Re: [gentoo-dev] Re: RFC: c++14 global USE flag

[Georg Rudoy]

2015-05-03 13:51 GMT+03:00 Duncan <1i5t5.duncan@×××.net>:

> What about a somewhat more generic flag such as newcode?  Like the bindist
> or minimal flags, this could be global, but with local descriptions very
> strongly recommended.  Similarly, like minimal, setting it globally would
> be strongly discouraged.
>
> In this case, the newcode local description would be something like:
>
> C++14 related: gcc doesn't support yet, requires clang
>
> ... with an appropriate use-conditional dep.
>
> The newcode flag would however be generic enough that it could be reused
> for C++17, etc, as well, and could obviously be phased out for any
> particular package once its specific newcode dependencies are met in
> stable -- in this case, when a supporting gcc stabilizes.
>

Nice idea, thanks! There are a couple of corner cases though.


> newcode would even be generic enough to be used for say qt6 when the time
> comes, if it turns out to be stuck in the qt overlay for quite some time,
> as was qt5, for the longest time,


What if a package would support (optional) builds with C++17-related
features and (optional) builds with say Qt6, and these could be toggled
independently? Does that imply having something like newcode_cpp17 and
newcode_qt4 on per-package basis?


> and the good bit is, generic meaning,
> that USE=newcode requires a dep that's still generally problematic or
> might be considered excessive to get, for optional functionality that may
> or may not be considered worth it, should be pretty obvious.
>

Does that imply that merely pulling clang for builds is not a
newcode-concern then, and, back to the original topic, in case of
leechcraft C++14 can be enabled unconditionally, again with unconditional
pulling of clang?

That's probably a way to go, but feels like not Gentoo-way enough (just
removing an option).


> Making that meaning even more obvious would be the fact that the flag
> would likely be packageuse-masked for many users for much of the the
> time.  That could for instance allow packages using it in-tree, before
> the dep it pulls in is itself in-tree, while still making it possible to
> unmask, for users who either already have the required overlay active, or
> who don't have it active ATM, but are willing to activate it to get the
> features it toggles.
>

Depending on the answer to the previous question, if all the deps are
in-tree, then there is no need in masking the useflag. It could be unmasked
on the per-package basis again, I guess? Then there is a question of the
default (globally unmasked and per-package masks vs globally masked and
per-package unmasks), but that's a relatively minor one.

-- 
  Georg Rudoy