Fails to build on Darwin:

clang++ -shared -s highlight_wrap.o  -L../../src/ -lhighlight -L/nix/store/bi85dm5dqzjfm0i9qj3ijjj9w9xayy8w-lua-5.2.4/lib -llua -lm -o highlight.so
ld: warning: option -s is obsolete and being ignored
Undefined symbols for architecture x86_64:
  "_PL_markstack_max", referenced from:
      __wrap_DataDir_getLangPath in highlight_wrap.o
      __wrap_DataDir_getThemePath in highlight_wrap.o
      __wrap_DataDir_getFiletypesConfPath in highlight_wrap.o
      __wrap_DataDir_getPluginPath in highlight_wrap.o
      __wrap_DataDir_guessFileType in highlight_wrap.o
      __wrap_SyntaxReader_initLuaState in highlight_wrap.o
      __wrap_new_RegexElement in highlight_wrap.o
      ...
  "_PL_markstack_ptr", referenced from:
      __wrap_DataDir_assocByExtension_set in highlight_wrap.o
      __wrap_DataDir_assocByExtension_get in highlight_wrap.o
      __wrap_DataDir_assocByFilename_set in highlight_wrap.o
      __wrap_DataDir_assocByFilename_get in highlight_wrap.o
      __wrap_DataDir_assocByShebang_set in highlight_wrap.o
      __wrap_DataDir_assocByShebang_get in highlight_wrap.o
      __wrap_DataDir_initSearchDirectories in highlight_wrap.o
      ...
  "_PL_stack_base", referenced from:
      __wrap_DataDir_assocByExtension_set in highlight_wrap.o
      __wrap_DataDir_assocByExtension_get in highlight_wrap.o
      __wrap_DataDir_assocByFilename_set in highlight_wrap.o
      __wrap_DataDir_assocByFilename_get in highlight_wrap.o
      __wrap_DataDir_assocByShebang_set in highlight_wrap.o
      __wrap_DataDir_assocByShebang_get in highlight_wrap.o
      __wrap_DataDir_initSearchDirectories in highlight_wrap.o
      ...
  "_PL_stack_sp", referenced from:
      __wrap_DataDir_assocByExtension_set in highlight_wrap.o
      __wrap_DataDir_assocByExtension_get in highlight_wrap.o
      __wrap_DataDir_assocByFilename_set in highlight_wrap.o
      __wrap_DataDir_assocByFilename_get in highlight_wrap.o
      __wrap_DataDir_assocByShebang_set in highlight_wrap.o
      __wrap_DataDir_assocByShebang_get in highlight_wrap.o
      __wrap_DataDir_initSearchDirectories in highlight_wrap.o
      ...
  "_PL_sv_immortals", referenced from:
      __wrap_DataDir_getLangPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getLangPath__SWIG_1 in highlight_wrap.o
      __wrap_DataDir_getSystemDataPath in highlight_wrap.o
      __wrap_DataDir_getPluginPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_1 in highlight_wrap.o
      SWIG_AsVal_bool(sv*, bool*) in highlight_wrap.o
      ...
  "_Perl_croak", referenced from:
      SWIG_croak_null() in highlight_wrap.o
      __wrap_DataDir_getLangPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getLangPath__SWIG_1 in highlight_wrap.o
      __wrap_DataDir_getLangPath in highlight_wrap.o
      __wrap_DataDir_getSystemDataPath in highlight_wrap.o
      __wrap_DataDir_getPluginPath__SWIG_0 in highlight_wrap.o
      ...
  "_Perl_get_sv", referenced from:
      __wrap_DataDir_assocByExtension_set in highlight_wrap.o
      SWIG_croak_null() in highlight_wrap.o
      __wrap_DataDir_assocByExtension_get in highlight_wrap.o
      __wrap_DataDir_assocByFilename_set in highlight_wrap.o
      __wrap_DataDir_assocByFilename_get in highlight_wrap.o
      __wrap_DataDir_assocByShebang_set in highlight_wrap.o
      __wrap_DataDir_assocByShebang_get in highlight_wrap.o
      ...
  "_Perl_gv_add_by_type", referenced from:
      SWIG_Perl_ConvertPtr(sv*, void**, swig_type_info*, int) in highlight_wrap.o
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_gv_init_pvn", referenced from:
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_hv_common", referenced from:
      SWIG_Perl_ConvertPtr(sv*, void**, swig_type_info*, int) in highlight_wrap.o
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_hv_common_key_len", referenced from:
      SWIG_Perl_ConvertPtr(sv*, void**, swig_type_info*, int) in highlight_wrap.o
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_markstack_grow", referenced from:
      __wrap_DataDir_getLangPath in highlight_wrap.o
      __wrap_DataDir_getThemePath in highlight_wrap.o
      __wrap_DataDir_getFiletypesConfPath in highlight_wrap.o
      __wrap_DataDir_getPluginPath in highlight_wrap.o
      __wrap_DataDir_guessFileType in highlight_wrap.o
      __wrap_SyntaxReader_initLuaState in highlight_wrap.o
      __wrap_new_RegexElement in highlight_wrap.o
      ...
  "_Perl_mg_find", referenced from:
      SWIG_Perl_ConvertPtr(sv*, void**, swig_type_info*, int) in highlight_wrap.o
      _boot_highlight in highlight_wrap.o
  "_Perl_mg_get", referenced from:
      SWIG_Perl_ConvertPtr(sv*, void**, swig_type_info*, int) in highlight_wrap.o
      SWIG_AsVal_bool(sv*, bool*) in highlight_wrap.o
  "_Perl_newRV_noinc", referenced from:
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_newSV", referenced from:
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_newSV_type", referenced from:
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_newSViv", referenced from:
      __wrap_SyntaxReader_load in highlight_wrap.o
      __wrap_SyntaxReader_getKeywordListGroup in highlight_wrap.o
      __wrap_SyntaxReader_getPersistentSnippetsNum in highlight_wrap.o
      __wrap_SyntaxReader_getOpenDelimiterID in highlight_wrap.o
      __wrap_RegexElement_open_get in highlight_wrap.o
      __wrap_RegexElement_end_get in highlight_wrap.o
      __wrap_RegexElement_capturingGroup_get in highlight_wrap.o
      ...
  "_Perl_newSVuv", referenced from:
      __wrap_SyntaxReader_getRawStringPrefix in highlight_wrap.o
      __wrap_SyntaxReader_getContinuationChar in highlight_wrap.o
      __wrap_RegexElement_kwClass_get in highlight_wrap.o
      __wrap_RegexElement_priority_get in highlight_wrap.o
      __wrap_RegexElement_constraintLineNum_get in highlight_wrap.o
      __wrap_ReGroup_length_get in highlight_wrap.o
      __wrap_ReGroup_kwClass_get in highlight_wrap.o
      ...
  "_Perl_newXS", referenced from:
      _boot_highlight in highlight_wrap.o
  "_Perl_sv_2bool_flags", referenced from:
      SWIG_AsVal_bool(sv*, bool*) in highlight_wrap.o
  "_Perl_sv_2iv_flags", referenced from:
      SWIG_Perl_ConvertPtr(sv*, void**, swig_type_info*, int) in highlight_wrap.o
      SWIG_AsVal_unsigned_SS_int(sv*, unsigned int*) in highlight_wrap.o
      _boot_highlight in highlight_wrap.o
      SWIG_AsVal_long(sv*, long*) in highlight_wrap.o
      SWIG_AsVal_double(sv*, double*) in highlight_wrap.o
  "_Perl_sv_2mortal", referenced from:
      __wrap_SyntaxReader_load in highlight_wrap.o
      __wrap_SyntaxReader_getRawStringPrefix in highlight_wrap.o
      __wrap_SyntaxReader_getContinuationChar in highlight_wrap.o
      __wrap_SyntaxReader_getKeywordListGroup in highlight_wrap.o
      __wrap_SyntaxReader_getPersistentSnippetsNum in highlight_wrap.o
      __wrap_SyntaxReader_getOpenDelimiterID in highlight_wrap.o
      __wrap_RegexElement_open_get in highlight_wrap.o
      ...
  "_Perl_sv_2nv_flags", referenced from:
      SWIG_AsVal_double(sv*, double*) in highlight_wrap.o
  "_Perl_sv_2pv_flags", referenced from:
      SWIG_croak_null() in highlight_wrap.o
      __wrap_DataDir_getLangPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getLangPath__SWIG_1 in highlight_wrap.o
      __wrap_DataDir_getSystemDataPath in highlight_wrap.o
      __wrap_DataDir_getPluginPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_1 in highlight_wrap.o
      ...
  "_Perl_sv_2uv_flags", referenced from:
      SWIG_AsVal_unsigned_SS_int(sv*, unsigned int*) in highlight_wrap.o
      SWIG_AsVal_long(sv*, long*) in highlight_wrap.o
  "_Perl_sv_bless", referenced from:
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_sv_free2", referenced from:
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_sv_isobject", referenced from:
      SWIG_Perl_ConvertPtr(sv*, void**, swig_type_info*, int) in highlight_wrap.o
      SWIG_croak_null() in highlight_wrap.o
      __wrap_DataDir_getLangPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getLangPath__SWIG_1 in highlight_wrap.o
      __wrap_DataDir_getSystemDataPath in highlight_wrap.o
      __wrap_DataDir_getPluginPath__SWIG_0 in highlight_wrap.o
      ...
  "_Perl_sv_magic", referenced from:
      _boot_highlight in highlight_wrap.o
      SWIG_Perl_MakePtr(sv*, void*, swig_type_info*, int) in highlight_wrap.o
  "_Perl_sv_newmortal", referenced from:
      __wrap_DataDir_assocByExtension_set in highlight_wrap.o
      __wrap_DataDir_assocByExtension_get in highlight_wrap.o
      __wrap_DataDir_assocByFilename_set in highlight_wrap.o
      __wrap_DataDir_assocByFilename_get in highlight_wrap.o
      __wrap_DataDir_assocByShebang_set in highlight_wrap.o
      __wrap_DataDir_assocByShebang_get in highlight_wrap.o
      __wrap_DataDir_initSearchDirectories in highlight_wrap.o
      ...
  "_Perl_sv_setiv", referenced from:
      _boot_highlight in highlight_wrap.o
  "_Perl_sv_setpvf", referenced from:
      __wrap_DataDir_assocByExtension_set in highlight_wrap.o
      __wrap_DataDir_assocByExtension_get in highlight_wrap.o
      __wrap_DataDir_assocByFilename_set in highlight_wrap.o
      __wrap_DataDir_assocByFilename_get in highlight_wrap.o
      __wrap_DataDir_assocByShebang_set in highlight_wrap.o
      __wrap_DataDir_assocByShebang_get in highlight_wrap.o
      __wrap_DataDir_initSearchDirectories in highlight_wrap.o
      ...
  "_Perl_sv_setpvn", referenced from:
      __wrap_DataDir_getLangPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getLangPath__SWIG_1 in highlight_wrap.o
      __wrap_DataDir_getSystemDataPath in highlight_wrap.o
      __wrap_DataDir_getPluginPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_1 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_2 in highlight_wrap.o
      ...
  "_Perl_sv_setref_pv", referenced from:
      __wrap_DataDir_assocByExtension_get in highlight_wrap.o
      __wrap_DataDir_assocByFilename_get in highlight_wrap.o
      __wrap_DataDir_assocByShebang_get in highlight_wrap.o
      __wrap_SyntaxReader_getKeywords in highlight_wrap.o
      __wrap_SyntaxReader_getKeywordClasses in highlight_wrap.o
      __wrap_SyntaxReader_getRegexElements in highlight_wrap.o
      __wrap_SyntaxReader_getPersistentSnippets in highlight_wrap.o
      ...
  "_Perl_sv_setsv_flags", referenced from:
      __wrap_DataDir_getLangPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getLangPath__SWIG_1 in highlight_wrap.o
      __wrap_DataDir_getSystemDataPath in highlight_wrap.o
      __wrap_DataDir_getPluginPath__SWIG_0 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_1 in highlight_wrap.o
      __wrap_DataDir_getThemePath__SWIG_2 in highlight_wrap.o
      ...
ld: symbol(s) not found for architecture x86_64
clang-7: error: linker command failed with exit code 1 (use -v to see invocation)

highlight's Perl bindings are currently disabled on Darwin, but I
didn't make the dependency here conditional so that if that is ever
fixed, this function won't need to be updated. p-i is smart enough to
disable the test for highlight if it can't find the Perl module.