Re: [PATCH] kconfig: make 'imply' obey the direct dependency

[Nicolas Pitre]

On Thu, 20 Feb 2020, Masahiro Yamada wrote:

> Hi Nicolas,
> 
> On Thu, Feb 20, 2020 at 1:16 AM Nicolas Pitre <nico@xxxxxxxxxxx> wrote:
> >
> > On Wed, 19 Feb 2020, Masahiro Yamada wrote:
> >
> > > As for the combination of FOO=y and BAR=m, the case of BAZ=m is excluded
> > > by the 'imply', and BAZ=y is also excluded by 'depends on'. So, only the
> > > possible value is BAZ=n.
> >
> > I don't think this is right. The imply keyword provide influence over
> > another symbol but it should not impose any restrictions. If BAR=m then
> > BAZ should still be allowed to be m or n.
> >
> > > @@ -174,6 +174,9 @@ applicable everywhere (see syntax).
> > >       n               y               n               N/m/y
> > >       m               y               m               M/y/n
> > >       y               y               y               Y/n
> > > +     n               m               n               N/m
> > > +     m               m               m               M/n
> > > +     y               m               n               N
> >
> > Here the last line shoule be y m n N/m.
> >
> > Generally speaking, the code enabled by FOO may rely on functionalities
> > provided by BAZ only when BAZ >= FOO. This is accomplished with
> > IS_REACHABLE():
> >
> >         foo_init()
> >         {
> >                 if (IS_REACHABLE(CONFIG_BAZ))
> >                         baz_register(&foo);
> >                 ...
> >         }
> >
> > So if FOO=y and BAZ=m then IS_REACHABLE(CONFIG_BAZ) will be false. Maybe
> > adding a note to that effect linked to the "y m n N/m" line in the table
> > would be a good idea.
> >
> 
> I also thought so.
> 
> I agree IS_REACHABLE() is much saner approach.
> 
> So, do you agree to change the current behavior
> as follows?
> 
> 
> index d0111dd26410..47dbfd1ee003 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -173,7 +173,7 @@ applicable everywhere (see syntax).
>         ===             ===             =============   ==============
>         n               y               n               N/m/y
>         m               y               m               M/y/n
> -       y               y               y               Y/n
> +       y               y               y               Y/m/n
>         y               n               *               N
>         ===             ===             =============   ==============
> 

Yes. That should have been the case all along.


Nicolas