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feat(build): add a macOS cross-architecture dev shell #724

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feat(build): add a macOS cross-architecture dev shell #724

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48 changes: 47 additions & 1 deletion flake.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,52 @@
let
systems = [ "aarch64-darwin" "x86_64-darwin" "aarch64-linux" "x86_64-linux" ];
forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});

# Cross dev shell (macOS only): build the *other* darwin arch locally.
# The native clang already cross-EMITS object code via -arch (scripts/env.sh
# exports ARCHFLAGS); this shell only puts the target-arch zlib (a hard
# `-lz` dependency) and libgit2 (optional, found via pkg-config) on the
# link path, since the host-arch copies can't satisfy an x86_64/arm64 link.
# Building needs no Rosetta; *running* an x86_64 binary on Apple Silicon
# does. The target-arch libs are fetched as prebuilt substitutes. Returns
# {} on Linux/Windows (no cross target).
crossDevShells = pkgs:
let
inherit (nixpkgs) lib;
crossTarget =
{
"aarch64-darwin" = "x86_64-darwin";
"x86_64-darwin" = "aarch64-darwin";
}
.${pkgs.system} or null;
mkCrossShell =
targetSystem:
let
tpkgs = nixpkgs.legacyPackages.${targetSystem};
targetArch = if targetSystem == "x86_64-darwin" then "x86_64" else "arm64";
in
pkgs.mkShell {
# Host toolchain only (clang comes from the shell stdenv); do NOT
# pull host zlib/libgit2 in — that's the wrong-arch copy we avoid.
nativeBuildInputs = [ pkgs.pkg-config pkgs.gnumake ];
shellHook = ''
# libgit2 headers + libs come through pkg-config (the Makefile
# auto-detects it). zlib is a bare `-lz`/`#include <zlib.h>`, so
# supply its include (header is arch-independent) and lib dir by
# hand. NIX_LDFLAGS is searched before the link's own -L, so the
# target-arch slice resolves; the host-arch copy (if any reaches
# ld) is skipped as "wrong architecture".
export PKG_CONFIG_PATH="${lib.getDev tpkgs.libgit2}/lib/pkgconfig:${lib.getDev tpkgs.zlib}/lib/pkgconfig''${PKG_CONFIG_PATH:+:$PKG_CONFIG_PATH}"
export NIX_CFLAGS_COMPILE="-I${lib.getDev tpkgs.zlib}/include ''${NIX_CFLAGS_COMPILE:-}"
export NIX_LDFLAGS="-L${lib.getLib tpkgs.zlib}/lib -L${lib.getLib tpkgs.libgit2}/lib ''${NIX_LDFLAGS:-}"
echo "[cross] target ${targetSystem} — build with: scripts/build.sh --arch ${targetArch}"
'';
};
in
lib.optionalAttrs (crossTarget != null) {
# `nix develop .#cross` then `scripts/build.sh --arch <target>`.
cross = mkCrossShell crossTarget;
};
in
{
packages = forAllSystems (pkgs: {
Expand Down Expand Up @@ -49,6 +95,6 @@
# otherwise the build falls back to shelling out to `git log`.
packages = [ pkgs.pkg-config pkgs.libgit2 ];
};
});
} // crossDevShells pkgs);
};
}
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