This file is indexed.

/usr/bin/autoupdate-dickey is in autoconf-dickey 2.52+20150926-1.

This file is owned by root:root, with mode 0o755.

The actual contents of the file can be viewed below.

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
#! /usr/bin/perl -w
# -*- perl -*-
# autoupdate - modernize an Autoconf file.
# Copyright 1994, 1999, 2000, 2001 Free Software Foundation, Inc.

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2, or (at your option)
# any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
# 02111-1307, USA.

# Originally written by David MacKenzie <djm@gnu.ai.mit.edu>.
# Rewritten by Akim Demaille <akim@freefriends.org>.

use 5.005;
use Getopt::Long;
use File::Basename;
use strict;

(my $me = $0) =~ s,.*[\\/],,;

# Lib files.
my $autoconf_dir = $ENV{"AC_MACRODIR"} || "/usr/share/autoconf-dickey/autoconf";
my $autoconf = '';
my $debug = 0;
my $localdir = '.';
# m4.
my $m4 = $ENV{"M4"} || "/usr/bin/m4";
my $verbose = 0;
my $SIMPLE_BACKUP_SUFFIX = $ENV{'SIMPLE_BACKUP_SUFFIX'} || '~';
my $tmp = '';


## ---------- ##
## Routines.  ##
## ---------- ##


# &mktmpdir ()
# ------------
sub mktmpdir ()
{
  my $TMPDIR = $ENV{'TMPDIR'} || '/tmp';

  # If mktemp supports dirs, use it to please Marc E.
  $tmp = `(umask 077 && mktemp -d -q "$TMPDIR/auXXXXXX") 2>/dev/null`;
  chomp $tmp;

  if (!$tmp || !-d $tmp)
    {
      $tmp = "$TMPDIR/au" . int (rand 10000) . ".$$";
      mkdir $tmp, 0700
	or die "$me: cannot create $tmp: $!\n";
    }

  print STDERR "$me:$$: working in $tmp\n"
    if $debug;
}


# END
# ---
# Exit nonzero whenever closing STDOUT fails.
sub END
{
  use POSIX qw (_exit);

  my ($q) = ($?);

  # FIXME: Heelp!  Can't find a means to properly catch system's
  # exit status (without hair I mean).
  # my $status = $? >> 8;

  if (!$debug && -d $tmp)
    {
      unlink <$tmp/*>
	or warn ("$me: cannot empty $tmp: $!\n"), _exit (1);
      rmdir $tmp
	or warn ("$me: cannot remove $tmp: $!\n"), _exit (1);
    }

  # This is required if the code might send any output to stdout
  # E.g., even --version or --help.  So it's best to do it unconditionally.
  close STDOUT
    or (warn "$me: closing standard output: $!\n"), _exit (1);

  ($!, $?) = (0, $q);
}


# print_usage ()
# --------------
# Display usage (--help).
sub print_usage ()
{
  print <<"END";
Usage: $0 [OPTION] ...  [TEMPLATE-FILE...]

Update the TEMPLATE-FILE... if given, or \`configure.ac' if present,
or else \`configure.in', to the syntax of the current version of
Autoconf.  The original files are backed up.

Operation modes:
  -h, --help           print this help, then exit
  -V, --version        print version number, then exit
  -v, --verbose        verbosely report processing
  -d, --debug          don't remove temporary files

Library directories:
  -A, --autoconf-dir=ACDIR  Autoconf's macro files location (rarely needed)
  -l, --localdir=DIR        location of \`aclocal.m4'

Environment variables:
  M4         GNU M4 1.4 or above
  AUTOCONF   autoconf 2.52.20150926

Report bugs to <dickey\@invisible-island.net>.
END
  exit 0;
}


# print_version ()
# ----------------
# Display version (--version).
sub print_version
{
  print <<END;
autoupdate (GNU Autoconf) 2.52.20150926
Written by David J. MacKenzie and Akim Demaille.

Copyright 1994, 1999, 2000, 2001 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
END
  exit 0;
}


# $CONFIGURE_AC
# &find_configure_ac ()
# ---------------------
sub find_configure_ac ()
{
  if (-f 'configure.ac')
    {
      if (-f 'configure.in')
	{
	  warn "warning: `configure.ac' and `configure.in' both present.\n";
	  warn "warning: proceeding with `configure.ac'.\n";
	}
      return 'configure.ac';
    }
  elsif (-f 'configure.in')
    {
      return 'configure.in';
    }
  return;
}


# parse_args ()
# -------------
# Process any command line arguments.
sub parse_args ()
{
  my $srcdir;
  # F*k.  Getopt seems bogus and dies when given `-' with `bundling'.
  # If fixed some day, use this: '' => sub { push @ARGV, "-" }
  my $update_stdin = grep /^-$/, @ARGV;
  @ARGV = grep !/^-$/, @ARGV;
  Getopt::Long::config ("bundling");
  Getopt::Long::GetOptions ('A|autoconf-dir|m|macrodir=s' => \$autoconf_dir,
			    'l|localdir=s' => \$localdir,
			    'd|debug'      => \$debug,
			    'h|help'    => \&print_usage,
			    'V|version' => \&print_version,
			    'v|verbose' => \$verbose)
    or exit 1;
  push @ARGV, '-'
    if $update_stdin;
  if (! @ARGV)
    {
      my $configure_ac = find_configure_ac;
      die 'no input file'
	unless $configure_ac;
      push @ARGV, $configure_ac;
    }
}


# find_slaves
# -----------
# Find the lib files and autoconf.
sub find_slaves ()
{
  # Some non-GNU m4's don't reject the --help option, so give them /dev/null.
  die "Autoconf requires GNU m4 1.4 or later\n"
    if system "$m4 --help </dev/null 2>&1 | fgrep reload-state >/dev/null";

  # autoconf.
  (my $dir = $0) =~ s,[^\\/]*$,,;

  # We test "$dir/autoconf" in case we are in the build tree, in which case
  # the names are not transformed yet.
  foreach my $file ($ENV{"AUTOCONF"} || '',
		    "$dir/autoconf-dickey",
		    "$dir/autoconf",
		    "/usr/bin/autoconf-dickey")
    {
      if (-x $file)
	{
	  $autoconf = $file;
	  last;
	}
    }

  # This is needed because perl's '-x' isn't a smart as bash's; that
  # is, it won't find autoconf.sh.
  $autoconf = 'autoconf'
    if !$autoconf;
}


## -------------- ##
## Main program.  ##
## -------------- ##
find_slaves;
parse_args;
mktmpdir;
$autoconf .= " --autoconf-dir $autoconf_dir --localdir $localdir";


# @M4_BUILTINS -- M4 builtins and a useful comment.
my @m4_builtins = `echo dumpdef | $m4 2>&1 >/dev/null`;
map { s/:.*//;s/\W// } @m4_builtins;


# m4.m4 -- enable the m4 builtins.
# unm4.m4 -- disable the m4 builtins.
# savem4.m4 -- save the m4 builtins.
open M4_M4, ">$tmp/m4.m4"
  or die "$me: cannot open: $!\n";
open UNM4_M4, ">$tmp/unm4.m4"
  or die "$me: cannot open: $!\n";
open M4SAVE_M4, ">$tmp/m4save.m4"
  or die "$me: cannot open: $!\n";
foreach (@m4_builtins)
  {
    print M4_M4     "_au_define([$_], _au_defn([_au_$_]))\n";
    print UNM4_M4   "_au_undefine([$_])\n";
    print M4SAVE_M4 "define([_au_$_], defn([$_]))\n";
  }
close M4SAVE_M4
  or die "$me: cannot close: $!\n";
close UNM4_M4
  or die "$me: cannot close: $!\n";
close M4_M4
  or die "$me: cannot close: $!\n";


# @AU_MACROS & AC_MACROS -- AU and AC macros and yet another useful comment.
open MACROS, ("$autoconf "
	      . "--trace AU_DEFUN:'AU:\$f:\$1' --trace define:'AC:\$f:\$1' "
	      . "-i /dev/null |")
  or die "$me: cannot open: $!\n";
my (%ac_macros, %au_macros);
while (<MACROS>)
  {
    chomp;
    /^(AC|AU):(.*):([^:]*)$/ or next;
    my $filename = basename ($2);
    if ($1 eq "AC")
      {
	$ac_macros{$3} = $filename;
      }
    else
      {
	$au_macros{$3} = $filename;
      }
  }
close MACROS
  or die "$me: cannot close: $!\n";
# Don't keep AU macros in @AC_MACROS.
delete $ac_macros{$_}
  foreach (keys %au_macros);
if ($debug)
  {
    print STDERR "Current Autoconf macros:\n";
    print STDERR join (' ', sort keys %ac_macros) . "\n\n";
    print STDERR "Obsolete Autoconf macros:\n";
    print STDERR join (' ', sort keys %au_macros) . "\n\n";
  }

# $au_changequote -- enable the quote `[', `]' right before any AU macro.
my $au_changequote =
  's/\b(' . join ('|', keys %au_macros) . ')\b/_au_changequote([,])$1/g';

# au.m4 -- definitions the AU macros.
system ("$autoconf --trace AU_DEFUN:'_au_defun(\@<:\@\$1\@:>\@,
\@<:\@\$2\@:>\@)' -i /dev/null "
	. ">$tmp/au.m4");

# ac.m4 -- autoquoting definitions of the AC macros (M4sugar excluded).
# disable.m4 -- undefine the macros of AC and m4sugar.
open AC_M4, ">$tmp/ac.m4"
  or die "$me: cannot open: $!\n";
open DISABLE_M4, ">$tmp/disable.m4"
  or die "$me: cannot open: $!\n";
foreach (sort keys %ac_macros)
  {
    print AC_M4      "_au_define([$_], [[\$0(\$\@)]])\n"
      unless $ac_macros{$_} eq "m4sugar.m4";
    print DISABLE_M4 "_au_undefine([$_])\n";
  }
close DISABLE_M4
  or die "$me: cannot close: $!\n";
close AC_M4
  or die "$me: cannot close: $!\n";



## ------------------- ##
## Process the files.  ##
## ------------------- ##

foreach my $file (@ARGV)
  {
    my $filename = $file;
    # We need an actual file.
    if ($file eq '-')
      {
	$file = "$tmp/stdin";
	system "cat >$file";
      }
    elsif (! -r "$file")
      {
	die "$me: $file: No such file or directory";
      }

    # input.m4 -- m4 program to produce the updated file.
    # Load the values, the dispatcher, neutralize m4, and the prepared
    # input file.
    my $input_m4 = <<EOF;
      divert(-1)                                            -*- Autoconf -*-
      changequote([, ])

      # Move all the builtins into the \`_au_' pseudo namespace
      include([$tmp/m4save.m4])

      # _au_defun(NAME, BODY)
      # ---------------------
      # Define NAME to BODY, plus AU activation/deactivation.
      _au_define([_au_defun],
      [_au_define([\$1],
      [_au_enable()dnl
      \$2[]dnl
      _au_disable()])])

      # Import the definition of the obsolete macros.
      _au_include([$tmp/au.m4])


      ## ------------------------ ##
      ## _au_enable/_au_disable.  ##
      ## ------------------------ ##

      # They work by pair: each time an AU macro is activated, it runs
      # _au_enable, and at its end its runs _au_disable (see _au_defun
      # above).  But since AU macros might use AU macros, which should
      # enable/disable only for the outter AU macros.
      #
      # \`_au_enabled' is used to this end, condionning whether we really
      # enable/disable.


      # __au_enable
      # -----------
      # Reenable the builtins, and m4sugar.
      _au_define([__au_enable],
      [_au_divert(-1)
      # Enable special characters.
      _au_changecom([#])

      # Enable the m4 builtins, m4sugar and the autoquoting AC macros.
      _au_include([$tmp/m4.m4])
      _au_include([$autoconf_dir/m4sugar.m4])
      _au_include([$tmp/ac.m4])

      _au_divert(0)])

      # _au_enable
      # ----------
      # Called at the beginning of all the obsolete macros.  Reenable the
      # builtins, and m4sugar if needed.
      _au_define([_au_enable],
      [_au_ifdef([_au_enabled],
                 [],
                 [__au_enable()])_au_dnl
      _au_pushdef([_au_enabled])])


      # __au_disable
      # ------------
      # Disable the builtins, and m4sugar.
      _au_define([__au_disable],
      [_au_divert(-1)
      # Disable m4sugar, the AC autoquoting macros, and m4.
      _au_include([$tmp/disable.m4])
      _au_include([$tmp/unm4.m4])

      # Disable special characters.
      _au_changequote()
      _au_changecom()

      _au_divert(0)])

      # _au_disable
      # -----------
      # Called at the end of all the obsolete macros.  Disable the
      # builtins, and m4sugar if needed..
      _au_define([_au_disable],
      [_au_popdef([_au_enabled])_au_dnl
      _au_ifdef([_au_enabled],
                [],
                [__au_disable()])])


      ## ------------------------------- ##
      ## Disable, and process the file.  ##
      ## ------------------------------- ##
      _au_disable()_au_dnl
EOF

    $input_m4 =~ s/^      //mg;

    # prepared input -- input, but reenables the quote before each AU macro.
    open INPUT_M4, ">$tmp/input.m4"
       or die "$me: cannot open: $!\n";
    open FILE, "<$file"
       or die "$me: cannot open: $!\n";
    print INPUT_M4 "$input_m4";
    while (<FILE>)
       {
	 eval $au_changequote;
	 print INPUT_M4;
       }
    close FILE
       or die "$me: cannot close: $!\n";
    close INPUT_M4
       or die "$me: cannot close: $!\n";

    # Now ask m4 to perform the update.
    print STDERR "$me: running $m4 $tmp/input.m4\n"
       if $verbose;
    if (system ("$m4 $tmp/input.m4 >$tmp/updated"))
       {
	 # Exit status of system() is in the upper byte.
	 $! >>= 8;
	 die "$me: cannot update \`$filename'\n";
       };

    if ("$file" eq "$tmp/stdin")
       {
	 system ("cat $tmp/updated");
       }
    elsif (! system ("cmp -s $tmp/updated $file"))
       {
	 # File didn't change, so don't update its mod time.
	 print STDERR "$me: \`$file' is unchanged\n"
       }
    else
       {
	 # Back up and install the new one.
	 if (system ("mv $file $file${SIMPLE_BACKUP_SUFFIX} && "
		     . "mv $tmp/updated $file") == 0)
	   {
	     print STDERR "$me: \`$file' is updated\n";
	   }
	 else
	   {
	     die "$me: cannot update \`$file'\n";
	   }
       }
  }

exit 0;


# 		  ## ---------------------------- ##
# 		  ## How `autoupdate' functions.  ##
# 		  ## ---------------------------- ##
#
# The task of `autoupdate' is not trivial: the biggest difficulty being
# that you must limit the changes to the parts that really need to be
# updated.  Finding a satisfying implementation proved to be quite hard,
# as this is the fourth implementation of `autoupdate'.
#
# Below, we will use a simple example of obsolete macro:
#
#     AU_DEFUN([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))])
#     AC_DEFUN([NEW], [echo "sum($1) = $2"])
#
# the input file contains
#
#     dnl The Unbelievable Truth
#     OLD(1, 2)
#     NEW([0, 0], [0])
#
# Of course the expected output is
#
#     dnl The Unbelievable Truth
#     NEW([1, 2], [3])
#     NEW([0, 0], [0])
#
#
# # First implementation: sed
# # =========================
#
# The first implementation was only able to change the name of obsolete
# macros.
#
# The file `acoldnames.m4' defined the old names based on the new names.
# It was simple then to produce a sed script such as:
#
#     s/OLD/NEW/g
#
# Updating merely consisted in running this script on the file to
# update.
#
# This scheme suffers an obvious limitation: that `autoupdate' was
# unable to cope with new macros that just swap some of its arguments
# compared to the old macro.  Fortunately, that was enough to upgrade
# from Autoconf 1 to Autoconf 2.  (But I have no idea whether the
# changes in Autoconf 2 were precisely limited by this constraint.)
#
#
# # Second implementation: hooks
# # ============================
#
# The version 2.15 of Autoconf brought a vast number of changes compared
# to 2.13, so a solution was needed.  One could think to extend the
# `sed' scripts with specialized code for complex macros.  But this
# approach is of course full of flaws:
#
# a. the Autoconf maintainers have to write these snippets, which we
#    just don't want to,
#
# b. I really don't think you'll ever manage to handle the quoting of
#    m4 from sed.
#
# To satisfy a., let's remark that the code which implements the old
# features in term of the new feature is exactly the code which should
# replace the old code.
#
# To answer point b, as usual in the history of Autoconf, the answer, at
# least on the paper, is simple: m4 is the best tool to parse m4, so
# let's use m4.
#
# Therefore the specification is:
#
#     I want to be able to tell Autoconf, well, m4, that the macro I
#     am currently defining is an obsolete macro (so that the user is
#     warned), which code is the code to use when running autoconf,
#     but that the very same code has to be used when running
#     autoupdate.  To summarize, the interface I want is
#     `AU_DEFUN(OLD-NAME, NEW-CODE)'.
#
#
# Now for the technical details.
#
# When running autoconf, except for the warning, AU_DEFUN is basically
# AC_DEFUN.
#
# When running autoupdate, we want *only* OLD-NAMEs to be expanded.
# This obviously means that acgeneral.m4 and acspecific.m4 must not be
# loaded.  Nonetheless, because we want to use a rich set of m4
# features, m4sugar.m4 is needed.  Please note that the fact that
# Autoconf's macros are not loaded is positive on two points:
#
# - we do get an updated `configure.ac', not a `configure'!
#
# - the old macros are replaced by *calls* to the new-macros, not the
#   body of the new macros, since their body is not defined!!!
#   (Whoa, that's really beautiful!).
#
# Additionally we need to disable the quotes when reading the input for
# two reasons: first because otherwise `m4' will swallow the quotes of
# other macros:
#
#     NEW([1, 2], 3)
#     => NEW(1, 2, 3)
#
# and second, because we want to update the macro calls which are
# quoted, i.e., we want
#
#     FOO([OLD(1, 2)])
#     => FOO([NEW([1, 2], [3])])
#
# If we don't disable the quotes, only the macros called at the top
# level would be updated.
#
# So, let's disable the quotes.
#
# Well, not quite: m4sugar.m4 still needs to use quotes for some macros.
# Well, in this case, when running in autoupdate code, each macro first
# reestablishes the quotes, expands itself, and disables the quotes.
#
# Thinking a bit more, you realize that in fact, people may use `define'
# `ifelse' etc. in their files, and you certainly don't want to process
# them.  Another example is `dnl': you don't want to remove the
# comments.  You then realize you don't want exactly to import m4sugar:
# you want to specify when it is enabled (macros active), and disabled.
# m4sugar provides m4_disable/m4_enable to this end.
#
# You're getting close to it.  Now remains one task: how to handle
# twofold definitions?
#
# Remember that the same AU_DEFUN must be understood in two different
# ways, the AC way, and the AU way.
#
# One first solution is to check whether acgeneral.m4 was loaded.  But
# that's definitely not cute.  Another is simply to install `hooks',
# that is to say, to keep in some place m4 knows, late `define' to be
# triggered *only* in AU mode.
#
# You first think to design AU_DEFUN like this:
#
# 1. AC_DEFUN(OLD-NAME,
# 	      [Warn the user OLD-NAME is obsolete.
# 	       NEW-CODE])
#
# 2. Store for late AU binding([define(OLD_NAME,
# 				[Reestablish the quotes.
# 				 NEW-CODE
# 				 Disable the quotes.])])
#
# but this will not work: NEW-CODE has probably $1, $2 etc. and these
# guys will be replaced with the argument of `Store for late AU binding'
# when you call it.
#
# I don't think there is a means to avoid this using this technology
# (remember that $1 etc. are *always* expanded in m4).  You may also try
# to replace them with $[1] to preserve them for a later evaluation, but
# if `Store for late AU binding' is properly written, it will remain
# quoted till the end...
#
# You have to change technology.  Since the problem is that `$1'
# etc. should be `consumed' right away, one solution is to define now a
# second macro, `AU_OLD-NAME', and to install a hook than binds OLD-NAME
# to AU_OLD-NAME.  Then, autoupdate.m4 just need to run the hooks.  By
# the way, the same method was used in autoheader.
#
#
# # Third implementation: m4 namespaces by m4sugar
# # ==============================================
#
# Actually, this implementation was just a clean up of the previous
# implementation: instead of defining hooks by hand, m4sugar was equipped
# with `namespaces'.  What are they?
#
# Sometimes we want to disable some *set* of macros, and restore them
# later.  We provide support for this via namespaces.
#
# There are basically three characters playing this scene: defining a
# macro in a namespace, disabling a namespace, and restoring a namespace
# (i.e., all the definitions it holds).
#
# Technically, to define a MACRO in NAMESPACE means to define the macro
# named `NAMESPACE::MACRO' to the VALUE.  At the same time, we append
# `undefine(NAME)' in the macro named `m4_disable(NAMESPACE)', and
# similarly a binding of NAME to the value of `NAMESPACE::MACRO' in
# `m4_enable(NAMESPACE)'.  These mechanisms allow to bind the macro of
# NAMESPACE and to unbind them at will.
#
# Of course this implementation is really inefficient: m4 has to grow
# strings which can become quickly huge, which slows it significantly.
#
# In particular one should avoid as much as possible to use `define' for
# temporaries.  Now that `define' as quite a complex meaning, it is an
# expensive operations that should be limited to macros.  Use
# `m4_define' for temporaries.
#
# Private copies of the macros we used in entering / exiting the m4sugar
# namespace.  It is much more convenient than fighting with the renamed
# version of define etc.
#
#
#
# Those two implementations suffered from serious problems:
#
# - namespaces were really expensive, and incurred a major performance
#   loss on `autoconf' itself, not only `autoupdate'.  One solution
#   would have been the limit the use of namespaces to `autoupdate', but
#   that's again some complications on m4sugar, which really doesn't need
#   this.  So we wanted to get rid of the namespaces.
#
# - since the quotes were disabled, autoupdate was sometimes making
#   wrong guesses, for instance on:
#
#     foo([1, 2])
#
#   m4 saw 2 arguments: `[1'and `2]'.  A simple solution, somewhat
#   fragile, is to reestablish the quotes right before all the obsolete
#   macros, i.e., to use sed so that the previous text becomes
#
#     changequote([, ])foo([1, 2])
#
#   To this end, one wants to trace the definition of obsolete macros.
#
# It was there that the limitations of the namespace approach became
# painful: because it was a complex machinery playing a lot with the
# builtins of m4 (hence, quite fragile), tracing was almost impossible.
#
#
# So this approach was dropped.
#
#
# # The fourth implementation: two steps
# # ====================================
#
# If you drop the uses of namespaces, you no longer can compute the
# updated value, and replace the old call with it simultaneously.
#
# Obviously you will use m4 to compute the updated values, but you may
# use some other tool to achieve the replacement.  Personally, I trust
# nobody but m4 to parse m4, so below, m4 will perform the two tasks.
#
# How can m4 be used to replace *some* macros calls with newer values.
# Well, that's dead simple: m4 should learn the definitions of obsolete
# macros, forget its builtins, disable the quotes, and then run on the
# input file, which amounts to doing this:
#
#     divert(-1)dnl
#     changequote([, ])
#     define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
#     undefine([dnl])
#     undefine([m4_eval])
#     # Some more undefines...
#     changequote()
#     divert(0)dnl
#     dnl The Unbelievable Truth
#     changequote([, ])OLD(1, 2)
#     NEW([0, 0],
# 	  0)
#
# which will result in
#
#     dnl The Unbelievable Truth
#     NEW(1, 2, m4_eval(1 + 2))
#     NEW([0, 0],
# 	  0)
#
# Grpmh.  Two problems.  A minor problem: it would have been much better
# to have the `m4_eval' computed, and a major problem: you lost the
# quotation in the result.
#
# Let's address the big problem first.  One solution is to define any
# modern macro to rewrite its calls with the proper quotation, thanks to
# `$@'.  Again, tracing the `define's makes it possible to know which
# are these macros, so you input is:
#
#     divert(-1)dnl
#     changequote([, ])
#     define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
#     define([NEW], [[NEW($@)]changequote()])
#     undefine([dnl])
#     undefine([m4_eval])
#     # Some more undefines...
#     changequote()
#     divert(0)dnl
#     dnl The Unbelievable Truth
#     changequote([, ])OLD(1, 2)
#     changequote([, ])NEW([0, 0],
# 	  0)
#
# which results in
#
#     dnl The Unbelievable Truth
#     NEW([1, 2],[m4_eval(1 + 2)])
#     NEW([0, 0],[0])
#
# Our problem is solved, i.e., the first call to `NEW' is properly
# quoted, but introduced another problem: we changed the layout of the
# second calls, which can be a drama in the case of huge macro calls
# (think of `AC_TRY_RUN' for instance).  This example didn't show it,
# but we also introduced parens to macros which did not have some:
#
#     AC_INIT
#     => AC_INIT()
#
# No big deal for the semantics (unless the macro depends upon $#, which
# is bad), but the users would not be happy.
#
# Additionally, we introduced quotes that we not there before, which is
# OK in most cases, but could change the semantics of the file.
#
# Cruel dilemma: we do want the auto-quoting definition of `NEW' when
# evaluating `OLD', but we don't when we evaluate the second `NEW'.
# Back to namespaces?
#
# No.
#
#
# # Second step: replacement
# # ------------------------
#
# No, as announced above, we will work in two steps: in a first step we
# compute the updated values, and in a second step we replace them.  Our
# goal is something like this:
#
#     divert(-1)dnl
#     changequote([, ])
#     define([OLD], [NEW([1, 2], [3])changequote()])
#     undefine([dnl])
#     undefine([m4_eval])
#     # Some more undefines...
#     changequote()
#     divert(0)dnl
#     dnl The Unbelievable Truth
#     changequote([, ])OLD(1, 2)
#     NEW([0, 0],
# 	  0)
#
# i.e., the new value of `OLD' is precomputed using the auto-quoting
# definition of `NEW' and the m4 builtins.  We'll see how afterwards,
# let's finish with the replacement.
#
# Of course the solution above is wrong: if there were other calls to
# `OLD' with different values, we would smash them to the same value.
# But it is quite easy to generalize the scheme above:
#
#     divert(-1)dnl
#     changequote([, ])
#     define([OLD([1],[2])], [NEW([1, 2], [3])])
#     define([OLD], [defn([OLD($@)])changequote()])
#     undefine([dnl])
#     undefine([m4_eval])
#     # Some more undefines...
#     changequote()
#     divert(0)dnl
#     dnl The Unbelievable Truth
#     changequote([, ])OLD(1, 2)
#     NEW([0, 0],
# 	  0)
#
# i.e., for each call to obsolete macros, we build an array `call =>
# value', and use a macro to dispatch these values.  This results in:
#
#     dnl The Unbelievable Truth
#     NEW([1, 2], [3])
#     NEW([0, 0],
# 	  0)
#
# In French, we say `Youpi !', which you might roughly translate as
# `yipeee!'.
#
#
# # First step: computation
# # -----------------------
#
# Let's study the anatomy of the file, and name its sections:
#
# prologue
#     divert(-1)dnl
#     changequote([, ])
# values
#     define([OLD([1],[2])], [NEW([1, 2], [3])])
# dispatcher
#     define([OLD], [defn([OLD($@)])changequote()])
# disabler
#     undefine([dnl])
#     undefine([m4_eval])
#     # Some more undefines...
#     changequote()
#     divert(0)dnl
# input
#     dnl The Unbelievable Truth
#     changequote([, ])OLD(1, 2)
#     NEW([0, 0],
# 	  0)
#
#
# # Computing the `values' section
# # ..............................
#
# First we need to get the list of all the AU macro uses.  To this end,
# first get the list of all the AU macros names by tracing `AU_DEFUN' in
# the initialization of autoconf.  This list is computed in the file
# `au.txt' below.
#
# Then use this list to trace all the AU macro uses in the input.  The
# goal is obtain in the case of our example:
#
#     [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
#
# This is the file `values.in' below.
#
# We want to evaluate this with only the builtins (in fact m4sugar), the
# auto-quoting definitions of the new macros (`new.m4'), and the
# definition of the old macros (`old.m4').  Computing these last two
# files is easy: it's just a matter of using the right `--trace' option.
#
# So the content of `values.in' is:
#
#     include($autoconf_dir/m4sugar.m4)
#     m4_include(new.m4)
#     m4_include(old.m4)
#     divert(0)dnl
#     [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
#
# We run m4 on it, which yields:
#
#     define([OLD([1],[2])],@<<@NEW([1, 2], [3])@>>@)
#
# Transform `@<<@' and `@>>@' into quotes and we get
#
#     define([OLD([1],[2])],[NEW([1, 2], [3])])
#
# This is `values.m4'.
#
#
# # Computing the `dispatcher' section
# # ..................................
#
# The `prologue', and the `disabler' are simple and need no commenting.
#
# To compute the `dispatcher' (`dispatch.m4'), again, it is a simple
# matter of using the right `--trace'.
#
# Finally, the input is not exactly the input file, rather it is the
# input file with the added `changequote'.  To this end, we build
# `quote.sed'.
#
#
# # Putting it all together
# # .......................
#
# We build the file `input.m4' which contains:
#
#     divert(-1)dnl
#     changequote([, ])
#     include(values.m4)
#     include(dispatch.m4)
#     undefine([dnl])
#     undefine([eval])
#     # Some more undefines...
#     changequote()
#     divert(0)dnl
#     dnl The Unbelievable Truth
#     changequote([, ])OLD(1, 2)
#     NEW([0, 0],
# 	  0)
#
# And we just run m4 on it.  Et voila`, Monsieur !  Mais oui, mais oui.
#
# Well, there are a few additional technicalities.  For instance, we
# rely on `changequote', `ifelse' and `defn', but we don't want to
# interpret the changequotes of the user, so we simply use another name:
# `_au_changequote' etc.
#
#
# # Failure of the fourth approach
# # ------------------------------
#
# This approach is heavily based on traces, but then there is an obvious
# problem: non expanded code will never be seen/ In particular, the body
# of a `define' definition is not seen, so on the input
#
# 	  define([idem], [OLD(0, [$1])])
#
# autoupdate would never see the `OLD', and wouldn't have updated it.
# Worse yet, if `idem(0)' was used later, then autoupdate sees that
# `OLD' is used, computes the result for `OLD(0, 0)' and sets up a
# dispatcher for `OLD'.  Since there was no computed value for `OLD(0,
# [$1])', the dispatcher would have replaced with... nothinhg, leading
# to
#
# 	  define([idem], [])
#
# With some more thinking, you see that the two step approach is wrong,
# the namespace approach was much saner.
#
# But you learned a lot, in particular you realized that using traces
# can make it possible to simulate namespaces!
#
#
#
# # The fifth implementation: m4 namespaces by files
# # ================================================
#
# The fourth implementation demonstrated something unsurprising: you
# cannot precompute, i.e., the namespace approach was the right one.
# Still, we no longer want them, they're too expensive.  Let's have a
# look at the way it worked.
#
# When updating
#
#     dnl The Unbelievable Truth
#     OLD(1, 2)
#     NEW([0, 0], [0])
#
# you evaluate `input.m4':
#
#     divert(-1)
#     changequote([, ])
#     define([OLD],
#     [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
#     ...
#     m4_disable()
#     dnl The Unbelievable Truth
#     OLD(1, 2)
#     NEW([0, 0], [0])
#
# where `m4_disable' undefines the m4 and m4sugar, and disables the quotes
# and comments:
#
#     define([m4_disable],
#     [undefine([__file__])
#     ...
#     changecom(#)
#     changequote()])
#
# `m4_enable' does the converse: reestablish quotes and comments
# --easy--, reestablish m4sugar --easy: just load `m4sugar.m4' again-- and
# reenable the builtins.  This later task requires that you first save
# the builtins.  And BTW, the definition above of `m4_disable' cannot
# work: you undefined `changequote' before using it!  So you need to use
# your privates copies of the builtins.  Let's introduce three files for
# this:
#
#  `m4save.m4'
#    moves the m4 builtins into the `_au_' pseudo namespace
#  `unm4.m4'
#    undefines the builtins
#  `m4.m4'
#    restores them
#
# So `input.m4' is:
#
#     divert(-1)
#     changequote([, ])
#
#     include([m4save.m4])
#
#     # Import AU.
#     define([OLD],
#     [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
#
#     define([_au_enable],
#     [_au_changecom([#])
#     _au_include([m4.m4])
#     _au_include(m4sugar.m4)])
#
#     define([_au_disable],
#     [# Disable m4sugar.
#     # Disable the m4 builtins.
#     _au_include([unm4.m4])
#     # 1. Disable special characters.
#     _au_changequote()
#     _au_changecom()])
#
#     m4_disable()
#     dnl The Unbelievable Truth
#     OLD(1, 2)
#     NEW([0, 0], [0])
#
# Based on what we learned in the fourth implementation we know that we
# have to enable the quotes *before* any AU macro, and we know we need
# to build autoquoting versions of the AC macros.  But the autoquoting
# AC definitions must be disabled in the rest of the file, and enabled
# inside AU macros.
#
# Using `autoconf --trace' it is easy to build the files
#
#   `ac.m4'
#     define the autoquoting AC fake macros
#   `disable.m4'
#     undefine the m4sugar and AC autoquoting macros.
#   `au.m4'
#     definitions of the AU macros (such as `OLD' above).
#
# Now, `input.m4' is:
#
#     divert(-1)
#     changequote([, ])
#
#     include([m4save.m4])
#     # Import AU.
#     include([au.m4])
#
#     define([_au_enable],
#     [_au_changecom([#])
#     _au_include([m4.m4])
#     _au_include(m4sugar.m4)
#     _au_include(ac.m4)])
#
#     define([_au_disable],
#     [_au_include([disable.m4])
#     _au_include([unm4.m4])
#     # 1. Disable special characters.
#     _au_changequote()
#     _au_changecom()])
#
#     m4_disable()
#     dnl The Unbelievable Truth
#     _au_changequote([, ])OLD(1, 2)
#     NEW([0, 0], [0])
#
# Finally, version V is ready.
#
# Well... almost.
#
# There is a slight problem that remains: if an AU macro OUTTER includes
# an AU macro INNER, then _au_enable will be run when entering OUTTER
# and when entering INNER (not good, but not too bad yet).  But when
# getting out of INNER, _au_disable will disable everything while we
# were still in OUTTER.  Badaboom.
#
# Therefore _au_enable and _au_disable have to be written to work by
# pairs: each _au_enable pushdef's _au_enabled, and each _au_disable
# popdef's _au_enabled.  And of course _au_enable and _au_disable are
# effective when _au_enabled is *not* defined.
#
# Finally, version V' is ready.  And there is much rejoicing.  (And I
# have free time again.  I think.  Yeah, right.)