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f2py (1.20) drops definition`typedef signed char signed_char;` for callbacks in some circumstances

See original GitHub issue

Reproducing code example:

Unfortunately this is part of a larger project. And may be tricky to reproduce. Depending on other definition of callback functions, I get the error message below for the second routine.

this causes the error:

subroutine pyexit(code)

  implicit none
  integer(kind=4), intent(IN):: code

  !f2py    integer intent(in): code
  !f2py    intent(callback, hide) endkepler()
  external endkepler

  call endkepler()

end subroutine pyexit

!=======================================================================

subroutine pygets(ttymsg)

  implicit none
  character*(*), intent(inout) :: ttymsg

  integer, parameter :: n = 132
  integer :: i
  integer(kind=1), dimension(n) :: data

  !f2py    intent(callback, hide) ttykepler(data)
  external ttykepler

  call ttykepler(data)

  do i = 1, min(n, len(ttymsg))
     ttymsg(i:i) = char(data(i))
  end do

end subroutine pygets

but if I change the first routine to

subroutine pyexit(code)

  implicit none
  integer(kind=4), intent(IN):: code

  !f2py    integer intent(in): code
  !f2py    intent(callback, hide) endkepler(code)
  external endkepler

  call endkepler(code)
end subroutine pyexit

then the compilation error in the second routine does not occur.

Error message:

...
/tmp/tmp2skuwcza/src.linux-x86_64-3.9/_kepler_NBURN_8192_JMZ_1983_FULDAT_fuldat1_f_CPU_Intel_R_Xeon_R_W_2145_CPU_3_70GHzmodule.c:29:63: error: unknown type name ‘signed_char’; did you mean ‘signed char’?
   29 | typedef void(*cb_ttykepler_in_pygets__user__routines_typedef)(signed_char *);
...