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# Copyright 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017 Kevin Ryde
# This file is part of Perl-Critic-Pulp.
# Perl-Critic-Pulp 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 3, or (at your option) any later
# version.
#
# Perl-Critic-Pulp 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 Perl-Critic-Pulp. If not, see <http://www.gnu.org/licenses/>.
package Perl::Critic::Policy::ValuesAndExpressions::ProhibitEmptyCommas;
use 5.006;
use strict;
use warnings;
use base 'Perl::Critic::Policy';
use Perl::Critic::Utils;
use Perl::Critic::Pulp::Utils;
# uncomment this to run the ### lines
# use Smart::Comments;
our $VERSION = 96;
use constant supported_parameters => ();
use constant default_severity => $Perl::Critic::Utils::SEVERITY_LOW;
use constant default_themes => qw(pulp cosmetic);
use constant applies_to => ('PPI::Token::Operator');
sub violates {
my ($self, $elem, $document) = @_;
$Perl::Critic::Pulp::Utils::COMMA{$elem} or return;
my $prev = $elem->sprevious_sibling;
if ($prev && ! ($prev->isa('PPI::Token::Operator')
&& $Perl::Critic::Pulp::Utils::COMMA{$prev})) {
# have a previous element and it's not a comma operator
return;
}
# A statement like
#
# return bless({@_}, $class)
#
# is parsed by PPI as
#
# PPI::Structure::List ( ... )
# PPI::Statement::Compound
# PPI::Structure::Block { ... }
# PPI::Statement
# PPI::Token::Magic '@_'
# PPI::Statement::Expression
# PPI::Token::Operator ','
# PPI::Token::Symbol '$class'
#
# so the "{@_}" bit is not an immediate predecessor of the "," operator.
# If our $elem has no $prev then also look outwards to see if it's at the
# start of an expression which is in a list and there's something
# preceding in the list.
#
if (! $prev) {
my $parent = $elem->parent;
if ($parent->isa('PPI::Statement::Expression')
&& $parent->parent->isa('PPI::Structure::List')
&& $parent->sprevious_sibling) {
return;
}
}
# An expression like
#
# [{%a},{}]
#
# is parsed by PPI 1.215 as
#
# PPI::Statement
# PPI::Structure::Constructor [ ... ]
# PPI::Statement::Compound
# PPI::Structure::Block { ... }
# PPI::Statement
# PPI::Token::Symbol '%a'
# PPI::Statement
# PPI::Token::Operator ','
# PPI::Structure::Constructor { ... }
#
# so the "{%a}" bit is not an immediate predecessor of the "," operator.
# If our $elem has no $prev then also look upwards to see if it's at the
# start of an statement which is in a constructor and there's something
# preceding in that constructor.
#
if (! $prev) {
my $parent = $elem->parent;
### parent: ref $parent
if ($parent->isa('PPI::Statement')
&& $parent->parent->isa('PPI::Structure::Constructor')
&& $parent->sprevious_sibling) {
return;
}
}
# $prev is either nothing or a comma operator
return $self->violation ('Empty comma operator',
'',
$elem);
}
1;
__END__
=for stopwords Ryde
=head1 NAME
Perl::Critic::Policy::ValuesAndExpressions::ProhibitEmptyCommas - disallow empty consecutive commas
=head1 DESCRIPTION
This policy is part of the L<C<Perl::Critic::Pulp>|Perl::Critic::Pulp>
add-on. It prohibits empty comma operators C<,> or C<=E<gt>> meaning either
consecutive commas or a comma at the start of a list or expression.
print 'foo',,'bar'; # bad
@a = (,1,2); # bad
foo (x, => 123); # bad
a =>=> 456; # bad
for (; $i++<10; $i++,,) # bad
func (,) # bad
Extra commas like this are harmless and simply collapse out when the program
runs (see L<perldata/List value constructors>), so this policy is only under
the "cosmetic" theme (see L<Perl::Critic/POLICY THEMES>). Usually this sort
of thing is just a stray, or leftover from cut and paste, or perhaps some
over-enthusiastic column layout. Occasionally it can be something more
dubious,
# did you mean 1..6 range operator?
@a = (1,,6); # bad
# this is two args, did you want three?
foo (1, , 2); # bad
# this is three args, probably you forgot a value
bar (abc => , # bad
def => 20);
A comma at the end of a list or call is allowed. That's quite usual and can
be a good thing when cutting and pasting lines (see C<RequireTrailingCommas>
to mandate them!).
@b = ("foo",
"bar", # ok
);
If you use multiple commas in some systematic way for code layout you can
always disable C<ProhibitEmptyCommas> from your F<.perlcriticrc> file in the
usual way (see L<Perl::Critic/CONFIGURATION>),
[-ValuesAndExpressions::ProhibitEmptyCommas]
=head1 SEE ALSO
L<Perl::Critic::Pulp>,
L<Perl::Critic>,
L<Perl::Critic::Policy::CodeLayout::RequireTrailingCommas>,
L<Perl::Critic::Policy::ValuesAndExpressions::ProhibitCommaSeparatedStatements>,
L<Perl::Critic::Policy::Tics::ProhibitManyArrows>
=head1 HOME PAGE
http://user42.tuxfamily.org/perl-critic-pulp/index.html
=head1 COPYRIGHT
Copyright 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017 Kevin Ryde
Perl-Critic-Pulp 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 3, or (at your option) any later
version.
Perl-Critic-Pulp 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
Perl-Critic-Pulp. If not, see <http://www.gnu.org/licenses/>.
=cut
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