Last night I had the baffling error "possibly undefined macro: AC_MSG_WARN". Surely "impossibly undefined macro"!
Anyway, I was led to the following excellent analysis of the problem: https://ae1020.github.io/undefined-macro-pkg-config/ In my case, I was briefly baffled even further, as I *had* installed pkg-config. But after a little thought I realised that my case was the "opposite": I had failed to install a required autoconf-archive macro in my project. Problem solved! I wonder though if it might be possible to adopt the simplest suggestion of the article I cite above, and improve the error message to something like the following (lightly edited from the blog post to conform better to what I take for autoconf house style): configure.ac:34: error: unexpanded AC_XXX macro: AC_MSG_ERROR A token that looks like an autoconf macro was left unexpanded in the output. It may be undefined, or passed by `quote' to another macro that should have invoked it but isn't installed to do so. If this token and others are legitimate, please use m4_pattern_allow. See the Autoconf documentation.configure.ac:143: error: unexpanded AC_XXX macro: AC_DEFINE autoreconf: /usr/bin/autoconf failed with exit status: 1 Quite wordy, but might help more users get straight to the real problem! -- https://rrt.sc3d.org
