[gentoo-dev] Reliance upon || ( use? ( ) ) behaviour

[Ciaran McCreesh]

Is the current || ( use? ( ) ) behaviour something that is desirable?
As far as I know, every package manager currently implements it, but
it's also one of those things that's a nuisance to explain and it
appears to exist only because of how early Portage versions did
flattening.

More specifically:

Inside || ( ) blocks, the package manager first removes any use? ( )
blocks that are *immediate* (that is to say, not inside ( ) themselves)
children if the use flag is not enabled (or disabled for !use?). Then,
if the || ( ) block is empty, it is discarded.

The example given in ebuild(5) is:

    || (
        sdl? ( media-libs/libsdl )    
        svga? ( media-libs/svgalib )
        opengl? ( virtual/opengl )
        ggi? ( media-libs/libggi )
        virtual/x
    )

As has been discussed in the past, the only correct way of handling
this from an ebuild perspective is lots of use && has_version calls
(relying upon use only is insufficient, since if two or more flags are
used, only one of the dependencies need be installed; relying upon
has_version only is insufficient, since a dependency may be installed
but its associated use flag could still be turned off).

So, is there a legitimate reason for this complication to exist? Or
should use? blocks being direct children of || ( ) be forbidden?

-- 
Ciaran McCreesh
Mail                                : ciaranm at ciaranm.org
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