[Bug fortran/61933] Inquire on internal units

["Joost.VandeVondele at mat dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61933

--- Comment #11 from Joost VandeVondele <Joost.VandeVondele at mat dot ethz.ch> ---
(In reply to Jerry DeLisle from comment #10)
> It occurs to me another possible interpretation of what a unit existence
> might be.
> 
> Behind the scenes when opening a unit with no filename we create a file
> named for example fort.10.  That file name is processor dependent and the
> user should not know what that filename is. (we know by convention of course)
>
> I wonder now whether we should define unit existence to be whether or not
> the corresponding file (or device, or whatever it is....) exists on the
> system.  This starts to make some sense when you think about it and could
> assist a user from inadvertently overwriting some existing data.

I don't think this is the intended behavior. I really think the meaning rather
is, can we in principle open a file on that unit number (like from the good old
days, is a tape drive mechanically connected to it). 

I'm reading the F2008 standard, and the guidance given in 9.5.3 is not much...
However, external files and external units seem to be conceptually quite
different (see also note 9.16)

> 
> I am going to reopen this for further discussion.  I do agree with your
> issue.

thanks also for your efforts in fixing these things!