RE: [PATCH 1/2][PR fortran/26373][PR fortran/22497] gdb/fortran: add support for accessing fields of extended types

["Kempke, Nils-Christian" <nils-christian.kempke@intel.com>]

[PING**3]

Cheers,
Nils

> -----Original Message-----
> From: Kempke, Nils-Christian
> Sent: Thursday, February 10, 2022 2:20 PM
> To: 'Tom Tromey' <tom@tromey.com>; 'Nils-Christian Kempke via Gdb-
> patches' <gdb-patches@sourceware.org>
> Subject: RE: [PATCH 1/2][PR fortran/26373][PR fortran/22497] gdb/fortran:
> add support for accessing fields of extended types
> 
> [PING**2]
> 
> Cheers,
> Nils
> 
> > -----Original Message-----
> > From: Kempke, Nils-Christian
> > Sent: Tuesday, February 1, 2022 4:07 PM
> > To: Tom Tromey <tom@tromey.com>; Nils-Christian Kempke via Gdb-
> > patches <gdb-patches@sourceware.org>
> > Subject: RE: [PATCH 1/2][PR fortran/26373][PR fortran/22497] gdb/fortran:
> > add support for accessing fields of extended types
> >
> > Kindly pinging for thoughts.
> >
> > Cheers,
> > Nils
> >
> > > -----Original Message-----
> > > From: Gdb-patches <gdb-patches-bounces+nils-
> > > christian.kempke=intel.com@sourceware.org> On Behalf Of Kempke,
> Nils-
> > > Christian via Gdb-patches
> > > Sent: Monday, January 17, 2022 11:28 AM
> > > To: Tom Tromey <tom@tromey.com>; Nils-Christian Kempke via Gdb-
> > > patches <gdb-patches@sourceware.org>
> > > Subject: RE: [PATCH 1/2][PR fortran/26373][PR fortran/22497]
> gdb/fortran:
> > > add support for accessing fields of extended types
> > >
> > > Hi Tom,
> > >
> > > > -----Original Message-----
> > > > From: Tom Tromey <tom@tromey.com>
> > > > Sent: Friday, January 14, 2022 9:06 PM
> > > > To: Nils-Christian Kempke via Gdb-patches <gdb-
> > > patches@sourceware.org>
> > > > Cc: Kempke, Nils-Christian <nils-christian.kempke@intel.com>;
> Bernhard
> > > > Heckel <bernhard.heckel@intel.com>
> > > > Subject: Re: [PATCH 1/2][PR fortran/26373][PR fortran/22497]
> > gdb/fortran:
> > > > add support for accessing fields of extended types
> > > >
> > > > >>>>> ">" == Nils-Christian Kempke via Gdb-patches <gdb-
> > > > patches@sourceware.org> writes:
> > > >
> > > > >> From: Bernhard Heckel <bernhard.heckel@intel.com>
> > > > >> Fortran 2003 supports type extension.  This patch allows access
> > > > >> to inherited members by using their fully qualified name as
> described
> > > > >> in the Fortran standard.
> > > >
> > > > Thanks for the patch.
> > > >
> > > > >> In doing so the patch also fixes a bug in GDB when trying to access
> the
> > > > >> members of a base class in a derived class via the derived class' base
> > > > >> class member.
> > > >
> > > > >> @@ -2374,6 +2374,12 @@ value_struct_elt (struct value **argp,
> > > > >>        if (v)
> > > > >>  	return v;
> > > >
> > > > >> +      /* Fortran: If it is not a field it is the type name of an inherited
> > > > >> +	 structure.  */
> > > > >> +      v = search_struct_field (name, *argp, t, 1);
> > > > >> +      if (v)
> > > > >> +	return v;
> > > >
> > > > Putting this here makes me wonder if it's possible to construct test
> > > > cases in other languages that would work without this patch and then
> > > > fail with it.
> > >
> > > Well, since this patch so far did not care about the language actually used,
> > > it enables one to do things like
> > >
> > >   (gdb) p derived_obj
> > >   $1 = {<base> = {...}, <No data fields>}
> > >   (gdb) p derived_obj.base
> > >   $2 = {...}
> > >
> > > in all languages, which probably is unexpected.  The above example
> would
> > be
> > > C++ and some class "derived" inheriting from "base".  The syntax
> > > derived_obj.base is no standard C++..
> > > I am not sure whether one would actually break things since the only
> > leftover
> > > check in the method is a (according to the comment) C++ specific one for
> > > member variables and I do not think that one can break C++ with the
> > change.
> > >
> > > >
> > > > I'm not sure what the options are though.  Doing the work elsewhere,
> say
> > > > in a custom Fortran expression operation, might make the Python API
> > > > harder to work with.  Maybe having value_struct_elt check
> > > > current_language would work... that's also quite ugly but other value
> > > > operations are doing that.
> > >
> > > Mh, I am not too sure about the Fortran expression - would that not
> > require
> > > a Fortran specific version of value_struct_elt?  The methods
> > > search_struct_method and search_struct_field are local to the valops.c
> file
> > > so
> > > this would be a bigger redesign? I know that Ada has its own
> > value_struct_elt
> > > but it also implements the two helper methods.
> > >
> > > Checking the language seems ok to me, considering the style of the rest
> of
> > > valops.
> > >
> > > On more option that is also cleaner than directly checking the type might
> be
> > > to
> > > generalize the concept of this "member access by base name" a bit and
> add
> > a
> > > method - say base_access_by_base_type_name - to language.h allowing
> > or
> > > disallowing an access to the base type by its type name.  Then one would
> > > have to
> > > loop over all base types in valops.c as well.  I am not sure whether there
> > exist
> > > other
> > > languages that allow this kind of access though.. If not it might be a bit
> > much?
> > >
> > > Cheers,
> > >
> > > Nils
> > >
> > > >
> > > > Or maybe my fears are overblown.
> > > >
> > > > Any thoughts on this?
> > > >
> > > > Tom
> > > Intel Deutschland GmbH
> > > Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
> > > Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
> > > Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva
> > > Chairperson of the Supervisory Board: Nicole Lau
> > > Registered Office: Munich
> > > Commercial Register: Amtsgericht Muenchen HRB 186928

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928