bin/autoupdate

   1 #! /bin/perl -w
   2 # -*- perl -*-
   3 # autoupdate - modernize an Autoconf file.
   4 # Copyright (C) 1994, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
   5
   6 # This program is free software; you can redistribute it and/or modify
   7 # it under the terms of the GNU General Public License as published by
   8 # the Free Software Foundation; either version 2, or (at your option)
   9 # any later version.
  10
  11 # This program is distributed in the hope that it will be useful,
  12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 # GNU General Public License for more details.
  15
  16 # You should have received a copy of the GNU General Public License
  17 # along with this program; if not, write to the Free Software
  18 # Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
  19 # 02111-1307, USA.
  20
  21 # Originally written by David MacKenzie <djm@gnu.ai.mit.edu>.
  22 # Rewritten by Akim Demaille <akim@freefriends.org>.
  23
  24 eval 'case $# in 0) exec /bin/perl -S "$0";; *) exec /bin/perl -S "$0" "$@";; esac'
  25     if 0;
  26
  27 BEGIN
  28 {
  29   my $perllibdir = $ENV{'autom4te_perllibdir'} || "/usr/share/autoconf";
  30   unshift @INC, "$perllibdir";
  31 }
  32
  33 use File::Basename;
  34 use Autom4te::General;
  35 use Autom4te::XFile;
  36 use strict;
  37
  38 # Lib files.
  39 my $autom4te = $ENV{'AUTOM4TE'} || '/usr/bin/autom4te';
  40 my $autoconf = "$autom4te --language=autoconf";
  41 # We need to find m4sugar.
  42 my @prepend_include;
  43 my @include = ('/usr/share/autoconf');
  44 my $force = 0;
  45 # m4.
  46 my $m4 = $ENV{"M4"} || "/bin/m4";
  47
  48
  49 # $HELP
  50 # -----
  51 $help = "Usage: $0 [OPTION] ...  [TEMPLATE-FILE...]
  52
  53 Update the TEMPLATE-FILE... if given, or `configure.ac' if present,
  54 or else `configure.in', to the syntax of the current version of
  55 Autoconf.  The original files are backed up.
  56
  57 Operation modes:
  58   -h, --help                 print this help, then exit
  59   -V, --version              print version number, then exit
  60   -v, --verbose              verbosely report processing
  61   -d, --debug                don't remove temporary files
  62   -f, --force                consider all files obsolete
  63
  64 Library directories:
  65   -B, --prepend-include=DIR  prepend directory DIR to search path
  66   -I, --include=DIR          append directory DIR to search path
  67
  68 Report bugs to <bug-autoconf\@gnu.org>.
  69 ";
  70
  71 # $VERSION
  72 # --------
  73 $version = "autoupdate (GNU Autoconf) 2.56
  74 Written by David J. MacKenzie and Akim Demaille.
  75
  76 Copyright 2002 Free Software Foundation, Inc.
  77 This is free software; see the source for copying conditions.  There is NO
  78 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  79 ";
  80
  81 ## ---------- ##
  82 ## Routines.  ##
  83 ## ---------- ##
  84
  85
  86 # parse_args ()
  87 # -------------
  88 # Process any command line arguments.
  89 sub parse_args ()
  90 {
  91   my $srcdir;
  92
  93   getopt ('I|include=s'         => \@include,
  94           'B|prepend-include=s' => \@prepend_include,
  95           'f|force'             => \$force);
  96
  97   if (! @ARGV)
  98     {
  99       my $configure_ac = find_configure_ac;
 100       error "no input file"
 101         unless $configure_ac;
 102       push @ARGV, $configure_ac;
 103     }
 104 }
 105
 106
 107 # ------------- #
 108 # M4 builtins.  #
 109 # ------------- #
 110
 111 my @m4_builtins;
 112
 113 # &handle_m4_symbols ()
 114 # ---------------------
 115 # Create the following $tmp files:
 116 # m4.m4 -- enable the m4 builtins.
 117 # unm4.m4 -- disable the m4 builtins.
 118 # savem4.m4 -- save the m4 builtins.
 119 sub handle_m4_macros ()
 120 {
 121   # Get the list of builtins.
 122   xsystem ("echo dumpdef | $m4 2>$tmp/m4.defs >/dev/null");
 123   my $m4_defs = new Autom4te::XFile "$tmp/m4.defs";
 124   while ($_ = $m4_defs->getline)
 125     {
 126       push @m4_builtins, $1
 127         if /^(\w+):/;
 128     }
 129   $m4_defs->close;
 130
 131   # Output the files.
 132   my $m4_m4 = new Autom4te::XFile ">$tmp/m4.m4";
 133   print $m4_m4 "# m4.m4 -- enable the m4 builtins.\n";
 134   my $unm4_m4 = new Autom4te::XFile ">$tmp/unm4.m4";
 135   print $unm4_m4 "# unm4.m4 -- disable the m4 builtins.\n";
 136   print $unm4_m4 "# Because Autoconf, via M4sugar, redefines some of these\n";
 137   print $unm4_m4 "# macros, and therefore since unac.m4 disables them,\n";
 138   print $unm4_m4 "# disable only if defined.\n";
 139   my $m4save_m4 = new Autom4te::XFile ">$tmp/m4save.m4";
 140   print $m4save_m4 "# savem4.m4 -- save the m4 builtins.\n";
 141   foreach (@m4_builtins)
 142     {
 143       print $m4save_m4 "define([_au_$_], defn([$_]))\n";
 144       print $unm4_m4   "_au_ifdef([$_], [_au_undefine([$_])])\n";
 145       print $m4_m4     "_au_define([$_], _au_defn([_au_$_]))\n";
 146     }
 147 }
 148
 149
 150
 151 # ----------------- #
 152 # Autoconf macros.  #
 153 # ----------------- #
 154
 155
 156 # @AU_MACROS & AC_MACROS -- AU and AC macros and yet another useful comment.
 157 my (%ac_macros, %au_macros);
 158
 159
 160 # HANDLE_AUTOCONF_MACROS ()
 161 # -------------------------
 162 # @M4_BUILTINS -- M4 builtins and a useful comment.
 163 sub handle_autoconf_macros ()
 164 {
 165   my $macros = new Autom4te::XFile ("$autoconf"
 166                              . " --trace AU_DEFUN:'AU:\$f:\$1'"
 167                              . " --trace define:'AC:\$f:\$1'"
 168                              . " --melt /dev/null |");
 169   while ($_ = $macros->getline)
 170     {
 171       chomp;
 172       my ($domain, $file, $macro) = /^(AC|AU):(.*):([^:]*)$/ or next;
 173       # ../lib/m4sugar/m4sugar.m4  -> m4sugar
 174       # ../lib/autoconf/general.m4 -> autoconf
 175       # aclocal.m4 -> aclocal
 176       my $set = basename (dirname ($file));
 177       $set = 'aclocal' if $file eq 'aclocal.m4';
 178       error "unknown set: $set: $_"
 179         unless $set =~ /^(m4sugar|aclocal|autoconf)$/;
 180       if ($domain eq "AC")
 181         {
 182           $ac_macros{$macro} = $set;
 183         }
 184       else
 185         {
 186           $au_macros{$macro} = $set;
 187         }
 188     }
 189   $macros->close;
 190
 191   # Don't keep AU macros in @AC_MACROS.
 192   delete $ac_macros{$_}
 193     foreach (keys %au_macros);
 194   # Don't keep M4sugar macros which are redefined by Autoconf,
 195   # such as `builtin', `changequote' etc.  See autoconf/autoconf.m4.
 196   delete $ac_macros{$_}
 197     foreach (@m4_builtins);
 198   error "no current Autoconf macros found"
 199     unless keys %ac_macros;
 200   error "no obsolete Autoconf macros found"
 201     unless keys %au_macros;
 202
 203   if ($debug)
 204     {
 205       print STDERR "Current Autoconf macros:\n";
 206       print STDERR join (' ', sort keys %ac_macros) . "\n\n";
 207       print STDERR "Obsolete Autoconf macros:\n";
 208       print STDERR join (' ', sort keys %au_macros) . "\n\n";
 209     }
 210
 211   # ac.m4 -- autoquoting definitions of the AC macros (M4sugar excluded).
 212   # unac.m4 -- undefine the AC macros.
 213   my $ac_m4 = new Autom4te::XFile ">$tmp/ac.m4";
 214   print $ac_m4 "# ac.m4 -- autoquoting definitions of the AC macros.\n";
 215   my $unac_m4 = new Autom4te::XFile ">$tmp/unac.m4";
 216   print $unac_m4 "# unac.m4 -- undefine the AC macros.\n";
 217   foreach (sort grep { $ac_macros{$_} ne 'm4sugar' } keys %ac_macros)
 218     {
 219       print $ac_m4   "_au_define([$_], [[\$0(\$\@)]])\n";
 220       print $unac_m4 "_au_undefine([$_])\n";
 221     }
 222 }
 223
 224
 225 ## -------------- ##
 226 ## Main program.  ##
 227 ## -------------- ##
 228
 229 parse_args;
 230 $autoconf .= " --debug" if $debug;
 231 $autoconf .= " --force" if $force;
 232 $autoconf .= " --verbose" if $verbose;
 233 $autoconf .= join (' --include=', '', @include);
 234 $autoconf .= join (' --prepend-include=', '', @prepend_include);
 235
 236 mktmpdir ('au');
 237 handle_m4_macros;
 238 handle_autoconf_macros;
 239
 240 # $au_changequote -- enable the quote `[', `]' right before any AU macro.
 241 my $au_changequote =
 242   's/\b(' . join ('|', keys %au_macros) . ')\b/_au_changequote([,])$1/g';
 243
 244 # au.m4 -- definitions the AU macros.
 245 xsystem ("$autoconf --trace AU_DEFUN:'_au_defun(\@<:\@\$1\@:>\@,
 246 \@<:\@\$2\@:>\@)' --melt /dev/null "
 247         . ">$tmp/au.m4");
 248
 249
 250
 251 ## ------------------- ##
 252 ## Process the files.  ##
 253 ## ------------------- ##
 254
 255 foreach my $file (@ARGV)
 256   {
 257     my $filename = $file;
 258     # We need an actual file.
 259     if ($file eq '-')
 260       {
 261         $file = "$tmp/stdin";
 262         system "cat >$file";
 263       }
 264     elsif (! -r "$file")
 265       {
 266         die "$me: $file: No such file or directory";
 267       }
 268
 269     # input.m4 -- m4 program to produce the updated file.
 270     # Load the values, the dispatcher, neutralize m4, and the prepared
 271     # input file.
 272     my $input_m4 = <<\EOF;
 273       divert(-1)                                            -*- Autoconf -*-
 274       changequote([, ])
 275
 276       # Move all the builtins into the `_au_' pseudo namespace
 277       include([m4save.m4])
 278
 279       # _au_defun(NAME, BODY)
 280       # ---------------------
 281       # Define NAME to BODY, plus AU activation/deactivation.
 282       _au_define([_au_defun],
 283       [_au_define([$1],
 284       [_au_enable()dnl
 285       $2[]dnl
 286       _au_disable()])])
 287
 288       # Import the definition of the obsolete macros.
 289       _au_include([au.m4])
 290
 291
 292       ## ------------------------ ##
 293       ## _au_enable/_au_disable.  ##
 294       ## ------------------------ ##
 295
 296       # They work by pair: each time an AU macro is activated, it runs
 297       # _au_enable, and at its end its runs _au_disable (see _au_defun
 298       # above).  AU macros might use AU macros, which should
 299       # enable/disable only for the outer AU macros.
 300       #
 301       # `_au_enabled' is used to this end, determining whether we really
 302       # enable/disable.
 303
 304
 305       # __au_enable
 306       # -----------
 307       # Reenable the builtins, and m4sugar.
 308       _au_define([__au_enable],
 309       [_au_divert(-1)
 310       # Enable special characters.
 311       _au_changecom([#])
 312
 313       # Enable the m4 builtins, m4sugar and the autoquoting AC macros.
 314       _au_include([m4.m4])
 315       _au_include([m4sugar/m4sugar.m4])
 316       _au_include([ac.m4])
 317
 318       _au_divert(0)])
 319
 320       # _au_enable
 321       # ----------
 322       # Called at the beginning of all the obsolete macros.  Reenable the
 323       # builtins, and m4sugar if needed.
 324       _au_define([_au_enable],
 325       [_au_ifdef([_au_enabled],
 326                  [],
 327                  [__au_enable()])_au_dnl
 328       _au_pushdef([_au_enabled])])
 329
 330
 331       # __au_disable
 332       # ------------
 333       # Disable the builtins, and m4sugar.
 334       _au_define([__au_disable],
 335       [_au_divert(-1)
 336       # Disable m4sugar, the AC autoquoting macros, and m4.
 337       _au_include([unac.m4])
 338       _au_include([unm4.m4])
 339
 340       # Disable special characters.
 341       _au_changequote()
 342       _au_changecom()
 343
 344       _au_divert(0)])
 345
 346       # _au_disable
 347       # -----------
 348       # Called at the end of all the obsolete macros.  Disable the
 349       # builtins, and m4sugar if needed..
 350       _au_define([_au_disable],
 351       [_au_popdef([_au_enabled])_au_dnl
 352       _au_ifdef([_au_enabled],
 353                 [],
 354                 [__au_disable()])])
 355
 356
 357       ## ------------------------------- ##
 358       ## Disable, and process the file.  ##
 359       ## ------------------------------- ##
 360       _au_divert(-1)
 361       # Disable m4: M4sugar and the AC autoquoting macros are not loaded yet,
 362       # hence invoking `_au_disable' is wrong.
 363       _au_include([unm4.m4])
 364
 365       # Disable special characters.
 366       _au_changequote()
 367       _au_changecom()
 368
 369       _au_divert(0)_au_dnl
 370 EOF
 371
 372     $input_m4 =~ s/^      //mg;
 373
 374     # prepared input -- input, but reenables the quote before each AU macro.
 375     open INPUT_M4, ">$tmp/input.m4"
 376        or error "cannot open: $!";
 377     open FILE, "<$file"
 378        or error "cannot open: $!";
 379     print INPUT_M4 "$input_m4";
 380     while (<FILE>)
 381        {
 382          eval $au_changequote;
 383          print INPUT_M4;
 384        }
 385     close FILE
 386        or error "cannot close $file: $!";
 387     close INPUT_M4
 388        or error "cannot close $tmp/input.m4: $!";
 389
 390     # Now ask m4 to perform the update.
 391     xsystem ("$m4 --include=$tmp"
 392              . join (' --include=', '', reverse (@prepend_include))
 393              . join (' --include=', '', @include)
 394              . " $tmp/input.m4 >$tmp/updated");
 395     update_file ("$tmp/updated",
 396                  "$file" eq "$tmp/stdin" ? '-' : "$file");
 397   }
 398 exit 0;
 399
 400
 401 #                 ## ---------------------------- ##
 402 #                 ## How `autoupdate' functions.  ##
 403 #                 ## ---------------------------- ##
 404 #
 405 # The task of `autoupdate' is not trivial: the biggest difficulty being
 406 # that you must limit the changes to the parts that really need to be
 407 # updated.  Finding a satisfying implementation proved to be quite hard,
 408 # as this is the fourth implementation of `autoupdate'.
 409 #
 410 # Below, we will use a simple example of obsolete macro:
 411 #
 412 #     AU_DEFUN([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))])
 413 #     AC_DEFUN([NEW], [echo "sum($1) = $2"])
 414 #
 415 # the input file contains
 416 #
 417 #     dnl The Unbelievable Truth
 418 #     OLD(1, 2)
 419 #     NEW([0, 0], [0])
 420 #
 421 # Of course the expected output is
 422 #
 423 #     dnl The Unbelievable Truth
 424 #     NEW([1, 2], [3])
 425 #     NEW([0, 0], [0])
 426 #
 427 #
 428 # # First implementation: sed
 429 # # =========================
 430 #
 431 # The first implementation was only able to change the name of obsolete
 432 # macros.
 433 #
 434 # The file `acoldnames.m4' defined the old names based on the new names.
 435 # It was simple then to produce a sed script such as:
 436 #
 437 #     s/OLD/NEW/g
 438 #
 439 # Updating merely consisted in running this script on the file to
 440 # update.
 441 #
 442 # This scheme suffers an obvious limitation: that `autoupdate' was
 443 # unable to cope with new macros that just swap some of its arguments
 444 # compared to the old macro.  Fortunately, that was enough to upgrade
 445 # from Autoconf 1 to Autoconf 2.  (But I have no idea whether the
 446 # changes in Autoconf 2 were precisely limited by this constraint.)
 447 #
 448 #
 449 # # Second implementation: hooks
 450 # # ============================
 451 #
 452 # The version 2.15 of Autoconf brought a vast number of changes compared
 453 # to 2.13, so a solution was needed.  One could think to extend the
 454 # `sed' scripts with specialized code for complex macros.  But this
 455 # approach is of course full of flaws:
 456 #
 457 # a. the Autoconf maintainers have to write these snippets, which we
 458 #    just don't want to,
 459 #
 460 # b. I really don't think you'll ever manage to handle the quoting of
 461 #    m4 from sed.
 462 #
 463 # To satisfy a., let's remark that the code which implements the old
 464 # features in term of the new feature is exactly the code which should
 465 # replace the old code.
 466 #
 467 # To answer point b, as usual in the history of Autoconf, the answer, at
 468 # least on the paper, is simple: m4 is the best tool to parse m4, so
 469 # let's use m4.
 470 #
 471 # Therefore the specification is:
 472 #
 473 #     I want to be able to tell Autoconf, well, m4, that the macro I
 474 #     am currently defining is an obsolete macro (so that the user is
 475 #     warned), which code is the code to use when running autoconf,
 476 #     but that the very same code has to be used when running
 477 #     autoupdate.  To summarize, the interface I want is
 478 #     `AU_DEFUN(OLD-NAME, NEW-CODE)'.
 479 #
 480 #
 481 # Now for the technical details.
 482 #
 483 # When running autoconf, except for the warning, AU_DEFUN is basically
 484 # AC_DEFUN.
 485 #
 486 # When running autoupdate, we want *only* OLD-NAMEs to be expanded.
 487 # This obviously means that acgeneral.m4 and acspecific.m4 must not be
 488 # loaded.  Nonetheless, because we want to use a rich set of m4
 489 # features, m4sugar.m4 is needed.  Please note that the fact that
 490 # Autoconf's macros are not loaded is positive on two points:
 491 #
 492 # - we do get an updated `configure.ac', not a `configure'!
 493 #
 494 # - the old macros are replaced by *calls* to the new-macros, not the
 495 #   body of the new macros, since their body is not defined!!!
 496 #   (Whoa, that's really beautiful!).
 497 #
 498 # Additionally we need to disable the quotes when reading the input for
 499 # two reasons: first because otherwise `m4' will swallow the quotes of
 500 # other macros:
 501 #
 502 #     NEW([1, 2], 3)
 503 #     => NEW(1, 2, 3)
 504 #
 505 # and second, because we want to update the macro calls which are
 506 # quoted, i.e., we want
 507 #
 508 #     FOO([OLD(1, 2)])
 509 #     => FOO([NEW([1, 2], [3])])
 510 #
 511 # If we don't disable the quotes, only the macros called at the top
 512 # level would be updated.
 513 #
 514 # So, let's disable the quotes.
 515 #
 516 # Well, not quite: m4sugar.m4 still needs to use quotes for some macros.
 517 # Well, in this case, when running in autoupdate code, each macro first
 518 # reestablishes the quotes, expands itself, and disables the quotes.
 519 #
 520 # Thinking a bit more, you realize that in fact, people may use `define'
 521 # `ifelse' etc. in their files, and you certainly don't want to process
 522 # them.  Another example is `dnl': you don't want to remove the
 523 # comments.  You then realize you don't want exactly to import m4sugar:
 524 # you want to specify when it is enabled (macros active), and disabled.
 525 # m4sugar provides m4_disable/m4_enable to this end.
 526 #
 527 # You're getting close to it.  Now remains one task: how to handle
 528 # twofold definitions?
 529 #
 530 # Remember that the same AU_DEFUN must be understood in two different
 531 # ways, the AC way, and the AU way.
 532 #
 533 # One first solution is to check whether acgeneral.m4 was loaded.  But
 534 # that's definitely not cute.  Another is simply to install `hooks',
 535 # that is to say, to keep in some place m4 knows, late `define' to be
 536 # triggered *only* in AU mode.
 537 #
 538 # You first think to design AU_DEFUN like this:
 539 #
 540 # 1. AC_DEFUN(OLD-NAME,
 541 #             [Warn the user OLD-NAME is obsolete.
 542 #              NEW-CODE])
 543 #
 544 # 2. Store for late AU binding([define(OLD_NAME,
 545 #                               [Reestablish the quotes.
 546 #                                NEW-CODE
 547 #                                Disable the quotes.])])
 548 #
 549 # but this will not work: NEW-CODE has probably $1, $2 etc. and these
 550 # guys will be replaced with the argument of `Store for late AU binding'
 551 # when you call it.
 552 #
 553 # I don't think there is a means to avoid this using this technology
 554 # (remember that $1 etc. are *always* expanded in m4).  You may also try
 555 # to replace them with $[1] to preserve them for a later evaluation, but
 556 # if `Store for late AU binding' is properly written, it will remain
 557 # quoted till the end...
 558 #
 559 # You have to change technology.  Since the problem is that `$1'
 560 # etc. should be `consumed' right away, one solution is to define now a
 561 # second macro, `AU_OLD-NAME', and to install a hook than binds OLD-NAME
 562 # to AU_OLD-NAME.  Then, autoupdate.m4 just need to run the hooks.  By
 563 # the way, the same method was used in autoheader.
 564 #
 565 #
 566 # # Third implementation: m4 namespaces by m4sugar
 567 # # ==============================================
 568 #
 569 # Actually, this implementation was just a clean up of the previous
 570 # implementation: instead of defining hooks by hand, m4sugar was equipped
 571 # with `namespaces'.  What are they?
 572 #
 573 # Sometimes we want to disable some *set* of macros, and restore them
 574 # later.  We provide support for this via namespaces.
 575 #
 576 # There are basically three characters playing this scene: defining a
 577 # macro in a namespace, disabling a namespace, and restoring a namespace
 578 # (i.e., all the definitions it holds).
 579 #
 580 # Technically, to define a MACRO in NAMESPACE means to define the macro
 581 # named `NAMESPACE::MACRO' to the VALUE.  At the same time, we append
 582 # `undefine(NAME)' in the macro named `m4_disable(NAMESPACE)', and
 583 # similarly a binding of NAME to the value of `NAMESPACE::MACRO' in
 584 # `m4_enable(NAMESPACE)'.  These mechanisms allow to bind the macro of
 585 # NAMESPACE and to unbind them at will.
 586 #
 587 # Of course this implementation is really inefficient: m4 has to grow
 588 # strings which can become quickly huge, which slows it significantly.
 589 #
 590 # In particular one should avoid as much as possible to use `define' for
 591 # temporaries.  Now that `define' as quite a complex meaning, it is an
 592 # expensive operations that should be limited to macros.  Use
 593 # `m4_define' for temporaries.
 594 #
 595 # Private copies of the macros we used in entering / exiting the m4sugar
 596 # namespace.  It is much more convenient than fighting with the renamed
 597 # version of define etc.
 598 #
 599 #
 600 #
 601 # Those two implementations suffered from serious problems:
 602 #
 603 # - namespaces were really expensive, and incurred a major performance
 604 #   loss on `autoconf' itself, not only `autoupdate'.  One solution
 605 #   would have been the limit the use of namespaces to `autoupdate', but
 606 #   that's again some complications on m4sugar, which really doesn't need
 607 #   this.  So we wanted to get rid of the namespaces.
 608 #
 609 # - since the quotes were disabled, autoupdate was sometimes making
 610 #   wrong guesses, for instance on:
 611 #
 612 #     foo([1, 2])
 613 #
 614 #   m4 saw 2 arguments: `[1'and `2]'.  A simple solution, somewhat
 615 #   fragile, is to reestablish the quotes right before all the obsolete
 616 #   macros, i.e., to use sed so that the previous text becomes
 617 #
 618 #     changequote([, ])foo([1, 2])
 619 #
 620 #   To this end, one wants to trace the definition of obsolete macros.
 621 #
 622 # It was there that the limitations of the namespace approach became
 623 # painful: because it was a complex machinery playing a lot with the
 624 # builtins of m4 (hence, quite fragile), tracing was almost impossible.
 625 #
 626 #
 627 # So this approach was dropped.
 628 #
 629 #
 630 # # The fourth implementation: two steps
 631 # # ====================================
 632 #
 633 # If you drop the uses of namespaces, you no longer can compute the
 634 # updated value, and replace the old call with it simultaneously.
 635 #
 636 # Obviously you will use m4 to compute the updated values, but you may
 637 # use some other tool to achieve the replacement.  Personally, I trust
 638 # nobody but m4 to parse m4, so below, m4 will perform the two tasks.
 639 #
 640 # How can m4 be used to replace *some* macros calls with newer values.
 641 # Well, that's dead simple: m4 should learn the definitions of obsolete
 642 # macros, forget its builtins, disable the quotes, and then run on the
 643 # input file, which amounts to doing this:
 644 #
 645 #     divert(-1)dnl
 646 #     changequote([, ])
 647 #     define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
 648 #     undefine([dnl])
 649 #     undefine([m4_eval])
 650 #     # Some more undefines...
 651 #     changequote()
 652 #     divert(0)dnl
 653 #     dnl The Unbelievable Truth
 654 #     changequote([, ])OLD(1, 2)
 655 #     NEW([0, 0],
 656 #         0)
 657 #
 658 # which will result in
 659 #
 660 #     dnl The Unbelievable Truth
 661 #     NEW(1, 2, m4_eval(1 + 2))
 662 #     NEW([0, 0],
 663 #         0)
 664 #
 665 # Grpmh.  Two problems.  A minor problem: it would have been much better
 666 # to have the `m4_eval' computed, and a major problem: you lost the
 667 # quotation in the result.
 668 #
 669 # Let's address the big problem first.  One solution is to define any
 670 # modern macro to rewrite its calls with the proper quotation, thanks to
 671 # `$@'.  Again, tracing the `define's makes it possible to know which
 672 # are these macros, so you input is:
 673 #
 674 #     divert(-1)dnl
 675 #     changequote([, ])
 676 #     define([OLD], [NEW([$1, $2], m4_eval([$1 + $2]))changequote()])
 677 #     define([NEW], [[NEW($@)]changequote()])
 678 #     undefine([dnl])
 679 #     undefine([m4_eval])
 680 #     # Some more undefines...
 681 #     changequote()
 682 #     divert(0)dnl
 683 #     dnl The Unbelievable Truth
 684 #     changequote([, ])OLD(1, 2)
 685 #     changequote([, ])NEW([0, 0],
 686 #         0)
 687 #
 688 # which results in
 689 #
 690 #     dnl The Unbelievable Truth
 691 #     NEW([1, 2],[m4_eval(1 + 2)])
 692 #     NEW([0, 0],[0])
 693 #
 694 # Our problem is solved, i.e., the first call to `NEW' is properly
 695 # quoted, but introduced another problem: we changed the layout of the
 696 # second calls, which can be a drama in the case of huge macro calls
 697 # (think of `AC_TRY_RUN' for instance).  This example didn't show it,
 698 # but we also introduced parens to macros which did not have some:
 699 #
 700 #     AC_INIT
 701 #     => AC_INIT()
 702 #
 703 # No big deal for the semantics (unless the macro depends upon $#, which
 704 # is bad), but the users would not be happy.
 705 #
 706 # Additionally, we introduced quotes that we not there before, which is
 707 # OK in most cases, but could change the semantics of the file.
 708 #
 709 # Cruel dilemma: we do want the auto-quoting definition of `NEW' when
 710 # evaluating `OLD', but we don't when we evaluate the second `NEW'.
 711 # Back to namespaces?
 712 #
 713 # No.
 714 #
 715 #
 716 # # Second step: replacement
 717 # # ------------------------
 718 #
 719 # No, as announced above, we will work in two steps: in a first step we
 720 # compute the updated values, and in a second step we replace them.  Our
 721 # goal is something like this:
 722 #
 723 #     divert(-1)dnl
 724 #     changequote([, ])
 725 #     define([OLD], [NEW([1, 2], [3])changequote()])
 726 #     undefine([dnl])
 727 #     undefine([m4_eval])
 728 #     # Some more undefines...
 729 #     changequote()
 730 #     divert(0)dnl
 731 #     dnl The Unbelievable Truth
 732 #     changequote([, ])OLD(1, 2)
 733 #     NEW([0, 0],
 734 #         0)
 735 #
 736 # i.e., the new value of `OLD' is precomputed using the auto-quoting
 737 # definition of `NEW' and the m4 builtins.  We'll see how afterwards,
 738 # let's finish with the replacement.
 739 #
 740 # Of course the solution above is wrong: if there were other calls to
 741 # `OLD' with different values, we would smash them to the same value.
 742 # But it is quite easy to generalize the scheme above:
 743 #
 744 #     divert(-1)dnl
 745 #     changequote([, ])
 746 #     define([OLD([1],[2])], [NEW([1, 2], [3])])
 747 #     define([OLD], [defn([OLD($@)])changequote()])
 748 #     undefine([dnl])
 749 #     undefine([m4_eval])
 750 #     # Some more undefines...
 751 #     changequote()
 752 #     divert(0)dnl
 753 #     dnl The Unbelievable Truth
 754 #     changequote([, ])OLD(1, 2)
 755 #     NEW([0, 0],
 756 #         0)
 757 #
 758 # i.e., for each call to obsolete macros, we build an array `call =>
 759 # value', and use a macro to dispatch these values.  This results in:
 760 #
 761 #     dnl The Unbelievable Truth
 762 #     NEW([1, 2], [3])
 763 #     NEW([0, 0],
 764 #         0)
 765 #
 766 # In French, we say `Youpi !', which you might roughly translate as
 767 # `Yippee!'.
 768 #
 769 #
 770 # # First step: computation
 771 # # -----------------------
 772 #
 773 # Let's study the anatomy of the file, and name its sections:
 774 #
 775 # prologue
 776 #     divert(-1)dnl
 777 #     changequote([, ])
 778 # values
 779 #     define([OLD([1],[2])], [NEW([1, 2], [3])])
 780 # dispatcher
 781 #     define([OLD], [defn([OLD($@)])changequote()])
 782 # disabler
 783 #     undefine([dnl])
 784 #     undefine([m4_eval])
 785 #     # Some more undefines...
 786 #     changequote()
 787 #     divert(0)dnl
 788 # input
 789 #     dnl The Unbelievable Truth
 790 #     changequote([, ])OLD(1, 2)
 791 #     NEW([0, 0],
 792 #         0)
 793 #
 794 #
 795 # # Computing the `values' section
 796 # # ..............................
 797 #
 798 # First we need to get the list of all the AU macro uses.  To this end,
 799 # first get the list of all the AU macros names by tracing `AU_DEFUN' in
 800 # the initialization of autoconf.  This list is computed in the file
 801 # `au.txt' below.
 802 #
 803 # Then use this list to trace all the AU macro uses in the input.  The
 804 # goal is obtain in the case of our example:
 805 #
 806 #     [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
 807 #
 808 # This is the file `values.in' below.
 809 #
 810 # We want to evaluate this with only the builtins (in fact m4sugar), the
 811 # auto-quoting definitions of the new macros (`new.m4'), and the
 812 # definition of the old macros (`old.m4').  Computing these last two
 813 # files is easy: it's just a matter of using the right `--trace' option.
 814 #
 815 # So the content of `values.in' is:
 816 #
 817 #     include($autoconf_dir/m4sugar.m4)
 818 #     m4_include(new.m4)
 819 #     m4_include(old.m4)
 820 #     divert(0)dnl
 821 #     [define([OLD([1],[2])],]@<<@OLD([1],[2])@>>@[)]
 822 #
 823 # We run m4 on it, which yields:
 824 #
 825 #     define([OLD([1],[2])],@<<@NEW([1, 2], [3])@>>@)
 826 #
 827 # Transform `@<<@' and `@>>@' into quotes and we get
 828 #
 829 #     define([OLD([1],[2])],[NEW([1, 2], [3])])
 830 #
 831 # This is `values.m4'.
 832 #
 833 #
 834 # # Computing the `dispatcher' section
 835 # # ..................................
 836 #
 837 # The `prologue', and the `disabler' are simple and need no commenting.
 838 #
 839 # To compute the `dispatcher' (`dispatch.m4'), again, it is a simple
 840 # matter of using the right `--trace'.
 841 #
 842 # Finally, the input is not exactly the input file, rather it is the
 843 # input file with the added `changequote'.  To this end, we build
 844 # `quote.sed'.
 845 #
 846 #
 847 # # Putting it all together
 848 # # .......................
 849 #
 850 # We build the file `input.m4' which contains:
 851 #
 852 #     divert(-1)dnl
 853 #     changequote([, ])
 854 #     include(values.m4)
 855 #     include(dispatch.m4)
 856 #     undefine([dnl])
 857 #     undefine([eval])
 858 #     # Some more undefines...
 859 #     changequote()
 860 #     divert(0)dnl
 861 #     dnl The Unbelievable Truth
 862 #     changequote([, ])OLD(1, 2)
 863 #     NEW([0, 0],
 864 #         0)
 865 #
 866 # And we just run m4 on it.  Et voila`, Monsieur !  Mais oui, mais oui.
 867 #
 868 # Well, there are a few additional technicalities.  For instance, we
 869 # rely on `changequote', `ifelse' and `defn', but we don't want to
 870 # interpret the changequotes of the user, so we simply use another name:
 871 # `_au_changequote' etc.
 872 #
 873 #
 874 # # Failure of the fourth approach
 875 # # ------------------------------
 876 #
 877 # This approach is heavily based on traces, but then there is an obvious
 878 # problem: non expanded code will never be seen/ In particular, the body
 879 # of a `define' definition is not seen, so on the input
 880 #
 881 #         define([idem], [OLD(0, [$1])])
 882 #
 883 # autoupdate would never see the `OLD', and wouldn't have updated it.
 884 # Worse yet, if `idem(0)' was used later, then autoupdate sees that
 885 # `OLD' is used, computes the result for `OLD(0, 0)' and sets up a
 886 # dispatcher for `OLD'.  Since there was no computed value for `OLD(0,
 887 # [$1])', the dispatcher would have replaced with... nothing, leading
 888 # to
 889 #
 890 #         define([idem], [])
 891 #
 892 # With some more thinking, you see that the two step approach is wrong,
 893 # the namespace approach was much saner.
 894 #
 895 # But you learned a lot, in particular you realized that using traces
 896 # can make it possible to simulate namespaces!
 897 #
 898 #
 899 #
 900 # # The fifth implementation: m4 namespaces by files
 901 # # ================================================
 902 #
 903 # The fourth implementation demonstrated something unsurprising: you
 904 # cannot precompute, i.e., the namespace approach was the right one.
 905 # Still, we no longer want them, they're too expensive.  Let's have a
 906 # look at the way it worked.
 907 #
 908 # When updating
 909 #
 910 #     dnl The Unbelievable Truth
 911 #     OLD(1, 2)
 912 #     NEW([0, 0], [0])
 913 #
 914 # you evaluate `input.m4':
 915 #
 916 #     divert(-1)
 917 #     changequote([, ])
 918 #     define([OLD],
 919 #     [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
 920 #     ...
 921 #     m4_disable()
 922 #     dnl The Unbelievable Truth
 923 #     OLD(1, 2)
 924 #     NEW([0, 0], [0])
 925 #
 926 # where `m4_disable' undefines the m4 and m4sugar, and disables the quotes
 927 # and comments:
 928 #
 929 #     define([m4_disable],
 930 #     [undefine([__file__])
 931 #     ...
 932 #     changecom(#)
 933 #     changequote()])
 934 #
 935 # `m4_enable' does the converse: reestablish quotes and comments
 936 # --easy--, reestablish m4sugar --easy: just load `m4sugar.m4' again-- and
 937 # reenable the builtins.  This later task requires that you first save
 938 # the builtins.  And BTW, the definition above of `m4_disable' cannot
 939 # work: you undefined `changequote' before using it!  So you need to use
 940 # your privates copies of the builtins.  Let's introduce three files for
 941 # this:
 942 #
 943 #  `m4save.m4'
 944 #    moves the m4 builtins into the `_au_' pseudo namespace
 945 #  `unm4.m4'
 946 #    undefines the builtins
 947 #  `m4.m4'
 948 #    restores them
 949 #
 950 # So `input.m4' is:
 951 #
 952 #     divert(-1)
 953 #     changequote([, ])
 954 #
 955 #     include([m4save.m4])
 956 #
 957 #     # Import AU.
 958 #     define([OLD],
 959 #     [m4_enable()NEW([$1, $2], m4_eval([$1 + $2]))m4_disable()])
 960 #
 961 #     define([_au_enable],
 962 #     [_au_changecom([#])
 963 #     _au_include([m4.m4])
 964 #     _au_include(m4sugar.m4)])
 965 #
 966 #     define([_au_disable],
 967 #     [# Disable m4sugar.
 968 #     # Disable the m4 builtins.
 969 #     _au_include([unm4.m4])
 970 #     # 1. Disable special characters.
 971 #     _au_changequote()
 972 #     _au_changecom()])
 973 #
 974 #     m4_disable()
 975 #     dnl The Unbelievable Truth
 976 #     OLD(1, 2)
 977 #     NEW([0, 0], [0])
 978 #
 979 # Based on what we learned in the fourth implementation we know that we
 980 # have to enable the quotes *before* any AU macro, and we know we need
 981 # to build autoquoting versions of the AC macros.  But the autoquoting
 982 # AC definitions must be disabled in the rest of the file, and enabled
 983 # inside AU macros.
 984 #
 985 # Using `autoconf --trace' it is easy to build the files
 986 #
 987 #   `ac.m4'
 988 #     define the autoquoting AC fake macros
 989 #   `disable.m4'
 990 #     undefine the m4sugar and AC autoquoting macros.
 991 #   `au.m4'
 992 #     definitions of the AU macros (such as `OLD' above).
 993 #
 994 # Now, `input.m4' is:
 995 #
 996 #     divert(-1)
 997 #     changequote([, ])
 998 #
 999 #     include([m4save.m4])
1000 #     # Import AU.
1001 #     include([au.m4])
1002 #
1003 #     define([_au_enable],
1004 #     [_au_changecom([#])
1005 #     _au_include([m4.m4])
1006 #     _au_include(m4sugar.m4)
1007 #     _au_include(ac.m4)])
1008 #
1009 #     define([_au_disable],
1010 #     [_au_include([disable.m4])
1011 #     _au_include([unm4.m4])
1012 #     # 1. Disable special characters.
1013 #     _au_changequote()
1014 #     _au_changecom()])
1015 #
1016 #     m4_disable()
1017 #     dnl The Unbelievable Truth
1018 #     _au_changequote([, ])OLD(1, 2)
1019 #     NEW([0, 0], [0])
1020 #
1021 # Finally, version V is ready.
1022 #
1023 # Well... almost.
1024 #
1025 # There is a slight problem that remains: if an AU macro OUTER includes
1026 # an AU macro INNER, then _au_enable will be run when entering OUTER
1027 # and when entering INNER (not good, but not too bad yet).  But when
1028 # getting out of INNER, _au_disable will disable everything while we
1029 # were still in OUTER.  Badaboom.
1030 #
1031 # Therefore _au_enable and _au_disable have to be written to work by
1032 # pairs: each _au_enable pushdef's _au_enabled, and each _au_disable
1033 # popdef's _au_enabled.  And of course _au_enable and _au_disable are
1034 # effective when _au_enabled is *not* defined.
1035 #
1036 # Finally, version V' is ready.  And there is much rejoicing.  (And I
1037 # have free time again.  I think.  Yeah, right.)
1038
1039 ### Setup "GNU" style for perl-mode and cperl-mode.
1040 ## Local Variables:
1041 ## perl-indent-level: 2
1042 ## perl-continued-statement-offset: 2
1043 ## perl-continued-brace-offset: 0
1044 ## perl-brace-offset: 0
1045 ## perl-brace-imaginary-offset: 0
1046 ## perl-label-offset: -2
1047 ## cperl-indent-level: 2
1048 ## cperl-brace-offset: 0
1049 ## cperl-continued-brace-offset: 0
1050 ## cperl-label-offset: -2
1051 ## cperl-extra-newline-before-brace: t
1052 ## cperl-merge-trailing-else: nil
1053 ## cperl-continued-statement-offset: 2
1054 ## End: