Re: [Boost-build] CVS: boost/tools/build/v2/build generators.jam, 1.100, 1.101 targets.jam, 1.197, 1.198

From: Vladimir Prus (ghost_at_[hidden])
Date: 2006-08-06 14:54:35

On 8/6/06, Vladimir Prus <ghost_at_[hidden]> wrote:
>
> Rene Rivera <grafikrobot <at> gmail.com> writes:
>
> >
> > Vladimir Prus wrote:
> > > On 8/2/06, Rene Rivera <grafik <at> users.sourceforge.net> wrote:
> >
> > >> Skip targets that can't be generated like BBv1 does.
> > >
> > > Just as a check -- did you run V2 testsuite before and after this
> > > change, to
> > > verify it causes no regressions?
> >
> > No, but that was because I didn't have the time. I'll get to that this
> > weekend.
>
> Hmm, generally it's better to run regression tests *before* checkin.
> That's
> what I do, at the very least.
>
> >
> > > Index: generators.jam
> > >> +    # Indicates if this generator can handle building the given
> target
> > >> +    # combination.
> > >
> > > I think this comment is not sufficient.
> >
> > It seems as sufficient as some of the other commented methods in that
> > class.
>
> Are you saying those other comments are not sufficient too? That most
> likely
> true, but that does not mean we should not try to improve commenting for
> new
> checkings. Those other comments were probably written years ago, when I
> did not
> realize how really important comments are.
>
> > It says exactly what it means and nothing else. Perhaps comments
> > need to be added to where can-build is called to explain what effect it
> > has there.
> >
> > > How returning false from this rule
> > > is different from
> > > returning nothing from the 'run' rule?
> >
> > I have no clue. But then again the run rule doesn't say what happens
> > when it returns nothing.
>
> I can fix that part; but that does not change the fact that 'can-build' is
> under-commented.
>
> >
> > > I think there are some differences,
> > > but the comment does not say what they are.
> >
> > Perhaps... What do you think are the differences?
>
> Well, returning nothing from 'run' method means the generator failed.
> If all possible generators fail, then building a targets failed and an
> error
> is produced. As for 'can-build' returning false, you know better, but it
> seem
> to be some "half-failed" situation.

On a second though, it looks like 'can-build' returning false make generator
fail during find-viable-generators call, instead of failing in 'run' method.
So, it's a mechanism for making generator fail earlier. I'm not sure if we
need this second mechanism, given that 'run' can return nothing already.

- Volodya