors
contains the test vectors for cryptography and should therefore always
have the same version. By linking the version of cryptography_vectors to
cryptography, this simply cannot be forgotten.

pkgs/development/python-modules/cryptography/default.nix

@@ -20,9 +20,8 @@
 }:
 
 buildPythonPackage rec {
-  # also bump cryptography_vectors
   pname = "cryptography";
-  version = "2.5";
+  version = "2.5"; # Also update the hash in vectors.nix
 
   src = fetchPypi {
     inherit pname version;

pkgs/development/python-modules/cryptography/vectors.nix

@@ -0,0 +1,23 @@
+{ buildPythonPackage, fetchPypi, lib, cryptography }:
+
+buildPythonPackage rec {
+  pname = "cryptography_vectors";
+  # The test vectors must have the same version as the cryptography package:
+  version = cryptography.version;
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "15qfl3pnw2f11r0z0zhwl56f6pb60ysav8fxmpnz5p80cfwljdik";
+  };
+
+  # No tests included
+  doCheck = false;
+
+  meta = with lib; {
+    description = "Test vectors for the cryptography package";
+    homepage = https://cryptography.io/en/latest/development/test-vectors/;
+    # Source: https://github.com/pyca/cryptography/tree/master/vectors;
+    license = with licenses; [ asl20 bsd3 ];
+    maintainers = with maintainers; [ primeos ];
+  };
+}