feat(android): add Rust cross-compilation setup for Android environment (#2650)

cibuildwheel/platforms/android.py

@@ -7,7 +7,7 @@ import shlex
 import shutil
 import subprocess
 import sysconfig
-from collections.abc import Iterable, Iterator
+from collections.abc import Iterable, Iterator, MutableMapping
 from dataclasses import dataclass
 from os.path import relpath
 from pathlib import Path
@@ -390,6 +390,9 @@ def setup_android_env(
     for key in ["CFLAGS", "CXXFLAGS"]:
         android_env[key] += " " + opt
 
+    # Cargo target linker needs to be specified after CC is set
+    setup_rust(config, python_dir, android_env)
+
     # Format the environment so it can be pasted into a shell when debugging.
     for key, value in sorted(android_env.items()):
         if os.environ.get(key) != value:
@@ -398,6 +401,34 @@ def setup_android_env(
     return android_env
 
 
+def setup_rust(
+    config: PythonConfiguration,
+    python_dir: Path,
+    env: MutableMapping[str, str],
+) -> None:
+    cargo_target = android_triplet(config.identifier)
+
+    # CARGO_BUILD_TARGET is the variable used by Cargo and setuptools_rust
+    env["CARGO_BUILD_TARGET"] = cargo_target
+
+    # The linker needs to be specified after CC is set by android-env.sh
+    cargo_target_linker_env_name = f"CARGO_TARGET_{cargo_target.upper().replace('-', '_')}_LINKER"
+    # CC has already been set by calling android.py (it calls android-env.sh)
+    env[cargo_target_linker_env_name] = env["CC"]
+
+    # All Python extension modules must be explicitly linked against libpython3.x.so when building for Android.
+    # See: https://peps.python.org/pep-0738/#linkage
+    # For projects using PyO3, this requires setting PYO3_CROSS_LIB_DIR to the directory containing libpython3.x.so.
+    # See: https://pyo3.rs/v0.27.1/building-and-distribution.html#cross-compiling
+    env["PYO3_CROSS_LIB_DIR"] = str(python_dir / "prefix" / "lib")
+
+    venv_bin = Path(env["VIRTUAL_ENV"]) / "bin"
+    for tool in ["cargo", "rustup"]:
+        shim_path = venv_bin / tool
+        shutil.copy(resources.PATH / "_rust_shim.py", shim_path)
+        shim_path.chmod(0o755)
+
+
 def before_build(state: BuildState) -> None:
     if state.options.before_build:
         log.step("Running before_build...")

cibuildwheel/resources/_rust_shim.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+
+import os
+import shutil
+import subprocess
+import sys
+from pathlib import Path
+
+
+def main() -> None:
+    # CIBW_HOST_TRIPLET is set in the android_env to the Android target triplet.
+    target = os.environ.get("CIBW_HOST_TRIPLET")
+
+    cmd_name = Path(sys.argv[0]).name
+
+    # Find the real command in PATH, excluding the current script's directory
+    path_env = os.environ.get("PATH", "")
+    script_dir = Path(__file__).resolve().parent
+
+    paths = path_env.split(os.pathsep)
+    # Filter out the script directory to avoid recursion
+    filtered_paths = [p for p in paths if Path(p).resolve() != script_dir]
+    filtered_path_env = os.pathsep.join(filtered_paths)
+
+    real_cmd = shutil.which(cmd_name, path=filtered_path_env)
+
+    if not real_cmd:
+        sys.stderr.write(f"cibuildwheel: Error: Could not find system {cmd_name}\n")
+        sys.exit(1)
+
+    # If we have a target (i.e. we are in the android_env), try to install it.
+    if target:
+        # Check if rustup is available to install the target
+        rustup_path = shutil.which("rustup", path=filtered_path_env)
+
+        if rustup_path:
+            try:
+                # We call rustup to ensure the target is installed.
+                subprocess.run(
+                    [rustup_path, "target", "add", target],
+                    check=True,
+                    stdout=subprocess.DEVNULL,
+                    stderr=subprocess.PIPE,
+                    text=True,
+                )
+            except subprocess.CalledProcessError as e:
+                sys.stderr.write(
+                    f"cibuildwheel: Error: Failed to install Rust target {target}: {e.stderr}\n"
+                )
+                sys.exit(1)
+
+    # Execute the real command
+    os.execv(real_cmd, [real_cmd, *sys.argv[1:]])
+
+
+if __name__ == "__main__":
+    main()