bin/autoupdate

   1 #! /bin/perl -w
   2 # -*- perl -*-
   3 # Generated from autoupdate.in; do not edit by hand.
   4
   5 # autoupdate - modernize an Autoconf file.
   6 # Copyright (C) 1994, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
   7 # Free Software Foundation, Inc.
   8
   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.
  13
  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.
  18
  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.
  23
  24 # Originally written by David MacKenzie <djm@gnu.ai.mit.edu>.
  25 # Rewritten by Akim Demaille <akim@freefriends.org>.
  26
  27 eval 'case $# in 0) exec /bin/perl -S "$0";; *) exec /bin/perl -S "$0" "$@";; esac'
  28     if 0;
  29
  30 BEGIN
  31 {
  32   my $datadir = $ENV{'autom4te_perllibdir'} || '/usr/share/autoconf';
  33   unshift @INC, $datadir;
  34
  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   $ENV{'SHELL'} = '/bin/sh' if ($^O eq 'dos');
  40 }
  41
  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;
  50
  51 # Lib files.
  52 my $autom4te = $ENV{'AUTOM4TE'} || '/usr/bin/autom4te';
  53 my $autoconf = "$autom4te --language=autoconf";
  54 # We need to find m4sugar.
  55 my @prepend_include;
  56 my @include = ('/usr/share/autoconf');
  57 my $force = 0;
  58 # m4.
  59 my $m4 = $ENV{"M4"} || '/bin/m4';
  60
  61
  62 # $HELP
  63 # -----
  64 $help = "Usage: $0 [OPTION] ...  [TEMPLATE-FILE...]
  65
  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.
  69
  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
  76
  77 Library directories:
  78   -B, --prepend-include=DIR  prepend directory DIR to search path
  79   -I, --include=DIR          append directory DIR to search path
  80
  81 Report bugs to <bug-autoconf\@gnu.org>.
  82 ";
  83
  84 # $VERSION
  85 # --------
  86 $version = "autoupdate (GNU Autoconf) 2.61
  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.
  91
  92 Written by David J. MacKenzie and Akim Demaille.
  93 ";
  94
  95 ## ---------- ##
  96 ## Routines.  ##
  97 ## ---------- ##
  98
  99
 100 # parse_args ()
 101 # -------------
 102 # Process any command line arguments.
 103 sub parse_args ()
 104 {
 105   my $srcdir;
 106
 107   getopt ('I|include=s'         => \@include,
 108           'B|prepend-include=s' => \@prepend_include,
 109           'f|force'             => \$force);
 110
 111   if (! @ARGV)
 112     {
 113       my $configure_ac = require_configure_ac;
 114       push @ARGV, $configure_ac;
 115     }
 116 }
 117
 118
 119
 120 # ----------------- #
 121 # Autoconf macros.  #
 122 # ----------------- #
 123
 124 my (%ac_macros, %au_macros, %m4_builtins);
 125
 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;
 140
 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;
 165
 166
 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;
 178
 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     }
 186
 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     }
 198
 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 }
 215
 216
 217 ## -------------- ##
 218 ## Main program.  ##
 219 ## -------------- ##
 220
 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);
 227
 228 mktmpdir ('au');
 229 handle_autoconf_macros;
 230
 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([,])$1/g';
 234
 235 # au.m4 -- definitions the AU macros.
 236 xsystem ("$autoconf --trace AU_DEFINE:'_au_defun(\@<:\@\$1\@:>\@,
 237 \@<:\@\$2\@:>\@)' --melt /dev/null "
 238         . ">$tmp/au.m4");
 239
 240
 241
 242 ## ------------------- ##
 243 ## Process the files.  ##
 244 ## ------------------- ##
 245
 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       }
 258
 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([,])
 265
 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]))])])
 275
 276       # Set up m4sugar.
 277       include(m4sugar/m4sugar.m4)
 278
 279       # Redefine __file__ to make warnings nicer; $file is replaced below.
 280       m4_define([__file__], [$file])
 281
 282       # Redefine m4_location to fix the line number.
 283       m4_define([m4_location], [__file__:m4_eval(__line__ - _au__first_line)])
 284
 285       # Move all the builtins into the `_au_' pseudo namespace
 286       m4_include([m4save.m4])
 287
 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()])])
 296
 297       # Import the definition of the obsolete macros.
 298       _au__include([au.m4])
 299
 300
 301       ## ------------------------ ##
 302       ## _au_enable/_au_disable.  ##
 303       ## ------------------------ ##
 304
 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.
 312
 313
 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([#])
 321
 322       _au__include([m4.m4])
 323       _au__include([ac.m4])
 324
 325       _au__divert(0)])
 326
 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])])
 336
 337
 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])
 345
 346       # Disable special characters.
 347       _au_m4_changequote()
 348       _au_m4_changecom()
 349
 350       _au__divert(0)])
 351
 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()])])
 361
 362
 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])
 369
 370       # Disable special characters, and set the first line number.
 371       _au_m4_changequote()
 372       _au_m4_changecom()
 373
 374       _au_m4_define(_au__first_line, _au___line__)_au__divert(0)_au_dnl
 375 EOF
 376
 377     $input_m4 =~ s/^      //mg;
 378     $input_m4 =~ s/\$file/$file/g;
 379
 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: $!";
 395
 396     # Now ask m4 to perform the update.
 397     xsystem ("$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;
 405
 406
 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.)
1044
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: