The bootstrap script generates the same files ‘autoreconf -vi’ would,
in a normal package, but it uses autoconf *from the git sources* to do
it. This means people building from git do not need autoconf to be
installed already. More importantly, it eliminates the extra steps
when building from git, of re-generating autoconf’s own configure
script with the just-built autoconf, then rebuilding the entire tree.
(This process still requires Automake to be installed already, and
Automake’s bootstrap script requires Autoconf to be installed already,
so there is still a dependency loop between Autoconf and Automake when
building from git—you need at least one of them installed from a
tarball to get started.)
The bootstrap script works by creating a partial installation tree in
a temporary directory, containing bin/autoconf, bin/autom4te, and just
enough of the usual contents of $(pkgdatadir) for autoconf and
autom4te to work. It then runs a hardcoded list of commands,
corresponding to what ‘autoreconf -i -Wall,error’ would run, but
setting environment variables AUTOCONF and AUTOM4TE to ensure the
bootstrap versions of these tools are used. (We have to create both,
because automake runs autoconf, not autom4te, to trace configure.ac.)
The ‘Autom4te’, ‘autoconf’, and ‘m4sugar’ subdirectories of the
partial installation tree are symlinked back to the source tree; this
is why version.m4 needed to be moved out of the m4sugar subdirectory,
so the bootstrap script can create it without scribbling on the source
tree. autom4te is run in --melt mode, so we don’t need to create
freeze files in any subdirectories either. All of the substitution
variables that are needed for autoconf and autom4te to both run, and
create the same output that they would have if fully configured, are
honored (unfortunately this does involve digging around in
configure.ac with sed expressions).
