Hi Nicolas,
On Thu, Feb 20, 2020 at 1:16 AM Nicolas Pitre <nico@xxxxxxxxxxx> wrote:
>
> On Wed, 19 Feb 2020, Masahiro Yamada wrote:
>
> > The 'imply' statement may create unmet direct dependency when the
> > implied symbol depends on m.
> >
> > [Test Code]
> >
> > config FOO
> > tristate "foo"
> > imply BAZ
> >
> > config BAZ
> > tristate "baz"
> > depends on BAR
> >
> > config BAR
> > def_tristate m
> >
> > config MODULES
> > def_bool y
> > option modules
> >
> > If you set FOO=y, BAZ is also promoted to y, which results in the
> > following .config file:
> >
> > CONFIG_FOO=y
> > CONFIG_BAZ=y
> > CONFIG_BAR=m
> > CONFIG_MODULES=y
> >
> > This ignores the dependency "BAZ depends on BAR".
> >
> > Unlike 'select', what is worse, Kconfig never shows the
> > "WARNING: unmet direct dependencies detected for ..." for this case.
> >
> > Because 'imply' should be weaker than 'depends on', Kconfig should
> > take the direct dependency into account.
> >
> > Describe this case in Documentation/kbuild/kconfig-language.rst for
> > clarification.
> >
> > Commit 237e3ad0f195 ("Kconfig: Introduce the "imply" keyword") says that
> > a symbol implied by y is restricted to y or n, excluding m.
> >
> > 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
=== === ============= ==============
--
Best Regards
Masahiro Yamada
