[MacPorts] #71669: macports-libcxx: uses older c++ headers on newer macports-clang compilers

[MacPorts]

#71669: macports-libcxx: uses older c++ headers on newer macports-clang compilers
------------------------------+--------------------
  Reporter:  kencu            |      Owner:  (none)
      Type:  defect           |     Status:  new
  Priority:  Normal           |  Milestone:
 Component:  ports            |    Version:
Resolution:                   |   Keywords:
      Port:  macports-libcxx  |
------------------------------+--------------------

Comment (by tomio-arisaka):

 On macOS High Sierra (10.13), {{{legacysupport}}} PG and {{{macports-
 libcxx}}} are very useful.
 But some ports cannot be built with them due to {{{c++20}}} and
 {{{c++23}}}.\\

 So I tried to add the following keywords to the
 {{{legacysupport-1.1.tcl}}} file in order to build {{{poppler}}},
 {{{bitcoin}}}, and others.

 * {{{legacysupport.use_mp_cxx_header}}}: Use C++ header files included in
 macports clang instead of macports libcxx
 * {{{legacysupport.use_mp_cxx_libcxx}}}: Use a libcxx runtime included in
 macports clang instead of macports libcxx

 These keywords work only if macports clang is chosen.

 For example, how to use the new keywords:\\

 In the {{{poppler}}} portfile, the following keywords work out:

 {{{
 legacysupport.use_mp_libcxx yes
 legacysupport.use_mp_cxx_header yes
 }}}

 or

 {{{
 legacysupport.use_mp_cxx_libcxx yes
 legacysupport.use_mp_cxx_header yes
 }}}

 The patch which adds the new keywords is as follows:

 {{{
 $ diff -u legacysupport-1.1.tcl.orig legacysupport-1.1.tcl
 --- legacysupport-1.1.tcl.orig  2026-08-03 18:29:44.000000000 +0900
 +++ legacysupport-1.1.tcl       2026-08-18 21:00:00.000000000 +0900
 @@ -16,6 +16,10 @@
  #                                create a wrapper so that only MacPorts
 libstdc++ is used
  #
  #   legacysupport.use_mp_libcxx: Use an update libcxx runtime from a
 recent macports clang build
 +#
 +#   legacysupport.use_mp_cxx_header: Use C++ header files included in
 macports clang instead of macports libcxx
 +#
 +#   legacysupport.use_mp_cxx_libcxx: Use a libcxx runtime included in
 macports clang instead of macports libcxx

  namespace eval legacysupport {
      # Newest Darwin version that requires legacy support.
 @@ -38,6 +42,12 @@
  options legacysupport.use_mp_libcxx
  default legacysupport.use_mp_libcxx     no

 +options legacysupport.use_mp_cxx_header
 +default legacysupport.use_mp_cxx_header no
 +
 +options legacysupport.use_mp_cxx_libcxx
 +default legacysupport.use_mp_cxx_libcxx no
 +
  if {[exists makefile.override]} {
      pre-configure {
          ui_error "The legacysupport PG must be included *before* the
 makefile PG"
 @@ -162,11 +172,29 @@
          set ls_cache_cppflags "[legacysupport::get_cpp_flags]"

          # Flags for using MP libcxx
 -        if { [option legacysupport.use_mp_libcxx] &&
 ${configure.cxx_stdlib} eq "libc++" } {
 -            legacysupport::add_once depends_lib append port:macports-
 libcxx
 -            append ls_cache_incpath  " ${prefix}/include/libcxx/v1"
 -            append ls_cache_ldflags  " -L${prefix}/lib/libcxx"
 -            append ls_cache_cppflags " -nostdinc++
 -isystem${prefix}/include/libcxx/v1"
 +        if { ([option legacysupport.use_mp_libcxx] || [option
 legacysupport.use_mp_cxx_libcxx]) && ${configure.cxx_stdlib} eq "libc++" }
 {
 +            global configure.compiler
 +            set ls_cxx_inc  "${prefix}/include/libcxx/v1"
 +            # Flags for using C++ header files which are included in MP
 clang instead of MP libcxx
 +            if { [option legacysupport.use_mp_cxx_header] && [regexp
 {^macports-clang-([0-9]+\.*[0-9]*$)} ${configure.compiler} matched
 mp_clang_ver] == 1 } {
 +                set ls_cxx_inc
 "${prefix}/libexec/llvm-${mp_clang_ver}/include/c++/v1"
 +                append ls_cache_cppflags "
 -D_LIBCPP_DISABLE_AVAILABILITY"
 +            }
 +            set ls_cxx_lib  "${prefix}/lib/libcxx"
 +            # Flags for using a libcxx runtime which is included in MP
 clang instead of MP libcxx
 +            if { [option legacysupport.use_mp_cxx_libcxx] && [regexp
 {^macports-clang-([0-9]+\.*[0-9]*$)} ${configure.compiler} matched
 mp_clang_ver] == 1 } {
 +                set ls_cxx_lib
 "${prefix}/libexec/llvm-${mp_clang_ver}/lib/libc++"
 +                append ls_cache_ldflags  " -Wl,-rpath,${ls_cxx_lib}"
 +                if {${mp_clang_ver} > 17} {
 +                    append ls_cache_ldflags  "
 -Wl,-rpath,${prefix}/libexec/llvm-${mp_clang_ver}/lib/libunwind"
 +                }
 +                legacysupport::add_once depends_lib append
 port:clang-${mp_clang_ver}
 +            } else {
 +                legacysupport::add_once depends_lib append port:macports-
 libcxx
 +            }
 +            append ls_cache_incpath  " ${ls_cxx_inc}"
 +            append ls_cache_ldflags  " -L${ls_cxx_lib}"
 +            append ls_cache_cppflags " -nostdinc++ -isystem${ls_cxx_inc}"
          }

          ui_debug "legacysupport: ldflags  ${ls_cache_ldflags}"
 @@ -215,6 +243,8 @@
  option_proc legacysupport.newest_darwin_requires_legacy
 legacysupport::legacysupport_proc
  option_proc legacysupport.legacysupport.use_mp_libcxx
 legacysupport::legacysupport_proc
  option_proc legacysupport.legacysupport.use_static
 legacysupport::legacysupport_proc
 +option_proc legacysupport.legacysupport.use_mp_cxx_header
 legacysupport::legacysupport_proc
 +option_proc legacysupport.legacysupport.use_mp_cxx_libcxx
 legacysupport::legacysupport_proc

  # see https://trac.macports.org/ticket/59832
  post-destroot {
 }}}

 I guess {{{legacysupport.use_mp_cxx_libcxx}}} is out of the main purpose
 of {{{macports-libcxx}}}.
 But it is useful for me in order to build {{{nodejs24}}} and
 {{{NGSolve}}}.

 I am using these keywords only on macOS High Sierra (10.13).
 So I don't know whether they work right on the other macOS or not.
 But I hope this patch will be an example for someone who wants to use
 later {{{clang++}}} on earlier macOS.

-- 
Ticket URL: <https://trac.macports.org/ticket/71669#comment:5>
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