| blob | 5eaa9f886885f644538f1d4bb78a9f73f11868ea |
1 #! @PERL@ -w
2 # -*- perl -*-
3 # @configure_input@
5 # autoupdate - modernize an Autoconf file.
6 # Copyright (C) 1994, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
7 # Free Software Foundation, Inc.
9 # This program is free software; you can redistribute it and/or modify
10 # it under the terms of the GNU General Public License as published by
11 # the Free Software Foundation; either version 2, or (at your option)
12 # any later version.
14 # This program is distributed in the hope that it will be useful,
15 # but WITHOUT ANY WARRANTY; without even the implied warranty of
16 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 # GNU General Public License for more details.
19 # You should have received a copy of the GNU General Public License
20 # along with this program; if not, write to the Free Software
21 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
22 # 02110-1301, USA.
24 # Originally written by David MacKenzie <djm@gnu.ai.mit.edu>.
25 # Rewritten by Akim Demaille <akim@freefriends.org>.
27 eval 'case $# in 0) exec @PERL@ -S "$0";; *) exec @PERL@ -S "$0" "$@";; esac'
28 if 0;
30 BEGIN
31 {
32 my $datadir = $ENV{'autom4te_perllibdir'} || '@datadir@';
33 unshift @INC, $datadir;
35 # Override SHELL. On DJGPP SHELL may not be set to a shell
36 # that can handle redirection and quote arguments correctly,
37 # e.g.: COMMAND.COM. For DJGPP always use the shell that configure
38 # has detected.
39 $ENV{'SHELL'} = '@SHELL@' if ($^O eq 'dos');
40 }
42 use Autom4te::ChannelDefs;
43 use Autom4te::Channels;
44 use Autom4te::Configure_ac;
45 use Autom4te::FileUtils;
46 use Autom4te::General;
47 use Autom4te::XFile;
48 use File::Basename;
49 use strict;
51 # Lib files.
52 my $autom4te = $ENV{'AUTOM4TE'} || '@bindir@/@autom4te-name@';
53 my $autoconf = "$autom4te --language=autoconf";
54 # We need to find m4sugar.
55 my @prepend_include;
56 my @include = ('@datadir@');
57 my $force = 0;
58 # m4.
59 my $m4 = $ENV{"M4"} || '@M4@';
62 # $HELP
63 # -----
64 $help = "Usage: $0 [OPTION] ... [TEMPLATE-FILE...]
66 Update the TEMPLATE-FILE... if given, or `configure.ac' if present,
67 or else `configure.in', to the syntax of the current version of
68 Autoconf. The original files are backed up.
70 Operation modes:
71 -h, --help print this help, then exit
72 -V, --version print version number, then exit
73 -v, --verbose verbosely report processing
74 -d, --debug don't remove temporary files
75 -f, --force consider all files obsolete
77 Library directories:
78 -B, --prepend-include=DIR prepend directory DIR to search path
79 -I, --include=DIR append directory DIR to search path
81 Report bugs to <bug-autoconf\@gnu.org>.
82 ";
84 # $VERSION
85 # --------
86 $version = "autoupdate (@PACKAGE_NAME@) @VERSION@
87 Copyright (C) 2006 Free Software Foundation, Inc.
88 This is free software. You may redistribute copies of it under the terms of
89 the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
90 There is NO WARRANTY, to the extent permitted by law.
92 Written by David J. MacKenzie and Akim Demaille.
93 ";
95 ## ---------- ##
96 ## Routines. ##
97 ## ---------- ##
100 # parse_args ()
101 # -------------
102 # Process any command line arguments.
103 sub parse_args ()
104 {
105 my $srcdir;
107 getopt ('I|include=s' => \@include,
108 'B|prepend-include=s' => \@prepend_include,
109 'f|force' => \$force);
111 if (! @ARGV)
112 {
113 my $configure_ac = require_configure_ac;
114 push @ARGV, $configure_ac;
115 }
116 }
120 # ----------------- #
121 # Autoconf macros. #
122 # ----------------- #
124 my (%ac_macros, %au_macros, %m4_builtins);
126 # HANDLE_AUTOCONF_MACROS ()
127 # -------------------------
128 # @M4_BUILTINS -- M4 builtins and a useful comment.
129 sub handle_autoconf_macros ()
130 {
131 # Get the builtins.
132 xsystem ("echo dumpdef | $m4 2>$tmp/m4.defs >/dev/null");
133 my $m4_defs = new Autom4te::XFile "$tmp/m4.defs";
134 while ($_ = $m4_defs->getline)
135 {
136 $m4_builtins{$1} = 1
137 if /^(\w+):/;
138 }
139 $m4_defs->close;
141 my $macros = new Autom4te::XFile ("$autoconf"
142 . " --trace AU_DEFINE:'AU:\$f:\$1'"
143 . " --trace define:'AC:\$f:\$1'"
144 . " --melt /dev/null |");
145 while ($_ = $macros->getline)
146 {
147 chomp;
148 my ($domain, $file, $macro) = /^(AC|AU):(.*):([^:]*)$/ or next;
149 if ($domain eq "AU")
150 {
151 $au_macros{$macro} = 1;
152 }
153 elsif ($file =~ /(^|\/)m4sugar\/(m4sugar|version)\.m4$/)
154 {
155 # Add the m4sugar macros to m4_builtins.
156 $m4_builtins{$macro} = 1;
157 }
158 else
159 {
160 # Autoconf, aclocal, and m4sh macros.
161 $ac_macros{$macro} = 1;
162 }
163 }
164 $macros->close;
167 # Don't keep AU macros in @AC_MACROS.
168 delete $ac_macros{$_}
169 foreach (keys %au_macros);
170 # Don't keep M4sugar macros which are redefined by Autoconf,
171 # such as `builtin', `changequote' etc. See autoconf/autoconf.m4.
172 delete $ac_macros{$_}
173 foreach (keys %m4_builtins);
174 error "no current Autoconf macros found"
175 unless keys %ac_macros;
176 error "no obsolete Autoconf macros found"
177 unless keys %au_macros;
179 if ($debug)
180 {
181 print STDERR "Current Autoconf macros:\n";
182 print STDERR join (' ', sort keys %ac_macros) . "\n\n";
183 print STDERR "Obsolete Autoconf macros:\n";
184 print STDERR join (' ', sort keys %au_macros) . "\n\n";
185 }
187 # ac.m4 -- autoquoting definitions of the AC macros (M4sugar excluded).
188 # unac.m4 -- undefine the AC macros.
189 my $ac_m4 = new Autom4te::XFile ">$tmp/ac.m4";
190 print $ac_m4 "# ac.m4 -- autoquoting definitions of the AC macros.\n";
191 my $unac_m4 = new Autom4te::XFile ">$tmp/unac.m4";
192 print $unac_m4 "# unac.m4 -- undefine the AC macros.\n";
193 foreach (sort keys %ac_macros)
194 {
195 print $ac_m4 "_au_m4_define([$_], [m4_if(\$#, 0, [[\$0]], [[\$0(\$\@)]])])\n";
196 print $unac_m4 "_au_m4_undefine([$_])\n";
197 }
199 # m4save.m4 -- save the m4 builtins.
200 # unm4.m4 -- disable the m4 builtins.
201 # m4.m4 -- enable the m4 builtins.
202 my $m4save_m4 = new Autom4te::XFile ">$tmp/m4save.m4";
203 print $m4save_m4 "# m4save.m4 -- save the m4 builtins.\n";
204 my $unm4_m4 = new Autom4te::XFile ">$tmp/unm4.m4";
205 print $unm4_m4 "# unm4.m4 -- disable the m4 builtins.\n";
206 my $m4_m4 = new Autom4te::XFile ">$tmp/m4.m4";
207 print $m4_m4 "# m4.m4 -- enable the m4 builtins.\n";
208 foreach (sort keys %m4_builtins)
209 {
210 print $m4save_m4 "_au__save([$_])\n";
211 print $unm4_m4 "_au__undefine([$_])\n";
212 print $m4_m4 "_au__restore([$_])\n";
213 }
214 }
217 ## -------------- ##
218 ## Main program. ##
219 ## -------------- ##
221 parse_args;
222 $autoconf .= " --debug" if $debug;
223 $autoconf .= " --force" if $force;
224 $autoconf .= " --verbose" if $verbose;
225 $autoconf .= join (' --include=', '', @include);
226 $autoconf .= join (' --prepend-include=', '', @prepend_include);
228 mktmpdir ('au');
229 handle_autoconf_macros;
231 # $au_changequote -- enable the quote `[', `]' right before any AU macro.
232 my $au_changequote =
233 's/\b(' . join ('|', keys %au_macros) . ')\b/_au_m4_changequote([,])$1/g';
235 # au.m4 -- definitions the AU macros.
236 xsystem ("$autoconf --trace AU_DEFINE:'_au_defun(\@<:\@\$1\@:>\@,
237 \@<:\@\$2\@:>\@)' --melt /dev/null "
238 . ">$tmp/au.m4");
242 ## ------------------- ##
243 ## Process the files. ##
244 ## ------------------- ##
246 foreach my $file (@ARGV)
247 {
248 # We need an actual file.
249 if ($file eq '-')
250 {
251 $file = "$tmp/stdin";
252 system "cat >$file";
253 }
254 elsif (! -r "$file")
255 {
256 die "$me: $file: No such file or directory";
257 }
259 # input.m4 -- m4 program to produce the updated file.
260 # Load the values, the dispatcher, neutralize m4, and the prepared
261 # input file.
262 my $input_m4 = <<\EOF;
263 divert(-1) -*- Autoconf -*-
264 changequote([,])
266 # Define our special macros:
267 define([_au__defn], defn([defn]))
268 define([_au__divert], defn([divert]))
269 define([_au__include], defn([include]))
270 define([_au__undefine], defn([undefine]))
271 define([_au__save], [m4_ifdef([$1], [m4_copy([$1], [_au_$1])])])
272 define([_au__restore],
273 [_au_m4_ifdef([_au_$1],
274 [_au_m4_define([$1], _au__defn([_au_$1]))])])
276 # Set up m4sugar.
277 include(m4sugar/m4sugar.m4)
279 # Redefine __file__ to make warnings nicer; $file is replaced below.
280 m4_define([__file__], [$file])
282 # Redefine m4_location to fix the line number.
283 m4_define([m4_location], [__file__:m4_eval(__line__ - _au__first_line)])
285 # Move all the builtins into the `_au_' pseudo namespace
286 m4_include([m4save.m4])
288 # _au_defun(NAME, BODY)
289 # ---------------------
290 # Define NAME to BODY, plus AU activation/deactivation.
291 _au_m4_define([_au_defun],
292 [_au_m4_define([$1],
293 [_au_enable()dnl
294 $2[]dnl
295 _au_disable()])])
297 # Import the definition of the obsolete macros.
298 _au__include([au.m4])
301 ## ------------------------ ##
302 ## _au_enable/_au_disable. ##
303 ## ------------------------ ##
305 # They work by pair: each time an AU macro is activated, it runs
306 # _au_enable, and at its end its runs _au_disable (see _au_defun
307 # above). AU macros might use AU macros, which should
308 # enable/disable only for the outer AU macros.
309 #
310 # `_au_enabled' is used to this end, determining whether we really
311 # enable/disable.
314 # __au_enable
315 # -----------
316 # Reenable the builtins, m4sugar, and the autoquoting AC macros.
317 _au_m4_define([__au_enable],
318 [_au__divert(-1)
319 # Enable special characters.
320 _au_m4_changecom([#])
322 _au__include([m4.m4])
323 _au__include([ac.m4])
325 _au__divert(0)])
327 # _au_enable
328 # ----------
329 # Called at the beginning of all the obsolete macros. If this is the
330 # outermost level, call __au_enable.
331 _au_m4_define([_au_enable],
332 [_au_m4_ifdef([_au_enabled],
333 [],
334 [__au_enable()])_au_dnl
335 _au_m4_pushdef([_au_enabled])])
338 # __au_disable
339 # ------------
340 # Disable the AC autoquoting macros, m4sugar, and m4.
341 _au_m4_define([__au_disable],
342 [_au__divert(-1)
343 _au__include([unac.m4])
344 _au__include([unm4.m4])
346 # Disable special characters.
347 _au_m4_changequote()
348 _au_m4_changecom()
350 _au__divert(0)])
352 # _au_disable
353 # -----------
354 # Called at the end of all the obsolete macros. If we are at the
355 # outermost level, call __au_disable.
356 _au_m4_define([_au_disable],
357 [_au_m4_popdef([_au_enabled])_au_dnl
358 _au_m4_ifdef([_au_enabled],
359 [],
360 [__au_disable()])])
363 ## ------------------------------- ##
364 ## Disable, and process the file. ##
365 ## ------------------------------- ##
366 # The AC autoquoting macros are not loaded yet, hence invoking
367 # `_au_disable' would be wrong.
368 _au__include([unm4.m4])
370 # Disable special characters, and set the first line number.
371 _au_m4_changequote()
372 _au_m4_changecom()
374 _au_m4_define(_au__first_line, _au___line__)_au__divert(0)_au_dnl
375 EOF
377 $input_m4 =~ s/^ //mg;
378 $input_m4 =~ s/\$file/$file/g;
380 # prepared input -- input, but reenables the quote before each AU macro.
381 open INPUT_M4, ">$tmp/input.m4"
382 or error "cannot open: $!";
383 open FILE, "<$file"
384 or error "cannot open: $!";
385 print INPUT_M4 "$input_m4";
386 while (<FILE>)
387 {
388 eval $au_changequote;
389 print INPUT_M4;
390 }
391 close FILE
392 or error "cannot close $file: $!";
393 close INPUT_M4
394 or error "cannot close $tmp/input.m4: $!";
396 # Now ask m4 to perform the update.
397 xsystem ("$m4 --include=$tmp"
398 . join (' --include=', '', reverse (@prepend_include))
399 . join (' --include=', '', @include)
400 . " $tmp/input.m4 >$tmp/updated");
401 update_file ("$tmp/updated",
402 "$file" eq "$tmp/stdin" ? '-' : "$file");
403 }
404 exit 0;
407 # ## ---------------------------- ##
408 # ## How `autoupdate' functions. ##
409 # ## ---------------------------- ##
410 #
411 # The task of `autoupdate' is not trivial: the biggest difficulty being
412 # that you must limit the changes to the parts that really need to be
413 # updated. Finding a satisfying implementation proved to be quite hard,
414 # as this is the fifth implementation of `autoupdate'.
415 #
416 # Below, we will use a simple example of obsolete macro:
417 #
418 # AU_DEFUN([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))])
419 # AC_DEFUN([NEW], [echo "sum($1) = $2"])
420 #
421 # the input file contains
422 #
423 # dnl The Unbelievable Truth
424 # OLD(1, 2)
425 # NEW([0, 0], [0])
426 #
427 # Of course the expected output is
428 #
429 # dnl The Unbelievable Truth
430 # NEW([1, 2], [3])
431 # NEW([0, 0], [0])
432 #
433 #
434 # # First implementation: sed
435 # # =========================
436 #
437 # The first implementation was only able to change the name of obsolete
438 # macros.
439 #
440 # The file `acoldnames.m4' defined the old names based on the new names.
441 # It was simple then to produce a sed script such as:
442 #
443 # s/OLD/NEW/g
444 #
445 # Updating merely consisted in running this script on the file to
446 # update.
447 #
448 # This scheme suffers an obvious limitation: that `autoupdate' was
449 # unable to cope with new macros that just swap some of its arguments
450 # compared to the old macro. Fortunately, that was enough to upgrade
451 # from Autoconf 1 to Autoconf 2. (But I have no idea whether the
452 # changes in Autoconf 2 were precisely limited by this constraint.)
453 #
454 #
455 # # Second implementation: hooks
456 # # ============================
457 #
458 # The version 2.15 of Autoconf brought a vast number of changes compared
459 # to 2.13, so a solution was needed. One could think to extend the
460 # `sed' scripts with specialized code for complex macros. But this
461 # approach is of course full of flaws:
462 #
463 # a. the Autoconf maintainers have to write these snippets, which we
464 # just don't want to,
465 #
466 # b. I really don't think you'll ever manage to handle the quoting of
467 # m4 from sed.
468 #
469 # To satisfy a., let's remark that the code which implements the old
470 # features in term of the new feature is exactly the code which should
471 # replace the old code.
472 #
473 # To answer point b, as usual in the history of Autoconf, the answer, at
474 # least on the paper, is simple: m4 is the best tool to parse m4, so
475 # let's use m4.
476 #
477 # Therefore the specification is:
478 #
479 # I want to be able to tell Autoconf, well, m4, that the macro I
480 # am currently defining is an obsolete macro (so that the user is
481 # warned), which code is the code to use when running autoconf,
482 # but that the very same code has to be used when running
483 # autoupdate. To summarize, the interface I want is
484 # `AU_DEFUN(OLD-NAME, NEW-CODE)'.
485 #
486 #
487 # Now for the technical details.
488 #
489 # When running autoconf, except for the warning, AU_DEFUN is basically
490 # AC_DEFUN.
491 #
492 # When running autoupdate, we want *only* OLD-NAMEs to be expanded.
493 # This obviously means that acgeneral.m4 and acspecific.m4 must not be
494 # loaded. Nonetheless, because we want to use a rich set of m4
495 # features, m4sugar.m4 is needed. Please note that the fact that
496 # Autoconf's macros are not loaded is positive on two points:
497 #
498 # - we do get an updated `configure.ac', not a `configure'!
499 #
500 # - the old macros are replaced by *calls* to the new-macros, not the
501 # body of the new macros, since their body is not defined!!!
502 # (Whoa, that's really beautiful!).
503 #
504 # Additionally we need to disable the quotes when reading the input for
505 # two reasons: first because otherwise `m4' will swallow the quotes of
506 # other macros:
507 #
508 # NEW([1, 2], 3)
509 # => NEW(1, 2, 3)
510 #
511 # and second, because we want to update the macro calls which are
512 # quoted, i.e., we want
513 #
514 # FOO([OLD(1, 2)])
515 # => FOO([NEW([1, 2], [3])])
516 #
517 # If we don't disable the quotes, only the macros called at the top
518 # level would be updated.
519 #
520 # So, let's disable the quotes.
521 #
522 # Well, not quite: m4sugar.m4 still needs to use quotes for some macros.
523 # Well, in this case, when running in autoupdate code, each macro first
524 # reestablishes the quotes, expands itself, and disables the quotes.
525 #
526 # Thinking a bit more, you realize that in fact, people may use `define'
527 # `ifelse' etc. in their files, and you certainly don't want to process
528 # them. Another example is `dnl': you don't want to remove the
529 # comments. You then realize you don't want exactly to import m4sugar:
530 # you want to specify when it is enabled (macros active), and disabled.
531 # m4sugar provides m4_disable/m4_enable to this end.
532 #
533 # You're getting close to it. Now remains one task: how to handle
534 # twofold definitions?
535 #
536 # Remember that the same AU_DEFUN must be understood in two different
537 # ways, the AC way, and the AU way.
538 #
539 # One first solution is to check whether acgeneral.m4 was loaded. But
540 # that's definitely not cute. Another is simply to install `hooks',
541 # that is to say, to keep in some place m4 knows, late `define' to be
542 # triggered *only* in AU mode.
543 #
544 # You first think to design AU_DEFUN like this:
545 #
546 # 1. AC_DEFUN(OLD-NAME,
547 # [Warn the user OLD-NAME is obsolete.
548 # NEW-CODE])
549 #
550 # 2. Store for late AU binding([define(OLD_NAME,
551 # [Reestablish the quotes.
552 # NEW-CODE
553 # Disable the quotes.])])
554 #
555 # but this will not work: NEW-CODE has probably $1, $2 etc. and these
556 # guys will be replaced with the argument of `Store for late AU binding'
557 # when you call it.
558 #
559 # I don't think there is a means to avoid this using this technology
560 # (remember that $1 etc. are *always* expanded in m4). You may also try
561 # to replace them with $[1] to preserve them for a later evaluation, but
562 # if `Store for late AU binding' is properly written, it will remain
563 # quoted till the end...
564 #
565 # You have to change technology. Since the problem is that `$1'
566 # etc. should be `consumed' right away, one solution is to define now a
567 # second macro, `AU_OLD-NAME', and to install a hook than binds OLD-NAME
568 # to AU_OLD-NAME. Then, autoupdate.m4 just need to run the hooks. By
569 # the way, the same method was used in autoheader.
570 #
571 #
572 # # Third implementation: m4 namespaces by m4sugar
573 # # ==============================================
574 #
575 # Actually, this implementation was just a clean up of the previous
576 # implementation: instead of defining hooks by hand, m4sugar was equipped
577 # with `namespaces'. What are they?
578 #
579 # Sometimes we want to disable some *set* of macros, and restore them
580 # later. We provide support for this via namespaces.
581 #
582 # There are basically three characters playing this scene: defining a
583 # macro in a namespace, disabling a namespace, and restoring a namespace
584 # (i.e., all the definitions it holds).
585 #
586 # Technically, to define a MACRO in NAMESPACE means to define the macro
587 # named `NAMESPACE::MACRO' to the VALUE. At the same time, we append
588 # `undefine(NAME)' in the macro named `m4_disable(NAMESPACE)', and
589 # similarly a binding of NAME to the value of `NAMESPACE::MACRO' in
590 # `m4_enable(NAMESPACE)'. These mechanisms allow to bind the macro of
591 # NAMESPACE and to unbind them at will.
592 #
593 # Of course this implementation is really inefficient: m4 has to grow
594 # strings which can become quickly huge, which slows it significantly.
595 #
596 # In particular one should avoid as much as possible to use `define' for
597 # temporaries. Now that `define' has quite a complex meaning, it is an
598 # expensive operations that should be limited to macros. Use
599 # `m4_define' for temporaries.
600 #
601 # Private copies of the macros we used in entering / exiting the m4sugar
602 # namespace. It is much more convenient than fighting with the renamed
603 # version of define etc.
604 #
605 #
606 #
607 # Those two implementations suffered from serious problems:
608 #
609 # - namespaces were really expensive, and incurred a major performance
610 # loss on `autoconf' itself, not only `autoupdate'. One solution
611 # would have been the limit the use of namespaces to `autoupdate', but
612 # that's again some complications on m4sugar, which really doesn't need
613 # this. So we wanted to get rid of the namespaces.
614 #
615 # - since the quotes were disabled, autoupdate was sometimes making
616 # wrong guesses, for instance on:
617 #
618 # foo([1, 2])
619 #
620 # m4 saw 2 arguments: `[1'and `2]'. A simple solution, somewhat
621 # fragile, is to reestablish the quotes right before all the obsolete
622 # macros, i.e., to use sed so that the previous text becomes
623 #
624 # changequote([, ])foo([1, 2])
625 #
626 # To this end, one wants to trace the definition of obsolete macros.
627 #
628 # It was there that the limitations of the namespace approach became
629 # painful: because it was a complex machinery playing a lot with the
630 # builtins of m4 (hence, quite fragile), tracing was almost impossible.
631 #
632 #
633 # So this approach was dropped.
634 #
635 #
636 # # The fourth implementation: two steps
637 # # ====================================
638 #
639 # If you drop the uses of namespaces, you no longer can compute the
640 # updated value, and replace the old call with it simultaneously.
641 #
642 # Obviously you will use m4 to compute the updated values, but you may
643 # use some other tool to achieve the replacement. Personally, I trust
644 # nobody but m4 to parse m4, so below, m4 will perform the two tasks.
645 #
646 # How can m4 be used to replace *some* macros calls with newer values.
647 # Well, that's dead simple: m4 should learn the definitions of obsolete
648 # macros, forget its builtins, disable the quotes, and then run on the
649 # input file, which amounts to doing this:
650 #
651 # divert(-1)dnl
652 # changequote([, ])
653 # define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
654 # undefine([dnl])
655 # undefine([m4_eval])
656 # # Some more undefines...
657 # changequote()
658 # divert(0)dnl
659 # dnl The Unbelievable Truth
660 # changequote([, ])OLD(1, 2)
661 # NEW([0, 0],
662 # 0)
663 #
664 # which will result in
665 #
666 # dnl The Unbelievable Truth
667 # NEW(1, 2, m4_eval(1 + 2))
668 # NEW([0, 0],
669 # 0)
670 #
671 # Grpmh. Two problems. A minor problem: it would have been much better
672 # to have the `m4_eval' computed, and a major problem: you lost the
673 # quotation in the result.
674 #
675 # Let's address the big problem first. One solution is to define any
676 # modern macro to rewrite its calls with the proper quotation, thanks to
677 # `$@'. Again, tracing the `define's makes it possible to know which
678 # are these macros, so you input is:
679 #
680 # divert(-1)dnl
681 # changequote([, ])
682 # define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
683 # define([NEW], [[NEW($@)]changequote()])
684 # undefine([dnl])
685 # undefine([m4_eval])
686 # # Some more undefines...
687 # changequote()
688 # divert(0)dnl
689 # dnl The Unbelievable Truth
690 # changequote([, ])OLD(1, 2)
691 # changequote([, ])NEW([0, 0],
692 # 0)
693 #
694 # which results in
695 #
696 # dnl The Unbelievable Truth
697 # NEW([1, 2],[m4_eval(1 + 2)])
698 # NEW([0, 0],[0])
699 #
700 # Our problem is solved, i.e., the first call to `NEW' is properly
701 # quoted, but introduced another problem: we changed the layout of the
702 # second calls, which can be a drama in the case of huge macro calls
703 # (think of `AC_TRY_RUN' for instance). This example didn't show it,
704 # but we also introduced parens to macros which did not have some:
705 #
706 # AC_INIT
707 # => AC_INIT()
708 #
709 # No big deal for the semantics (unless the macro depends upon $#, which
710 # is bad), but the users would not be happy.
711 #
712 # Additionally, we introduced quotes that were not there before, which is
713 # OK in most cases, but could change the semantics of the file.
714 #
715 # Cruel dilemma: we do want the auto-quoting definition of `NEW' when
716 # evaluating `OLD', but we don't when we evaluate the second `NEW'.
717 # Back to namespaces?
718 #
719 # No.
720 #
721 #
722 # # Second step: replacement
723 # # ------------------------
724 #
725 # No, as announced above, we will work in two steps: in a first step we
726 # compute the updated values, and in a second step we replace them. Our
727 # goal is something like this:
728 #
729 # divert(-1)dnl
730 # changequote([, ])
731 # define([OLD], [NEW([1, 2], [3])changequote()])
732 # undefine([dnl])
733 # undefine([m4_eval])
734 # # Some more undefines...
735 # changequote()
736 # divert(0)dnl
737 # dnl The Unbelievable Truth
738 # changequote([, ])OLD(1, 2)
739 # NEW([0, 0],
740 # 0)
741 #
742 # i.e., the new value of `OLD' is precomputed using the auto-quoting
743 # definition of `NEW' and the m4 builtins. We'll see how afterwards,
744 # let's finish with the replacement.
745 #
746 # Of course the solution above is wrong: if there were other calls to
747 # `OLD' with different values, we would smash them to the same value.
748 # But it is quite easy to generalize the scheme above:
749 #
750 # divert(-1)dnl
751 # changequote([, ])
752 # define([OLD([1],[2])], [NEW([1, 2], [3])])
753 # define([OLD], [defn([OLD($@)])changequote()])
754 # undefine([dnl])
755 # undefine([m4_eval])
756 # # Some more undefines...
757 # changequote()
758 # divert(0)dnl
759 # dnl The Unbelievable Truth
760 # changequote([, ])OLD(1, 2)
761 # NEW([0, 0],
762 # 0)
763 #
764 # i.e., for each call to obsolete macros, we build an array `call =>
765 # value', and use a macro to dispatch these values. This results in:
766 #
767 # dnl The Unbelievable Truth
768 # NEW([1, 2], [3])
769 # NEW([0, 0],
770 # 0)
771 #
772 # In French, we say `Youpi !', which you might roughly translate as
773 # `Yippee!'.
774 #
775 #
776 # # First step: computation
777 # # -----------------------
778 #
779 # Let's study the anatomy of the file, and name its sections:
780 #
781 # prologue
782 # divert(-1)dnl
783 # changequote([, ])
784 # values
785 # define([OLD([1],[2])], [NEW([1, 2], [3])])
786 # dispatcher
787 # define([OLD], [defn([OLD($@)])changequote()])
788 # disabler
789 # undefine([dnl])
790 # undefine([m4_eval])
791 # # Some more undefines...
792 # changequote()
793 # divert(0)dnl
794 # input
795 # dnl The Unbelievable Truth
796 # changequote([, ])OLD(1, 2)
797 # NEW([0, 0],
798 # 0)
799 #
800 #
801 # # Computing the `values' section
802 # # ..............................
803 #
804 # First we need to get the list of all the AU macro uses. To this end,
805 # first get the list of all the AU macros names by tracing `AU_DEFUN' in
806 # the initialization of autoconf. This list is computed in the file
807 # `au.txt' below.
808 #
809 # Then use this list to trace all the AU macro uses in the input. The
810 # goal is obtain in the case of our example:
811 #
812 # [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
813 #
814 # This is the file `values.in' below.
815 #
816 # We want to evaluate this with only the builtins (in fact m4sugar), the
817 # auto-quoting definitions of the new macros (`new.m4'), and the
818 # definition of the old macros (`old.m4'). Computing these last two
819 # files is easy: it's just a matter of using the right `--trace' option.
820 #
821 # So the content of `values.in' is:
822 #
823 # include($autoconf_dir/m4sugar.m4)
824 # m4_include(new.m4)
825 # m4_include(old.m4)
826 # divert(0)dnl
827 # [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
828 #
829 # We run m4 on it, which yields:
830 #
831 # define([OLD([1],[2])],@<<@NEW([1, 2], [3])@>>@)
832 #
833 # Transform `@<<@' and `@>>@' into quotes and we get
834 #
835 # define([OLD([1],[2])],[NEW([1, 2], [3])])
836 #
837 # This is `values.m4'.
838 #
839 #
840 # # Computing the `dispatcher' section
841 # # ..................................
842 #
843 # The `prologue', and the `disabler' are simple and need no commenting.
844 #
845 # To compute the `dispatcher' (`dispatch.m4'), again, it is a simple
846 # matter of using the right `--trace'.
847 #
848 # Finally, the input is not exactly the input file, rather it is the
849 # input file with the added `changequote'. To this end, we build
850 # `quote.sed'.
851 #
852 #
853 # # Putting it all together
854 # # .......................
855 #
856 # We build the file `input.m4' which contains:
857 #
858 # divert(-1)dnl
859 # changequote([, ])
860 # include(values.m4)
861 # include(dispatch.m4)
862 # undefine([dnl])
863 # undefine([eval])
864 # # Some more undefines...
865 # changequote()
866 # divert(0)dnl
867 # dnl The Unbelievable Truth
868 # changequote([, ])OLD(1, 2)
869 # NEW([0, 0],
870 # 0)
871 #
872 # And we just run m4 on it. Et voila`, Monsieur ! Mais oui, mais oui.
873 #
874 # Well, there are a few additional technicalities. For instance, we
875 # rely on `changequote', `ifelse' and `defn', but we don't want to
876 # interpret the changequotes of the user, so we simply use another name:
877 # `_au_changequote' etc.
878 #
879 #
880 # # Failure of the fourth approach
881 # # ------------------------------
882 #
883 # This approach is heavily based on traces, but then there is an obvious
884 # problem: non expanded code will never be seen. In particular, the body
885 # of a `define' definition is not seen, so on the input
886 #
887 # define([idem], [OLD(0, [$1])])
888 #
889 # autoupdate would never see the `OLD', and wouldn't have updated it.
890 # Worse yet, if `idem(0)' was used later, then autoupdate sees that
891 # `OLD' is used, computes the result for `OLD(0, 0)' and sets up a
892 # dispatcher for `OLD'. Since there was no computed value for `OLD(0,
893 # [$1])', the dispatcher would have replaced with... nothing, leading
894 # to
895 #
896 # define([idem], [])
897 #
898 # With some more thinking, you see that the two step approach is wrong,
899 # the namespace approach was much saner.
900 #
901 # But you learned a lot, in particular you realized that using traces
902 # can make it possible to simulate namespaces!
903 #
904 #
905 #
906 # # The fifth implementation: m4 namespaces by files
907 # # ================================================
908 #
909 # The fourth implementation demonstrated something unsurprising: you
910 # cannot precompute, i.e., the namespace approach was the right one.
911 # Still, we no longer want them, they're too expensive. Let's have a
912 # look at the way it worked.
913 #
914 # When updating
915 #
916 # dnl The Unbelievable Truth
917 # OLD(1, 2)
918 # NEW([0, 0], [0])
919 #
920 # you evaluate `input.m4':
921 #
922 # divert(-1)
923 # changequote([, ])
924 # define([OLD],
925 # [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
926 # ...
927 # m4_disable()
928 # dnl The Unbelievable Truth
929 # OLD(1, 2)
930 # NEW([0, 0], [0])
931 #
932 # where `m4_disable' undefines the m4 and m4sugar, and disables the quotes
933 # and comments:
934 #
935 # define([m4_disable],
936 # [undefine([__file__])
937 # ...
938 # changecom(#)
939 # changequote()])
940 #
941 # `m4_enable' does the converse: reestablish quotes and comments
942 # --easy--, reestablish m4sugar --easy: just load `m4sugar.m4' again-- and
943 # reenable the builtins. This later task requires that you first save
944 # the builtins. And BTW, the definition above of `m4_disable' cannot
945 # work: you undefined `changequote' before using it! So you need to use
946 # your privates copies of the builtins. Let's introduce three files for
947 # this:
948 #
949 # `m4save.m4'
950 # moves the m4 builtins into the `_au_' pseudo namespace,
951 # `unm4.m4'
952 # undefines the builtins,
953 # `m4.m4'
954 # restores them.
955 #
956 # So `input.m4' is:
957 #
958 # divert(-1)
959 # changequote([, ])
960 #
961 # include([m4save.m4])
962 #
963 # # Import AU.
964 # define([OLD],
965 # [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
966 #
967 # define([_au_enable],
968 # [_au_changecom([#])
969 # _au_include([m4.m4])
970 # _au_include(m4sugar.m4)])
971 #
972 # define([_au_disable],
973 # [# Disable m4sugar.
974 # # Disable the m4 builtins.
975 # _au_include([unm4.m4])
976 # # 1. Disable special characters.
977 # _au_changequote()
978 # _au_changecom()])
979 #
980 # m4_disable()
981 # dnl The Unbelievable Truth
982 # OLD(1, 2)
983 # NEW([0, 0], [0])
984 #
985 # Based on what we learned in the fourth implementation we know that we
986 # have to enable the quotes *before* any AU macro, and we know we need
987 # to build autoquoting versions of the AC macros. But the autoquoting
988 # AC definitions must be disabled in the rest of the file, and enabled
989 # inside AU macros.
990 #
991 # Using `autoconf --trace' it is easy to build the files
992 #
993 # `ac.m4'
994 # define the autoquoting AC fake macros
995 # `disable.m4'
996 # undefine the m4sugar and AC autoquoting macros.
997 # `au.m4'
998 # definitions of the AU macros (such as `OLD' above).
999 #
1000 # Now, `input.m4' is:
1001 #
1002 # divert(-1)
1003 # changequote([, ])
1004 #
1005 # include([m4save.m4])
1006 # # Import AU.
1007 # include([au.m4])
1008 #
1009 # define([_au_enable],
1010 # [_au_changecom([#])
1011 # _au_include([m4.m4])
1012 # _au_include(m4sugar.m4)
1013 # _au_include(ac.m4)])
1014 #
1015 # define([_au_disable],
1016 # [_au_include([disable.m4])
1017 # _au_include([unm4.m4])
1018 # # 1. Disable special characters.
1019 # _au_changequote()
1020 # _au_changecom()])
1021 #
1022 # m4_disable()
1023 # dnl The Unbelievable Truth
1024 # _au_changequote([, ])OLD(1, 2)
1025 # NEW([0, 0], [0])
1026 #
1027 # Finally, version V is ready.
1028 #
1029 # Well... almost.
1030 #
1031 # There is a slight problem that remains: if an AU macro OUTER includes
1032 # an AU macro INNER, then _au_enable will be run when entering OUTER
1033 # and when entering INNER (not good, but not too bad yet). But when
1034 # getting out of INNER, _au_disable will disable everything while we
1035 # were still in OUTER. Badaboom.
1036 #
1037 # Therefore _au_enable and _au_disable have to be written to work by
1038 # pairs: each _au_enable pushdef's _au_enabled, and each _au_disable
1039 # popdef's _au_enabled. And of course _au_enable and _au_disable are
1040 # effective when _au_enabled is *not* defined.
1041 #
1042 # Finally, version V' is ready. And there is much rejoicing. (And I
1043 # have free time again. I think. Yeah, right.)
1045 ### Setup "GNU" style for perl-mode and cperl-mode.
1046 ## Local Variables:
1047 ## perl-indent-level: 2
1048 ## perl-continued-statement-offset: 2
1049 ## perl-continued-brace-offset: 0
1050 ## perl-brace-offset: 0
1051 ## perl-brace-imaginary-offset: 0
1052 ## perl-label-offset: -2
1053 ## cperl-indent-level: 2
1054 ## cperl-brace-offset: 0
1055 ## cperl-continued-brace-offset: 0
1056 ## cperl-label-offset: -2
1057 ## cperl-extra-newline-before-brace: t
1058 ## cperl-merge-trailing-else: nil
1059 ## cperl-continued-statement-offset: 2
1060 ## End: