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Text File | 2006-04-25 | 33KB | 1,064 lines

#! /usr/bin/perl -w # -*- perl -*- # autoupdate - modernize an Autoconf file. # Copyright (C) 1994, 1999, 2000, 2001, 2002, 2003 # 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>. eval 'case $# in 0) exec /usr/bin/perl -S "$0";; *) exec /usr/bin/perl -S "$0" "$@";; esac' if 0; BEGIN { my $datadir = $ENV{'autom4te_perllibdir'} || '/usr/share/autoconf'; unshift @INC, $datadir; # Override SHELL. On DJGPP SHELL may not be set to a shell # that can handle redirection and quote arguments correctly, # e.g.: COMMAND.COM. For DJGPP always use the shell that configure # has detected. $ENV{'SHELL'} = '/bin/sh' if ($^O eq 'dos'); } use Autom4te::ChannelDefs; use Autom4te::Channels; use Autom4te::Configure_ac; use Autom4te::FileUtils; use Autom4te::General; use Autom4te::XFile; use File::Basename; use strict; # Lib files. my $autom4te = $ENV{'AUTOM4TE'} || '/usr/bin/autom4te-2.59'; my $autoconf = "$autom4te --language=autoconf"; # We need to find m4sugar. my @prepend_include; my @include = ('/usr/share/autoconf'); my $force = 0; # m4. my $m4 = $ENV{"M4"} || '/usr/bin/m4'; # $HELP # ----- $help = "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 -f, --force consider all files obsolete Library directories: -B, --prepend-include=DIR prepend directory DIR to search path -I, --include=DIR append directory DIR to search path Report bugs to <bug-autoconf\@gnu.org>. "; # $VERSION # -------- $version = "autoupdate (GNU Autoconf) 2.59 Written by David J. MacKenzie and Akim Demaille. Copyright (C) 2003 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. "; ## ---------- ## ## Routines. ## ## ---------- ## # parse_args () # ------------- # Process any command line arguments. sub parse_args () { my $srcdir; getopt ('I|include=s' => \@include, 'B|prepend-include=s' => \@prepend_include, 'f|force' => \$force); if (! @ARGV) { my $configure_ac = require_configure_ac; push @ARGV, $configure_ac; } } # ------------- # # M4 builtins. # # ------------- # my @m4_builtins; # &handle_m4_symbols () # --------------------- # Create the following $tmp files: # m4.m4 -- enable the m4 builtins. # unm4.m4 -- disable the m4 builtins. # savem4.m4 -- save the m4 builtins. sub handle_m4_macros () { # Get the list of builtins. xsystem ("echo dumpdef | $m4 2>$tmp/m4.defs >/dev/null"); my $m4_defs = new Autom4te::XFile "$tmp/m4.defs"; while ($_ = $m4_defs->getline) { push @m4_builtins, $1 if /^(\w+):/; } $m4_defs->close; # Output the files. my $m4_m4 = new Autom4te::XFile ">$tmp/m4.m4"; print $m4_m4 "# m4.m4 -- enable the m4 builtins.\n"; my $unm4_m4 = new Autom4te::XFile ">$tmp/unm4.m4"; print $unm4_m4 "# unm4.m4 -- disable the m4 builtins.\n"; print $unm4_m4 "# Because Autoconf, via M4sugar, redefines some of these\n"; print $unm4_m4 "# macros, and therefore since unac.m4 disables them,\n"; print $unm4_m4 "# disable only if defined.\n"; my $m4save_m4 = new Autom4te::XFile ">$tmp/m4save.m4"; print $m4save_m4 "# savem4.m4 -- save the m4 builtins.\n"; foreach (@m4_builtins) { print $m4save_m4 "define([_au_$_], defn([$_]))\n"; print $unm4_m4 "_au_ifdef([$_], [_au_undefine([$_])])\n"; print $m4_m4 "_au_define([$_], _au_defn([_au_$_]))\n"; } } # ----------------- # # Autoconf macros. # # ----------------- # # @AU_MACROS & AC_MACROS -- AU and AC macros and yet another useful comment. my (%ac_macros, %au_macros); # HANDLE_AUTOCONF_MACROS () # ------------------------- # @M4_BUILTINS -- M4 builtins and a useful comment. sub handle_autoconf_macros () { my $macros = new Autom4te::XFile ("$autoconf" . " --trace AU_DEFUN:'AU:\$f:\$1'" . " --trace define:'AC:\$f:\$1'" . " --melt /dev/null |"); while ($_ = $macros->getline) { chomp; my ($domain, $file, $macro) = /^(AC|AU):(.*):([^:]*)$/ or next; # ../lib/m4sugar/m4sugar.m4 -> m4sugar # ../lib/autoconf/general.m4 -> autoconf # aclocal.m4 -> aclocal my $set = basename (dirname ($file)); $set = 'aclocal' if $file eq 'aclocal.m4'; error "unknown set: $set: $_" unless $set =~ /^(m4sugar|aclocal|autoconf)$/; if ($domain eq "AC") { $ac_macros{$macro} = $set; } else { $au_macros{$macro} = $set; } } $macros->close; # Don't keep AU macros in @AC_MACROS. delete $ac_macros{$_} foreach (keys %au_macros); # Don't keep M4sugar macros which are redefined by Autoconf, # such as `builtin', `changequote' etc. See autoconf/autoconf.m4. delete $ac_macros{$_} foreach (@m4_builtins); error "no current Autoconf macros found" unless keys %ac_macros; error "no obsolete Autoconf macros found" unless 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"; } # ac.m4 -- autoquoting definitions of the AC macros (M4sugar excluded). # unac.m4 -- undefine the AC macros. my $ac_m4 = new Autom4te::XFile ">$tmp/ac.m4"; print $ac_m4 "# ac.m4 -- autoquoting definitions of the AC macros.\n"; my $unac_m4 = new Autom4te::XFile ">$tmp/unac.m4"; print $unac_m4 "# unac.m4 -- undefine the AC macros.\n"; foreach (sort grep { $ac_macros{$_} ne 'm4sugar' } keys %ac_macros) { print $ac_m4 "_au_define([$_], [[\$0(\$\@)]])\n"; print $unac_m4 "_au_undefine([$_])\n"; } } ## -------------- ## ## Main program. ## ## -------------- ## parse_args; $autoconf .= " --debug" if $debug; $autoconf .= " --force" if $force; $autoconf .= " --verbose" if $verbose; $autoconf .= join (' --include=', '', @include); $autoconf .= join (' --prepend-include=', '', @prepend_include); mktmpdir ('au'); handle_m4_macros; handle_autoconf_macros; # $au_changequote -- enable the quote `[', `]' right before any AU macro. my $au_changequote = 's/\b(' . join ('|', keys %au_macros) . ')\b/_au_changequote([,])$1/g'; # au.m4 -- definitions the AU macros. xsystem ("$autoconf --trace AU_DEFUN:'_au_defun(\@<:\@\$1\@:>\@, \@<:\@\$2\@:>\@)' --melt /dev/null " . ">$tmp/au.m4"); ## ------------------- ## ## 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([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([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). AU macros might use AU macros, which should # enable/disable only for the outer AU macros. # # `_au_enabled' is used to this end, determining 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([m4.m4]) _au_include([m4sugar/m4sugar.m4]) _au_include([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([unac.m4]) _au_include([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_divert(-1) # Disable m4: M4sugar and the AC autoquoting macros are not loaded yet, # hence invoking `_au_disable' is wrong. _au_include([unm4.m4]) # Disable special characters. _au_changequote() _au_changecom() _au_divert(0)_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 error "cannot open: $!"; open FILE, "<$file" or error "cannot open: $!"; print INPUT_M4 "$input_m4"; while (<FILE>) { eval $au_changequote; print INPUT_M4; } close FILE or error "cannot close $file: $!"; close INPUT_M4 or error "cannot close $tmp/input.m4: $!"; # Now ask m4 to perform the update. xsystem ("$m4 --include=$tmp" . join (' --include=', '', reverse (@prepend_include)) . join (' --include=', '', @include) . " $tmp/input.m4 >$tmp/updated"); update_file ("$tmp/updated", "$file" eq "$tmp/stdin" ? '-' : "$file"); } 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 # `Yippee!'. # # # # 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... nothing, 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 OUTER includes # an AU macro INNER, then _au_enable will be run when entering OUTER # 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 OUTER. 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.) ### Setup "GNU" style for perl-mode and cperl-mode. ## Local Variables: ## perl-indent-level: 2 ## perl-continued-statement-offset: 2 ## perl-continued-brace-offset: 0 ## perl-brace-offset: 0 ## perl-brace-imaginary-offset: 0 ## perl-label-offset: -2 ## cperl-indent-level: 2 ## cperl-brace-offset: 0 ## cperl-continued-brace-offset: 0 ## cperl-label-offset: -2 ## cperl-extra-newline-before-brace: t ## cperl-merge-trailing-else: nil ## cperl-continued-statement-offset: 2 ## End: