libiconv: add UTF-8-MAC encoding patch

Author: reckenrode

pkgs/development/libraries/libiconv/default.nix

@@ -31,6 +31,13 @@ stdenv.mkDerivation rec {
   setupHooks = [
     ../../../build-support/setup-hooks/role.bash
     ./setup-hook.sh
+  patches = [
+    # Add support for the UTF-8-MAC encoding. This is needed for correct behavior of applications that interact with
+    # the filesystem on Darwin because it uses a variant of NFD to store filenames.
+    #
+    # Patch is vendored to avoid an infinite recursion in the Darwin bootstrap.
+    # Source: https://github.com/macports/macports-ports/blob/ce1083dbec406fcea0f2678308ae85639798aa6e/textproc/libiconv/files/patch-utf8mac.diff
+    ./patch-utf8mac.diff
   ];
 
   postPatch =
@@ -82,6 +89,12 @@ stdenv.mkDerivation rec {
   # remove after gnulib is updated
   ++ lib.optional stdenv.hostPlatform.isCygwin "gl_cv_clean_version_stddef=yes";
 
+  preBuild = ''
+    # The UTF-8-MAC patch requires regenerating `flags.h`
+    make -C lib genflags
+    lib/genflags > lib/flags.h
+  '';
+
   passthru = { inherit setupHooks; };
 
   meta = {