"Lazy" variables in GNU make (was: Re: Unexpected failure in tricky use of eval)

[Stefano Lattarini]

On 05/12/2012 07:42 PM, Stefano Lattarini wrote:
> On 05/12/2012 05:21 PM, Stefano Lattarini wrote:
>> On 05/12/2012 04:41 PM, Eldar Abusalimov wrote:
>>> Stefano,
>>>
>>> This is a bug, and it has been described and fixed here:
>>> https://savannah.gnu.org/patch/?7534
>>>
>> Thank you very much for the reference.  Too bad this bug will prevent
>> me from using the lazy-evaluation trick with any GNU make < 3.83 :-(
>>
> BTW: to make it more easy to discover at make runtime whether the bug has
> been fixed in the make version in use, could a proper new entry be added
> to .FEATURES?  Maybe 'can-have-lazy-variables'?  (I know, I suck at choosing
> names).
>
Update: this won't actually be required anymore by Automake-NG, since I've
somehow managed (mostly by chance and random tweaking) to find an idiom
that works also with the older GNU make versions:

  <http://lists.gnu.org/archive/html/automake-ng/2012-05/msg00067.html>

> Better again: would you consider the possibility of adding a new kind
> of variables (let's call them "lazy"), so that a definition like:
> 
>     LAZYVAR = val
> 
> behaves exactly as:
> 
>     LAZYVAR = $(override LAZYVAR := val)$(LAZY)
> 
But I still think having this feature built into GNU make would be
valuable (even though Automake-NG won't use it right away).

Regards,
  Stefano