controlled disabling of undefined variable warnings

[Greg McGary]

Hi Paul,

In an effort to find lingering bugs in my non-recursive framework, I used --warn-undefined-variables.  As expected, I got a zillion warnings from the framework around constructed variable names.   I wrote this little gadget:

    expand = $(if $(filter-out undefined,$(origin $(1))),$($(1)))

and replaced references of $(foo $(bar)) with $(expand foo $(bar)) to suppress warnings.

It was a useful exercise, since I found two bugs this way.  The trouble was that it doubled my makefile-processing overhead.  I really want to keep the warnings enabled, but I really don't want to pay the additional overhead.  The obvious solution is another builtin function, like so:

    $(expand VARNAME)
        expands as $(VARNAME) if VARNAME is defined
        expands as the empty string if VARNAME is undefined, but without undefined variable warnings.

"expand" is a rather bland name without distinction, though compact.  Better might be: $(expand-without-warnings ...) or $(maybe-expand ...)

What do you think?  If I submitted a patch for this, would you add it to the next release?

Greg