[Bug fortran/109358] Wrong formatting with T-descriptor during stream output

["kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109358

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
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                 CC|                            |kargl at gcc dot gnu.org

--- Comment #3 from kargl at gcc dot gnu.org ---
(In reply to Jerry DeLisle from comment #2)
> I am using my copy of the F2018 standard.
> 
> "13.8.1.2 The Tn edit descriptor indicates that the transmission of the next
> character to or from a record is to occur at the nth character position of
> the record, relative to the left tab limit. This position can be in either
> direction from the current position."
> 
> Currently we do this:
> 
> 1234567890123
> 1234         0123
> 1234         0123
> 
> We should do this:
> 
> 1234567890123
> 1234     0123
> 1234     0123
> 
> "13.5 (3) During formatted stream output, processing of an A edit descriptor
> can cause file positioning to occur (13.7.4)."
> 
> I am not finding anything that says file positioning is not allowed.  The
> above is just elaborating different ways that an A edit descriptor affects
> the positioning.  Positioning is always done no matter what with the T
> specifier.
> 
> Regardless, I do need to fix this.

Yes, there is a bug.  The A edit descriptor and whether or not it does
file positioning is not relevant.  The relevant words from F2018 are

   13.8.1.2 T, TL, and TR editing

   The left tab limit affects file positioning by the T and TL edit
   descriptors. Immediately prior to nonchild data transfer (12.6.4.8.3),
   the left tab limit becomes defined as the character position of the
   current record or the current position of the stream file.  If, during
   data transfer, the file is positioned to another record, the left tab
   limit becomes defined as character position one of that record.

with

  write(fd, "(a)") "1234567890123"
  write(fd, "(a, t10, a)") "1234", "0123"  ! A-descriptor, file positioning 

the left tab limit for the 2nd write is established before data
transfer to position 1.  The 'T10' edit descriptor is relative to
that position.  The write of "1234" in the 2nd write might place
the character position to 5, but it does not update the left tab
limit because the write() is not positioned to a new record.