[Bug fortran/77903] [F08] gfortran 6.1.0/7.0.0 accept invalid code with conflicting module/submodule interfaces

[pault at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77903

--- Comment #8 from Paul Thomas <pault at gcc dot gnu.org> ---
(In reply to Damian Rouson from comment #0)
> Gfortran accepts invalid code in which an implicitly typed interface body
> has the same name as a conflicting, explicitly typed module function
> implemented in a submodule.  See below.
> 
> Damian
> 
> 
> $ cat one.f90
> module one_module
>   implicit none
>   interface
>     module function one()
>     end function
>   end interface
> end module
> 
> submodule(one_module) one_submodule
>   implicit none
> contains
>   integer module function one()
>     one = 1
>   end function
> end submodule  
> 
> use one_module
> print *,one()," is not ",1
> end 
> 
> $ gfortran -std=f2008 -Wall -fcheck=all one.f90 
> 
> $ ./a.out
>    9.18340949E-41  is not            1
> 
> $ gfortran --version
> GNU Fortran (MacPorts gcc6 6.1.0_0) 6.1.0

Interestingly, ifort accepts this and imposes the interface definition to the
extent of making the type conversion.

I will have to dwell some more on this.

Paul