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autoconf/bin/autoupdate.in
Akim Demaille e808ba2ea7 * bin/autoupdate.in ($m4): Fix quotation. 
Reported by Martin Mokrejs.
2003-05-21 09:46:59 +00:00

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#! @PERL@ -w
# -*- perl -*-
# autoupdate - modernize an Autoconf file.
# Copyright (C) 1994, 1999, 2000, 2001, 2002, 2003
# Free Software Foundation, Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2, or (at your option)
# any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
# 02111-1307, USA.
# Originally written by David MacKenzie <djm@gnu.ai.mit.edu>.
# Rewritten by Akim Demaille <akim@freefriends.org>.
eval 'case $# in 0) exec @PERL@ -S "$0";; *) exec @PERL@ -S "$0" "$@";; esac'
if 0;
BEGIN
{
my $datadir = $ENV{'autom4te_perllibdir'} || '@datadir@';
unshift @INC, $datadir;
# Override SHELL. On DJGPP SHELL may not be set to a shell
# that can handle redirection and quote arguments correctly,
# e.g.: COMMAND.COM. For DJGPP always use the shell that configure
# has detected.
$ENV{'SHELL'} = '@SHELL@' if ($^O eq 'dos');
}
use File::Basename;
use Autom4te::General;
use Autom4te::XFile;
use strict;
# Lib files.
my $autom4te = $ENV{'AUTOM4TE'} || '@bindir@/@autom4te-name@';
my $autoconf = "$autom4te --language=autoconf";
# We need to find m4sugar.
my @prepend_include;
my @include = ('@datadir@');
my $force = 0;
# m4.
my $m4 = $ENV{"M4"} || '@M4@';
# $HELP
# -----
$help = "Usage: $0 [OPTION] ... [TEMPLATE-FILE...]
Update the TEMPLATE-FILE... if given, or `configure.ac' if present,
or else `configure.in', to the syntax of the current version of
Autoconf. The original files are backed up.
Operation modes:
-h, --help print this help, then exit
-V, --version print version number, then exit
-v, --verbose verbosely report processing
-d, --debug don't remove temporary files
-f, --force consider all files obsolete
Library directories:
-B, --prepend-include=DIR prepend directory DIR to search path
-I, --include=DIR append directory DIR to search path
Report bugs to <bug-autoconf\@gnu.org>.
";
# $VERSION
# --------
$version = "autoupdate (@PACKAGE_NAME@) @VERSION@
Written by David J. MacKenzie and Akim Demaille.
Copyright (C) 2003 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
";
## ---------- ##
## Routines. ##
## ---------- ##
# parse_args ()
# -------------
# Process any command line arguments.
sub parse_args ()
{
my $srcdir;
getopt ('I|include=s' => \@include,
'B|prepend-include=s' => \@prepend_include,
'f|force' => \$force);
if (! @ARGV)
{
my $configure_ac = find_configure_ac;
error "no input file"
unless $configure_ac;
push @ARGV, $configure_ac;
}
}
# ------------- #
# M4 builtins. #
# ------------- #
my @m4_builtins;
# &handle_m4_symbols ()
# ---------------------
# Create the following $tmp files:
# m4.m4 -- enable the m4 builtins.
# unm4.m4 -- disable the m4 builtins.
# savem4.m4 -- save the m4 builtins.
sub handle_m4_macros ()
{
# Get the list of builtins.
xsystem ("echo dumpdef | $m4 2>$tmp/m4.defs >/dev/null");
my $m4_defs = new Autom4te::XFile "$tmp/m4.defs";
while ($_ = $m4_defs->getline)
{
push @m4_builtins, $1
if /^(\w+):/;
}
$m4_defs->close;
# Output the files.
my $m4_m4 = new Autom4te::XFile ">$tmp/m4.m4";
print $m4_m4 "# m4.m4 -- enable the m4 builtins.\n";
my $unm4_m4 = new Autom4te::XFile ">$tmp/unm4.m4";
print $unm4_m4 "# unm4.m4 -- disable the m4 builtins.\n";
print $unm4_m4 "# Because Autoconf, via M4sugar, redefines some of these\n";
print $unm4_m4 "# macros, and therefore since unac.m4 disables them,\n";
print $unm4_m4 "# disable only if defined.\n";
my $m4save_m4 = new Autom4te::XFile ">$tmp/m4save.m4";
print $m4save_m4 "# savem4.m4 -- save the m4 builtins.\n";
foreach (@m4_builtins)
{
print $m4save_m4 "define([_au_$_], defn([$_]))\n";
print $unm4_m4 "_au_ifdef([$_], [_au_undefine([$_])])\n";
print $m4_m4 "_au_define([$_], _au_defn([_au_$_]))\n";
}
}
# ----------------- #
# Autoconf macros. #
# ----------------- #
# @AU_MACROS & AC_MACROS -- AU and AC macros and yet another useful comment.
my (%ac_macros, %au_macros);
# HANDLE_AUTOCONF_MACROS ()
# -------------------------
# @M4_BUILTINS -- M4 builtins and a useful comment.
sub handle_autoconf_macros ()
{
my $macros = new Autom4te::XFile ("$autoconf"
. " --trace AU_DEFUN:'AU:\$f:\$1'"
. " --trace define:'AC:\$f:\$1'"
. " --melt /dev/null |");
while ($_ = $macros->getline)
{
chomp;
my ($domain, $file, $macro) = /^(AC|AU):(.*):([^:]*)$/ or next;
# ../lib/m4sugar/m4sugar.m4 -> m4sugar
# ../lib/autoconf/general.m4 -> autoconf
# aclocal.m4 -> aclocal
my $set = basename (dirname ($file));
$set = 'aclocal' if $file eq 'aclocal.m4';
error "unknown set: $set: $_"
unless $set =~ /^(m4sugar|aclocal|autoconf)$/;
if ($domain eq "AC")
{
$ac_macros{$macro} = $set;
}
else
{
$au_macros{$macro} = $set;
}
}
$macros->close;
# Don't keep AU macros in @AC_MACROS.
delete $ac_macros{$_}
foreach (keys %au_macros);
# Don't keep M4sugar macros which are redefined by Autoconf,
# such as `builtin', `changequote' etc. See autoconf/autoconf.m4.
delete $ac_macros{$_}
foreach (@m4_builtins);
error "no current Autoconf macros found"
unless keys %ac_macros;
error "no obsolete Autoconf macros found"
unless keys %au_macros;
if ($debug)
{
print STDERR "Current Autoconf macros:\n";
print STDERR join (' ', sort keys %ac_macros) . "\n\n";
print STDERR "Obsolete Autoconf macros:\n";
print STDERR join (' ', sort keys %au_macros) . "\n\n";
}
# ac.m4 -- autoquoting definitions of the AC macros (M4sugar excluded).
# unac.m4 -- undefine the AC macros.
my $ac_m4 = new Autom4te::XFile ">$tmp/ac.m4";
print $ac_m4 "# ac.m4 -- autoquoting definitions of the AC macros.\n";
my $unac_m4 = new Autom4te::XFile ">$tmp/unac.m4";
print $unac_m4 "# unac.m4 -- undefine the AC macros.\n";
foreach (sort grep { $ac_macros{$_} ne 'm4sugar' } keys %ac_macros)
{
print $ac_m4 "_au_define([$_], [[\$0(\$\@)]])\n";
print $unac_m4 "_au_undefine([$_])\n";
}
}
## -------------- ##
## Main program. ##
## -------------- ##
parse_args;
$autoconf .= " --debug" if $debug;
$autoconf .= " --force" if $force;
$autoconf .= " --verbose" if $verbose;
$autoconf .= join (' --include=', '', @include);
$autoconf .= join (' --prepend-include=', '', @prepend_include);
mktmpdir ('au');
handle_m4_macros;
handle_autoconf_macros;
# $au_changequote -- enable the quote `[', `]' right before any AU macro.
my $au_changequote =
's/\b(' . join ('|', keys %au_macros) . ')\b/_au_changequote([,])$1/g';
# au.m4 -- definitions the AU macros.
xsystem ("$autoconf --trace AU_DEFUN:'_au_defun(\@<:\@\$1\@:>\@,
\@<:\@\$2\@:>\@)' --melt /dev/null "
. ">$tmp/au.m4");
## ------------------- ##
## Process the files. ##
## ------------------- ##
foreach my $file (@ARGV)
{
my $filename = $file;
# We need an actual file.
if ($file eq '-')
{
$file = "$tmp/stdin";
system "cat >$file";
}
elsif (! -r "$file")
{
die "$me: $file: No such file or directory";
}
# input.m4 -- m4 program to produce the updated file.
# Load the values, the dispatcher, neutralize m4, and the prepared
# input file.
my $input_m4 = <<\EOF;
divert(-1) -*- Autoconf -*-
changequote([, ])
# Move all the builtins into the `_au_' pseudo namespace
include([m4save.m4])
# _au_defun(NAME, BODY)
# ---------------------
# Define NAME to BODY, plus AU activation/deactivation.
_au_define([_au_defun],
[_au_define([$1],
[_au_enable()dnl
$2[]dnl
_au_disable()])])
# Import the definition of the obsolete macros.
_au_include([au.m4])
## ------------------------ ##
## _au_enable/_au_disable. ##
## ------------------------ ##
# They work by pair: each time an AU macro is activated, it runs
# _au_enable, and at its end its runs _au_disable (see _au_defun
# above). AU macros might use AU macros, which should
# enable/disable only for the outer AU macros.
#
# `_au_enabled' is used to this end, determining whether we really
# enable/disable.
# __au_enable
# -----------
# Reenable the builtins, and m4sugar.
_au_define([__au_enable],
[_au_divert(-1)
# Enable special characters.
_au_changecom([#])
# Enable the m4 builtins, m4sugar and the autoquoting AC macros.
_au_include([m4.m4])
_au_include([m4sugar/m4sugar.m4])
_au_include([ac.m4])
_au_divert(0)])
# _au_enable
# ----------
# Called at the beginning of all the obsolete macros. Reenable the
# builtins, and m4sugar if needed.
_au_define([_au_enable],
[_au_ifdef([_au_enabled],
[],
[__au_enable()])_au_dnl
_au_pushdef([_au_enabled])])
# __au_disable
# ------------
# Disable the builtins, and m4sugar.
_au_define([__au_disable],
[_au_divert(-1)
# Disable m4sugar, the AC autoquoting macros, and m4.
_au_include([unac.m4])
_au_include([unm4.m4])
# Disable special characters.
_au_changequote()
_au_changecom()
_au_divert(0)])
# _au_disable
# -----------
# Called at the end of all the obsolete macros. Disable the
# builtins, and m4sugar if needed..
_au_define([_au_disable],
[_au_popdef([_au_enabled])_au_dnl
_au_ifdef([_au_enabled],
[],
[__au_disable()])])
## ------------------------------- ##
## Disable, and process the file. ##
## ------------------------------- ##
_au_divert(-1)
# Disable m4: M4sugar and the AC autoquoting macros are not loaded yet,
# hence invoking `_au_disable' is wrong.
_au_include([unm4.m4])
# Disable special characters.
_au_changequote()
_au_changecom()
_au_divert(0)_au_dnl
EOF
$input_m4 =~ s/^ //mg;
# prepared input -- input, but reenables the quote before each AU macro.
open INPUT_M4, ">$tmp/input.m4"
or error "cannot open: $!";
open FILE, "<$file"
or error "cannot open: $!";
print INPUT_M4 "$input_m4";
while (<FILE>)
{
eval $au_changequote;
print INPUT_M4;
}
close FILE
or error "cannot close $file: $!";
close INPUT_M4
or error "cannot close $tmp/input.m4: $!";
# Now ask m4 to perform the update.
xsystem ("$m4 --include=$tmp"
. join (' --include=', '', reverse (@prepend_include))
. join (' --include=', '', @include)
. " $tmp/input.m4 >$tmp/updated");
update_file ("$tmp/updated",
"$file" eq "$tmp/stdin" ? '-' : "$file");
}
exit 0;
# ## ---------------------------- ##
# ## How `autoupdate' functions. ##
# ## ---------------------------- ##
#
# The task of `autoupdate' is not trivial: the biggest difficulty being
# that you must limit the changes to the parts that really need to be
# updated. Finding a satisfying implementation proved to be quite hard,
# as this is the fourth implementation of `autoupdate'.
#
# Below, we will use a simple example of obsolete macro:
#
# AU_DEFUN([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))])
# AC_DEFUN([NEW], [echo "sum($1) = $2"])
#
# the input file contains
#
# dnl The Unbelievable Truth
# OLD(1, 2)
# NEW([0, 0], [0])
#
# Of course the expected output is
#
# dnl The Unbelievable Truth
# NEW([1, 2], [3])
# NEW([0, 0], [0])
#
#
# # First implementation: sed
# # =========================
#
# The first implementation was only able to change the name of obsolete
# macros.
#
# The file `acoldnames.m4' defined the old names based on the new names.
# It was simple then to produce a sed script such as:
#
# s/OLD/NEW/g
#
# Updating merely consisted in running this script on the file to
# update.
#
# This scheme suffers an obvious limitation: that `autoupdate' was
# unable to cope with new macros that just swap some of its arguments
# compared to the old macro. Fortunately, that was enough to upgrade
# from Autoconf 1 to Autoconf 2. (But I have no idea whether the
# changes in Autoconf 2 were precisely limited by this constraint.)
#
#
# # Second implementation: hooks
# # ============================
#
# The version 2.15 of Autoconf brought a vast number of changes compared
# to 2.13, so a solution was needed. One could think to extend the
# `sed' scripts with specialized code for complex macros. But this
# approach is of course full of flaws:
#
# a. the Autoconf maintainers have to write these snippets, which we
# just don't want to,
#
# b. I really don't think you'll ever manage to handle the quoting of
# m4 from sed.
#
# To satisfy a., let's remark that the code which implements the old
# features in term of the new feature is exactly the code which should
# replace the old code.
#
# To answer point b, as usual in the history of Autoconf, the answer, at
# least on the paper, is simple: m4 is the best tool to parse m4, so
# let's use m4.
#
# Therefore the specification is:
#
# I want to be able to tell Autoconf, well, m4, that the macro I
# am currently defining is an obsolete macro (so that the user is
# warned), which code is the code to use when running autoconf,
# but that the very same code has to be used when running
# autoupdate. To summarize, the interface I want is
# `AU_DEFUN(OLD-NAME, NEW-CODE)'.
#
#
# Now for the technical details.
#
# When running autoconf, except for the warning, AU_DEFUN is basically
# AC_DEFUN.
#
# When running autoupdate, we want *only* OLD-NAMEs to be expanded.
# This obviously means that acgeneral.m4 and acspecific.m4 must not be
# loaded. Nonetheless, because we want to use a rich set of m4
# features, m4sugar.m4 is needed. Please note that the fact that
# Autoconf's macros are not loaded is positive on two points:
#
# - we do get an updated `configure.ac', not a `configure'!
#
# - the old macros are replaced by *calls* to the new-macros, not the
# body of the new macros, since their body is not defined!!!
# (Whoa, that's really beautiful!).
#
# Additionally we need to disable the quotes when reading the input for
# two reasons: first because otherwise `m4' will swallow the quotes of
# other macros:
#
# NEW([1, 2], 3)
# => NEW(1, 2, 3)
#
# and second, because we want to update the macro calls which are
# quoted, i.e., we want
#
# FOO([OLD(1, 2)])
# => FOO([NEW([1, 2], [3])])
#
# If we don't disable the quotes, only the macros called at the top
# level would be updated.
#
# So, let's disable the quotes.
#
# Well, not quite: m4sugar.m4 still needs to use quotes for some macros.
# Well, in this case, when running in autoupdate code, each macro first
# reestablishes the quotes, expands itself, and disables the quotes.
#
# Thinking a bit more, you realize that in fact, people may use `define'
# `ifelse' etc. in their files, and you certainly don't want to process
# them. Another example is `dnl': you don't want to remove the
# comments. You then realize you don't want exactly to import m4sugar:
# you want to specify when it is enabled (macros active), and disabled.
# m4sugar provides m4_disable/m4_enable to this end.
#
# You're getting close to it. Now remains one task: how to handle
# twofold definitions?
#
# Remember that the same AU_DEFUN must be understood in two different
# ways, the AC way, and the AU way.
#
# One first solution is to check whether acgeneral.m4 was loaded. But
# that's definitely not cute. Another is simply to install `hooks',
# that is to say, to keep in some place m4 knows, late `define' to be
# triggered *only* in AU mode.
#
# You first think to design AU_DEFUN like this:
#
# 1. AC_DEFUN(OLD-NAME,
# [Warn the user OLD-NAME is obsolete.
# NEW-CODE])
#
# 2. Store for late AU binding([define(OLD_NAME,
# [Reestablish the quotes.
# NEW-CODE
# Disable the quotes.])])
#
# but this will not work: NEW-CODE has probably $1, $2 etc. and these
# guys will be replaced with the argument of `Store for late AU binding'
# when you call it.
#
# I don't think there is a means to avoid this using this technology
# (remember that $1 etc. are *always* expanded in m4). You may also try
# to replace them with $[1] to preserve them for a later evaluation, but
# if `Store for late AU binding' is properly written, it will remain
# quoted till the end...
#
# You have to change technology. Since the problem is that `$1'
# etc. should be `consumed' right away, one solution is to define now a
# second macro, `AU_OLD-NAME', and to install a hook than binds OLD-NAME
# to AU_OLD-NAME. Then, autoupdate.m4 just need to run the hooks. By
# the way, the same method was used in autoheader.
#
#
# # Third implementation: m4 namespaces by m4sugar
# # ==============================================
#
# Actually, this implementation was just a clean up of the previous
# implementation: instead of defining hooks by hand, m4sugar was equipped
# with `namespaces'. What are they?
#
# Sometimes we want to disable some *set* of macros, and restore them
# later. We provide support for this via namespaces.
#
# There are basically three characters playing this scene: defining a
# macro in a namespace, disabling a namespace, and restoring a namespace
# (i.e., all the definitions it holds).
#
# Technically, to define a MACRO in NAMESPACE means to define the macro
# named `NAMESPACE::MACRO' to the VALUE. At the same time, we append
# `undefine(NAME)' in the macro named `m4_disable(NAMESPACE)', and
# similarly a binding of NAME to the value of `NAMESPACE::MACRO' in
# `m4_enable(NAMESPACE)'. These mechanisms allow to bind the macro of
# NAMESPACE and to unbind them at will.
#
# Of course this implementation is really inefficient: m4 has to grow
# strings which can become quickly huge, which slows it significantly.
#
# In particular one should avoid as much as possible to use `define' for
# temporaries. Now that `define' as quite a complex meaning, it is an
# expensive operations that should be limited to macros. Use
# `m4_define' for temporaries.
#
# Private copies of the macros we used in entering / exiting the m4sugar
# namespace. It is much more convenient than fighting with the renamed
# version of define etc.
#
#
#
# Those two implementations suffered from serious problems:
#
# - namespaces were really expensive, and incurred a major performance
# loss on `autoconf' itself, not only `autoupdate'. One solution
# would have been the limit the use of namespaces to `autoupdate', but
# that's again some complications on m4sugar, which really doesn't need
# this. So we wanted to get rid of the namespaces.
#
# - since the quotes were disabled, autoupdate was sometimes making
# wrong guesses, for instance on:
#
# foo([1, 2])
#
# m4 saw 2 arguments: `[1'and `2]'. A simple solution, somewhat
# fragile, is to reestablish the quotes right before all the obsolete
# macros, i.e., to use sed so that the previous text becomes
#
# changequote([, ])foo([1, 2])
#
# To this end, one wants to trace the definition of obsolete macros.
#
# It was there that the limitations of the namespace approach became
# painful: because it was a complex machinery playing a lot with the
# builtins of m4 (hence, quite fragile), tracing was almost impossible.
#
#
# So this approach was dropped.
#
#
# # The fourth implementation: two steps
# # ====================================
#
# If you drop the uses of namespaces, you no longer can compute the
# updated value, and replace the old call with it simultaneously.
#
# Obviously you will use m4 to compute the updated values, but you may
# use some other tool to achieve the replacement. Personally, I trust
# nobody but m4 to parse m4, so below, m4 will perform the two tasks.
#
# How can m4 be used to replace *some* macros calls with newer values.
# Well, that's dead simple: m4 should learn the definitions of obsolete
# macros, forget its builtins, disable the quotes, and then run on the
# input file, which amounts to doing this:
#
# divert(-1)dnl
# changequote([, ])
# define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
# undefine([dnl])
# undefine([m4_eval])
# # Some more undefines...
# changequote()
# divert(0)dnl
# dnl The Unbelievable Truth
# changequote([, ])OLD(1, 2)
# NEW([0, 0],
# 0)
#
# which will result in
#
# dnl The Unbelievable Truth
# NEW(1, 2, m4_eval(1 + 2))
# NEW([0, 0],
# 0)
#
# Grpmh. Two problems. A minor problem: it would have been much better
# to have the `m4_eval' computed, and a major problem: you lost the
# quotation in the result.
#
# Let's address the big problem first. One solution is to define any
# modern macro to rewrite its calls with the proper quotation, thanks to
# `$@'. Again, tracing the `define's makes it possible to know which
# are these macros, so you input is:
#
# divert(-1)dnl
# changequote([, ])
# define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
# define([NEW], [[NEW($@)]changequote()])
# undefine([dnl])
# undefine([m4_eval])
# # Some more undefines...
# changequote()
# divert(0)dnl
# dnl The Unbelievable Truth
# changequote([, ])OLD(1, 2)
# changequote([, ])NEW([0, 0],
# 0)
#
# which results in
#
# dnl The Unbelievable Truth
# NEW([1, 2],[m4_eval(1 + 2)])
# NEW([0, 0],[0])
#
# Our problem is solved, i.e., the first call to `NEW' is properly
# quoted, but introduced another problem: we changed the layout of the
# second calls, which can be a drama in the case of huge macro calls
# (think of `AC_TRY_RUN' for instance). This example didn't show it,
# but we also introduced parens to macros which did not have some:
#
# AC_INIT
# => AC_INIT()
#
# No big deal for the semantics (unless the macro depends upon $#, which
# is bad), but the users would not be happy.
#
# Additionally, we introduced quotes that we not there before, which is
# OK in most cases, but could change the semantics of the file.
#
# Cruel dilemma: we do want the auto-quoting definition of `NEW' when
# evaluating `OLD', but we don't when we evaluate the second `NEW'.
# Back to namespaces?
#
# No.
#
#
# # Second step: replacement
# # ------------------------
#
# No, as announced above, we will work in two steps: in a first step we
# compute the updated values, and in a second step we replace them. Our
# goal is something like this:
#
# divert(-1)dnl
# changequote([, ])
# define([OLD], [NEW([1, 2], [3])changequote()])
# undefine([dnl])
# undefine([m4_eval])
# # Some more undefines...
# changequote()
# divert(0)dnl
# dnl The Unbelievable Truth
# changequote([, ])OLD(1, 2)
# NEW([0, 0],
# 0)
#
# i.e., the new value of `OLD' is precomputed using the auto-quoting
# definition of `NEW' and the m4 builtins. We'll see how afterwards,
# let's finish with the replacement.
#
# Of course the solution above is wrong: if there were other calls to
# `OLD' with different values, we would smash them to the same value.
# But it is quite easy to generalize the scheme above:
#
# divert(-1)dnl
# changequote([, ])
# define([OLD([1],[2])], [NEW([1, 2], [3])])
# define([OLD], [defn([OLD($@)])changequote()])
# undefine([dnl])
# undefine([m4_eval])
# # Some more undefines...
# changequote()
# divert(0)dnl
# dnl The Unbelievable Truth
# changequote([, ])OLD(1, 2)
# NEW([0, 0],
# 0)
#
# i.e., for each call to obsolete macros, we build an array `call =>
# value', and use a macro to dispatch these values. This results in:
#
# dnl The Unbelievable Truth
# NEW([1, 2], [3])
# NEW([0, 0],
# 0)
#
# In French, we say `Youpi !', which you might roughly translate as
# `Yippee!'.
#
#
# # First step: computation
# # -----------------------
#
# Let's study the anatomy of the file, and name its sections:
#
# prologue
# divert(-1)dnl
# changequote([, ])
# values
# define([OLD([1],[2])], [NEW([1, 2], [3])])
# dispatcher
# define([OLD], [defn([OLD($@)])changequote()])
# disabler
# undefine([dnl])
# undefine([m4_eval])
# # Some more undefines...
# changequote()
# divert(0)dnl
# input
# dnl The Unbelievable Truth
# changequote([, ])OLD(1, 2)
# NEW([0, 0],
# 0)
#
#
# # Computing the `values' section
# # ..............................
#
# First we need to get the list of all the AU macro uses. To this end,
# first get the list of all the AU macros names by tracing `AU_DEFUN' in
# the initialization of autoconf. This list is computed in the file
# `au.txt' below.
#
# Then use this list to trace all the AU macro uses in the input. The
# goal is obtain in the case of our example:
#
# [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
#
# This is the file `values.in' below.
#
# We want to evaluate this with only the builtins (in fact m4sugar), the
# auto-quoting definitions of the new macros (`new.m4'), and the
# definition of the old macros (`old.m4'). Computing these last two
# files is easy: it's just a matter of using the right `--trace' option.
#
# So the content of `values.in' is:
#
# include($autoconf_dir/m4sugar.m4)
# m4_include(new.m4)
# m4_include(old.m4)
# divert(0)dnl
# [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
#
# We run m4 on it, which yields:
#
# define([OLD([1],[2])],@<<@NEW([1, 2], [3])@>>@)
#
# Transform `@<<@' and `@>>@' into quotes and we get
#
# define([OLD([1],[2])],[NEW([1, 2], [3])])
#
# This is `values.m4'.
#
#
# # Computing the `dispatcher' section
# # ..................................
#
# The `prologue', and the `disabler' are simple and need no commenting.
#
# To compute the `dispatcher' (`dispatch.m4'), again, it is a simple
# matter of using the right `--trace'.
#
# Finally, the input is not exactly the input file, rather it is the
# input file with the added `changequote'. To this end, we build
# `quote.sed'.
#
#
# # Putting it all together
# # .......................
#
# We build the file `input.m4' which contains:
#
# divert(-1)dnl
# changequote([, ])
# include(values.m4)
# include(dispatch.m4)
# undefine([dnl])
# undefine([eval])
# # Some more undefines...
# changequote()
# divert(0)dnl
# dnl The Unbelievable Truth
# changequote([, ])OLD(1, 2)
# NEW([0, 0],
# 0)
#
# And we just run m4 on it. Et voila`, Monsieur ! Mais oui, mais oui.
#
# Well, there are a few additional technicalities. For instance, we
# rely on `changequote', `ifelse' and `defn', but we don't want to
# interpret the changequotes of the user, so we simply use another name:
# `_au_changequote' etc.
#
#
# # Failure of the fourth approach
# # ------------------------------
#
# This approach is heavily based on traces, but then there is an obvious
# problem: non expanded code will never be seen/ In particular, the body
# of a `define' definition is not seen, so on the input
#
# define([idem], [OLD(0, [$1])])
#
# autoupdate would never see the `OLD', and wouldn't have updated it.
# Worse yet, if `idem(0)' was used later, then autoupdate sees that
# `OLD' is used, computes the result for `OLD(0, 0)' and sets up a
# dispatcher for `OLD'. Since there was no computed value for `OLD(0,
# [$1])', the dispatcher would have replaced with... nothing, leading
# to
#
# define([idem], [])
#
# With some more thinking, you see that the two step approach is wrong,
# the namespace approach was much saner.
#
# But you learned a lot, in particular you realized that using traces
# can make it possible to simulate namespaces!
#
#
#
# # The fifth implementation: m4 namespaces by files
# # ================================================
#
# The fourth implementation demonstrated something unsurprising: you
# cannot precompute, i.e., the namespace approach was the right one.
# Still, we no longer want them, they're too expensive. Let's have a
# look at the way it worked.
#
# When updating
#
# dnl The Unbelievable Truth
# OLD(1, 2)
# NEW([0, 0], [0])
#
# you evaluate `input.m4':
#
# divert(-1)
# changequote([, ])
# define([OLD],
# [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
# ...
# m4_disable()
# dnl The Unbelievable Truth
# OLD(1, 2)
# NEW([0, 0], [0])
#
# where `m4_disable' undefines the m4 and m4sugar, and disables the quotes
# and comments:
#
# define([m4_disable],
# [undefine([__file__])
# ...
# changecom(#)
# changequote()])
#
# `m4_enable' does the converse: reestablish quotes and comments
# --easy--, reestablish m4sugar --easy: just load `m4sugar.m4' again-- and
# reenable the builtins. This later task requires that you first save
# the builtins. And BTW, the definition above of `m4_disable' cannot
# work: you undefined `changequote' before using it! So you need to use
# your privates copies of the builtins. Let's introduce three files for
# this:
#
# `m4save.m4'
# moves the m4 builtins into the `_au_' pseudo namespace
# `unm4.m4'
# undefines the builtins
# `m4.m4'
# restores them
#
# So `input.m4' is:
#
# divert(-1)
# changequote([, ])
#
# include([m4save.m4])
#
# # Import AU.
# define([OLD],
# [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
#
# define([_au_enable],
# [_au_changecom([#])
# _au_include([m4.m4])
# _au_include(m4sugar.m4)])
#
# define([_au_disable],
# [# Disable m4sugar.
# # Disable the m4 builtins.
# _au_include([unm4.m4])
# # 1. Disable special characters.
# _au_changequote()
# _au_changecom()])
#
# m4_disable()
# dnl The Unbelievable Truth
# OLD(1, 2)
# NEW([0, 0], [0])
#
# Based on what we learned in the fourth implementation we know that we
# have to enable the quotes *before* any AU macro, and we know we need
# to build autoquoting versions of the AC macros. But the autoquoting
# AC definitions must be disabled in the rest of the file, and enabled
# inside AU macros.
#
# Using `autoconf --trace' it is easy to build the files
#
# `ac.m4'
# define the autoquoting AC fake macros
# `disable.m4'
# undefine the m4sugar and AC autoquoting macros.
# `au.m4'
# definitions of the AU macros (such as `OLD' above).
#
# Now, `input.m4' is:
#
# divert(-1)
# changequote([, ])
#
# include([m4save.m4])
# # Import AU.
# include([au.m4])
#
# define([_au_enable],
# [_au_changecom([#])
# _au_include([m4.m4])
# _au_include(m4sugar.m4)
# _au_include(ac.m4)])
#
# define([_au_disable],
# [_au_include([disable.m4])
# _au_include([unm4.m4])
# # 1. Disable special characters.
# _au_changequote()
# _au_changecom()])
#
# m4_disable()
# dnl The Unbelievable Truth
# _au_changequote([, ])OLD(1, 2)
# NEW([0, 0], [0])
#
# Finally, version V is ready.
#
# Well... almost.
#
# There is a slight problem that remains: if an AU macro OUTER includes
# an AU macro INNER, then _au_enable will be run when entering OUTER
# and when entering INNER (not good, but not too bad yet). But when
# getting out of INNER, _au_disable will disable everything while we
# were still in OUTER. Badaboom.
#
# Therefore _au_enable and _au_disable have to be written to work by
# pairs: each _au_enable pushdef's _au_enabled, and each _au_disable
# popdef's _au_enabled. And of course _au_enable and _au_disable are
# effective when _au_enabled is *not* defined.
#
# Finally, version V' is ready. And there is much rejoicing. (And I
# have free time again. I think. Yeah, right.)
### Setup "GNU" style for perl-mode and cperl-mode.
## Local Variables:
## perl-indent-level: 2
## perl-continued-statement-offset: 2
## perl-continued-brace-offset: 0
## perl-brace-offset: 0
## perl-brace-imaginary-offset: 0
## perl-label-offset: -2
## cperl-indent-level: 2
## cperl-brace-offset: 0
## cperl-continued-brace-offset: 0
## cperl-label-offset: -2
## cperl-extra-newline-before-brace: t
## cperl-merge-trailing-else: nil
## cperl-continued-statement-offset: 2
## End:
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