[patch,libgfortran] PR28335 flush() / write() statement on closed units

[Jerry DeLisle]

Brooks Moses wrote:
> Michael Paton wrote:
>> I've just run across the effects of this in the 20060729 snapshot, where
>> previously working code got runtime errors. It seems that Jerry's patch
>> makes it an error to attempt to CLOSE a unit which has not been 
>> OPENED, or
>> "associated". My reading of the f77 standard and a late draft of the 2003
>> standard show this to be explicitly permitted. I couldn't easily 
>> access the
>> F90 or F95 standards.
> 
> You are correct.  Fortran 95 standard, 9.3.5, third para: "Execution of 
> a CLOSE statement specifying a unit that does not exist or has no file 
> connected to it is permitted and affects no file."
> 
> It appears to me that the patch to io/close.c should simply be reverted 
> to fix this.  It may be useful to also add a comment referencing the 
> above line of the standard, e.g.:
> 
>   /* CLOSE on unconnected unit is legal and a no-op: F95 std., 9.3.5. */
> 
>> As a user whose (possibly misguided) program stopped working, I'll 
>> also confess to some brief irritation at the error text, "Can't find 
>> specified UNIT in CLOSE". In essence, the runtime knows I want to do a 
>> CLOSE on a specific UNIT, and it
>> has a problem with that, but it won't tell me which UNIT. I'm afraid 
>> that looking at error.c didn't give me a clearer idea of how a more 
>> useful error message could have been given within the existing program 
>> structure.
> 
> I would agree that "Can't find specified UNIT" is pretty unclear, and 
> could be improved even without putting the actual unit number in the 
> message.  Even though this is moot for CLOSE given the above, the error 
> message for FLUSH should probably be improved.
> 
> Perhaps "Specified UNIT in FLUSH is not connected"?
> 
> - Brooks
> 
> 
Changed error message as Brooks suggested for FLUSH. Reverted the error on 
CLOSE.  Added comments to reference the standard.  Kicked myself.

Committed to 4.1 and 4.2 under obvious and simple rule.

Sorry folks,

Jerry