Re: gcc7 build error with recent tip

[Daniel J Sebald]

On 06/24/2017 02:58 PM, John W. Eaton wrote:
> On 06/24/2017 02:23 PM, Daniel J Sebald wrote:
> > On 06/24/2017 11:21 AM, Dmitri A. Sergatskov wrote:
> > > On Sat, Jun 24, 2017 at 10:59 AM, John W. Eaton <address@hidden
> > > <mailto:address@hidden>> wrote:
> > >
> > >
> > >     I admit this code is a bit tricky.  I was trying to come up with a
> > >     way to use a single template that would cover both of these cases:
> > >
> > >       static octave_value
> > >       dump_container_map (const std::map<std::string,
> > >     std::list<std::string>>&)
> > >
> > >       static octave_value
> > >       dump_container_map (const std::map<std::string,
> > >     std::map<std::string>>&)
> > >
> > >     It works for me with gcc version 6.3.0 20170516 (Debian 6.3.0-18).
> > >
> > >
> > > ​It is quite possible this is a bug in gcc7.1.1.
> > > I filled a bug:
> > >
> > > ​https://bugzilla.redhat.com/show_bug.cgi?id=1464612
> > >
> > > would like to see what Jakub has to say about it.
> >
> > Yes, that is quite possible, based upon the error message.  The compiler
> > identifies the proper candidate, but it is telling us that the candidate
> > expects only one argument.  I.e.,
> >
> > ../src/libinterp/corefcn/symtab.cc:1424:1: note: candidate:
> > template<class V, template<class ...> class C> octave_value
> > dump_container_map(const std::map<std::__cxx11::basic_string<char>, C<V>
> > > &)
> >  dump_container_map (const std::map<std::string, C<V>>& container_map)
> >  ^~~~~~~~~~~~~~~~~~
> > ../src/libinterp/corefcn/symtab.cc:1424:1: note:   template argument
> > deduction/substitution failed:
> > ../src/libinterp/corefcn/symtab.cc:1446:73: note:   candidate expects 1
> > argument, 3 provided
> >         {"precedence_table", dump_container_map
> > (m_class_precedence_table)},
> >
> > but I don't understand where the compiler is getting those number 3
> > from.  Here's the definition of m_class_precedence_table:
>
> The template substitution that is failing is for std::set which takes 1,
> 2, or 3 template parameters.  The other, for std::list, takes 1 or 2.

Oh.  Looking at the second error in Dmitri's original email, I see now 
that one says "2 provided" as opposed to "3 provided" from the first 
error.  The error message points directly at dump_container_map() which 
made me think that was the source of error when in fact it is the 
expansion inside the template.

Well, that works then.


> I checked in the following changeset and the problem seems to be fixed
> for both GCC 6 and 7:
>
>   http://hg.savannah.gnu.org/hgweb/octave/rev/93371ce5378d
>
> Now I'm not sure whether this is a bug in GCC 7 or if it was a bug in
> previous versions to accept the template without the "A..." argument.

Or maybe that is a difference between C++11 and its predecessors, i.e., 
more explicit definition of templates rather than leaving it to 
interpretation.  (I see ::__cxx11:: in some variable names in the error 
messages so I assume the compiler is doing C++11.)

Dan