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m4_pattern_forbid matches itself


From: Phil Edwards
Subject: m4_pattern_forbid matches itself
Date: Wed, 23 Jul 2003 00:07:56 -0400
User-agent: Mutt/1.5.3i

Two problems with m4_pattern_forbid (or rather, with my understanding of
how it's meant to be used) follow:

Uses of $target_alias keep sneaking back into libstdc++'s configury, which
is generally a Very Bad Thing for a GCC target library.  So I thought I'd
play with m4_pattern_forbid to try and prevent mistakes before they happen.

This

    m4_pattern_forbid([target_alias],[informative message goes here])

triggers

    configure.in:44: error: target alias is not what you think it is
        If this token and others are legitimate, please use m4_pattern_allow.
        See the Autoconf documentation.

Line 44 is the m4_pattern_forbid command.

So, I'm assuming that it points to that line for explanatory purposes,
and the user is supposed to look there.  All good.  But it /doesn't/
mention the other lines in configure.in where I've deliberately stuck
some occurrances of target_alias for testing.  It mentions the output line
numbers in configure, but that's not nearly as helpful.


Second problem:  since "target_alias" could show up as part of a larger
variable name, I'd like to only match it when it's used as a variable, e.g.,

    \${?target_alias\>

But even this fails to match anything at all:

    m4_pattern_forbid([\$target_alias],[informative message goes here])

I tried escaping the '$' more and more, thinking that perhaps the \
was being lost and m4 was trying to do an end-of-line match.  No joy.
So right now I'm stuck with only listing the simple text name, which
doesn't seem to do what I want.


Am I misusing m4_pattern_forbid?


Phil

-- 
If ye love wealth greater than liberty, the tranquility of servitude greater
than the animating contest for freedom, go home and leave us in peace.  We seek
not your counsel, nor your arms.  Crouch down and lick the hand that feeds you;
and may posterity forget that ye were our countrymen.            - Samuel Adams




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