[bug #49093] ifdef checks for non-empty value, not definition

[Danek Duvall]

Follow-up Comment #3, bug #49093 (project make):

I'm not asking for behavioral change -- I figured that would have been a long
shot at best.  But I still feel like the docs are inconsistent, or at least
could be clarified a bit.

Specifically, the sentences "Note that 'ifdef' only tests whether a variable
has a value. It does not expand the variable to see if that value is
nonempty." are, to my mind, incorrect, and not consistent with the earlier
definition, or with the following examples.

In your first example here, FOO has a value, even if it's empty, so according
to those sentences, it should evaluate to true.  I don't know whether that
counts as "expansion", or whether "expansion" only matters when there's
another variable for indirection, as in the second example.

Perhaps something like "Note that 'ifdef' only tests the named variable for a
non-empty value, and does not further expand any variables it might
reference." in place of those two sentences.  I'm not positive that would have
told me what I needed to know, but I think it's a bit better than what's there
now.

That said, I know the answer now, and this bug can be found if people search
for ifdef and gnu make, so if you're averse to the change, perhaps that's
enough.

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