>>>>> On Tue, 30 May 2017, Alexis Ballier wrote: > The way I see it, this boils down to spec'ing something that > guarantees there's a unique solution given an input. The solution > does not have to be good or bad (we don't have a good metric on that > anyway), it just has to be deterministic so that developers can > arrange their REQUIRED_USE constraints to have PM chose the proper > solution.
Right. As I see it, the problem we must solve is that for k USE flags there are 2**k possible combinations, but there may be only n combinations that are valid, with n < 2**k. For example, for IUSE="foo bar baz" there are 2**3 = 8 possible combinations, but with REQUIRED_USE="|| ( foo bar baz )" or "^^ ( foo bar baz )" only 7 or 3 of them are valid, respectively. Now we can either just specify which of the combinations are valid; this is what REQUIRED_USE currently does. Or we can specify a complete mapping from every invalid input combination of flags to a valid output combination. I think we should do the latter. Ulrich
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