Re: [gentoo-dev] RFD : .ebuild is only bash

[Brian Harring <ferringb@gmail.com>]

On Tue, Mar 13, 2012 at 07:05:57PM -0700, Zac Medico wrote:
> On 03/13/2012 06:42 PM, Brian Harring wrote:
> > Leaving it such that the PM has to enforce things like "don't have 
> > multiple EAPI assignments" means by default, one of them isn't going 
> > to... leading to the ebuilds breaking... specifically the common case 
> > being the ebuild becoming acclimated to some quirk of portage.
> 
> My intention is for PMS to specify the search algorithm that's used to
> probe the EAPI, and also for it to specify that package managers must
> treat an ebuild as invalid if the probed EAPI is not identical to the
> one that's obtained from bash.

*Now* is when you should be applying your KISS wikipedia links 
(moreso, the principle applied to your proposal).

What you're talking about is requiring PMs to monitor what occured 
and bail- rather than precluding it from even occuring.  I repeat; try 
to spot the situation and make things blow up, rather than disallowing 
it from occuring in the first place.

It's really that simple; this is why the "grep the assignment" out of 
the source is at its core, a well intentioned but fundamentally bad 
idea.  It's glue on a bad situation rather than just removing the bad 
situation.


> If all package managers adhere strictly
> to these two requirements, then we won't have any incompatibilities
> between package managers here.

You're missing a lot of the point here; defining some search algo is 
basically screwed at its core due to the flexibility of bash.  Simple 
example:

if [ "$PV" -eq 9999 ]; then
EAPI=3
else
EAPI=2
fi

The flexibility of bash means that your attempt to enforce simplistic 
rules like "it must be greppable" are at loggerheads; if the rules 
were "last is the one thats used", then I just invert the if check.

Yep, the above is stupid code.  Frankly, the sort of stupid code 
I'd expect out of a newbie ebuild dev.  The EAPI bit there is 
synthetic, but that sort of construct (putting everything into a 
single file, then using symlinks to expose differing versions) is out 
in the wild and used.

The fact that potential exists is a flat out sign the approach is 
broken.   Worse, it's a way to trip up people- specifically new devs 
who don't know fun rules like "the PM has this lovely search algo for 
getting EAPI that you must abide by".

~brian