Re: [PATCH] Fortran: procedures with BIND(C) attribute require explicit interface [PR85877]

[Harald Anlauf <anlauf@gmx.de>]

Hi Thomas,

Am 18.03.23 um 19:52 schrieb Thomas Koenig via Gcc-patches:
> Hi Harald,
> 
>> the Fortran standard requires an explicit procedure interface in certain
>> situations, such as when they have a BIND(C) attribute (F2018:15.4.2.2).
>> The attached patch adds a check for this.
>>
>> Regtested on x86_64-pc-linux-gnu.  OK for mainline?
> 
> While this fixes the ICE, it misses
> 
> function f() bind(c)
>    f = 42.
> end
> 
> subroutine p
>    bind(c) f     ! { dg-error "must be explicit" }
>    x = f()
> end

what do you mean by "it misses"?  I do not see an explicit interface
here, only a global symbol.  All compiler I tried with the above
code reject it one way or the other, e g. Cray:

   x = f()
   ^
ftn-954 crayftn: ERROR P, File = pr85877-2.f90, Line = 12, Column = 3
   Procedure "f", referenced at line 6 (pr85877-2.f90) must have an 
explicit interface because one or more arguments have the BIND attribute.


> subroutine s
>    interface
>       function g() bind(c)
>       end function g
>    end interface
>    x = g()
> end
> 
> where the interface is picked up via a global symbol.

Is it really true that this is in the spirit of the standard?
Is the global declaration above really equivalent to an explicit
interface?

I would expect legal code to be like:

function g() bind(c)
   g = 42.
end

subroutine s
   interface
      function g() bind(c)
      end function g
   end interface
   x = g()
end

unless you do it in the context of a module and in the right way.

> This code
> may not be valid; nagfor rejects it, but I cannot find a
> constraint at least in the F2022 draft that prohibits it.

I thought that F2018:15.4.2.2 and F2023:15.4.2.2(7) are rather
clear and "explicit" on this.  IMHO the case of "f" above seems
to be excluded and thus not conforming.

> Hm... might it be better to check for attr->module_procedure ||
> attr->if_source == IFSRC_IFBODY?

Maybe we should find a set of legal and illegal cases that we
can agree upon.

Thanks,
Harald

> Best regards
> 
>      Thomas
> 
>