[Bug fortran/84513] New: gfortran -M generates circular dependency

[eh.toussaint at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84513

            Bug ID: 84513
           Summary: gfortran -M generates circular dependency
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eh.toussaint at gmail dot com
  Target Milestone: ---

When using the -M option to let gfortran generate a rule for inclusion in
makefiles, the following code (all in one file) results in a circular
dependency for the .mod file.

$ cat foobar.f90
module bar
end module

program foo
use bar
end program
---end foobar.f90

$ gfortran -cpp -M foobar.f90
foobar.o bar.mod: foobar.f90 bar.mod

It's not a major problem, because (GNU) Make simply drops it with the following
message, but I'd still like to report it for the sake of neatness.

make: Circular bar.mod <- bar.mod dependency dropped.