From: Paul Smith <paul@mad-scientist.net>
Date: Mon, 07 Nov 2016 17:49:33 GMT
Subject: Re: [PATCH v1 1/2] config.mak.in: set NO_OPENSSL and APPLE_COMMON_CRYPTO for macOS >10.11
Message-ID: <1478540973.4171.22.camel@mad-scientist.net>
In-Reply-To: <20161107174559.t72vxxkckqdbxmbg@sigill.intra.peff.net>

On Mon, 2016-11-07 at 12:46 -0500, Jeff King wrote:
> Specifically I wanted to make sure that
> 
>   FOO = bar
>   FOO =
>   ifdef FOO
>   ... something ...
>   endif
> 
> works as if FOO had never been set in the first place. Which it seems
> to, at least in GNU make (and that is the only one we support, for
> other reasons).

Yes, it will work.  Confusingly, "ifdef" actually tests whether the
variable has a non-empty value, not whether it's defined:

> The 'ifdef' form takes the _name_ of a variable as its argument, not
> a reference to a variable.  The value of that variable has a non-
> empty value, the TEXT-IF-TRUE is effective; otherwise, the TEXT-IF-
> FALSE, if any, is effective

*sigh* History...