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From: "kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/109275] Bad error messages for interfaces describing
 surrounding program unit
Date: Fri, 24 Mar 2023 14:14:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109275

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kargl at gcc dot gnu.org

--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to Raoul Hidalgo Charman from comment #0)
> The following example, where an interface is defined for the surrounding
> program unit fails to compile:
>=20
>       function foo(arg1) result(res)
>=20
>       interface foo
>         function foo(arg1)
>           integer*2 foo(3)
>           integer*8 arg1
>         end function foo
>       end interface
>=20
>       integer*2 res(3)
>       integer*8 arg1
>       res =3D (/1,2,int(arg1,4)/)
>       end function
>=20
> Giving the error:
>=20
> recursive-interface.f:4:8:
>=20
>     4 |         function foo(arg1)
>       |        1
> Error: Procedure pointer result =E2=80=98foo=E2=80=99 at (1) is missing t=
he pointer attribute
>=20
> Given you can use this function with that interface, this appears to be an
> incorrect warning.

It's not a warning.  It is an error.  And, yes it seems wrong.

>=20
> While I don't see any reason why a correctly defined interface would not =
be
> allowed, especially if it's not even used and result is used to disambigu=
ate
> the symbol, other compilers do fail to compile and complain about using an
> interface with the same name as the surrounding program unit. XLF complai=
ned
> for normal interfaces, while Sun Studio just complains for generic interf=
ace.
>=20
> GFortrans error message should at least be more informative, explicitly
> saying it's not allowed if this is the case.
>=20
> I came across this issue because a library had an include with many
> interfaces, and was then trying to use some of those interfaces in the
> definitions of those program units.

It seems to be invalid Fortran.  From Fortran 2018

     C1501 (R1501) An interface-block in a subprogram shall not contain
     an interface-body for a procedure defined by that subprogram.

It seems gfortran is missing a check for C1501.=