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style(ffi): trim overdone build.rs comments to load-bearing whys only

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Lahfir 2026-04-17 03:45:14 -07:00
parent 2a8b8709b2
commit f95647f721
1 changed files with 9 additions and 27 deletions
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36
crates/ffi/build.rs
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@ -5,17 +5,9 @@ fn main() {
println!("cargo:rerun-if-changed=cbindgen.toml");
println!("cargo:rerun-if-changed=src/");
// macOS Mach-O install_name: consumers that link the dylib at build
// time (Swift Package Manager, cmake, meson) embed the library's
// install_name into the consuming binary's load commands. Cargo
// defaults to the absolute build-machine path — useless once the
// dylib is extracted from a release tarball on someone else's
// machine. Baking `@rpath/...` here lets consumers resolve the
// library through their own `-rpath` / `DYLD_LIBRARY_PATH` /
// `@loader_path` lookup chain exactly the way every other
// distributed macOS dylib does it (wasmtime, rustls-ffi, etc.).
// Python `ctypes.CDLL("./libfoo.dylib")` and Go cgo tolerate either
// install_name; Swift linkers do not.
// Cargo's default install_name is the absolute build-machine path,
// which breaks linking consumers (Swift/SPM, clang) once the dylib
// is extracted from a release tarball. @rpath is the portable form.
if std::env::var("CARGO_CFG_TARGET_OS").as_deref() == Ok("macos") {
println!("cargo:rustc-cdylib-link-arg=-Wl,-install_name,@rpath/libagent_desktop_ffi.dylib");
}
@ -51,28 +43,18 @@ fn main() {
Err(err) => panic!("cbindgen generation failed: {}", err),
};
// cbindgen 0.27 returns `false` when the header file content hasn't changed and the
// existing file already matches — that's a clean no-op, not an error. We just need a
// valid file at `out_path` for downstream build consumers.
bindings.write_to_file(&out_path);
if !out_path.exists() {
panic!("cbindgen produced no header at {:?}", out_path);
}
// NOTE: We intentionally do NOT copy the generated header back into
// `crates/ffi/include/`. That committed header is the ABI contract
// checked into source control. CI's "FFI header drift check" compares
// $OUT_DIR/agent_desktop.h against the committed copy; if the build
// script auto-copied it, the drift check would self-heal instead of
// catching stale headers. Developers update the committed header by
// running `scripts/update-ffi-header.sh`.
// Deliberately NOT copying into crates/ffi/include/ — the committed
// header is the ABI contract. Auto-copy would self-heal CI drift checks.
// Developers refresh it via scripts/update-ffi-header.sh.
// Stamp the absolute path to the just-generated header at a stable,
// deterministic location that CI and scripts can read without ever
// resorting to `find target | head -1` (which picks arbitrarily when
// multiple `agent-desktop-ffi-<hash>/` build dirs are cached). Walking
// 4 parents up from OUT_DIR yields the cargo target root:
// {target}/{profile}/build/{pkg-hash}/out → {target}
// Stamp the absolute path of the generated header at a stable location
// so CI and scripts don't have to `find target | head -1` (ambiguous
// under warm caches with multiple pkg-hash dirs).
if let Some(target_root) = target_root_from_out_dir(Path::new(&out_dir)) {
let stamp = target_root.join("ffi-header-path.txt");
if let Err(err) = std::fs::write(&stamp, out_path.to_string_lossy().as_bytes()) {