[PATCH] Fortran: improve compile-time checking of character dummy arguments [PR93330]

[Jerry D]

On 8/28/25 1:51 PM, Harald Anlauf wrote:
> Dear all,
> 
> the attached patch tries to improve diagnostics at compile time
> for character arguments in various ways:
> 
> - we did unconditionally give a warning for too short character
>    actual arguments passed to a scalar dummy; we now give an error
>    when -std=f* is specified.  The warning is retained for
>    -std=legacy/gnu as several testcases depend on it.
> 
> - if the actual argument has length zero, no warning was given.
>    This had been remedied.
> 
> - if a character actual argument is longer than the dummy, we now
>    give a truncation warning if -Wcharacter-truncation is given.
> 
> - If a character formal argument has the pointer or allocatable
>    attribute, or is an array that is not assumed or explicit size,
>    we now generate an error by default unless -std=legacy is
>    specified, which falls back to just giving a warning as before.
>    (One testcase depends on it.)
> 
> The errors emitted as described above have been checked to be
> consistent with NAG. :-)
> 
> There is one thing where we (still?) deviate from F2018:15.5.2.4.
> The standard text explicitly mentions default character kind and
> C character kind in several contexts, which could be interpreted
> as excluding kind=4 character.  However, I do not see why this
> should be the case - there is no actual technical reason, and
> also NAG handles kind=4 character the same as kind=1 character
> in the tests.  If someone feels strongly about it, we could
> make an interp request to resolve this.  I would consider this
> a gfortran extension for the time being.
> 
> Regtested on x86_64-pc-linux-gnu.  OK for mainline?
> 
> Thanks,
> Harald
> 

Yes, OK Harald.

Thanks for the work.

Jerry