crypthography cross build produces host's rust library

[Cynerd]

Describe the bug

By attempting to cross-compile python cryptography I get build but rust bindings are build for host architecture.

Steps To Reproduce

Steps to reproduce the behavior:

1. nix build .#legacyPackages.x86_64-linux.pkgsCross.aarch64-multiplatform.python3Packages.cryptography
2. file result/lib/python3.10/site-packages/cryptography/hazmat/bindings/_rust.abi3.so gives x86-64
3. file result/lib/python3.10/site-packages/cryptography/hazmat/bindings/_openssl.abi3.so gives aarch64

Expected behavior

The rust should be cross compiled as well.

Additional context

Add any other context about the problem here.

I tried to look into it and discovered this PyO3/setuptools-rust#294 but nothing more.

Notify maintainers

@SuperSandro2000

Metadata

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.0.10, NixOS, 23.05 (Stoat), 23.05.20221209.9e4a15b`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.12.0`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[SuperSandro2000]

FYI @Artturin didn't you work on python cross or am I mistaken your for someone else?

[Artturin]

FYI @Artturin didn't you work on python cross or am I mistaken your for someone else?

yeah i did but this is unrelated to python

python3.10-cryptography> error[E0463]: can't find crate for `core`
python3.10-cryptography>   |
python3.10-cryptography>   = note: the `aarch64-unknown-linux-gnu` target may not be installed
python3.10-cryptography>   = help: consider downloading the target with `rustup target add aarch64-unknown-linux-gnu`
python3.10-cryptography> error[E0463]: can't find crate for `compiler_builtins`
python3.10-cryptography> error[E0463]: can't find crate for `core`
python3.10-cryptography>    --> /build/cryptography-38.0.3-vendor.tar.gz/scopeguard/src/lib.rs:192:1
python3.10-cryptography>     |
python3.10-cryptography> 192 | extern crate core as std;
python3.10-cryptography>     | ^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate
python3.10-cryptography>     |
python3.10-cryptography>     = note: the `aarch64-unknown-linux-gnu` target may not be installed
python3.10-cryptography>     = help: consider downloading the target with `rustup target add aarch64-unknown-linux-gnu`
...

diff --git a/pkgs/development/python-modules/cryptography/default.nix b/pkgs/development/python-modules/cryptography/default.nix
index 0bbc30cd23c..828e20d7982 100644
--- a/pkgs/development/python-modules/cryptography/default.nix
+++ b/pkgs/development/python-modules/cryptography/default.nix
@@ -4,6 +4,7 @@
 , buildPythonPackage
 , fetchPypi
 , rustPlatform
+, rust
 , setuptools-rust
 , openssl
 , Security
@@ -49,7 +50,7 @@ buildPythonPackage rec {
   ] ++ [
     rustPlatform.cargoSetupHook
     setuptools-rust
-  ] ++ (with rustPlatform; [ rust.cargo rust.rustc ]);
+  ] ++ (with rustPlatform.rust; [ cargo rustc ]);
 
   buildInputs = [ openssl ]
     ++ lib.optionals stdenv.isDarwin [ Security libiconv ];
@@ -69,6 +70,11 @@ buildPythonPackage rec {
     pytz
   ];
 
+  CARGO_BUILD_TARGET = "${rust.toRustTargetSpec stdenv.hostPlatform}";
+
+  PKG_CONFIG_ALLOW_CROSS =
+    if stdenv.buildPlatform != stdenv.hostPlatform then 1 else 0;
+
   pytestFlagsArray = [
     "--disable-pytest-warnings"
   ];

[Cynerd]

This seems to be something generic for all python packages with rust extension. I also tried other packages that use setultools-rust, and all I tried were built for the host platform, not for the target.

Probably somebody skilled with Cargo should look into it.

[Cynerd]

I might have gotten a little bit further...

diff --git a/pkgs/development/python-modules/cryptography/default.nix b/pkgs/development/python-modules/cryptography/default.nix
index d5e4af33f60..560b8861fdc 100644
--- a/pkgs/development/python-modules/cryptography/default.nix
+++ b/pkgs/development/python-modules/cryptography/default.nix
@@ -2,8 +2,12 @@
 , stdenv
 , callPackage
 , buildPythonPackage
+, python
 , fetchPypi
 , rustPlatform
+, rust
+, rustc
+, cargo
 , setuptools-rust
 , openssl
 , Security
@@ -47,9 +51,11 @@ buildPythonPackage rec {
   nativeBuildInputs = lib.optionals (!isPyPy) [
     cffi
   ] ++ [
-    rustPlatform.cargoSetupHook
     setuptools-rust
-  ] ++ (with rustPlatform; [ rust.cargo rust.rustc ]);
+    rustPlatform.cargoSetupHook
+    rustc
+    cargo
+  ];
 
   buildInputs = [ openssl ]
     ++ lib.optionals stdenv.isDarwin [ Security libiconv ];
@@ -69,6 +75,9 @@ buildPythonPackage rec {
     pytz
   ];
 
+  CARGO_BUILD_TARGET = "${rust.toRustTargetSpec stdenv.hostPlatform}";
+  PYO3_CROSS_LIB_DIR = "${python}/lib/${python.libPrefix}";
+
   pytestFlagsArray = [
     "--disable-pytest-warnings"
   ];

But still, it fails to build when cross-compiling. For some reason, it can't find linker.

[Cynerd]

It seems that I might have crack it. The pull request is here #208401.