[Bug fortran/126872] New: Change in visibility of C bound functions with 16.2.0

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126872

            Bug ID: 126872
           Summary: Change in visibility of C bound functions with 16.2.0
           Product: gcc
           Version: 16.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rpmcnally at gmail dot com
  Target Milestone: ---

It appears to me that the 'private' keyword is now affecting C bound functions
in Fortran modules, though I believe that bind(C) is supposed to automatically
provide for external linkage.  I'm not sure if this is a bug or an intended
change.

    module moduleA

        implicit none

        private

    contains

    subroutine doThing() bind(C, name="doThing")
    end subroutine doThing

    end module moduleA

$ gfortran --version
GNU Fortran (GCC) 16.2.0

$ gfortran -fPIC -shared -o libmoduleA.so moduleA.f90

$ nm libmoduleA.so | grep -i dothing
0000000000000559 t doThing

Under gfortran versions 9.3, 12.2, 15.3, and 16.1 all produce a library with
external visibility instead of static.  It does appear the visibility can be
toggled by explicitly listing the C bound function as 'public'.