Re: AS_IF breakage

[Eric Blake]

Eric Blake <ebb9 <at> byu.net> writes:

> 
> which puts the burden back on the user, where calling:
> 
> AS_IF([false], [], [AC_REQUIRE(...)])
> 
> causes a syntax error.
> 
> If I could get AC_REQUIRE to play nicely with m4_expand, then that would be 
the 
> solution - pre-expand the user's text, at which point we then know for 
certain 
> whether the expansion is empty.  But right now, I don't know how to pull that 
> trick off.

Here's a thought - right now, AC_REQUIRE is identical to m4_require, and 
expands to an empty string.  What if we instead did:

m4_define([AC_REQUIRE], [m4_require($@):;])

which makes every use of AC_REQUIRE output a valid shell command?  The ; is 
necessary, since "AC_REQUIRE(...)dnl" is a common idiom.

That only helps one particular case of a macro that used to expand to an empty 
string, but it is probably the most common case.

-- 
Eric Blake