[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[kargl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

kargl at gcc dot gnu.org changed:

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

--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to Tobias Burnus from comment #0)
> For indenting the source code, gfortran warns only with -std=f* or with
> -Wtab.

Please, check the archive.  At one time gfortran would issue a warning
if a tab was used in a nonconforming context.  Too many people were
upset about this, so the -W[no-]tab option, which has a convoluted history,
was the compromise.

> However, for format strings, it always warns - and with -std=f* it even
> turns the warning into an error! (see io.c's next_char_not_space)
> 
> Example:
> 
> 1894  format(   '123')
>       end
> 
> (The tab is before '123'. A tab in the string itself is not warned for.)
> 
> Maybe the best would be to disable this warning with -std=legacy - and refer
> to -std=legacy in the -std=gnu warning?

Tab is not and never has been a member of the Fortran character set.
The above line of code is nonconforming.  Gfortran, IMNSHO, should
always issue an error, but I lost that battle years ago.