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Bug in AX_CHECK_POSIX_REGCOMP in current Autoconf Archive

From: Jonathan Kamens
Subject: Bug in AX_CHECK_POSIX_REGCOMP in current Autoconf Archive
Date: Wed, 22 Aug 2018 14:09:34 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:59.0) Gecko/20100101 Thunderbird/59.0a1

The current AX_CHECK_POSIX_REGCOMP macro in Autoconf Archive calls this:

  return regcomp( &re, "|no.*", flags ); }]])],[ax_cv_posix_regcomp=yes],[ax_cv_posix_regcomp=no],[ax_cv_posix_regcomp=no]

But according to the regex(7) man page on Linux, branches in a POSIX regex are required to be non-empty, so the regular _expression_ "|no.*" appears to be invalid since it conatins an empty branch.

And indeed, this macro fails on NetBSD, with regcomp returning 14, which is the error code REG_EMPTY.

This is such a specific regex that I find it hard to believe that it's just a coincidence that the test it's doing contains an empty branch. Unfortunately, the Git history doesn't go back far enough to determine why this is the way it is. I don't suppose you have any idea?

Interestingly, it doesn't fail on Linux.


Jonathan Kamens

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