<chapter xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xml:id="chap-platform-notes">
 <title>Platform Notes</title>
 <section xml:id="sec-darwin">
  <title>Darwin (macOS)</title>

  <para>
   Some common issues when packaging software for Darwin:
  </para>

  <itemizedlist>
   <listitem>
    <para>
     The Darwin <literal>stdenv</literal> uses clang instead of gcc. When referring to the compiler <varname>$CC</varname> or <command>cc</command> will work in both cases. Some builds hardcode gcc/g++ in their build scripts, that can usually be fixed with using something like <literal>makeFlags = [ "CC=cc" ];</literal> or by patching the build scripts.
    </para>
<programlisting>
stdenv.mkDerivation {
  name = "libfoo-1.2.3";
  # ...
  buildPhase = ''
    $CC -o hello hello.c
  '';
}
</programlisting>
   </listitem>
   <listitem>
    <para>
     On Darwin, libraries are linked using absolute paths, libraries are resolved by their <literal>install_name</literal> at link time. Sometimes packages won't set this correctly causing the library lookups to fail at runtime. This can be fixed by adding extra linker flags or by running <command>install_name_tool -id</command> during the <function>fixupPhase</function>.
    </para>
<programlisting>
stdenv.mkDerivation {
  name = "libfoo-1.2.3";
  # ...
  makeFlags = stdenv.lib.optional stdenv.isDarwin "LDFLAGS=-Wl,-install_name,$(out)/lib/libfoo.dylib";
}
</programlisting>
   </listitem>
   <listitem>
    <para>
     Even if the libraries are linked using absolute paths and resolved via their <literal>install_name</literal> correctly, tests can sometimes fail to run binaries. This happens because the <varname>checkPhase</varname> runs before the libraries are installed.
    </para>
    <para>
     This can usually be solved by running the tests after the <varname>installPhase</varname> or alternatively by using <varname>DYLD_LIBRARY_PATH</varname>. More information about this variable can be found in the <citerefentry>
     <refentrytitle>dyld</refentrytitle>
     <manvolnum>1</manvolnum></citerefentry> manpage.
    </para>
<programlisting>
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
</programlisting>
<programlisting>
stdenv.mkDerivation {
  name = "libfoo-1.2.3";
  # ...
  doInstallCheck = true;
  installCheckTarget = "check";
}
</programlisting>
   </listitem>
   <listitem>
    <para>
     Some packages assume xcode is available and use <command>xcrun</command> to resolve build tools like <command>clang</command>, etc. This causes errors like <code>xcode-select: error: no developer tools were found at '/Applications/Xcode.app'</code> while the build doesn't actually depend on xcode.
    </para>
<programlisting>
stdenv.mkDerivation {
  name = "libfoo-1.2.3";
  # ...
  prePatch = ''
    substituteInPlace Makefile \
        --replace '/usr/bin/xcrun clang' clang
  '';
}
</programlisting>
    <para>
     The package <literal>xcbuild</literal> 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.
    </para>
   </listitem>
  </itemizedlist>
 </section>
</chapter>
