Re: [gentoo-dev] pkg_pretend USE validation and VALID_USE alternative

[Ciaran McCreesh <ciaran.mccreesh@googlemail.com>]

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On Thu, 1 Apr 2010 00:56:08 -0700
Brian Harring <ferringb@gmail.com> wrote:
> Actually, I'm well aware I did.  See, if PMS wasn't developed in a 
> void you'd know build, bootstrap, acl and friends were already a
> known issue with use cycle breaking.

So since it's a known issue, why are you pushing for VALID_USE "because
it allows cycle breaking" without also pushing for a solution to flags
that can't be toggled at the same time?

> pkg_setup: ran just before the build of the pkg, after the pkg's 
> DEPENDS are all built.  Meaning you *can* do has_version checks, 
> kernel config checks, etc, because the proceeding deps are now 
> satisfied.

Except that they might change, because, as we established on the bug,
two packages that aren't interdependent can affect each other's
assumptions, and can be built in parallel. pkg_pretend does not alter
the problem here.

> Cherry picking the argument again.  Main != whole, meaning the 
> majority reason I could see w/in council logs for supporting 
> pkg_pretend was USE constraint validation.
> 
> As I've said, and as you seem to finally understand, VALID_USE isn't
> a replacement for pkg_pretend- it just replaces the *main* usage of
> it.

You said on the bug that you wanted pkg_pretend removed in favour of
VALID_USE. I don't object to VALID_USE; I object to you claiming that
it replaces pkg_pretend, and I object to you claiming that using
VALID_USE instead of pkg_pretend is enough to allow cycle breaking.

> > Simply adding VALID_USE won't let you do cycle breaking. You also
> > need extensive lists of which flags for which packages can safely
> > be toggled and when without breaking the system, and the only way
> > you'll get those lists is if developers care enough to update their
> > ebuilds to provide them.
> 
> That's one view, but sure, I'll run with it.
> 
> The thing is, *without* VALID_USE you cannot do use cycle breaking 
> *period*.  executable vs data for the representation of the 
> constraints (as I've spelled out for you 3 times now).

You also can't do it *with* VALID_USE, unless you also have extensive
help from ebuilds. Why are you pushing for VALID_USE without also
proposing a way for the package mangler to be told which flags it can
change?

> pkg_pretend however completely disallows even *doing* use cycle 
> breaking.  How in the hell is that a better next step?

pkg_pretend is a pragmatic, cheap solution that solves a larger number
of problems, whilst not ruling out anything that Portage will
realistically be able to do in a relevant timeframe.

If, in the distant future, Portage supports use cycle breaking, then
people can switch their ebuilds to use VALID_USE when they're also
updating their ebuilds to export the cycle breaking information the
package mangler requires to do it without trashing a system. But since
we don't know exactly what that information looks like yet, we might as
well just stick with the single solution that solves all of the
problems.

-- 
Ciaran McCreesh

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