make -U

[Ruslan Ermilov]

[ Moved to -arch ]

> From the message in freebsd-hackers which first introduced
> this patch:
> 
> - Date: Tue, 29 Jul 2003 09:09:17 -0700
> - From: Faried Nawaz <fn at hungry.com>
> - Subject: patch to add make -U
> 
>     While working around a port issue (ports/55013), I discovered
>     that make couldn't unset variables using make -U.  I've written
>     a small patch that adds -U functionality, but I haven't tested
>     it extensively.
> 
>     http://web.nilpotent.org/tmp/make.diff.bz2  (~ 3KB unpacked)
>     against yesterday's -CURRENT code.
> 
The patch looks sane.

>     A simple Makefile I used to test it:
> 
>     -- cut here --
>     FOO = bar
> 
>     .ifdef FOO
>     SAY = y
>     .else
>     SAY = n
>     .endif
> 
>     all:
>    	echo $(SAY)
>     -- cut here --
> 
>     Try "make -U FOO".
> 
> Personally I think this is a reasonable option to implement.
> An undefined variable is not the same as a variable which is
> defined to be a null string.
> 
I want that everyone understands the effect of the patch: the
-U FOO option causes the FOO variable to always be reported
by make(1) as undefined, not only in this makefile, but even
in sub-make processes, and affects all makefiles wishing to
set it -- it just doesn't let them do this, globally.

So the actual meaning of this option is "prevent variable FOO
from being set".  (The implementation is somewhat different;
it causes make(1) to lie that variable being is, but the net
effect is the same.)

Given the above, do we really want this option in our make?


Cheers,
-- 
Ruslan Ermilov		Sysadmin and DBA,
ru at sunbay.com		Sunbay Software Ltd,
ru at FreeBSD.org		FreeBSD committer
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