Hi all: I am trying to change the default of an AC_ARG_ENABLE option depending on the host architecture.
I am using the Autoconf 2.71 which comes with Ubuntu 22.04. I want to understand how Autoconf works, so let's not question for a moment whether changing an option's default this way actually makes sense. The gory details are here: https://review.openocd.org/c/openocd/+/8892 The configure.ac code is complicated, but basically it boils down to this (simplified): AC_ARG_ENABLE(some-option, AS_HELP_STRING([--enable-some-option=[[[yes/no/auto]]]], [blah blah (default is $someDefault)]) The trouble is, when I run "./configure --help", the $someDefault variable appears as a literal, that is, it is not being substituted. I tried with an M4 macro instead of a shell variable, to no avail. After a while struggling with this weird Autoconf behaviour, I came up with this test: AS_IF([test "a" = "a"], [ AC_MSG_NOTICE([true branch]) AC_ARG_ENABLE([argname-true-branch],AS_HELP_STRING([--enable-argname-true-branch],[Help string for the true branch])) ], [ AC_MSG_NOTICE([false branch]) AC_ARG_ENABLE([argname-false-branch],AS_HELP_STRING([--enable-argname-false-branch],[Help string for the false branch])) ]) The output when running "./configure --help" is: --enable-argname-true-branch Help string for the true branch --enable-argname-false-branch Help string for the false branch That is, both AS_IF branches are being evaluated when generating the help text. Compare with the output when running "./configure": configure: true branch In this case, only the true branch runs, as expected. My guess is that "./configure --help" is not evaluating the script properly, but it is just grepping all AC_ARG_ENABLE occurrences and doing some minimal M4 parsing which does not include normal variable or M4 macro substitution. Can someone confirm this suspicion? I searched for AC_ARG_ENABLE in the Autoconf manual, and the Internet for this behaviour, but I couldn't find anything relevant. Is there any way to have AC_ARG_ENABLE and/or AS_HELP_STRING evaluate arguments properly when running "./configure --help"? Or did I miss something? I am no Autoconf expert. Thanks in advance, rdiez
