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When upgrading quota to 4.03, I discovered all executables are linked to a library whose presence is checked by: AC_CHECK_LIB([ldap], [ldap_initialize], [], [ build_ldap=no AS_IF([test "x$enable_ldapmail" = "xyes"], [ AC_MSG_ERROR([LDAP support required but library not found.]); ]) ]) Because third argument (if-found action) is defined to empty literal, it should not fall back to default implementation (adding -lldap to LIBS etc.). Documentation reads: [..] If ACTION-IF-FOUND is not specified, the default action prepends `-lLIBRARY' to `LIBS' and defines `HAVE_LIBLIBRARY' (in all capitals). But autoconf-2.69-21.fc23.noarch seems breaking this rule and modifies LIBS. I had to work around the bug with this change in quota's configure.ac: - AC_CHECK_LIB([ldap], [ldap_initialize], [], [ + AC_CHECK_LIB([ldap], [ldap_initialize], [:;], [ I believe this is a bug in Autoconf.
If I understand this right, you think that '[]' makes it a explicitly defined value, but it does not. M4 compares against empty string and thus having 'macro(a,,c)' is equivalent to 'macro(a,[],c)'.
You can avoid changing the LIBS variable by: old_LIBS=$LIBS AC_CHECK_LIB([ldap], [ldap_initialize], , [ ... LIBS=$old_LIBS .. or more likely, properly specify the ACTION-IF-FOUND. Having 'true' there does not look much like work-around to me. But for really qualified answer this should be discussed upstream.
Thank you for the explanation. I will alert quota upstream to rework the configure.ac.