Re: [PATCH v1 1/2] config.mak.in: set NO_OPENSSL and APPLE_COMMON_CRYPTO for macOS >10.11

On Mon, Nov 07, 2016 at 12:36:34PM -0500, Paul Smith wrote:

On Mon, 2016-11-07 at 12:26 -0500, Jeff King wrote:

quoted

I have in the back of my mind a fear that it is harder to unset a
make variable than it is to override it with a new value (which is
what you'd want to do here to turn openssl back on),

It depends on what you mean by "unset".

If you mean it as per the shell "unset" command, where the variable is
completely forgotten as if it never was set at all, that's tricky.  You
have to use the "undefine" special command which was introduced in GNU
make 3.82 (released in 2010).

But if you just want to set the variable to the empty string, using
"FOO=" works fine for that in all versions of make (GNU and otherwise)
and using all the normal rules (command line override, etc.)

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).

-Peff