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kc3-lang/automake/lib/Automake/Rule.pm

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  • Author : Stefano Lattarini
    Date : 2012-02-23 20:25:26
    Hash : 3e887a13
    Message : pm: do not quote `like this', as per GCS recommendation This patch converts the internal perl modules used by automake and aclocal to the use of new quoting format 'like this' or "like this" rather than `like this'. * lib/Automake/ChannelDefs.pm, lib/Automake/Channels.pm, lib/Automake/Condition.pm, lib/Automake/Configure_ac.pm, lib/Automake/DisjConditions.pm, lib/Automake/FileUtils.pm, lib/Automake/General.pm, lib/Automake/Item.pm, lib/Automake/Rule.pm, lib/Automake/Getopt.pm, lib/Automake/Options.pm, lib/Automake/Struct.pm, lib/Automake/VarDef.pm, lib/Automake/Variable.pm, lib/Automake/Version.pm, lib/Automake/XFile.pm: Update and adjust quoting format throughout, in comments and diagnostic. Some minor related rewordings and reformatting since we are at it.

  • lib/Automake/Rule.pm
  • # Copyright (C) 2003-2012 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, see <http://www.gnu.org/licenses/>.
    
    package Automake::Rule;
    use strict;
    use Carp;
    
    use Automake::Item;
    use Automake::RuleDef;
    use Automake::ChannelDefs;
    use Automake::Channels;
    use Automake::Options;
    use Automake::Condition qw (TRUE FALSE);
    use Automake::DisjConditions;
    require Exporter;
    use vars '@ISA', '@EXPORT', '@EXPORT_OK';
    @ISA = qw/Automake::Item Exporter/;
    @EXPORT = qw (reset register_suffix_rule suffix_rules_count
    	      suffixes rules $suffix_rules $KNOWN_EXTENSIONS_PATTERN
    	      depend %dependencies %actions register_action
    	      accept_extensions
    	      reject_rule msg_rule msg_cond_rule err_rule err_cond_rule
    	      rule rrule ruledef rruledef);
    
    =head1 NAME
    
    Automake::Rule - support for rules definitions
    
    =head1 SYNOPSIS
    
      use Automake::Rule;
      use Automake::RuleDef;
    
    
    =head1 DESCRIPTION
    
    This package provides support for Makefile rule definitions.
    
    An C<Automake::Rule> is a rule name associated to possibly
    many conditional definitions.  These definitions are instances
    of C<Automake::RuleDef>.
    
    Therefore obtaining the value of a rule under a given
    condition involves two lookups.  One to look up the rule,
    and one to look up the conditional definition:
    
      my $rule = rule $name;
      if ($rule)
        {
          my $def = $rule->def ($cond);
          if ($def)
    	{
    	  return $def->location;
    	}
          ...
        }
      ...
    
    when it is known that the rule and the definition
    being looked up exist, the above can be simplified to
    
      return rule ($name)->def ($cond)->location; # do not write this.
    
    but is better written
    
      return rrule ($name)->rdef ($cond)->location;
    
    or even
    
      return rruledef ($name, $cond)->location;
    
    The I<r> variants of the C<rule>, C<def>, and C<ruledef> methods add
    an extra test to ensure that the lookup succeeded, and will diagnose
    failures as internal errors (with a message which is much more
    informative than Perl's warning about calling a method on a
    non-object).
    
    =head2 Global variables
    
    =over 4
    
    =cut
    
    my $_SUFFIX_RULE_PATTERN =
      '^(\.[a-zA-Z0-9_(){}$+@\-]+)(\.[a-zA-Z0-9_(){}$+@\-]+)' . "\$";
    
    # Suffixes found during a run.
    use vars '@_suffixes';
    
    # Same as $suffix_rules (declared below), but records only the
    # default rules supplied by the languages Automake supports.
    use vars '$_suffix_rules_default';
    
    =item C<%dependencies>
    
    Holds the dependencies of targets which dependencies are factored.
    Typically, C<.PHONY> will appear in plenty of F<*.am> files, but must
    be output once.  Arguably all pure dependencies could be subject to
    this factoring, but it is not unpleasant to have paragraphs in
    Makefile: keeping related stuff altogether.
    
    =cut
    
    use vars '%dependencies';
    
    =item <%actions>
    
    Holds the factored actions.  Tied to C<%dependencies>, i.e., filled
    only when keys exists in C<%dependencies>.
    
    =cut
    
    use vars '%actions';
    
    =item <$suffix_rules>
    
    This maps the source extension for all suffix rules seen to
    a C<hash> whose keys are the possible output extensions.
    
    Note that this is transitively closed by construction:
    if we have
          exists $suffix_rules{$ext1}{$ext2}
       && exists $suffix_rules{$ext2}{$ext3}
    then we also have
          exists $suffix_rules{$ext1}{$ext3}
    
    So it's easy to check whether C<.foo> can be transformed to
    C<.$(OBJEXT)> by checking whether
    C<$suffix_rules{'.foo'}{'.$(OBJEXT)'}> exists.  This will work even if
    transforming C<.foo> to C<.$(OBJEXT)> involves a chain of several
    suffix rules.
    
    The value of C<$suffix_rules{$ext1}{$ext2}> is a pair
    C<[ $next_sfx, $dist ]> where C<$next_sfx> is target suffix
    for the next rule to use to reach C<$ext2>, and C<$dist> the
    distance to C<$ext2'>.
    
    The content of this variable should be updated via the
    C<register_suffix_rule> function.
    
    =cut
    
    use vars '$suffix_rules';
    
    =item C<$KNOWN_EXTENSIONS_PATTERN>
    
    Pattern that matches all know input extensions (i.e. extensions used
    by the languages supported by Automake).  Using this pattern (instead
    of '\..*$') to match extensions allows Automake to support dot-less
    extensions.
    
    New extensions should be registered with C<accept_extensions>.
    
    =cut
    
    use vars qw ($KNOWN_EXTENSIONS_PATTERN @_known_extensions_list);
    $KNOWN_EXTENSIONS_PATTERN = "";
    @_known_extensions_list = ();
    
    =back
    
    =head2 Error reporting functions
    
    In these functions, C<$rule> can be either a rule name, or
    an instance of C<Automake::Rule>.
    
    =over 4
    
    =item C<err_rule ($rule, $message, [%options])>
    
    Uncategorized errors about rules.
    
    =cut
    
    sub err_rule ($$;%)
    {
      msg_rule ('error', @_);
    }
    
    =item C<err_cond_rule ($cond, $rule, $message, [%options])>
    
    Uncategorized errors about conditional rules.
    
    =cut
    
    sub err_cond_rule ($$$;%)
    {
      msg_cond_rule ('error', @_);
    }
    
    =item C<msg_cond_rule ($channel, $cond, $rule, $message, [%options])>
    
    Messages about conditional rules.
    
    =cut
    
    sub msg_cond_rule ($$$$;%)
    {
      my ($channel, $cond, $rule, $msg, %opts) = @_;
      my $r = ref ($rule) ? $rule : rrule ($rule);
      msg $channel, $r->rdef ($cond)->location, $msg, %opts;
    }
    
    =item C<msg_rule ($channel, $targetname, $message, [%options])>
    
    Messages about rules.
    
    =cut
    
    sub msg_rule ($$$;%)
    {
      my ($channel, $rule, $msg, %opts) = @_;
      my $r = ref ($rule) ? $rule : rrule ($rule);
      # Don't know which condition is concerned.  Pick any.
      my $cond = $r->conditions->one_cond;
      msg_cond_rule ($channel, $cond, $r, $msg, %opts);
    }
    
    
    =item C<$bool = reject_rule ($rule, $error_msg)>
    
    Bail out with C<$error_msg> if a rule with name C<$rule> has been
    defined.
    
    Return true iff C<$rule> is defined.
    
    =cut
    
    sub reject_rule ($$)
    {
      my ($rule, $msg) = @_;
      if (rule ($rule))
        {
          err_rule $rule, $msg;
          return 1;
        }
      return 0;
    }
    
    =back
    
    =head2 Administrative functions
    
    =over 4
    
    =item C<accept_extensions (@exts)>
    
    Update C<$KNOWN_EXTENSIONS_PATTERN> to recognize the extensions
    listed in C<@exts>.  Extensions should contain a dot if needed.
    
    =cut
    
    sub accept_extensions (@)
    {
        push @_known_extensions_list, @_;
        $KNOWN_EXTENSIONS_PATTERN =
    	'(?:' . join ('|', map (quotemeta, @_known_extensions_list)) . ')';
    }
    
    =item C<rules>
    
    Return the list of all L<Automake::Rule> instances.  (I.e., all
    rules defined so far.)
    
    =cut
    
    use vars '%_rule_dict';
    sub rules ()
    {
      return values %_rule_dict;
    }
    
    
    =item C<register_action($target, $action)>
    
    Append the C<$action> to C<$actions{$target}> taking care of special
    cases.
    
    =cut
    
    sub register_action ($$)
    {
      my ($target, $action) = @_;
      if ($actions{$target})
        {
          $actions{$target} .= "\n$action" if $action;
        }
      else
        {
          $actions{$target} = $action;
        }
    }
    
    
    =item C<Automake::Rule::reset>
    
    The I<forget all> function.  Clears all known rules and resets some
    other internal data.
    
    =cut
    
    sub reset()
    {
      %_rule_dict = ();
      @_suffixes = ();
      # The first time we initialize the variables,
      # we save the value of $suffix_rules.
      if (defined $_suffix_rules_default)
        {
          $suffix_rules = $_suffix_rules_default;
        }
      else
        {
          $_suffix_rules_default = $suffix_rules;
        }
    
      %dependencies =
        (
         # Texinfoing.
         'dvi'      => [],
         'dvi-am'   => [],
         'pdf'      => [],
         'pdf-am'   => [],
         'ps'       => [],
         'ps-am'    => [],
         'info'     => [],
         'info-am'  => [],
         'html'     => [],
         'html-am'  => [],
    
         # Installing/uninstalling.
         'install-data-am'      => [],
         'install-exec-am'      => [],
         'uninstall-am'         => [],
    
         'install-man'	    => [],
         'uninstall-man'	    => [],
    
         'install-dvi'          => [],
         'install-dvi-am'       => [],
         'install-html'         => [],
         'install-html-am'      => [],
         'install-info'         => [],
         'install-info-am'      => [],
         'install-pdf'          => [],
         'install-pdf-am'       => [],
         'install-ps'           => [],
         'install-ps-am'        => [],
    
         'installcheck-am'      => [],
    
         # Cleaning.
         'clean-am'             => [],
         'mostlyclean-am'       => [],
         'maintainer-clean-am'  => [],
         'distclean-am'         => [],
         'clean'                => [],
         'mostlyclean'          => [],
         'maintainer-clean'     => [],
         'distclean'            => [],
    
         # Tarballing.
         'dist-all'             => [],
    
         # Phonying.
         '.PHONY'               => [],
         # Recursive install targets (so "make -n install" works for BSD Make).
         '.MAKE'		    => [],
         );
      %actions = ();
    }
    
    =item C<register_suffix_rule ($where, $src, $dest)>
    
    Register a suffix rule defined on C<$where> that transforms
    files ending in C<$src> into files ending in C<$dest>.
    
    This upgrades the C<$suffix_rules> variables.
    
    =cut
    
    sub register_suffix_rule ($$$)
    {
      my ($where, $src, $dest) = @_;
    
      verb "Sources ending in $src become $dest";
      push @_suffixes, $src, $dest;
    
      # When transforming sources to objects, Automake uses the
      # %suffix_rules to move from each source extension to
      # '.$(OBJEXT)', not to '.o' or '.obj'.  However some people
      # define suffix rules for '.o' or '.obj', so internally we will
      # consider these extensions equivalent to '.$(OBJEXT)'.  We
      # CANNOT rewrite the target (i.e., automagically replace '.o'
      # and '.obj' by '.$(OBJEXT)' in the output), or warn the user
      # that (s)he'd better use '.$(OBJEXT)', because Automake itself
      # output suffix rules for '.o' or '.obj' ...
      $dest = '.$(OBJEXT)' if ($dest eq '.o' || $dest eq '.obj');
    
      # Reading the comments near the declaration of $suffix_rules might
      # help to understand the update of $suffix_rules that follows ...
    
      # Register $dest as a possible destination from $src.
      # We might have the create the \hash.
      if (exists $suffix_rules->{$src})
        {
          $suffix_rules->{$src}{$dest} = [ $dest, 1 ];
        }
      else
        {
          $suffix_rules->{$src} = { $dest => [ $dest, 1 ] };
        }
    
      # If we know how to transform $dest in something else, then
      # we know how to transform $src in that "something else".
      if (exists $suffix_rules->{$dest})
        {
          for my $dest2 (keys %{$suffix_rules->{$dest}})
    	{
    	  my $dist = $suffix_rules->{$dest}{$dest2}[1] + 1;
    	  # Overwrite an existing $src->$dest2 path only if
    	  # the path via $dest which is shorter.
    	  if (! exists $suffix_rules->{$src}{$dest2}
    	      || $suffix_rules->{$src}{$dest2}[1] > $dist)
    	    {
    	      $suffix_rules->{$src}{$dest2} = [ $dest, $dist ];
    	    }
    	}
        }
    
      # Similarly, any extension that can be derived into $src
      # can be derived into the same extensions as $src can.
      my @dest2 = keys %{$suffix_rules->{$src}};
      for my $src2 (keys %$suffix_rules)
        {
          if (exists $suffix_rules->{$src2}{$src})
    	{
    	  for my $dest2 (@dest2)
    	    {
    	      my $dist = $suffix_rules->{$src}{$dest2} + 1;
    	      # Overwrite an existing $src2->$dest2 path only if
    	      # the path via $src is shorter.
    	      if (! exists $suffix_rules->{$src2}{$dest2}
    		  || $suffix_rules->{$src2}{$dest2}[1] > $dist)
    		{
    		  $suffix_rules->{$src2}{$dest2} = [ $src, $dist ];
    		}
    	    }
    	}
        }
    }
    
    =item C<$count = suffix_rules_count>
    
    Return the number of suffix rules added while processing the current
    F<Makefile> (excluding predefined suffix rules).
    
    =cut
    
    sub suffix_rules_count ()
    {
      return (scalar keys %$suffix_rules) - (scalar keys %$_suffix_rules_default);
    }
    
    =item C<@list = suffixes>
    
    Return the list of known suffixes.
    
    =cut
    
    sub suffixes ()
    {
      return @_suffixes;
    }
    
    =item C<rule ($rulename)>
    
    Return the C<Automake::Rule> object for the rule
    named C<$rulename> if defined.  Return 0 otherwise.
    
    =cut
    
    sub rule ($)
    {
      my ($name) = @_;
      # Strip $(EXEEXT) from $name, so we can diagnose
      # a clash if 'ctags$(EXEEXT):' is redefined after 'ctags:'.
      $name =~ s,\$\(EXEEXT\)$,,;
      return $_rule_dict{$name} || 0;
    }
    
    =item C<ruledef ($rulename, $cond)>
    
    Return the C<Automake::RuleDef> object for the rule named
    C<$rulename> if defined in condition C<$cond>.  Return false
    if the condition or the rule does not exist.
    
    =cut
    
    sub ruledef ($$)
    {
      my ($name, $cond) = @_;
      my $rule = rule $name;
      return $rule && $rule->def ($cond);
    }
    
    =item C<rrule ($rulename)
    
    Return the C<Automake::Rule> object for the variable named
    C<$rulename>.  Abort with an internal error if the variable was not
    defined.
    
    The I<r> in front of C<var> stands for I<required>.  One
    should call C<rvar> to assert the rule's existence.
    
    =cut
    
    sub rrule ($)
    {
      my ($name) = @_;
      my $r = rule $name;
      prog_error ("undefined rule $name\n" . &rules_dump)
        unless $r;
      return $r;
    }
    
    =item C<rruledef ($varname, $cond)>
    
    Return the C<Automake::RuleDef> object for the rule named
    C<$rulename> if defined in condition C<$cond>.  Abort with an internal
    error if the condition or the rule does not exist.
    
    =cut
    
    sub rruledef ($$)
    {
      my ($name, $cond) = @_;
      return rrule ($name)->rdef ($cond);
    }
    
    # Create the variable if it does not exist.
    # This is used only by other functions in this package.
    sub _crule ($)
    {
      my ($name) = @_;
      my $r = rule $name;
      return $r if $r;
      return _new Automake::Rule $name;
    }
    
    sub _new ($$)
    {
      my ($class, $name) = @_;
    
      # Strip $(EXEEXT) from $name, so we can diagnose
      # a clash if 'ctags$(EXEEXT):' is redefined after 'ctags:'.
      (my $keyname = $name) =~ s,\$\(EXEEXT\)$,,;
    
      my $self = Automake::Item::new ($class, $name);
      $_rule_dict{$keyname} = $self;
      return $self;
    }
    
    
    =item C<@conds = define ($rulename, $source, $owner, $cond, $where)>
    
    Define a new rule.  C<$rulename> is the list of targets.  C<$source>
    is the filename the rule comes from.  C<$owner> is the owner of the
    rule (C<RULE_AUTOMAKE> or C<RULE_USER>).  C<$cond> is the
    C<Automake::Condition> under which the rule is defined.  C<$where> is
    the C<Automake::Location> where the rule is defined.
    
    Returns a (possibly empty) list of C<Automake::Condition>s where the
    rule's definition should be output.
    
    =cut
    
    sub define ($$$$$)
    {
      my ($target, $source, $owner, $cond, $where) = @_;
    
      prog_error "$where is not a reference"
        unless ref $where;
      prog_error "$cond is not a reference"
        unless ref $cond;
    
      # Don't even think about defining a rule in condition FALSE.
      return () if $cond == FALSE;
    
      # For now 'foo:' will override 'foo$(EXEEXT):'.  This is temporary,
      # though, so we emit a warning.
      (my $noexe = $target) =~ s,\$\(EXEEXT\)$,,;
      my $noexerule = rule $noexe;
      my $tdef = $noexerule ? $noexerule->def ($cond) : undef;
    
      if ($noexe ne $target
          && $tdef
          && $noexerule->name ne $target)
        {
          # The no-exeext option enables this feature.
          if (! option 'no-exeext')
    	{
    	  msg ('obsolete', $tdef->location,
    	       "deprecated feature: target '$noexe' overrides "
    	       . "'$noexe\$(EXEEXT)'\n"
    	       . "change your target to read '$noexe\$(EXEEXT)'",
    	       partial => 1);
    	  msg ('obsolete', $where, "target '$target' was defined here");
    	}
          # Don't 'return ()' now, as this might hide target clashes
          # detected below.
        }
    
    
      # A GNU make-style pattern rule has a single "%" in the target name.
      msg ('portability', $where,
           "'%'-style pattern rules are a GNU make extension")
        if $target =~ /^[^%]*%[^%]*$/;
    
      # Diagnose target redefinitions.
      if ($tdef)
        {
          my $oldowner  = $tdef->owner;
          # Ok, it's the name target, but the name maybe different because
          # 'foo$(EXEEXT)' and 'foo' have the same key in our table.
          my $oldname = $tdef->name;
    
          # Don't mention true conditions in diagnostics.
          my $condmsg =
    	$cond == TRUE ? '' : " in condition '" . $cond->human . "'";
    
          if ($owner == RULE_USER)
    	{
    	  if ($oldowner == RULE_USER)
    	    {
    	      # Ignore '%'-style pattern rules.  We'd need the
    	      # dependencies to detect duplicates, and they are
    	      # already diagnosed as unportable by -Wportability.
    	      if ($target !~ /^[^%]*%[^%]*$/)
    		{
    		  ## FIXME: Presently we can't diagnose duplicate user rules
    		  ## because we don't distinguish rules with commands
    		  ## from rules that only add dependencies.  E.g.,
    		  ##   .PHONY: foo
    		  ##   .PHONY: bar
    		  ## is legitimate. (This is phony.test.)
    
    		  # msg ('syntax', $where,
    		  #      "redefinition of '$target'$condmsg ...", partial => 1);
    		  # msg_cond_rule ('syntax', $cond, $target,
    		  #		   "... '$target' previously defined here");
    		}
    	      # Return so we don't redefine the rule in our tables,
    	      # don't check for ambiguous condition, etc.  The rule
    	      # will be output anyway because &read_am_file ignore the
    	      # return code.
    	      return ();
    	    }
    	  else
    	    {
    	      # Since we parse the user Makefile.am before reading
    	      # the Automake fragments, this condition should never happen.
    	      prog_error ("user target '$target'$condmsg seen after Automake's"
    			  . " definition\nfrom " . $tdef->source);
    	    }
    	}
          else # $owner == RULE_AUTOMAKE
    	{
    	  if ($oldowner == RULE_USER)
    	    {
    	      # -am targets listed in %dependencies support a -local
    	      # variant.  If the user tries to override TARGET or
    	      # TARGET-am for which there exists a -local variant,
    	      # just tell the user to use it.
    	      my $hint = 0;
    	      my $noam = $target;
    	      $noam =~ s/-am$//;
    	      if (exists $dependencies{"$noam-am"})
    		{
    		  $hint = "consider using $noam-local instead of $target";
    		}
    
    	      msg_cond_rule ('override', $cond, $target,
    			     "user target '$target' defined here"
    			     . "$condmsg ...", partial => 1);
    	      msg ('override', $where,
    		   "... overrides Automake target '$oldname' defined here",
    		   partial => $hint);
    	      msg_cond_rule ('override', $cond, $target, $hint)
    		if $hint;
    
    	      # Don't overwrite the user definition of TARGET.
    	      return ();
    	    }
    	  else # $oldowner == RULE_AUTOMAKE
    	    {
    	      # Automake should ignore redefinitions of its own
    	      # rules if they came from the same file.  This makes
    	      # it easier to process a Makefile fragment several times.
    	      # However it's an error if the target is defined in many
    	      # files.  E.g., the user might be using bin_PROGRAMS = ctags
    	      # which clashes with our 'ctags' rule.
    	      # (It would be more accurate if we had a way to compare
    	      # the *content* of both rules.  Then $targets_source would
    	      # be useless.)
    	      my $oldsource = $tdef->source;
    	      return () if $source eq $oldsource && $target eq $oldname;
    
    	      msg ('syntax', $where, "redefinition of '$target'$condmsg ...",
    		   partial => 1);
    	      msg_cond_rule ('syntax', $cond, $target,
    			     "... '$oldname' previously defined here");
    	      return ();
    	    }
    	}
          # Never reached.
          prog_error ("unreachable place reached");
        }
    
      # Conditions for which the rule should be defined.
      my @conds = $cond;
    
      # Check ambiguous conditional definitions.
      my $rule = _crule $target;
      my ($message, $ambig_cond) = $rule->conditions->ambiguous_p ($target, $cond);
      if ($message)			# We have an ambiguity.
        {
          if ($owner == RULE_USER)
    	{
    	  # For user rules, just diagnose the ambiguity.
    	  msg 'syntax', $where, "$message ...", partial => 1;
    	  msg_cond_rule ('syntax', $ambig_cond, $target,
    			 "... '$target' previously defined here");
    	  return ();
    	}
          else
    	{
    	  # FIXME: for Automake rules, we can't diagnose ambiguities yet.
    	  # The point is that Automake doesn't propagate conditions
    	  # everywhere.  For instance &handle_PROGRAMS doesn't care if
    	  # bin_PROGRAMS was defined conditionally or not.
    	  # On the following input
    	  #   if COND1
    	  #   foo:
    	  #           ...
    	  #   else
    	  #   bin_PROGRAMS = foo
    	  #   endif
    	  # &handle_PROGRAMS will attempt to define a 'foo:' rule
    	  # in condition TRUE (which conflicts with COND1).  Fixing
    	  # this in &handle_PROGRAMS and siblings seems hard: you'd
    	  # have to explain &file_contents what to do with a
    	  # condition.  So for now we do our best *here*.  If 'foo:'
    	  # was already defined in condition COND1 and we want to define
    	  # it in condition TRUE, then define it only in condition !COND1.
    	  # (See cond14.test and cond15.test for some test cases.)
    	  @conds = $rule->not_always_defined_in_cond ($cond)->conds;
    
    	  # No conditions left to define the rule.
    	  # Warn, because our workaround is meaningless in this case.
    	  if (scalar @conds == 0)
    	    {
    	      msg 'syntax', $where, "$message ...", partial => 1;
    	      msg_cond_rule ('syntax', $ambig_cond, $target,
    			     "... '$target' previously defined here");
    	      return ();
    	    }
    	}
        }
    
      # Finally define this rule.
      for my $c (@conds)
        {
          my $def = new Automake::RuleDef ($target, '', $where->clone,
    				       $owner, $source);
          $rule->set ($c, $def);
        }
    
      # We honor inference rules with multiple targets because many
      # makes support this and people use it.  However this is disallowed
      # by POSIX.  We'll print a warning later.
      my $target_count = 0;
      my $inference_rule_count = 0;
    
      for my $t (split (' ', $target))
        {
          ++$target_count;
          # Check if the rule is a suffix rule: either it's a rule for
          # two known extensions...
          if ($t =~ /^($KNOWN_EXTENSIONS_PATTERN)($KNOWN_EXTENSIONS_PATTERN)$/
    	  # ...or it's a rule with unknown extensions (i.e., the rule
    	  # looks like '.foo.bar:' but '.foo' or '.bar' are not
    	  # declared in SUFFIXES and are not known language
    	  # extensions).  Automake will complete SUFFIXES from
    	  # @suffixes automatically (see handle_footer).
    
    
    	  || ($t =~ /$_SUFFIX_RULE_PATTERN/o && accept_extensions($1)))
    	{
    	  ++$inference_rule_count;
    	  register_suffix_rule ($where, $1, $2);
    	}
        }
    
      # POSIX allows multiple targets before the colon, but disallows
      # definitions of multiple inference rules.  It's also
      # disallowed to mix plain targets with inference rules.
      msg ('portability', $where,
           "inference rules can have only one target before the colon (POSIX)")
        if $inference_rule_count > 0 && $target_count > 1;
    
      return @conds;
    }
    
    =item C<depend ($target, @deps)>
    
    Adds C<@deps> to the dependencies of target C<$target>.  This should
    be used only with factored targets (those appearing in
    C<%dependees>).
    
    =cut
    
    sub depend ($@)
    {
      my ($category, @dependees) = @_;
      push (@{$dependencies{$category}}, @dependees);
    }
    
    =back
    
    =head1 SEE ALSO
    
    L<Automake::RuleDef>, L<Automake::Condition>,
    L<Automake::DisjConditions>, L<Automake::Location>.
    
    =cut
    
    1;
    
    ### 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: