core/pkgs/by-name/xc/xcbuild/toolchains.nix

{
  runCommand,
  toolchainName,
  fetchurl,
  stdenv,
  buildPackages,
  lib,
  writeText,
}:

let

  inherit (lib) getBin optionalString;
  inherit (lib.generators) toPlist;

  ToolchainInfo = {
    Identifier = toolchainName;
  };

  # We could pull this out of developer_cmds but it adds an annoying
  # loop if we want to bootstrap and this is just a tiny script so I'm
  # not going to bother.
  mkdep-darwin-src = fetchurl {
    url = "https://opensource.apple.com/source/developer_cmds/developer_cmds-63/mkdep/mkdep.sh";
    sha256 = "0n4wpqfslfjs5zbys5yri8pfi2awyhlmknsf6laa5jzqbzq9x541";
    executable = true;
  };
in

runCommand "Toolchains" { } (
  ''
    toolchain=$out/XcodeDefault.xctoolchain
    mkdir -p $toolchain

    install -D ${
      writeText "ToolchainInfo.plist" (toPlist { } ToolchainInfo)
    } $toolchain/ToolchainInfo.plist

    ln -s $toolchain $toolchain/usr

    mkdir -p $toolchain/include
    mkdir -p $toolchain/lib
    mkdir -p $toolchain/libexec
    mkdir -p $toolchain/share
    mkdir -p $toolchain/bin

    for bin in ${getBin stdenv.cc}/bin/*; do
      ln -s $bin $toolchain/bin
    done

    for bin in ${getBin stdenv.cc.bintools.bintools}/bin/*; do
      if ! [ -e "$toolchain/bin/$(basename $bin)" ]; then
        ln -s $bin $toolchain/bin
      fi
    done

    ln -s ${buildPackages.bison}/bin/yacc $toolchain/bin/yacc
    ln -s ${buildPackages.bison}/bin/bison $toolchain/bin/bison
    ln -s ${buildPackages.flex}/bin/flex $toolchain/bin/flex
    ln -s ${buildPackages.flex}/bin/flex++ $toolchain/bin/flex++
    ln -s $toolchain/bin/flex $toolchain/bin/lex

    ln -s ${buildPackages.m4}/bin/m4 $toolchain/bin/m4
    ln -s $toolchain/bin/m4 $toolchain/bin/gm4

    ln -s ${buildPackages.unifdef}/bin/unifdef $toolchain/bin/unifdef
    ln -s ${buildPackages.unifdef}/bin/unifdefall $toolchain/bin/unifdefall

    ln -s ${buildPackages.gperf}/bin/gperf $toolchain/bin/gperf
    ln -s ${buildPackages.indent}/bin/indent $toolchain/bin/indent
    ln -s ${buildPackages.ctags}/bin/ctags $toolchain/bin/ctags
  ''
  + optionalString stdenv.isDarwin ''
    for bin in ${getBin buildPackages.darwin.cctools}/bin/*; do
      if ! [ -e "$toolchain/bin/$(basename $bin)" ]; then
        ln -s $bin $toolchain/bin
      fi
    done

    ln -s ${buildPackages.darwin.bootstrap_cmds}/bin/mig $toolchain/bin
    mkdir -p $toolchain/libexec
    ln -s ${buildPackages.darwin.bootstrap_cmds}/libexec/migcom $toolchain/libexec
    ln -s ${mkdep-darwin-src} $toolchain/bin/mkdep
  ''
)