Please find attached a patch, it is based on Steve Kargl's patch in 
PR93580 adding  a check for %len and test case.

The commit message in the patch includes change logs as I believe that 
is the intended way forward. One thing I'm unsure of it how handle 
multiple authors, it was easy in the ChangeLog files but it is not 
obvious for git commit messages.

OK for master and gcc 9 branch?

gcc/fortran/ChangeLog:

     Steven G. Kargl  <kargl@gcc.gnu.org>
     Mark Eggleston  <markeggleston@gcc.gnu.org>

     PR fortran/93580
     * primary.c (gfc_match_varspec): If the symbol following %
     is re or im and the primary expression type is not BT_COMPLEX
     issue an error. If the symbol is len and the primary
     expression type is not BT_CHARACTER is an error.

gcc/testsuite/ChangeLog:

     Mark Eggleston <markeggleston@gcc.gnu.org>

     PR fortran/93580
     * gfortran.dg/dg/pr93580.f90: New test.

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