Re: [Patch, Fortran, OOP] PR 56261: seg fault call procedure pointer on polymorphic array

[Tobias Burnus <burnus at net-b dot de>]

Am 10.04.2013 16:21, schrieb Janus Weil:
> 2013/4/7 Tobias Burnus <burnus@net-b.de>:
> > > > Thus, the only place where the check can be is for:
> > > >
> > > >     f => ff
> > > >
> > > > In your example, the explicit interface of "ff" is known thus it should
> > > > be
> > > > testable at resolution time of the proc-pointer assignment.
> > > Right. However, strictly speaking, the pointer assignment as such is
> > > probably valid. But of course there is not much one can do with the
> > > proc-ptr afterwards, if it's invalid to call it ...
> >   Well, if one doesn't want to error on it, one can still warn. However, the
> > following states that it is invalid:
> >
> > "If the characteristics of the pointer object or the pointer target are such
> > that an explicit interface is required, both the pointer object and the
> > pointer target shall have an explicit interface." (F2008, para 4 of "7.2.2.4
> > Procedure pointer assignment")
> Ok, here is an updated patch, which does the discussed checking for
> procedure pointer assignments. For this I have introduced a new
> function 'gfc_explicit_interface_required', which checks all the items
> in F08:12.4.2.2 and is loosely based on the present checks in
> 'resolve_global_procedure' (which are replaced by the new function).
>
> I hope the general idea of the patch is ok and the error messages are
> sufficiently comprehensible.
>
> One leftover problem: The patch currently fails on the auto_char_len_4
> test case, which is not being rejected any more. Actually I'm not
> fully convinced that the dg-errors there are correct: If the EXTERNAL
> statements in auto_char_len_{1,2} do not trigger an "explicit
> interface required" warning, I don't see why the ones in
> auto_char_len_4 should.

Regarding auto_char_len_[12].f90: A warning about an "explicit interface 
required" would be a bad joke as it contains an assumed character length 
function, which is a deprecated feature (cf. B.2.6) and it does *not* 
work with an explicit interface:

character(len=*) function func()
  func = 'ABC'
end function func

Question: Which length does the function result have? Answer, it depends 
on the declaration in the caller:
  character(len=2) :: func
  print *, func()
means that it has length 2. If you have len=4 in another procedures, it 
will have len=4 in that scoping unit.


By contrast, auto_char_len_4 uses "normal" function results, which could 
be used with an explicit interface.

As F2008 states ("12.4.2.2 Explicit interface"), an explicit interface 
is required if: "[...] (3) the procedure has a result that [...] (c) has 
a nonassumed type parameter value that is not a constant expression,"

The assumed-type-parameter is used in auto_char_len_{1,2}.f90.

In auto_char_len_4.f90:  The example does not have anything to do with 
whole-file diagnostic; the problem is just that the characteristics do 
not match. (The functions itself use a constant length.) But if "len=n" 
also had been used in the functions, the error would be correct. Thus, I 
would like to keep such a diagnostic for external function declarations, 
which should trigger even if the called function is not in the same 
file. (One could move the warning to, e.g., resolve_variable.) Quote 
from *_4.f90:

SUBROUTINE s(n)
  CHARACTER(LEN=n), EXTERNAL :: a ! { dg-error "must have an explicit 
interface" }
  CHARACTER(LEN=n), EXTERNAL :: d ! { dg-error "must have an explicit 
interface" }

Tobias