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On 07/25/2014 05:23 PM, William Hubbs wrote:
> On Fri, Jul 25, 2014 at 03:54:53PM -0400, Ian Stakenvicius wrote:
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>>
>> On 25/07/14 03:51 PM, Pacho Ramos wrote:
>>> El vie, 25-07-2014 a las 20:46 +0100, Ciaran McCreesh
>>> escribió:
>>>> On Fri, 25 Jul 2014 21:44:02 +0200 Luis Ressel
>>>> <ara...@aixah.de> wrote:
>>>>> Okay, I didn't think of that. I'm not sure if the blocker
>>>>> deps or the REQUIRED_USE would be more helpful for Portage,
>>>>> but generally I think that the REQUIRED_USE error message
>>>>> is quite hard to understand for unexperienced users -- much
>>>>> more so than the error generated by a blocker dep.
>>>>
>>>> ...and the fix for that is to scrap REQUIRED_USE and use
>>>> pkg_pretend instead.
>>>>
>>>
>>> Could you give an example to let us see how pkg_pretend could
>>> be used to achieve the same as REQUIRED_USE?
>>>
>>> Thanks
>>>
>>>
>>
>> pkg_pretend() { if use heimdal && use mit-krb5; then eerror
>> "Please set only one of the use following flags:" eerror
>> "heimdal, mit-krb5" die "conflicting use flags set" fi }
>
> I think this could get complicated really quick though. For
> example, if I have an ebuild with three use flags,
> flag1/flag2/flag3 with the requirement that one and only one of
> them must be set, unless bash has an xor operator I don't know
> about, that is going to need a lot of nesting etc to get right.
>
> William
>
If you want to say "At most one of the flags 'foo', 'bar', and 'baz'
may be selected", then you say it like so (requires EAPI=5):
REQUIRED_USE="?? ( foo bar baz )"
If you want to say "Exactly one of the flags ...", then you use:
REQUIRED_USE="^^ ( foo bar baz )"
And, as always, you can say "At least one of the flags ..." with:
REQUIRED_USE="|| ( foo bar baz )"
While each of these can be written using the "foo? ( !bar )"-type
primitives, the messages portage outputs are generally better with
'??', '^^', and '||', as you might see something like:
"
The following REQUIRED_USE flag constraints are unsatisfied:
at-most-one-of ( foo bar baz )
"
Which is, in my opinion, more readable.
- --
Jonathan Callen
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