Re: [fortran, 4.5] Implement errmsg for [de]allocate

[Steve Kargl <sgk at troutmask dot apl dot washington dot edu>]

On Wed, Dec 03, 2008 at 08:28:48PM +0100, Tobias Burnus wrote:
> Hi Steve,
> 
> Steve Kargl wrote:
> > The attached patch implements the F2003 feature of ERRMSG= in
> > the [DE]ALLOCATE statements.  The current patch makes use of
> > the infrastructure for STAT= to determine if a failure occurs.
> >   
> Somehow it does not work if one additionally requests a STAT= variable:
> 
>   deallocate(x, stat=i, errmsg=err)
>                      1
> Error: Syntax error in DEALLOCATE statement at (1)
> 
> (Ditto for: errmsg=..., stat=...)

I may have misinterpreted the 'or' in the BNF:

R623 allocate-stmt is ALLOCATE ( [ type-spec :: ] allocation-list
                        [, alloc-opt-list ] )
R624 alloc-opt     is STAT = stat-variable
                   or ERRMSG = errmsg-variable
                   or SOURCE = source-expr

alloc-opt-list is not defined but C630 suggests that a combination of
the alloc-opts can appear.

C630 (R624) No alloc-opt shall appear more than once in a given alloc-opt-list.

It's easy to fix.  I'll work out it this weekend.

> Additionally: Can we add a -Wsurprising which checks for the presence of
> STAT= when ERRMSG= is given? NAG f95 prints:
> 
> Warning: hfjgf.f90, line 6: ERRMSG= is useless without STAT=
> 
> >   deallocate(x, x, errmsg=err)
> >   print *, err
> There are several issues:
> a) "deallocate(x, x)" is invalid, which can be compile-time diagnosable
> (as e.g. ifort does), better place it in two lines

OK.  gfortran doesn't currently catch at compile time.

REMOVE:kargl[125] gfc4x -o z b.f90
REMOVE:kargl[126] ./z
At line 4 of file b.f90
Fortran runtime error: Attempt to DEALLOCATE unallocated 'i'
REMOVE:kargl[127] cat b.f90
program a
   integer, allocatable :: i(:)
   allocate(i(4))
   deallocate(i, i)
end program a


> b) "print *, err" is invalid - it always prints uninitialized value (in
> case of success). In case of a failure, it does not print anything as
> DEALLOCATE aborts

The code in the email was a quick hack to show the current error
message.  The testcase is completely legal.

> "If an error condition occurs during execution of an ALLOCATE statement
> that does not contain the STAT= specifier, execution of the program is
> terminated."

Hmmm, that's going to complicate the trans-*c code.  In fact, this
pretty makes errmsg useless without stat, so your -Wsurprising
should probably be a plain old warning.

> 
> I will review the patch itself later.
> 

Wait for an update.  I have a 5 hour flight home
tomorrow night.

-- 
Steve