Condition.pm

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Author : Stefano Lattarini
Date : 2012-03-04 15:44:46
Hash : 7df05a0b
Message : maint: require perl 5.6 throughout That version of perl is quite old already, so it should be OK to require it. More importantly, it is the older perl versions the developers can currently use for testing, thus it's safer and more honest to just require it throughout. And anyway, we were already requiring it in Automake::Getopt, which implied that both automake and aclocal wouldn't have worked in practice with an older perl version. See also the discussion related to automake bug#10925. * lib/Automake/ChannelDefs.pm: Adjusted to require perl 5.6. * lib/Automake/Channels.pm: Likewise. * lib/Automake/Condition.pm: Likewise. * lib/Automake/Configure_ac.pm: Likewise. * lib/Automake/DisjConditions.pm: Likewise. * lib/Automake/FileUtils.pm: Likewise. * lib/Automake/General.pm: Likewise. * lib/Automake/Item.pm: Likewise. * lib/Automake/ItemDef.pm: Likewise. * lib/Automake/Location.pm: Likewise. * lib/Automake/Options.pm: Likewise. * lib/Automake/Rule.pm: Likewise. * lib/Automake/RuleDef.pm: Likewise. * lib/Automake/Struct.pm: Likewise. * lib/Automake/VarDef.pm: Likewise. * lib/Automake/Variable.pm: Likewise. * lib/Automake/Version.pm: Likewise. * lib/Automake/Wrap.pm: Likewise. * lib/Automake/XFile.pm: Likewise.
lib/Automake/Condition.pm
# Copyright (C) 1997-2012 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::Condition;

use 5.006;
use strict;
use Carp;

require Exporter;
use vars '@ISA', '@EXPORT_OK';
@ISA = qw/Exporter/;
@EXPORT_OK = qw/TRUE FALSE reduce_and reduce_or/;

=head1 NAME

Automake::Condition - record a conjunction of conditionals

=head1 SYNOPSIS

  use Automake::Condition;

  # Create a condition to represent "COND1 and not COND2".
  my $cond = new Automake::Condition "COND1_TRUE", "COND2_FALSE";
  # Create a condition to represent "not COND3".
  my $other = new Automake::Condition "COND3_FALSE";

  # Create a condition to represent
  #   "COND1 and not COND2 and not COND3".
  my $both = $cond->merge ($other);

  # Likewise, but using a list of conditional strings
  my $both2 = $cond->merge_conds ("COND3_FALSE");

  # Strip from $both any subconditions which are in $other.
  # This is the opposite of merge.
  $cond = $both->strip ($other);

  # Return the list of conditions ("COND1_TRUE", "COND2_FALSE"):
  my @conds = $cond->conds;

  # Is $cond always true?  (Not in this example)
  if ($cond->true) { ... }

  # Is $cond always false? (Not in this example)
  if ($cond->false) { ... }

  # Return the list of conditionals as a string:
  #  "COND1_TRUE COND2_FALSE"
  my $str = $cond->string;

  # Return the list of conditionals as a human readable string:
  #  "COND1 and !COND2"
  my $str = $cond->human;

  # Return the list of conditionals as a AC_SUBST-style string:
  #  "@COND1_TRUE@@COND2_FALSE@"
  my $subst = $cond->subst_string;

  # Is $cond true when $both is true?  (Yes in this example)
  if ($cond->true_when ($both)) { ... }

  # Is $cond redundant w.r.t. {$other, $both}?
  # (Yes in this example)
  if ($cond->redundant_wrt ($other, $both)) { ... }

  # Does $cond imply any of {$other, $both}?
  # (Not in this example)
  if ($cond->implies_any ($other, $both)) { ... }

  # Remove superfluous conditionals assuming they will eventually
  # be multiplied together.
  # (Returns @conds = ($both) in this example, because
  # $other and $cond are implied by $both.)
  @conds = Automake::Condition::reduce_and ($other, $both, $cond);

  # Remove superfluous conditionals assuming they will eventually
  # be summed together.
  # (Returns @conds = ($cond, $other) in this example, because
  # $both is a subset condition of $cond: $cond is true whenever $both
  # is true.)
  @conds = Automake::Condition::reduce_or ($other, $both, $cond);

  # Invert a Condition.  This returns a list of Conditions.
  @conds = $both->not;

=head1 DESCRIPTION

A C<Condition> is a conjunction of conditionals (i.e., atomic conditions
defined in F<configure.ac> by C<AM_CONDITIONAL>.  In Automake they
are used to represent the conditions into which F<Makefile> variables and
F<Makefile> rules are defined.

If the variable C<VAR> is defined as

  if COND1
    if COND2
      VAR = value
    endif
  endif

then it will be associated a C<Condition> created with
the following statement.

  new Automake::Condition "COND1_TRUE", "COND2_TRUE";

Remember that a C<Condition> is a I<conjunction> of conditionals, so
the above C<Condition> means C<VAR> is defined when C<COND1>
B<and> C<COND2> are true. There is no way to express disjunctions
(i.e., I<or>s) with this class (but see L<DisjConditions>).

Another point worth to mention is that each C<Condition> object is
unique with respect to its conditionals.  Two C<Condition> objects
created for the same set of conditionals will have the same address.
This makes it easy to compare C<Condition>s: just compare the
references.

  my $c1 = new Automake::Condition "COND1_TRUE", "COND2_TRUE";
  my $c2 = new Automake::Condition "COND1_TRUE", "COND2_TRUE";
  $c1 == $c2;  # True!

=head2 Methods

=over 4

=item C<$cond = new Automake::Condition [@conds]>

Return a C<Condition> objects for the conjunctions of conditionals
listed in C<@conds> as strings.

An item in C<@conds> should be either C<"FALSE">, C<"TRUE">, or have
the form C<"NAME_FALSE"> or C<"NAME_TRUE"> where C<NAME> can be
anything (in practice C<NAME> should be the name of a conditional
declared in F<configure.ac> with C<AM_CONDITIONAL>, but it's not
C<Automake::Condition>'s responsibility to ensure this).

An empty C<@conds> means C<"TRUE">.

As explained previously, the reference (object) returned is unique
with respect to C<@conds>.  For this purpose, duplicate elements are
ignored, and C<@conds> is rewritten as C<("FALSE")> if it contains
C<"FALSE"> or two contradictory conditionals (such as C<"NAME_FALSE">
and C<"NAME_TRUE">.)

Therefore the following two statements create the same object (they
both create the C<"FALSE"> condition).

  my $c3 = new Automake::Condition "COND1_TRUE", "COND1_FALSE";
  my $c4 = new Automake::Condition "COND2_TRUE", "FALSE";
  $c3 == $c4;   # True!
  $c3 == FALSE; # True!

=cut

# Keys in this hash are conditional strings. Values are the
# associated object conditions.  This is used by 'new' to reuse
# Condition objects with identical conditionals.
use vars '%_condition_singletons';
# Do NOT reset this hash here.  It's already empty by default,
# and any setting would otherwise occur AFTER the 'TRUE' and 'FALSE'
# constants definitions.
#   %_condition_singletons = ();

sub new ($;@)
{
  my ($class, @conds) = @_;
  my $self = {
    hash => {},
  };
  bless $self, $class;

  for my $cond (@conds)
    {
      # Catch some common programming errors:
      # - A Condition passed to new
      confess "'$cond' is a reference, expected a string" if ref $cond;
      # - A Condition passed as a string to new
      confess "'$cond' does not look like a condition" if $cond =~ /::/;
    }

  # Accept strings like "FOO BAR" as shorthand for ("FOO", "BAR").
  @conds = map { split (' ', $_) } @conds;

  for my $cond (@conds)
    {
      next if $cond eq 'TRUE';

      # Detect cases when @conds can be simplified to FALSE.
      if (($cond eq 'FALSE' && $#conds > 0)
	  || ($cond =~ /^(.*)_TRUE$/ && exists $self->{'hash'}{"${1}_FALSE"})
	  || ($cond =~ /^(.*)_FALSE$/ && exists $self->{'hash'}{"${1}_TRUE"}))
	{
	  return &FALSE;
	}

      $self->{'hash'}{$cond} = 1;
    }

  my $key = $self->string;
  if (exists $_condition_singletons{$key})
    {
      return $_condition_singletons{$key};
    }
  $_condition_singletons{$key} = $self;
  return $self;
}

=item C<$newcond = $cond-E<gt>merge (@otherconds)>

Return a new condition which is the conjunction of
C<$cond> and C<@otherconds>.

=cut

sub merge ($@)
{
  my ($self, @otherconds) = @_;
  new Automake::Condition (map { $_->conds } ($self, @otherconds));
}

=item C<$newcond = $cond-E<gt>merge_conds (@conds)>

Return a new condition which is the conjunction of C<$cond> and
C<@conds>, where C<@conds> is a list of conditional strings, as
passed to C<new>.

=cut

sub merge_conds ($@)
{
  my ($self, @conds) = @_;
  new Automake::Condition $self->conds, @conds;
}

=item C<$newcond = $cond-E<gt>strip ($minuscond)>

Return a new condition which has all the conditionals of C<$cond>
except those of C<$minuscond>.  This is the opposite of C<merge>.

=cut

sub strip ($$)
{
  my ($self, $minus) = @_;
  my @res = grep { not $minus->_has ($_) } $self->conds;
  return new Automake::Condition @res;
}

=item C<@list = $cond-E<gt>conds>

Return the set of conditionals defining C<$cond>, as strings.  Note that
this might not be exactly the list passed to C<new> (or a
concatenation of such lists if C<merge> was used), because of the
cleanup mentioned in C<new>'s description.

For instance C<$c3-E<gt>conds> will simply return C<("FALSE")>.

=cut

sub conds ($ )
{
  my ($self) = @_;
  my @conds = keys %{$self->{'hash'}};
  return ("TRUE") unless @conds;
  return sort @conds;
}

# Undocumented, shouldn't be needed outside of this class.
sub _has ($$)
{
  my ($self, $cond) = @_;
  return exists $self->{'hash'}{$cond};
}

=item C<$cond-E<gt>false>

Return 1 iff this condition is always false.

=cut

sub false ($ )
{
  my ($self) = @_;
  return $self->_has ('FALSE');
}

=item C<$cond-E<gt>true>

Return 1 iff this condition is always true.

=cut

sub true ($ )
{
  my ($self) = @_;
  return 0 == keys %{$self->{'hash'}};
}

=item C<$cond-E<gt>string>

Build a string which denotes the condition.

For instance using the C<$cond> definition from L<SYNOPSYS>,
C<$cond-E<gt>string> will return C<"COND1_TRUE COND2_FALSE">.

=cut

sub string ($ )
{
  my ($self) = @_;

  return $self->{'string'} if defined $self->{'string'};

  my $res = '';
  if ($self->false)
    {
      $res = 'FALSE';
    }
  else
    {
      $res = join (' ', $self->conds);
    }
  $self->{'string'} = $res;
  return $res;
}

=item C<$cond-E<gt>human>

Build a human readable string which denotes the condition.

For instance using the C<$cond> definition from L<SYNOPSYS>,
C<$cond-E<gt>string> will return C<"COND1 and !COND2">.

=cut

sub _to_human ($ )
{
  my ($s) = @_;
  if ($s =~ /^(.*)_(TRUE|FALSE)$/)
    {
      return (($2 eq 'FALSE') ? '!' : '') . $1;
    }
  else
    {
      return $s;
    }
}

sub human ($ )
{
  my ($self) = @_;

  return $self->{'human'} if defined $self->{'human'};

  my $res = '';
  if ($self->false)
    {
      $res = 'FALSE';
    }
  else
    {
      $res = join (' and ', map { _to_human $_ } $self->conds);
    }
  $self->{'human'} = $res;
  return $res;
}

=item C<$cond-E<gt>subst_string>

Build a C<AC_SUBST>-style string for output in F<Makefile.in>.

For instance using the C<$cond> definition from L<SYNOPSYS>,
C<$cond-E<gt>subst_string> will return C<"@COND1_TRUE@@COND2_FALSE@">.

=cut

sub subst_string ($ )
{
  my ($self) = @_;

  return $self->{'subst_string'} if defined $self->{'subst_string'};

  my $res = '';
  if ($self->false)
    {
      $res = '#';
    }
  elsif (! $self->true)
    {
      $res = '@' . join ('@@', sort $self->conds) . '@';
    }
  $self->{'subst_string'} = $res;
  return $res;
}

=item C<$cond-E<gt>true_when ($when)>

Return 1 iff C<$cond> is true when C<$when> is true.
Return 0 otherwise.

Using the definitions from L<SYNOPSYS>, C<$cond> is true
when C<$both> is true, but the converse is wrong.

=cut

sub true_when ($$)
{
  my ($self, $when) = @_;

  # Nothing is true when FALSE (not even FALSE itself, but it
  # shouldn't hurt if you decide to change that).
  return 0 if $self->false || $when->false;

  # If we are true, we stay true when $when is true :)
  return 1 if $self->true;

  # $SELF is true under $WHEN if each conditional component of $SELF
  # exists in $WHEN.
  foreach my $cond ($self->conds)
    {
      return 0 unless $when->_has ($cond);
    }
  return 1;
}

=item C<$cond-E<gt>redundant_wrt (@conds)>

Return 1 iff C<$cond> is true for any condition in C<@conds>.
If @conds is empty, return 1 iff C<$cond> is C<FALSE>.
Return 0 otherwise.

=cut

sub redundant_wrt ($@)
{
  my ($self, @conds) = @_;

  foreach my $cond (@conds)
    {
      return 1 if $self->true_when ($cond);
    }
  return $self->false;
}

=item C<$cond-E<gt>implies_any (@conds)>

Return 1 iff C<$cond> implies any of the conditions in C<@conds>.
Return 0 otherwise.

=cut

sub implies_any ($@)
{
  my ($self, @conds) = @_;

  foreach my $cond (@conds)
    {
      return 1 if $cond->true_when ($self);
    }
  return 0;
}

=item C<$cond-E<gt>not>

Return a negation of C<$cond> as a list of C<Condition>s.
This list should be used to construct a C<DisjConditions>
(we cannot return a C<DisjConditions> from C<Automake::Condition>,
because that would make these two packages interdependent).

=cut

sub not ($ )
{
  my ($self) = @_;
  return @{$self->{'not'}} if defined $self->{'not'};
  my @res =
    map { new Automake::Condition &conditional_negate ($_) } $self->conds;
  $self->{'not'} = [@res];
  return @res;
}

=item C<$cond-E<gt>multiply (@conds)>

Assumption: C<@conds> represent a disjunction of conditions.

Return the result of multiplying C<$cond> with that disjunction.
The result will be a list of conditions suitable to construct a
C<DisjConditions>.

=cut

sub multiply ($@)
{
  my ($self, @set) = @_;
  my %res = ();
  for my $cond (@set)
    {
      my $ans = $self->merge ($cond);
      $res{$ans} = $ans;
    }

  # FALSE can always be removed from a disjunction.
  delete $res{FALSE};

  # Now, $self is a common factor of the remaining conditions.
  # If one of the conditions is $self, we can discard the rest.
  return ($self, ())
    if exists $res{$self};

  return (values %res);
}

=back

=head2 Other helper functions

=over 4

=item C<TRUE>

The C<"TRUE"> conditional.

=item C<FALSE>

The C<"FALSE"> conditional.

=cut

use constant TRUE => new Automake::Condition "TRUE";
use constant FALSE => new Automake::Condition "FALSE";

=item C<reduce_and (@conds)>

Return a subset of @conds with the property that the conjunction of
the subset is the same as the conjunction of @conds.  For example, if
both C<COND1_TRUE COND2_TRUE> and C<COND1_TRUE> are in the list,
discard the latter.  If the input list is empty, return C<(TRUE)>.

=cut

sub reduce_and (@)
{
  my (@conds) = @_;
  my @ret = ();
  my $cond;
  while (@conds > 0)
    {
      $cond = shift @conds;

      # FALSE is absorbent.
      return FALSE
	if $cond == FALSE;

      if (! $cond->redundant_wrt (@ret, @conds))
	{
	  push (@ret, $cond);
	}
    }

  return TRUE if @ret == 0;
  return @ret;
}

=item C<reduce_or (@conds)>

Return a subset of @conds with the property that the disjunction of
the subset is equivalent to the disjunction of @conds.  For example,
if both C<COND1_TRUE COND2_TRUE> and C<COND1_TRUE> are in the list,
discard the former.  If the input list is empty, return C<(FALSE)>.

=cut

sub reduce_or (@)
{
  my (@conds) = @_;
  my @ret = ();
  my $cond;
  while (@conds > 0)
    {
      $cond = shift @conds;

      next
       if $cond == FALSE;
      return TRUE
       if $cond == TRUE;

      push (@ret, $cond)
       unless $cond->implies_any (@ret, @conds);
    }

  return FALSE if @ret == 0;
  return @ret;
}

=item C<conditional_negate ($condstr)>

Negate a conditional string.

=cut

sub conditional_negate ($)
{
  my ($cond) = @_;

  $cond =~ s/TRUE$/TRUEO/;
  $cond =~ s/FALSE$/TRUE/;
  $cond =~ s/TRUEO$/FALSE/;

  return $cond;
}

=back

=head1 SEE ALSO

L<Automake::DisjConditions>.

=head1 HISTORY

C<AM_CONDITIONAL>s and supporting code were added to Automake 1.1o by
Ian Lance Taylor <ian@cygnus.org> in 1997.  Since then it has been
improved by Tom Tromey <tromey@redhat.com>, Richard Boulton
<richard@tartarus.org>, Raja R Harinath <harinath@cs.umn.edu>,
Akim Demaille <akim@epita.fr>, and  Alexandre Duret-Lutz <adl@gnu.org>.

=cut

1;

### Setup "GNU" style for perl-mode and cperl-mode.
## Local Variables:
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## cperl-indent-level: 2
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## cperl-extra-newline-before-brace: t
## cperl-merge-trailing-else: nil
## cperl-continued-statement-offset: 2
## End:
kc3-lang/automake/lib/Automake/Condition.pm

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