Platform Notes

Darwin (macOS)

Some common issues when packaging software for Darwin:

The Darwin stdenv uses clang instead of gcc. When referring to the compiler $CC or cc will work in both cases. Some builds hardcode gcc/g++ in their build scripts, that can usually be fixed with using something like makeFlags = [ "CC=cc" ]; or by patching the build scripts.
```
stdenv.mkDerivation {
  name = "libfoo-1.2.3";
  # ...
  buildPhase = ''
    $CC -o hello hello.c
  '';
}
```
On Darwin, libraries are linked using absolute paths, libraries are resolved by their install_name at link time. Sometimes packages won’t set this correctly causing the library lookups to fail at runtime. This can be fixed by adding extra linker flags or by running install_name_tool -id during the fixupPhase.
```
stdenv.mkDerivation {
  name = "libfoo-1.2.3";
  # ...
  makeFlags = lib.optional stdenv.isDarwin "LDFLAGS=-Wl,-install_name,$(out)/lib/libfoo.dylib";
}
```
Even if the libraries are linked using absolute paths and resolved via their install_name correctly, tests can sometimes fail to run binaries. This happens because the checkPhase runs before the libraries are installed.

This can usually be solved by running the tests after the installPhase or alternatively by using DYLD_LIBRARY_PATH. More information about this variable can be found in the dyld(1) manpage.
```
dyld: Library not loaded: /nix/store/7hnmbscpayxzxrixrgxvvlifzlxdsdir-jq-1.5-lib/lib/libjq.1.dylib
Referenced from: /private/tmp/nix-build-jq-1.5.drv-0/jq-1.5/tests/../jq
Reason: image not found
./tests/jqtest: line 5: 75779 Abort trap: 6
```
```
stdenv.mkDerivation {
  name = "libfoo-1.2.3";
  # ...
  doInstallCheck = true;
  installCheckTarget = "check";
}
```
Some packages assume xcode is available and use xcrun to resolve build tools like clang, etc. This causes errors like xcode-select: error: no developer tools were found at '/Applications/Xcode.app' while the build doesn’t actually depend on xcode.
```
stdenv.mkDerivation {
  name = "libfoo-1.2.3";
  # ...
  prePatch = ''
    substituteInPlace Makefile \
        --replace '/usr/bin/xcrun clang' clang
  '';
}
```
The package xcbuild can be used to build projects that really depend on Xcode. However, this replacement is not 100% compatible with Xcode and can occasionally cause issues.
x86_64-darwin uses the 10.12 SDK by default, but some software is not compatible with that version of the SDK. In that case, the 11.0 SDK used by aarch64-darwin is available for use on x86_64-darwin. To use it, reference apple_sdk_11_0 instead of apple_sdk in your derivation and use pkgs.darwin.apple_sdk_11_0.callPackage instead of pkgs.callPackage. On Linux, this will have the same effect as pkgs.callPackage, so you can use pkgs.darwin.apple_sdk_11_0.callPackage regardless of platform.