Gentoo Archives: gentoo-dev

From: Ciaran McCreesh <ciaran.mccreesh@××××××××××.com>
To: gentoo-dev@l.g.o
Subject: [gentoo-dev] Death to old-style virtuals!
Date: Fri, 17 Dec 2010 18:09:20
Message-Id: 20101217180833.6b3da8bb@snowcone
1 Old-style virtuals are extremely messy and introduce an awful lot of
2 complexity. They were supposed to be on the way out several years ago,
3 with GLEP 37, but that seems to have stalled.
5 Is there anything in particular holding back replacing most or all of
6 the remaining old-style virtuals with new 'package' virtuals?
8 There are a few possible issues:
10 Doing per-profile virtual defaults is a bit messy. If the desired
11 default for a given subprofile is different, and the 'normal' default
12 is masked, then || ( ) dependencies are fine. But otherwise you need to
13 use use flags. That's ok if you can do something like:
15 kernel_linux? ( || ( a b c ) )
16 !kernel_linux? ( || ( d e f ) )
18 (being careful to keep the flags outside of the || ( ) because
19 otherwise crazy stuff happens) but there might not be obvious flags for
20 certain cases. In the worst case, a new USE_EXPAND_HIDDEN thing could
21 be introduced to cover it.
23 There's still that stupid !virtual/blah thing to deal with. Old style
24 virtual providers are allowed to block their own virtual to mean "there
25 must not be any other provider of this installed" (although it's not
26 clear what that means if anything other than a simple !virtual/pkg is
27 used). Anything doing that would now have to explicitly list its own
28 blocks. Arguably, this is a good thing, since you'd have to say exactly
29 what you do and don't work with.
31 There's mention of package.prefer in the GLEP. It's probably not
32 necessary, thanks to the "if something's already installed, go with
33 that" behaviour of || ( ) dependencies -- to 'prefer' a provider, you
34 could just install it first.
36 However, I strongly suspect that all of these are less of a problem
37 than the cost of educating developers in all the weird oddities of how
38 old-style virtuals behave, and how dependencies on old-style virtuals
39 are nothing like normal dependencies...
41 --
42 Ciaran McCreesh


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Subject Author
[gentoo-dev] Old-style virtuals blocking feature needed for virtual/mta Torsten Veller <ml-en@××××××.net>
Re: [gentoo-dev] Death to old-style virtuals! "Petteri Räty" <betelgeuse@g.o>