From 5d072cb2a68506445844112e95b732c4287f39a0 Mon Sep 17 00:00:00 2001
From: Alexandru Ardelean <ardeleanalex@gmail.com>
Date: Wed, 27 May 2026 14:28:58 +0300
Subject: [PATCH] cffi: derive Python include dir from PYO3_CROSS_LIB_DIR when
 cross-compiling (#14904)

When cross-compiling, ``cryptography-cffi/build.rs`` queries the host
interpreter via ``setuptools.command.build_ext.build_ext.include_dirs``
and feeds the result into ``cc-rs`` as ``-I /usr/include/python3.X``.
On hosts that happen to ship Python development headers for the same
3.X line as the target (e.g. an Arch Linux build host with Python 3.14
installed), the host headers leak into the cross build and the target
compiler aborts with::

    /usr/include/python3.14/pyport.h:429:2: error: #error "LONG_BIT
    definition appears wrong for platform (bad gcc/glibc config?)."

``PYO3_CROSS_LIB_DIR`` is the documented PyO3 cross-compile signal and
points at the target's libpython directory. When it is set, derive the
matching Python include dir from it (``<prefix>/include/<py_ver>``) and
skip the host setuptools probe entirely. Native builds keep the
existing setuptools-based behaviour, so this is a no-op outside of
PyO3-style cross builds.

This is consistent with the existing ``PYO3_PYTHON`` handling in the
same file: cryptography-cffi already respects PyO3's cross-compile
environment for picking the interpreter, and this extends that to the
matching header directory.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

[OpenWrt: dropped the CHANGELOG.rst hunk — the 48.0.0 source tarball
does not yet carry the post-48.0.0 "unreleased" section the upstream
hunk targets. Drop this patch on next bump once the upstream change is
in a tagged release.]
Signed-off-by: Alexandru Ardelean <alex@shruggie.ro>
---
 src/rust/cryptography-cffi/build.rs | 44 ++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 10 deletions(-)

--- a/src/rust/cryptography-cffi/build.rs
+++ b/src/rust/cryptography-cffi/build.rs
@@ -56,16 +56,40 @@ fn main() {
     )
     .unwrap();
     println!("cargo:rustc-cfg=python_implementation=\"{python_impl}\"");
-    let python_includes = run_python_script(
-        &python,
-        "import os; \
-         import setuptools.dist; \
-         import setuptools.command.build_ext; \
-         b = setuptools.command.build_ext.build_ext(setuptools.dist.Distribution()); \
-         b.finalize_options(); \
-         print(os.pathsep.join(b.include_dirs), end='')",
-    )
-    .unwrap();
+    println!("cargo:rerun-if-env-changed=PYO3_CROSS_LIB_DIR");
+    // When cross-compiling, PyO3 expects the build system to point
+    // PYO3_CROSS_LIB_DIR at the target's libpython directory. Derive the
+    // matching include dir from it instead of querying the host
+    // interpreter's setuptools, which returns host headers (e.g.
+    // /usr/include/python3.x) and breaks the cross build whenever the host
+    // happens to have same-version Python development headers installed.
+    let python_includes = if let Ok(lib_dir) = env::var("PYO3_CROSS_LIB_DIR") {
+        let lib = Path::new(&lib_dir);
+        let py_ver = lib
+            .file_name()
+            .and_then(|s| s.to_str())
+            .unwrap_or("python3");
+        let prefix = lib
+            .parent()
+            .and_then(|p| p.parent())
+            .expect("PYO3_CROSS_LIB_DIR has unexpected layout");
+        prefix
+            .join("include")
+            .join(py_ver)
+            .to_string_lossy()
+            .into_owned()
+    } else {
+        run_python_script(
+            &python,
+            "import os; \
+             import setuptools.dist; \
+             import setuptools.command.build_ext; \
+             b = setuptools.command.build_ext.build_ext(setuptools.dist.Distribution()); \
+             b.finalize_options(); \
+             print(os.pathsep.join(b.include_dirs), end='')",
+        )
+        .unwrap()
+    };
     let openssl_c = Path::new(&out_dir).join("_openssl.c");
 
     let mut build = cc::Build::new();