From e3078ba61db873e77eef9f948f809edef7e32935 Mon Sep 17 00:00:00 2001
From: Edward Langley <el-github@elangley.org>
Date: Mon, 30 Mar 2026 22:22:11 -0700
Subject: [PATCH] fix: make nix flake and cargo config portable across Linux
 and macOS

musl tooling is Linux-only, so guard it behind an isLinux check in
flake.nix and remove the hardcoded musl build target from .cargo/config.toml
(the nix devShell already sets CARGO_BUILD_TARGET on Linux).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 .cargo/config.toml |  8 +++-----
 flake.nix          | 47 ++++++++++++++++++++++++++++------------------
 2 files changed, 32 insertions(+), 23 deletions(-)

diff --git a/.cargo/config.toml b/.cargo/config.toml
index d684ec8..ca10c34 100644
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -1,8 +1,6 @@
-[build]
-# Always build a fully-static musl binary by default.
-# The devShell sets CARGO_BUILD_TARGET and CARGO_TARGET_*_LINKER,
-# so the linker is resolved automatically via the environment.
-target = "x86_64-unknown-linux-musl"
+# The nix devShell sets CARGO_BUILD_TARGET=x86_64-unknown-linux-musl
+# and the matching linker env vars, so no [build] target is needed here.
+# This keeps the config portable across Linux and macOS.
 
 [target.x86_64-unknown-linux-gnu]
 # Use gcc (not rust-lld) for host-target build scripts on NixOS.
diff --git a/flake.nix b/flake.nix
index a598066..d2e93e8 100644
--- a/flake.nix
+++ b/flake.nix
@@ -15,48 +15,59 @@
       let
         overlays = [ (import rust-overlay) ];
         pkgs = import nixpkgs { inherit system overlays; };
+        isLinux = pkgs.lib.hasInfix "linux" system;
 
         rustToolchain = pkgs.rust-bin.stable.latest.default.override {
           extensions = [ "rust-src" "clippy" "rustfmt" ];
-          targets = [ "x86_64-unknown-linux-musl" ];
+          targets = pkgs.lib.optionals isLinux [ "x86_64-unknown-linux-musl" ];
         };
-
-        muslCC = pkgs.pkgsMusl.stdenv.cc;
       in
       {
-        devShells.default = pkgs.mkShell {
+        devShells.default = pkgs.mkShell ({
           nativeBuildInputs = [
             rustToolchain
             pkgs.pkg-config
+          ] ++ pkgs.lib.optionals isLinux [
             # Provide cc (gcc) for building proc-macro / build-script crates
             # that target the host (x86_64-unknown-linux-gnu).
             pkgs.gcc
             # musl-gcc wrapper for the static musl target.
-            muslCC
+            pkgs.pkgsMusl.stdenv.cc
           ];
 
+          RUST_BACKTRACE = "1";
+        } // pkgs.lib.optionalAttrs isLinux {
           # Tell Cargo which linker to use for each target so it never
           # falls back to rust-lld (which can't find glibc on NixOS).
           CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER =
             "${pkgs.gcc}/bin/gcc";
           CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_LINKER =
-            "${muslCC}/bin/cc";
+            "${pkgs.pkgsMusl.stdenv.cc}/bin/cc";
 
           # Default build target: static musl binary.
           CARGO_BUILD_TARGET = "x86_64-unknown-linux-musl";
-
-          RUST_BACKTRACE = "1";
-        };
+        });
 
         packages.default =
-          (pkgs.pkgsMusl.makeRustPlatform {
-            cargo = rustToolchain;
-            rustc = rustToolchain;
-          }).buildRustPackage {
-            pname = "improvise";
-            version = "0.1.0";
-            src = ./.;
-            cargoLock.lockFile = ./Cargo.lock;
-          };
+          if isLinux then
+            (pkgs.pkgsMusl.makeRustPlatform {
+              cargo = rustToolchain;
+              rustc = rustToolchain;
+            }).buildRustPackage {
+              pname = "improvise";
+              version = "0.1.0";
+              src = ./.;
+              cargoLock.lockFile = ./Cargo.lock;
+            }
+          else
+            (pkgs.makeRustPlatform {
+              cargo = rustToolchain;
+              rustc = rustToolchain;
+            }).buildRustPackage {
+              pname = "improvise";
+              version = "0.1.0";
+              src = ./.;
+              cargoLock.lockFile = ./Cargo.lock;
+            };
       });
 }