[Bug fortran/77978] New: stop codes misinterpreted in both f2003 and f2008

[john.harper at vuw dot ac.nz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77978

            Bug ID: 77978
           Summary: stop codes misinterpreted in both f2003 and f2008
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: john.harper at vuw dot ac.nz
  Target Milestone: ---

Stop codes changed from the f2003 standard to f2008. The first of these 2 
programs has a stop code valid in f2003 but not in f2008, the second has a stop
code valid in f2008 but not in f2003. But gfortran 6.1.1 happily compiles and
runs both programs with either -std=f2003 or -f2008.

Here are the program listings, gfortran -v result, and the results of compiling
with the -std options that should not have worked:

cayley[~/Jfh] % cat stopnumber.f90
! stop666 (no space before 666) is valid f95 or f2003 but bad f2008
  implicit none
  stop666
end program
cayley[~/Jfh] % cat stopnumber2.f90
! stop expression is valid f2008 but bad f2003
  implicit none                                                                 
  stop merge(667,668,.true.)                                                    
end program                                                                     
cayley[~/Jfh] % gfortran -v
Using built-in specs.                                                           
COLLECT_GCC=gfortran                                                            
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/6.1.1/lto-wrapper          
Target: x86_64-pc-linux-gnu                                                     
Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
--enable-threads=posix --enable-libmpx --with-system-zlib --with-isl
--enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu
--disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object
--enable-linker-build-id --enable-lto --enable-plugin
--enable-install-libiberty --with-linker-hash-style=gnu
--enable-gnu-indirect-function --disable-multilib --disable-werror
--enable-checking=release                                          
Thread model: posix                                                             
gcc version 6.1.1 20160602 (GCC)                                                
cayley[~/Jfh] % gfortran -std=f2008 stopnumber.f90
cayley[~/Jfh] % ./a.out                                                         
STOP 666                                                                        
cayley[~/Jfh] % gfortran -std=f2003 stopnumber2.f90                             
cayley[~/Jfh] % ./a.out
STOP 667                                                                        
cayley[~/Jfh] %