Merge pull request #238993 from reckenrode/libiconvReal-darwin

libiconvReal: implement ABI compatibility on Darwin

pkgs/development/libraries/libiconv/default.nix

@@ -1,6 +1,7 @@
 { fetchurl, stdenv, lib
 , enableStatic ? stdenv.hostPlatform.isStatic
 , enableShared ? !stdenv.hostPlatform.isStatic
+, enableDarwinABICompat ? false
 }:
 
 # assert !stdenv.hostPlatform.isLinux || stdenv.hostPlatform != stdenv.buildPlatform; # TODO: improve on cross
@@ -28,8 +29,35 @@ stdenv.mkDerivation rec {
       ''
     + lib.optionalString (!enableShared) ''
       sed -i -e '/preload/d' Makefile.in
+    ''
+    # The system libiconv is based on libiconv 1.11 with some ABI differences. The following changes
+    # build a compatible libiconv on Darwin, allowing it to be sustituted in place of the system one
+    # using `install_name_tool`. This removes the need to for a separate, Darwin-specific libiconv
+    # derivation and allows Darwin to benefit from upstream updates and fixes.
+    + lib.optionalString enableDarwinABICompat ''
+      for iconv_h_in in iconv.h.in iconv.h.build.in; do
+        substituteInPlace "include/$iconv_h_in" \
+          --replace "#define iconv libiconv" "" \
+          --replace "#define iconv_close libiconv_close" "" \
+          --replace "#define iconv_open libiconv_open" "" \
+          --replace "#define iconv_open_into libiconv_open_into" "" \
+          --replace "#define iconvctl libiconvctl" "" \
+          --replace "#define iconvlist libiconvlist" ""
+      done
     '';
 
+  # This is hacky, but `libiconv.dylib` needs to reexport `libcharset.dylib` to match the behavior
+  # of the system libiconv on Darwin. Trying to do this by modifying the `Makefile` results in an
+  # error linking `iconv` because `libcharset.dylib` is not at its final path yet. Avoid the error
+  # by building without the reexport then clean and rebuild `libiconv.dylib` with the reexport.
+  #
+  # For an explanation why `libcharset.dylib` is reexported, see:
+  # https://github.com/apple-oss-distributions/libiconv/blob/a167071feb7a83a01b27ec8d238590c14eb6faff/xcodeconfig/libiconv.xcconfig
+  postBuild = lib.optionalString enableDarwinABICompat ''
+    make clean -C lib
+    NIX_CFLAGS_COMPILE+=" -Wl,-reexport-lcharset -L. " make -C lib -j$NIX_BUILD_CORES SHELL=$SHELL
+  '';
+
   configureFlags = [
     (lib.enableFeature enableStatic "static")
     (lib.enableFeature enableShared "shared")