| blob | c9235596b85130954daaae544550cf9205cd5dfc |
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 # 2007, 2008 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 each 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) @RELEASE_YEAR@ Free Software Foundation, Inc.
88 License GPLv2+: GNU GPL version 2 or later
89 <http://gnu.org/licenses/old-licenses/gpl-2.0.html>
90 This is free software: you are free to change and redistribute it.
91 There is NO WARRANTY, to the extent permitted by law.
93 Written by David J. MacKenzie and Akim Demaille.
94 ";
96 ## ---------- ##
97 ## Routines. ##
98 ## ---------- ##
101 # parse_args ()
102 # -------------
103 # Process any command line arguments.
104 sub parse_args ()
105 {
106 my $srcdir;
108 getopt ('I|include=s' => \@include,
109 'B|prepend-include=s' => \@prepend_include,
110 'f|force' => \$force);
112 if (! @ARGV)
113 {
114 my $configure_ac = require_configure_ac;
115 push @ARGV, $configure_ac;
116 }
117 }
121 # ----------------- #
122 # Autoconf macros. #
123 # ----------------- #
125 my (%ac_macros, %au_macros, %m4_builtins);
127 # HANDLE_AUTOCONF_MACROS ()
128 # -------------------------
129 # @M4_BUILTINS -- M4 builtins and a useful comment.
130 sub handle_autoconf_macros ()
131 {
132 # Get the builtins.
133 xsystem ("echo dumpdef | $m4 2>" . shell_quote ("$tmp/m4.defs") . " >/dev/null");
134 my $m4_defs = new Autom4te::XFile "< " . open_quote ("$tmp/m4.defs");
135 while ($_ = $m4_defs->getline)
136 {
137 $m4_builtins{$1} = 1
138 if /^(\w+):/;
139 }
140 $m4_defs->close;
142 my $macros = new Autom4te::XFile ("$autoconf"
143 . " --trace AU_DEFINE:'AU:\$f:\$1'"
144 . " --trace define:'AC:\$f:\$1'"
145 . " --melt /dev/null |");
146 while ($_ = $macros->getline)
147 {
148 chomp;
149 my ($domain, $file, $macro) = /^(AC|AU):(.*):([^:]*)$/ or next;
150 if ($domain eq "AU")
151 {
152 $au_macros{$macro} = 1;
153 }
154 elsif ($file =~ /(^|\/)m4sugar\/(m4sugar|version)\.m4$/)
155 {
156 # Add the m4sugar macros to m4_builtins.
157 $m4_builtins{$macro} = 1;
158 }
159 else
160 {
161 # Autoconf, aclocal, and m4sh macros.
162 $ac_macros{$macro} = 1;
163 }
164 }
165 $macros->close;
168 # Don't keep AU macros in @AC_MACROS.
169 delete $ac_macros{$_}
170 foreach (keys %au_macros);
171 # Don't keep M4sugar macros which are redefined by Autoconf,
172 # such as `builtin', `changequote' etc. See autoconf/autoconf.m4.
173 delete $ac_macros{$_}
174 foreach (keys %m4_builtins);
175 error "no current Autoconf macros found"
176 unless keys %ac_macros;
177 error "no obsolete Autoconf macros found"
178 unless keys %au_macros;
180 if ($debug)
181 {
182 print STDERR "Current Autoconf macros:\n";
183 print STDERR join (' ', sort keys %ac_macros) . "\n\n";
184 print STDERR "Obsolete Autoconf macros:\n";
185 print STDERR join (' ', sort keys %au_macros) . "\n\n";
186 }
188 # ac.m4 -- autoquoting definitions of the AC macros (M4sugar excluded).
189 # unac.m4 -- undefine the AC macros.
190 my $ac_m4 = new Autom4te::XFile "> " . open_quote ("$tmp/ac.m4");
191 print $ac_m4 "# ac.m4 -- autoquoting definitions of the AC macros.\n";
192 my $unac_m4 = new Autom4te::XFile "> " . open_quote ("$tmp/unac.m4");
193 print $unac_m4 "# unac.m4 -- undefine the AC macros.\n";
194 foreach (sort keys %ac_macros)
195 {
196 print $ac_m4 "_au_m4_define([$_], [m4_if(\$#, 0, [[\$0]], [[\$0(\$\@)]])])\n";
197 print $unac_m4 "_au_m4_undefine([$_])\n";
198 }
200 # m4save.m4 -- save the m4 builtins.
201 # unm4.m4 -- disable the m4 builtins.
202 # m4.m4 -- enable the m4 builtins.
203 my $m4save_m4 = new Autom4te::XFile "> " . open_quote ("$tmp/m4save.m4");
204 print $m4save_m4 "# m4save.m4 -- save the m4 builtins.\n";
205 my $unm4_m4 = new Autom4te::XFile "> " . open_quote ("$tmp/unm4.m4");
206 print $unm4_m4 "# unm4.m4 -- disable the m4 builtins.\n";
207 my $m4_m4 = new Autom4te::XFile "> " . open_quote ("$tmp/m4.m4");
208 print $m4_m4 "# m4.m4 -- enable the m4 builtins.\n";
209 foreach (sort keys %m4_builtins)
210 {
211 print $m4save_m4 "_au__save([$_])\n";
212 print $unm4_m4 "_au__undefine([$_])\n";
213 print $m4_m4 "_au__restore([$_])\n";
214 }
215 }
218 ## -------------- ##
219 ## Main program. ##
220 ## -------------- ##
222 parse_args;
223 $autoconf .= " --debug" if $debug;
224 $autoconf .= " --force" if $force;
225 $autoconf .= " --verbose" if $verbose;
226 $autoconf .= join (' --include=', '', map { shell_quote ($_) } @include);
227 $autoconf .= join (' --prepend-include=', '', map { shell_quote ($_) } @prepend_include);
229 mktmpdir ('au');
230 handle_autoconf_macros;
232 # $au_changequote -- enable the quote `[', `]' right before any AU macro.
233 my $au_changequote =
234 's/\b(' . join ('|', keys %au_macros) . ')\b/_au_m4_changequote([,])$1/g';
236 # au.m4 -- definitions the AU macros.
237 xsystem ("$autoconf --trace AU_DEFINE:'_au_defun(\@<:\@\$1\@:>\@,
238 \@<:\@\$2\@:>\@)' --melt /dev/null "
239 . ">" . shell_quote ("$tmp/au.m4"));
243 ## ------------------- ##
244 ## Process the files. ##
245 ## ------------------- ##
247 foreach my $file (@ARGV)
248 {
249 # We need an actual file.
250 if ($file eq '-')
251 {
252 $file = "$tmp/stdin";
253 system "cat >" . shell_quote ($file);
254 }
255 elsif (! -r "$file")
256 {
257 die "$me: $file: No such file or directory";
258 }
260 # input.m4 -- m4 program to produce the updated file.
261 # Load the values, the dispatcher, neutralize m4, and the prepared
262 # input file.
263 my $input_m4 = <<\EOF;
264 divert(-1) -*- Autoconf -*-
265 changequote([,])
267 # Define our special macros:
268 define([_au__defn], defn([defn]))
269 define([_au__divert], defn([divert]))
270 define([_au__ifdef], defn([ifdef]))
271 define([_au__include], defn([include]))
272 define([_au___undefine], defn([undefine]))
273 define([_au__undefine], [_au__ifdef([$1], [_au___undefine([$1])])])
274 define([_au__save], [m4_ifdef([$1],
275 [m4_define([_au_$1], _m4_defn([$1]))])])
276 define([_au__restore],
277 [_au_m4_ifdef([_au_$1],
278 [_au_m4_define([$1], _au__defn([_au_$1]))])])
280 # Set up m4sugar.
281 include(m4sugar/m4sugar.m4)
283 # Redefine __file__ to make warnings nicer; $file is replaced below.
284 m4_define([__file__], [$file])
286 # Redefine m4_location to fix the line number.
287 m4_define([m4_location], [__file__:m4_eval(__line__ - _au__first_line)])
289 # Move all the builtins into the `_au_' pseudo namespace
290 m4_include([m4save.m4])
292 # _au_defun(NAME, BODY)
293 # ---------------------
294 # Define NAME to BODY, plus AU activation/deactivation.
295 _au_m4_define([_au_defun],
296 [_au_m4_define([$1],
297 [_au_enable()dnl
298 $2[]dnl
299 _au_disable()])])
301 # Import the definition of the obsolete macros.
302 _au__include([au.m4])
305 ## ------------------------ ##
306 ## _au_enable/_au_disable. ##
307 ## ------------------------ ##
309 # They work by pair: each time an AU macro is activated, it runs
310 # _au_enable, and at its end its runs _au_disable (see _au_defun
311 # above). AU macros might use AU macros, which should
312 # enable/disable only for the outer AU macros.
313 #
314 # `_au_enabled' is used to this end, determining whether we really
315 # enable/disable.
318 # __au_enable
319 # -----------
320 # Reenable the builtins, m4sugar, and the autoquoting AC macros.
321 _au_m4_define([__au_enable],
322 [_au__divert(-1)
323 # Enable special characters.
324 _au_m4_changecom([#])
326 _au__include([m4.m4])
327 _au__include([ac.m4])
329 _au__divert(0)])
331 # _au_enable
332 # ----------
333 # Called at the beginning of all the obsolete macros. If this is the
334 # outermost level, call __au_enable.
335 _au_m4_define([_au_enable],
336 [_au_m4_ifdef([_au_enabled],
337 [],
338 [__au_enable()])_au_dnl
339 _au_m4_pushdef([_au_enabled])])
342 # __au_disable
343 # ------------
344 # Disable the AC autoquoting macros, m4sugar, and m4.
345 _au_m4_define([__au_disable],
346 [_au__divert(-1)
347 _au__include([unac.m4])
348 _au__include([unm4.m4])
350 # Disable special characters.
351 _au_m4_changequote()
352 _au_m4_changecom()
354 _au__divert(0)])
356 # _au_disable
357 # -----------
358 # Called at the end of all the obsolete macros. If we are at the
359 # outermost level, call __au_disable.
360 _au_m4_define([_au_disable],
361 [_au_m4_popdef([_au_enabled])_au_dnl
362 _au_m4_ifdef([_au_enabled],
363 [],
364 [__au_disable()])])
367 ## ------------------------------- ##
368 ## Disable, and process the file. ##
369 ## ------------------------------- ##
370 # The AC autoquoting macros are not loaded yet, hence invoking
371 # `_au_disable' would be wrong.
372 _au__include([unm4.m4])
374 # Disable special characters, and set the first line number.
375 _au_m4_changequote()
376 _au_m4_changecom()
378 _au_m4_define(_au__first_line, _au___line__)_au__divert(0)_au_dnl
379 EOF
381 $input_m4 =~ s/^ //mg;
382 $input_m4 =~ s/\$file/$file/g;
384 # prepared input -- input, but reenables the quote before each AU macro.
385 open INPUT_M4, "> " . open_quote ("$tmp/input.m4")
386 or error "cannot open: $!";
387 open FILE, "< " . open_quote ($file)
388 or error "cannot open: $!";
389 print INPUT_M4 "$input_m4";
390 while (<FILE>)
391 {
392 eval $au_changequote;
393 print INPUT_M4;
394 }
395 close FILE
396 or error "cannot close $file: $!";
397 close INPUT_M4
398 or error "cannot close $tmp/input.m4: $!";
400 # Now ask m4 to perform the update.
401 xsystem ("$m4 --include=" . shell_quote ($tmp)
402 . join (' --include=', '', map { shell_quote ($_) } reverse (@prepend_include))
403 . join (' --include=', '', map { shell_quote ($_) } @include)
404 . " " . shell_quote ("$tmp/input.m4") . " > " . shell_quote ("$tmp/updated"));
405 update_file ("$tmp/updated",
406 "$file" eq "$tmp/stdin" ? '-' : "$file");
407 }
408 exit 0;
411 # ## ---------------------------- ##
412 # ## How `autoupdate' functions. ##
413 # ## ---------------------------- ##
414 #
415 # The task of `autoupdate' is not trivial: the biggest difficulty being
416 # that you must limit the changes to the parts that really need to be
417 # updated. Finding a satisfying implementation proved to be quite hard,
418 # as this is the fifth implementation of `autoupdate'.
419 #
420 # Below, we will use a simple example of obsolete macro:
421 #
422 # AU_DEFUN([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))])
423 # AC_DEFUN([NEW], [echo "sum($1) = $2"])
424 #
425 # the input file contains
426 #
427 # dnl The Unbelievable Truth
428 # OLD(1, 2)
429 # NEW([0, 0], [0])
430 #
431 # Of course the expected output is
432 #
433 # dnl The Unbelievable Truth
434 # NEW([1, 2], [3])
435 # NEW([0, 0], [0])
436 #
437 #
438 # # First implementation: sed
439 # # =========================
440 #
441 # The first implementation was only able to change the name of obsolete
442 # macros.
443 #
444 # The file `acoldnames.m4' defined the old names based on the new names.
445 # It was simple then to produce a sed script such as:
446 #
447 # s/OLD/NEW/g
448 #
449 # Updating merely consisted in running this script on the file to
450 # update.
451 #
452 # This scheme suffers an obvious limitation: that `autoupdate' was
453 # unable to cope with new macros that just swap some of its arguments
454 # compared to the old macro. Fortunately, that was enough to upgrade
455 # from Autoconf 1 to Autoconf 2. (But I have no idea whether the
456 # changes in Autoconf 2 were precisely limited by this constraint.)
457 #
458 #
459 # # Second implementation: hooks
460 # # ============================
461 #
462 # The version 2.15 of Autoconf brought a vast number of changes compared
463 # to 2.13, so a solution was needed. One could think to extend the
464 # `sed' scripts with specialized code for complex macros. But this
465 # approach is of course full of flaws:
466 #
467 # a. the Autoconf maintainers have to write these snippets, which we
468 # just don't want to,
469 #
470 # b. I really don't think you'll ever manage to handle the quoting of
471 # m4 from sed.
472 #
473 # To satisfy a., let's remark that the code which implements the old
474 # features in term of the new feature is exactly the code which should
475 # replace the old code.
476 #
477 # To answer point b, as usual in the history of Autoconf, the answer, at
478 # least on the paper, is simple: m4 is the best tool to parse m4, so
479 # let's use m4.
480 #
481 # Therefore the specification is:
482 #
483 # I want to be able to tell Autoconf, well, m4, that the macro I
484 # am currently defining is an obsolete macro (so that the user is
485 # warned), which code is the code to use when running autoconf,
486 # but that the very same code has to be used when running
487 # autoupdate. To summarize, the interface I want is
488 # `AU_DEFUN(OLD-NAME, NEW-CODE)'.
489 #
490 #
491 # Now for the technical details.
492 #
493 # When running autoconf, except for the warning, AU_DEFUN is basically
494 # AC_DEFUN.
495 #
496 # When running autoupdate, we want *only* OLD-NAMEs to be expanded.
497 # This obviously means that acgeneral.m4 and acspecific.m4 must not be
498 # loaded. Nonetheless, because we want to use a rich set of m4
499 # features, m4sugar.m4 is needed. Please note that the fact that
500 # Autoconf's macros are not loaded is positive on two points:
501 #
502 # - we do get an updated `configure.ac', not a `configure'!
503 #
504 # - the old macros are replaced by *calls* to the new-macros, not the
505 # body of the new macros, since their body is not defined!!!
506 # (Whoa, that's really beautiful!).
507 #
508 # Additionally we need to disable the quotes when reading the input for
509 # two reasons: first because otherwise `m4' will swallow the quotes of
510 # other macros:
511 #
512 # NEW([1, 2], 3)
513 # => NEW(1, 2, 3)
514 #
515 # and second, because we want to update the macro calls which are
516 # quoted, i.e., we want
517 #
518 # FOO([OLD(1, 2)])
519 # => FOO([NEW([1, 2], [3])])
520 #
521 # If we don't disable the quotes, only the macros called at the top
522 # level would be updated.
523 #
524 # So, let's disable the quotes.
525 #
526 # Well, not quite: m4sugar.m4 still needs to use quotes for some macros.
527 # Well, in this case, when running in autoupdate code, each macro first
528 # reestablishes the quotes, expands itself, and disables the quotes.
529 #
530 # Thinking a bit more, you realize that in fact, people may use `define'
531 # `ifelse' etc. in their files, and you certainly don't want to process
532 # them. Another example is `dnl': you don't want to remove the
533 # comments. You then realize you don't want exactly to import m4sugar:
534 # you want to specify when it is enabled (macros active), and disabled.
535 # m4sugar provides m4_disable/m4_enable to this end.
536 #
537 # You're getting close to it. Now remains one task: how to handle
538 # twofold definitions?
539 #
540 # Remember that the same AU_DEFUN must be understood in two different
541 # ways, the AC way, and the AU way.
542 #
543 # One first solution is to check whether acgeneral.m4 was loaded. But
544 # that's definitely not cute. Another is simply to install `hooks',
545 # that is to say, to keep in some place m4 knows, late `define' to be
546 # triggered *only* in AU mode.
547 #
548 # You first think to design AU_DEFUN like this:
549 #
550 # 1. AC_DEFUN(OLD-NAME,
551 # [Warn the user OLD-NAME is obsolete.
552 # NEW-CODE])
553 #
554 # 2. Store for late AU binding([define(OLD_NAME,
555 # [Reestablish the quotes.
556 # NEW-CODE
557 # Disable the quotes.])])
558 #
559 # but this will not work: NEW-CODE has probably $1, $2 etc. and these
560 # guys will be replaced with the argument of `Store for late AU binding'
561 # when you call it.
562 #
563 # I don't think there is a means to avoid this using this technology
564 # (remember that $1 etc. are *always* expanded in m4). You may also try
565 # to replace them with $[1] to preserve them for a later evaluation, but
566 # if `Store for late AU binding' is properly written, it will remain
567 # quoted till the end...
568 #
569 # You have to change technology. Since the problem is that `$1'
570 # etc. should be `consumed' right away, one solution is to define now a
571 # second macro, `AU_OLD-NAME', and to install a hook than binds OLD-NAME
572 # to AU_OLD-NAME. Then, autoupdate.m4 just need to run the hooks. By
573 # the way, the same method was used in autoheader.
574 #
575 #
576 # # Third implementation: m4 namespaces by m4sugar
577 # # ==============================================
578 #
579 # Actually, this implementation was just a clean up of the previous
580 # implementation: instead of defining hooks by hand, m4sugar was equipped
581 # with `namespaces'. What are they?
582 #
583 # Sometimes we want to disable some *set* of macros, and restore them
584 # later. We provide support for this via namespaces.
585 #
586 # There are basically three characters playing this scene: defining a
587 # macro in a namespace, disabling a namespace, and restoring a namespace
588 # (i.e., all the definitions it holds).
589 #
590 # Technically, to define a MACRO in NAMESPACE means to define the macro
591 # named `NAMESPACE::MACRO' to the VALUE. At the same time, we append
592 # `undefine(NAME)' in the macro named `m4_disable(NAMESPACE)', and
593 # similarly a binding of NAME to the value of `NAMESPACE::MACRO' in
594 # `m4_enable(NAMESPACE)'. These mechanisms allow to bind the macro of
595 # NAMESPACE and to unbind them at will.
596 #
597 # Of course this implementation is really inefficient: m4 has to grow
598 # strings which can become quickly huge, which slows it significantly.
599 #
600 # In particular one should avoid as much as possible to use `define' for
601 # temporaries. Now that `define' has quite a complex meaning, it is an
602 # expensive operations that should be limited to macros. Use
603 # `m4_define' for temporaries.
604 #
605 # Private copies of the macros we used in entering / exiting the m4sugar
606 # namespace. It is much more convenient than fighting with the renamed
607 # version of define etc.
608 #
609 #
610 #
611 # Those two implementations suffered from serious problems:
612 #
613 # - namespaces were really expensive, and incurred a major performance
614 # loss on `autoconf' itself, not only `autoupdate'. One solution
615 # would have been the limit the use of namespaces to `autoupdate', but
616 # that's again some complications on m4sugar, which really doesn't need
617 # this. So we wanted to get rid of the namespaces.
618 #
619 # - since the quotes were disabled, autoupdate was sometimes making
620 # wrong guesses, for instance on:
621 #
622 # foo([1, 2])
623 #
624 # m4 saw 2 arguments: `[1'and `2]'. A simple solution, somewhat
625 # fragile, is to reestablish the quotes right before all the obsolete
626 # macros, i.e., to use sed so that the previous text becomes
627 #
628 # changequote([, ])foo([1, 2])
629 #
630 # To this end, one wants to trace the definition of obsolete macros.
631 #
632 # It was there that the limitations of the namespace approach became
633 # painful: because it was a complex machinery playing a lot with the
634 # builtins of m4 (hence, quite fragile), tracing was almost impossible.
635 #
636 #
637 # So this approach was dropped.
638 #
639 #
640 # # The fourth implementation: two steps
641 # # ====================================
642 #
643 # If you drop the uses of namespaces, you no longer can compute the
644 # updated value, and replace the old call with it simultaneously.
645 #
646 # Obviously you will use m4 to compute the updated values, but you may
647 # use some other tool to achieve the replacement. Personally, I trust
648 # nobody but m4 to parse m4, so below, m4 will perform the two tasks.
649 #
650 # How can m4 be used to replace *some* macros calls with newer values.
651 # Well, that's dead simple: m4 should learn the definitions of obsolete
652 # macros, forget its builtins, disable the quotes, and then run on the
653 # input file, which amounts to doing this:
654 #
655 # divert(-1)dnl
656 # changequote([, ])
657 # define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
658 # undefine([dnl])
659 # undefine([m4_eval])
660 # # Some more undefines...
661 # changequote()
662 # divert(0)dnl
663 # dnl The Unbelievable Truth
664 # changequote([, ])OLD(1, 2)
665 # NEW([0, 0],
666 # 0)
667 #
668 # which will result in
669 #
670 # dnl The Unbelievable Truth
671 # NEW(1, 2, m4_eval(1 + 2))
672 # NEW([0, 0],
673 # 0)
674 #
675 # Grpmh. Two problems. A minor problem: it would have been much better
676 # to have the `m4_eval' computed, and a major problem: you lost the
677 # quotation in the result.
678 #
679 # Let's address the big problem first. One solution is to define any
680 # modern macro to rewrite its calls with the proper quotation, thanks to
681 # `$@'. Again, tracing the `define's makes it possible to know which
682 # are these macros, so you input is:
683 #
684 # divert(-1)dnl
685 # changequote([, ])
686 # define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
687 # define([NEW], [[NEW($@)]changequote()])
688 # undefine([dnl])
689 # undefine([m4_eval])
690 # # Some more undefines...
691 # changequote()
692 # divert(0)dnl
693 # dnl The Unbelievable Truth
694 # changequote([, ])OLD(1, 2)
695 # changequote([, ])NEW([0, 0],
696 # 0)
697 #
698 # which results in
699 #
700 # dnl The Unbelievable Truth
701 # NEW([1, 2],[m4_eval(1 + 2)])
702 # NEW([0, 0],[0])
703 #
704 # Our problem is solved, i.e., the first call to `NEW' is properly
705 # quoted, but introduced another problem: we changed the layout of the
706 # second calls, which can be a drama in the case of huge macro calls
707 # (think of `AC_TRY_RUN' for instance). This example didn't show it,
708 # but we also introduced parens to macros which did not have some:
709 #
710 # AC_INIT
711 # => AC_INIT()
712 #
713 # No big deal for the semantics (unless the macro depends upon $#, which
714 # is bad), but the users would not be happy.
715 #
716 # Additionally, we introduced quotes that were not there before, which is
717 # OK in most cases, but could change the semantics of the file.
718 #
719 # Cruel dilemma: we do want the auto-quoting definition of `NEW' when
720 # evaluating `OLD', but we don't when we evaluate the second `NEW'.
721 # Back to namespaces?
722 #
723 # No.
724 #
725 #
726 # # Second step: replacement
727 # # ------------------------
728 #
729 # No, as announced above, we will work in two steps: in a first step we
730 # compute the updated values, and in a second step we replace them. Our
731 # goal is something like this:
732 #
733 # divert(-1)dnl
734 # changequote([, ])
735 # define([OLD], [NEW([1, 2], [3])changequote()])
736 # undefine([dnl])
737 # undefine([m4_eval])
738 # # Some more undefines...
739 # changequote()
740 # divert(0)dnl
741 # dnl The Unbelievable Truth
742 # changequote([, ])OLD(1, 2)
743 # NEW([0, 0],
744 # 0)
745 #
746 # i.e., the new value of `OLD' is precomputed using the auto-quoting
747 # definition of `NEW' and the m4 builtins. We'll see how afterwards,
748 # let's finish with the replacement.
749 #
750 # Of course the solution above is wrong: if there were other calls to
751 # `OLD' with different values, we would smash them to the same value.
752 # But it is quite easy to generalize the scheme above:
753 #
754 # divert(-1)dnl
755 # changequote([, ])
756 # define([OLD([1],[2])], [NEW([1, 2], [3])])
757 # define([OLD], [defn([OLD($@)])changequote()])
758 # undefine([dnl])
759 # undefine([m4_eval])
760 # # Some more undefines...
761 # changequote()
762 # divert(0)dnl
763 # dnl The Unbelievable Truth
764 # changequote([, ])OLD(1, 2)
765 # NEW([0, 0],
766 # 0)
767 #
768 # i.e., for each call to obsolete macros, we build an array `call =>
769 # value', and use a macro to dispatch these values. This results in:
770 #
771 # dnl The Unbelievable Truth
772 # NEW([1, 2], [3])
773 # NEW([0, 0],
774 # 0)
775 #
776 # In French, we say `Youpi !', which you might roughly translate as
777 # `Yippee!'.
778 #
779 #
780 # # First step: computation
781 # # -----------------------
782 #
783 # Let's study the anatomy of the file, and name its sections:
784 #
785 # prologue
786 # divert(-1)dnl
787 # changequote([, ])
788 # values
789 # define([OLD([1],[2])], [NEW([1, 2], [3])])
790 # dispatcher
791 # define([OLD], [defn([OLD($@)])changequote()])
792 # disabler
793 # undefine([dnl])
794 # undefine([m4_eval])
795 # # Some more undefines...
796 # changequote()
797 # divert(0)dnl
798 # input
799 # dnl The Unbelievable Truth
800 # changequote([, ])OLD(1, 2)
801 # NEW([0, 0],
802 # 0)
803 #
804 #
805 # # Computing the `values' section
806 # # ..............................
807 #
808 # First we need to get the list of all the AU macro uses. To this end,
809 # first get the list of all the AU macros names by tracing `AU_DEFUN' in
810 # the initialization of autoconf. This list is computed in the file
811 # `au.txt' below.
812 #
813 # Then use this list to trace all the AU macro uses in the input. The
814 # goal is obtain in the case of our example:
815 #
816 # [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
817 #
818 # This is the file `values.in' below.
819 #
820 # We want to evaluate this with only the builtins (in fact m4sugar), the
821 # auto-quoting definitions of the new macros (`new.m4'), and the
822 # definition of the old macros (`old.m4'). Computing these last two
823 # files is easy: it's just a matter of using the right `--trace' option.
824 #
825 # So the content of `values.in' is:
826 #
827 # include($autoconf_dir/m4sugar.m4)
828 # m4_include(new.m4)
829 # m4_include(old.m4)
830 # divert(0)dnl
831 # [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
832 #
833 # We run m4 on it, which yields:
834 #
835 # define([OLD([1],[2])],@<<@NEW([1, 2], [3])@>>@)
836 #
837 # Transform `@<<@' and `@>>@' into quotes and we get
838 #
839 # define([OLD([1],[2])],[NEW([1, 2], [3])])
840 #
841 # This is `values.m4'.
842 #
843 #
844 # # Computing the `dispatcher' section
845 # # ..................................
846 #
847 # The `prologue', and the `disabler' are simple and need no commenting.
848 #
849 # To compute the `dispatcher' (`dispatch.m4'), again, it is a simple
850 # matter of using the right `--trace'.
851 #
852 # Finally, the input is not exactly the input file, rather it is the
853 # input file with the added `changequote'. To this end, we build
854 # `quote.sed'.
855 #
856 #
857 # # Putting it all together
858 # # .......................
859 #
860 # We build the file `input.m4' which contains:
861 #
862 # divert(-1)dnl
863 # changequote([, ])
864 # include(values.m4)
865 # include(dispatch.m4)
866 # undefine([dnl])
867 # undefine([eval])
868 # # Some more undefines...
869 # changequote()
870 # divert(0)dnl
871 # dnl The Unbelievable Truth
872 # changequote([, ])OLD(1, 2)
873 # NEW([0, 0],
874 # 0)
875 #
876 # And we just run m4 on it. Et voila`, Monsieur ! Mais oui, mais oui.
877 #
878 # Well, there are a few additional technicalities. For instance, we
879 # rely on `changequote', `ifelse' and `defn', but we don't want to
880 # interpret the changequotes of the user, so we simply use another name:
881 # `_au_changequote' etc.
882 #
883 #
884 # # Failure of the fourth approach
885 # # ------------------------------
886 #
887 # This approach is heavily based on traces, but then there is an obvious
888 # problem: non expanded code will never be seen. In particular, the body
889 # of a `define' definition is not seen, so on the input
890 #
891 # define([idem], [OLD(0, [$1])])
892 #
893 # autoupdate would never see the `OLD', and wouldn't have updated it.
894 # Worse yet, if `idem(0)' was used later, then autoupdate sees that
895 # `OLD' is used, computes the result for `OLD(0, 0)' and sets up a
896 # dispatcher for `OLD'. Since there was no computed value for `OLD(0,
897 # [$1])', the dispatcher would have replaced with... nothing, leading
898 # to
899 #
900 # define([idem], [])
901 #
902 # With some more thinking, you see that the two step approach is wrong,
903 # the namespace approach was much saner.
904 #
905 # But you learned a lot, in particular you realized that using traces
906 # can make it possible to simulate namespaces!
907 #
908 #
909 #
910 # # The fifth implementation: m4 namespaces by files
911 # # ================================================
912 #
913 # The fourth implementation demonstrated something unsurprising: you
914 # cannot precompute, i.e., the namespace approach was the right one.
915 # Still, we no longer want them, they're too expensive. Let's have a
916 # look at the way it worked.
917 #
918 # When updating
919 #
920 # dnl The Unbelievable Truth
921 # OLD(1, 2)
922 # NEW([0, 0], [0])
923 #
924 # you evaluate `input.m4':
925 #
926 # divert(-1)
927 # changequote([, ])
928 # define([OLD],
929 # [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
930 # ...
931 # m4_disable()
932 # dnl The Unbelievable Truth
933 # OLD(1, 2)
934 # NEW([0, 0], [0])
935 #
936 # where `m4_disable' undefines the m4 and m4sugar, and disables the quotes
937 # and comments:
938 #
939 # define([m4_disable],
940 # [undefine([__file__])
941 # ...
942 # changecom(#)
943 # changequote()])
944 #
945 # `m4_enable' does the converse: reestablish quotes and comments
946 # --easy--, reestablish m4sugar --easy: just load `m4sugar.m4' again-- and
947 # reenable the builtins. This later task requires that you first save
948 # the builtins. And BTW, the definition above of `m4_disable' cannot
949 # work: you undefined `changequote' before using it! So you need to use
950 # your privates copies of the builtins. Let's introduce three files for
951 # this:
952 #
953 # `m4save.m4'
954 # moves the m4 builtins into the `_au_' pseudo namespace,
955 # `unm4.m4'
956 # undefines the builtins,
957 # `m4.m4'
958 # restores them.
959 #
960 # So `input.m4' is:
961 #
962 # divert(-1)
963 # changequote([, ])
964 #
965 # include([m4save.m4])
966 #
967 # # Import AU.
968 # define([OLD],
969 # [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
970 #
971 # define([_au_enable],
972 # [_au_changecom([#])
973 # _au_include([m4.m4])
974 # _au_include(m4sugar.m4)])
975 #
976 # define([_au_disable],
977 # [# Disable m4sugar.
978 # # Disable the m4 builtins.
979 # _au_include([unm4.m4])
980 # # 1. Disable special characters.
981 # _au_changequote()
982 # _au_changecom()])
983 #
984 # m4_disable()
985 # dnl The Unbelievable Truth
986 # OLD(1, 2)
987 # NEW([0, 0], [0])
988 #
989 # Based on what we learned in the fourth implementation we know that we
990 # have to enable the quotes *before* any AU macro, and we know we need
991 # to build autoquoting versions of the AC macros. But the autoquoting
992 # AC definitions must be disabled in the rest of the file, and enabled
993 # inside AU macros.
994 #
995 # Using `autoconf --trace' it is easy to build the files
996 #
997 # `ac.m4'
998 # define the autoquoting AC fake macros
999 # `disable.m4'
1000 # undefine the m4sugar and AC autoquoting macros.
1001 # `au.m4'
1002 # definitions of the AU macros (such as `OLD' above).
1003 #
1004 # Now, `input.m4' is:
1005 #
1006 # divert(-1)
1007 # changequote([, ])
1008 #
1009 # include([m4save.m4])
1010 # # Import AU.
1011 # include([au.m4])
1012 #
1013 # define([_au_enable],
1014 # [_au_changecom([#])
1015 # _au_include([m4.m4])
1016 # _au_include(m4sugar.m4)
1017 # _au_include(ac.m4)])
1018 #
1019 # define([_au_disable],
1020 # [_au_include([disable.m4])
1021 # _au_include([unm4.m4])
1022 # # 1. Disable special characters.
1023 # _au_changequote()
1024 # _au_changecom()])
1025 #
1026 # m4_disable()
1027 # dnl The Unbelievable Truth
1028 # _au_changequote([, ])OLD(1, 2)
1029 # NEW([0, 0], [0])
1030 #
1031 # Finally, version V is ready.
1032 #
1033 # Well... almost.
1034 #
1035 # There is a slight problem that remains: if an AU macro OUTER includes
1036 # an AU macro INNER, then _au_enable will be run when entering OUTER
1037 # and when entering INNER (not good, but not too bad yet). But when
1038 # getting out of INNER, _au_disable will disable everything while we
1039 # were still in OUTER. Badaboom.
1040 #
1041 # Therefore _au_enable and _au_disable have to be written to work by
1042 # pairs: each _au_enable pushdef's _au_enabled, and each _au_disable
1043 # popdef's _au_enabled. And of course _au_enable and _au_disable are
1044 # effective when _au_enabled is *not* defined.
1045 #
1046 # Finally, version V' is ready. And there is much rejoicing. (And I
1047 # have free time again. I think. Yeah, right.)
1049 ### Setup "GNU" style for perl-mode and cperl-mode.
1050 ## Local Variables:
1051 ## perl-indent-level: 2
1052 ## perl-continued-statement-offset: 2
1053 ## perl-continued-brace-offset: 0
1054 ## perl-brace-offset: 0
1055 ## perl-brace-imaginary-offset: 0
1056 ## perl-label-offset: -2
1057 ## cperl-indent-level: 2
1058 ## cperl-brace-offset: 0
1059 ## cperl-continued-brace-offset: 0
1060 ## cperl-label-offset: -2
1061 ## cperl-extra-newline-before-brace: t
1062 ## cperl-merge-trailing-else: nil
1063 ## cperl-continued-statement-offset: 2
1064 ## End: