Refactoring code into a subroutine

1

I often create a subroutine by

  • pasting a block of code into an empty subroutine
  • compiling with IMPLICIT NONE
  • copying declarations from the source file the code was copied from. Sometimes what the compiler thinks is an undeclared variable is actually a function which needs to be imported from a module.
  • making some variables INTENT(IN) or INTENT(out) arguments

I wonder if there are any tools to automate this. Something that did 80% of the job would still be useful.

A Windows batch file that uses Unix tools to list undeclared variables is

@ echo off
:: list undeclared variables in Fortran source file, compiled with gfortran
:: usage: gfundec.bat foo.f90
setlocal
set gfout=temp_gf.txt
gfortran -c -Wall %1 2> %gfout%
echo undeclared in %1:
grep IMPLICIT %gfout% | tr -d "'" | cut -d ' ' -f 3

When run on the code

module foo_mod
implicit none
contains
subroutine bar()
! code below copied from another source file
ndays = size(xx,1)
nret = ndays - 1
nsym = size(xx,2)
allocate (profits(nret,nsym),xpos(ndays))
do nma2=nma2_min,nma2_max
   write (*,"(/,a,1x,i0)") "nma2",nma2
   xpos = merge(1.0_dp,-0.5_dp,rollmean_ratio(xx(:,1),1,nma2) > 1.0_dp)
   profits = spread(xpos(:nret),2,nsym) * xret
   if (.false.) call print_stats(cstats_ret,profits,sym,title="profits")
   call print_tangent_port(profits,sym,cstats_ret=cstats_ret,print_uncon=print_tangent_portfolio, &
                        print_long_only=print_tangent_port_long_only)
end do
end subroutine bar

it says

undeclared in temp_mac_tangent.f90:
cstats_ret
ndays
nma2
nma2_max
nma2_min
nret
nsym
print_tangent_port_long_only
print_tangent_portfolio
profits
sym
xx
2

You could pass the report through a small, almost trivial, Fortran program to generate default declarations:

  • Variable names that start with one of i … n are probably meant to be integers (given that they are not declared makes that likely)
  • Variable names that start with something else are probably reals

The program could also make a copy of the code and insert these declarations and do the other boilerplating stuff (module … end module, etc.)
Running it through the compiler again will alert you to the flagrant mistakes: taking a substring from a real variable for instance.

3

Instead of IMPLICIT NONE you might consider IMPLICIT NONE(TYPE,EXTERNAL) that would require declaration of functions as well.

Note that an IMPLICIT NONE in the specification part of a module also applies to any contained subprograms in the module, which explains the error messages you got for subroutine bar.

4

What compiler supports that? Ifort still chokes .

5

The Cray compiler supports it (along with most of F2018). Intel claims ifort supports 2018. Are you using an old version? A newish Intel compiler seems to work:

% /opt/intel/oneapi/compiler/2021.1.1/mac/bin/intel64/ifort -c test.f90
% cat test.f90
implicit none (type,external)
end program
%

6

The Eclipse IDE photran plug-in has a refactoring set of functionalities that do what you are after and more.

7

Latest ifort. It “supports” it but it does not work.