autoconf/man/autom4te.w
Zack Weinberg 9b5c0f1774
Generate manpages directly from source code.
We generate manpages for autoconf’s installed programs (autoconf,
autoheader, etc.) using help2man, which runs each program in order to
learn its --help output.  Each manpage therefore has a dependency on
the existence of the corresponding program, but this dependency is
intentionally left out of the Makefile so that one can build from a
tarball release (which will include prebuilt manpages) without having
help2man installed.

But when building from a git checkout with high levels of
parallelism (-j20 or so), the missing dependency can lead to build
failures, because help2man will try to run the program before it
exists.  In an earlier patch I tried to work around this with a
recursive make invocation in the ‘.x.1’ rule, to ensure the existence
of the program.  That only traded one concurrency bug for another, now
we could have two jobs trying to build the same program simultaneously
and they would clobber each other’s work and the build would still
fail.

Instead, this patch introduces a utility script ‘help-extract.pl’ that
reads --help and --version information directly from the source code
for each program.  This utility, wrapped appropriately for each
program, is what help2man now runs.  Usage is a little weird because
help2man doesn’t let you specify any arguments to the “executable”
that it runs, but it works, and lets us write all of the true
dependencies of each manpage into the Makefile without naming any file
that would be created during a build from a tarball.  help-extract.pl
is a Perl script, so it introduces no new build-time requirements.

A downside is that we have to make sure each of the script sources in
bin/, and also part of lib/Autom4te/ChannelDefs.pm, are parseable by
help-extract.  The most important constraints are that the text output
by --help must be defined in a global variable named ‘help’, and its
definition has to be formatted just the way these definitions are
currently formatted.  Similarly for --version.  Furthermore, only some
non-literal substitutions are possible in these texts; each has to be
explicitly supported in help-extract.pl.  The current list of supported
substitutions is $0, @PACKAGE_NAME@, @VERSION@, @RELEASE_YEAR@, and
Autom4te::ChannelDefs::usage.

The generated manpages themselves are character-for-character
identical before and after this patch.

 * build-aux/help-extract.pl: New build script that extracts --help
  and --version output from manpages.

 * man/autoconf.w, man/autoheader.w, man/autom4te.w, man/autoreconf.w
 * man/autoscan.w, man/autoupdate.w, man/ifnames.w: New shell scripts
   which wrap build-aux/help-extract.pl.

 * man/local.mk: Generate each manpage by running help2man on the
   corresponding .w script, not on the built utility itself.
   Revise all dependencies to match.

 * bin/autoconf.as: Rename ‘usage’ variable to ‘help’ and
   ‘help’ variable to ‘usage_err’.
 * bin/autoheader.in: Call Autom4te::ChannelDefs::usage with no
   function-call parentheses, matching all the other scripts.
 * bin/autom4te.in: Initialize $version with a regular double-quoted
   string, not a heredoc, matching all the other scripts.
 * bin/autoscan.in: Remove global variable $configure_scan.
2020-08-21 16:23:32 -04:00

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Executable File

#! /bin/sh
# help-extract wrapper, see build-aux/help-extract.pl and man/local.mk
exec "${PERL-perl}" "${top_srcdir}/build-aux/help-extract.pl" \
bin/autom4te.in "$@"