Re: *Ping**2 [Patch] Fortran: Fix bind(C) character length checks

[Jerry D <jvdelisle2@gmail.com>]

Good to go Tobias.

Jerry

On 7/14/21 5:50 AM, Burnus, Tobias wrote:
> Ping**2
>
> On Juli 8, 2021 I wrote:
>
> *Ping*
>
> I intent to incorporate Sandra's suggestions, except for the beginning of line spacing - that's needed to avoid exceeding the 80 character line limit. I did not include an updated patch as just pinging is easier on a mobile during vacation :-)
>
> Thanks,
>
> Tobias
>
> Loosemore, Sandra wrote:
>
> On 7/1/21 11:08 AM, Tobias Burnus wrote:
>> Hi all,
>>
>> this patch came up when discussing Sandra's TS29113 patch internally.
>> There is presumably also some overlap with José's patches.
>>
>> This patch tries to rectify the BIND(C) CHARACTER handling on the
>> diagnostic side, only. That is: what to accept and what
>> to reject for which Fortran standard.
>>
>>
>> The rules are:
>>
>> * [F2003-F2018] Interoperable is character(len=1)
>>     → F2018, 18.3.1  Interoperability of intrinsic types
>>     (General, unchanged)
>>
>> * Fortran 2008: In some cases, const-length chars are
>>     permitted as well:
>>     → F2018, 18.3.4  Interoperability of scalar variables
>>     → F2018, 18.3.5  Interoperability of array variables
>>     → F2018, 18.3.6  Interoperability of procedures and procedure interfaces
>>    [= F2008, 15.3.{4,5,6}
>> For global vars with bind(C), 18.3.4 + 18.3.5 applies directly (TODO:
>> Add support, not in this patch)
>> For passed-by ref dummy arguments, 18.3.4 + 18.3.5 are referenced in
>> - F2008: R1229  proc-language-binding-spec is language-binding-spec
>>            C1255 (R1229) <see wording there>
>> - F2018, F2018, C1554
>>
>> While it is not very clearly spelt out, I regard 'char parm[4]'
>> interoperable with 'character(len=4) :: a', 'character(len=2) :: b(2)'
>> and 'character(len=1) :: c(4)' for both global variables and for
>> dummy arguments.
>>
>> * Fortran 2018/TS29113:  Uses additionally CFI array descriptor
>>     - allocatable, pointer:  must be len=:
>>     - nonallocatable/nonpointer: len=* → implies array descriptor also
>>       for assumed-size/explicit-size/scalar arguments.
>>     - All which all passed by an array descriptor already without further
>>       restrictions: assumed-shape, assumed-rank, i.e. len=<nonconst> seems
>>       to be also fine
>> → 18.3.6 under item (5) bullet point 2 and 3 plus (6).
>>
>>
>> I hope I got the conditions right. I also fixed an issue with
>> character(len=5) :: str – the code in trans-expr.c did crash for
>> scalars  (decl.c did not check any constraints for arrays).
>> I believe the condition is wrong and for len=<const> no descriptor
>> is used.
>>
>> Any comments, remarks?
> I gave this patch a try on my TS 29113 last night.  Changing the error
> messages kind of screwed up my list of FAILs, but I did see that it also
> caught some invalid character arguments in
> interoperability/typecodes-scalar.f90 and
> interoperability/typecodes-scalar-ext.f90 (which are already broken by 2
> other major gfortran bugs I still need to file PRs for).  :-S
>
> I haven't tried to review the patch WRT correctness with the
> requirements of the standard yet, but I have a few nits about error
> messages....
>
>> +               /* F2018, 18.3.6 (6).  */
>> +               if (!sym->ts.deferred)
>> +                 {
>> +                   gfc_error ("Allocatable and pointer character dummy "
>> +                              "argument %qs at %L must have deferred length "
>> +                              "as procedure %qs is BIND(C)", sym->name,
>> +                              &sym->declared_at, sym->ns->proc_name->name);
>> +                   retval = false;
>> +                 }
> This is the error the two aforementioned test cases started giving, but
> message is confusing and doesn't read well (it was a pointer dummy, not
> "allocatable and pointer").  Maybe just s/and/or/, or customize the
> message depending on which one it is?
>
>> +                   gfc_error ("Character dummy argument %qs at %L must be "
>> +                              "of constant length or assumed length, "
>> +                              "unless it has assumed-shape or assumed-rank, "
>> +                              "as procedure %qs has the BIND(C) attribute",
>> +                              sym->name, &sym->declared_at,
>> +                              sym->ns->proc_name->name);
> I don't think either "assumed-shape" or "assumed-rank" should be
> hyphenated in this context unless that exact hyphenation is a term of
> art in the Fortran standard or other technical documentation.  In normal
> English, adjective phrases are usually only hyphenated when they appear
> immediately before the noun they modify; "assumed-shape array", but "an
> array with assumed shape".
>
>> +               else if (!gfc_notify_std (GFC_STD_F2018,
>> +                                         "Character dummy argument %qs at %L"
>> +                                         " with nonconstant length as "
>> +                                         "procedure %qs is BIND(C)",
>> +                                         sym->name, &sym->declared_at,
>> +                                         sym->ns->proc_name->name))
>> +                 retval = false;
>> +             }
> Elsewhere the convention seems to be to format strings split across
> multiple lines with a space at the end of each chunk rather than at the
> beginning.
>
> -Sandra
> -----------------
> Siemens Electronic Design Automation GmbH; Anschrift: Arnulfstraße 201, 80634 München; Gesellschaft mit beschränkter Haftung; Geschäftsführer: Thomas Heurung, Frank Thürauf; Sitz der Gesellschaft: München; Registergericht München, HRB 106955