[Bug fortran/61069] Gfortran allows functions to be called as subroutines when defined in a separate source file

["kargl at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61069

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |kargl at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #3 from kargl at gcc dot gnu.org ---
(In reply to Tristan Moody from comment #0)
> This might not be the easiest thing to fix, as (1) it appears that verifying
> the semantics of a function call happen on a per-source-file basis, and (2)
> there is no apparent way of marking a procedure as either a subroutine or a
> function once it has been translated to assembly or object code.

Yes, there is an apparent way, but one must learn the Fortran
language to use properly use it.

> When the main program and the two subprograms are all in the same file, the
> error is correctly caught by gfortran:

This happens because gfortran can build the INTERFACEs for
bar and baz.

> However, when the main program is a separate file from the two subprograms,
> (i.e. program foo in foo.f90, bar and baz in bar.f90, then compiled with
> "gfortran foo.f90 bar.f90" ), then compilation proceeds without issue and
> the resulting executable behaves as though bar() was called and its result
> discarded.  Filing this bug report as this non-standard behavior does not
> appear in any of the documentation I have seen.

When you compile the main program and the 2 subprogram as separate
files, each is valid fortran code.  The code in each file is standard
conforming.  There is no non-standard behavior.

Now, to address your problem.  There are two mechanism you can use to
fix the situation.  (1) Put bar() and baz() in a module and USE it; or,
(2) Use INTERFACE statements to *explicitly* tell the compiler about 
bar and baz. 


Your favorite reference on modern Fortran should include a discussion
on implicit and explicit interfaces.