Re: [gentoo-dev] [RFC] Forced/automatic USE flag constraints (codename: ENFORCED_USE)

[Michał Górny]

On wto, 2017-06-06 at 14:08 +0200, Alexis Ballier wrote:
> On Mon, 05 Jun 2017 20:10:12 +0200
> Michał Górny <mgorny@g.o> wrote:
> [...]
> > > > Stand-alone makes little sense (and little trouble) but as you
> > > > could have seen it's used nested in other thingies:
> > > >
> > > > 1. || ( ( a b ) ( c d ) e )
> > > >
> > > > 2. ?? ( ( a b ) ( c d ) e )
> > > >
> > > > 3. ^^ ( ( a b ) ( c d ) e )
> > >
> > > Yeah that's the nesting problem causing a parse error.
> > > Those should be expanded to implications. What I'm relying onto is
> > > all clauses to be of the form '[list of conditions]? [list of
> > > constraints]'
> >
> > I've noticed that you turned the implications into multi-conditions,
> > breaking all my scripts ;-). Is the [list of conditions] conjunctive
> > or disjunctive?
>
> conjunctive as in foo? ( bar? ( baz ) ) -> [foo,bar]?[baz]

Yeah, I guess that's useful. I didn't do that originally because I
wanted the AST to be fully compatible with REQUIRED_USE in Gentoo. But I
guess it doesn't hurt, and makes a lot of the code simpler.

I've backported this change and adjusted all the remaining modules to
work with it correctly.

>
> [...]
> > > > The question is whether we want to:
> > > >
> > > > a. actually try to solve this nesting insanity,
> > > >
> > > > b. declare it unsupported and throw REQUIRED_USE mismatch on user,
> > > >
> > > > c. ban it altogether.
> > >
> > >
> > > I don't think it is *that* insane to support nesting :)
> > >
> > > > ( ^^ ( ?? ( a b ) c ( d e ) ) f )
>
> If you really need that then you'd need to expand it manually. It seems
> better to have it expanded internally automatically.
> Remember you were the one wanting to keep || & co because they're
> simpler to read and write ;)
>

Well, I was able to implement the logic for all-of blocks outside
and inside other n-ary constraints, including the necessary logic
transformations. Fun fact is, I was able to do it without implementing
a complete set of logic functions and transformations in AST ;-).

I've just made it fail (correctly this time) with any other kind of
nesting -- I don't think it's going to have a real use case and even if
it did, there are more readable ways of solving the same problem.

The question is -- will you rebase now on top of my changes
(and preferably use nice logical changes with good commit messages),
or should I try later to merge the rest of your code in? ;-)

Also, do I presume correctly that for all supported cases (i.e. those
which your nsolve does not reject), solve and nsolve are compatible?

-- 
Best regards,
Michał Górny