supported_parameters()
supported_parameters() to Get It Done For You
supported_parameters() and initialize_if_enabled()
supported_parameters().
Perl::Critic::DEVELOPER - How to make new Perl::Critic::Policy modules.
For developers who want to create custom coding standards, the following tells how to create a Policy module for Perl::Critic. Although the Perl::Critic distribution already includes a number of Policies based on Damian Conway's book Perl Best Practices (which will be referred to via "PBP" from here on), Perl::Critic is not limited to his guidelines and can be used to enforce any practice, preference, or style that you want to follow. You can even write Policies to enforce contradictory guidelines. All you need to do is write a corresponding Perl::Critic::Policy subclass, which may require as little as 10 lines of code.
The heart of Perl::Critic is PPI, a parser and lexer for Perl. PPI transforms Perl source code into a Document Object Model (DOM). Each token in the document is represented by a PPI class, such as PPI::Token::Operator or PPI::Token::Word, and then organized into structure classes, like PPI::Statement::Expression and PPI::Structure::Subroutine. The root node of the hierarchy is the PPI::Document.
The Perl::Critic engine traverses each node in the PPI::Document tree and invokes each of the Perl::Critic::Policy subclasses at the appropriate node. The Policy can inspect the node, look at the surrounding nodes, and do whatever else it wants. If the Policy decides that that a coding standard has been violated, it returns one or more Perl::Critic::Violation objects. If there are no violations, then the Policy returns nothing.
Policies are usually written based on existing policies, so let's look
at one to see how it works. The RequireBlockGrep.pm Policy is
relatively simple and demonstrates most of the important issues. The
goal of this Policy is to enforce that every call to grep uses a
block for the first argument and not an expression. The reasons for
this Policy are discussed in detail in PBP.
First, the Policy module needs to have a name. Perl::Critic uses
Module::Pluggable to automatically discover all modules in the
Perl::Critic::Policy namespace. Also, we've adopted the convention
of grouping Policies into directories according to the chapters of
PBP. Since the goal of this Policy is to enforce the use of block
arguments to grep and it comes from the "Builtin Functions" chapter
of PBP, we call it
"Perl::Critic::Policy::BuiltinFunctions::RequireBlockGrep".
package Perl::Critic::Policy::BuiltinFunctions::RequireBlockGrep;
Next, we set some pragmas and load the modules that we'll need. All Policy modules inherit from the Perl::Critic::Policy class, which provides no-op implementations of the basic methods. Our job is to override these methods to make them do something useful.
Technically, use strict and use warnings are optional, but we
don't want Perl::Critic to be a hypocrite, now do we?
use strict;
use warnings;
use Readonly;
use Perl::Critic::Utils qw{ :severities :classification :ppi };
use base 'Perl::Critic::Policy';
our $VERSION = '1.05';
Next, we'll declare a description and explanation for this Policy.
The description is always just a string that basically says "this is
what's wrong." The explanation can be either a string with further
details, or a reference to an array of integers that correspond to
page numbers in PBP. We make them read-only because they never
change. (See
Perl::Critic::ValuesAndExpressions::ProhibitConstantPragma for why
we don't use constant.)
Readonly::Scalar my $DESC => q{Expression form of "grep"};
Readonly::Scalar my $EXPL => [ 169 ];
Most policies don't need to override the initialize_if_enabled()
method provided by Perl::Critic::Policy. However, if your Policy
is configurable via .perlcriticrc, you should implement a
supported_parameters() method and need to implement
initialize_if_enabled() to examine the $config values. Since
this Policy isn't configurable, we'll declare that by providing an
implementation of supported_parameters() that returns an empty
list.
sub supported_parameters { return () }
Next, we define the default_severity() method, which must return an
integer indicating the severity of violating this Policy. Severity
values range from 1 to 5, where 5 is the "most severe." In general,
level 5 is reserved for things that are frequently misused and/or
cause bugs. Level 1 is for things that are highly subjective or
purely cosmetic. The Perl::Critic::Utils package exports several
severity constants that you can use here via the :severities tag.
sub default_severity { return $SEVERITY_HIGH }
Likewise, the default_themes() method returns a list of theme
names. Themes are intended to be named groups of Policies. All
Policies that ship with Perl::Critic have a "core" theme. Since
use of grep without blocks often leads to bugs, we include a
"bugs" theme. And since this Policy comes directly from PBP,
this Policy should be a member of the "pbp" theme.
sub default_themes { return qw( core bugs pbp ) }
As a Policy author, you can assign any themes you want to the Policy.
If you're publishing a suite of custom Policies, we suggest that you
create a unique theme that covers all the Policies in the
distribution. That way, users can easily enable or disable all of
your policies at once. For example, Policies in the
Perl::Critic::More distribution all have a "more" theme.
Next, we indicate what elements of the code this Policy will analyze,
like statements or variables or conditionals or POD. These elements
are specified as PPI classes such as PPI::Statement,
PPI::Token::Symbol, PPI::Structure::Conditional or
PPI::Token::Pod respectively. The applies_to() method returns a
list of PPI package names. (You can get that list of available
package names via perldoc PPI.) As Perl::Critic traverses the
document, it will call the violates() method from this module
whenever it encounters one of the PPI types that are given here. In
this case, we just want to test calls to grep. Since the token
"grep" is a PPI::Token::Word, we return that package name from the
applies_to() method.
sub applies_to { return 'PPI::Token::Word' }
If your Policy needs to analyze several different types of elements,
the applies_to method may return the name of several PPI packages.
If your Policy needs to examine the file as a whole, then the
applies_to method should return PPI::Document. Since there is
only one PPI::Document element, your Policy would only be invoked once
per file.
Now comes the interesting part. The violates() method does all the
work. It is always called with 2 arguments: a reference to the
current PPI element that Perl::Critic is traversing, and a reference
to the entire PPI document. [And since this is an object method, there
will be an additional argument that is a reference to this object
($self), but you already knew that!] Since this Policy does not
need access to the document as a whole, we ignore the last parameter
by assigning to undef.
sub violates {
my ( $self, $elem, undef ) = @_;
The violates() method then often performs some tests to make sure we
have the right "type" of element. In our example, we know that the
element will be a PPI::Token::Word because that's what we declared
back in the applies_to() method. However, we didn't specify
exactly which "word" we were looking for. Evaluating a PPI element in
a string context returns the literal form of the code. (You can also
use the c<content()> method.) So we make sure that this
PPI::Token::Word is, in fact, "grep". If it's not, then we don't'
need to bother examining it.
return if $elem ne 'grep';
The PPI::Token::Word class is also used for barewords and methods
called on object references. It is possible for someone to declare a
bareword hash key as <%hash = ( grep = 'foo' )>>. We don't want to
test those types of elements because they don't represent function
calls to grep. So we use one of handy utility functions from
Perl::Critic::Utils to make sure that this "grep" is actually in
the right context. (The is_function_call() subroutine is brought
in via the :classification tag.)
return if ! is_function_call($elem);
Now that we know this element is a call to the grep function, we
can look at the nearby elements to see what kind of arguments are
being passed to it. In the following paragraphs, we discuss how to do
this manually in order to explore PPI; after that, we'll show how
this Policy actually uses facilities provided by
Perl::Critic::Utils to get this done.
Every PPI element is linked to its siblings, parent, and children (if
it has any). Since those siblings could just be whitespace, we use
the snext_sibling() to get the next code-sibling (the "s" in
snext_sibling stands for "significant").
my $sib = $elem->snext_sibling() or return;
In Perl, the parenthesis around argument lists are usually optional,
and PPI packs the elements into a PPI::Structure::List object when
parentheses are used. So if the sibling is a PPI::Structure::List, we
pull out the first (significant) child of that list. This child will
be the first argument to grep. If parentheses were not used, then
the sibling itself is the first argument.
my $arg = $sib->isa('PPI::Structure::List') ? $sib->schild(0) : $sib;
In actuality, this sort of function argument lookup is common, so
there is a Perl::Critic::Utils/"first_arg" subroutine available via
the :ppi tag. So we use that instead.
my $arg = first_arg($elem);
Finally, we now have a reference to the first argument to grep. If
that argument is a block (i.e. something in curly braces), then it
will be a PPI::Structure::Block, in which case our Policy is
satisfied and we just return nothing.
return if !$arg;
return if $arg->isa('PPI::Structure::Block');
But if it is not a PPI::Structure::Block, then we know that this
call to grep must be using the expression form, and that violates
our Policy. So we create and return a new Perl::Critic::Violation
object via the Perl::Critic::Policy/"violation" method, passing in
the description, explanation, and a reference to the PPI element that
caused the violation. And that's all there is to it!
return $self->violation( $DESC, $EXPL, $elem );
}
1;
One last thing -- people are going to need to understand what is wrong with the code when your Policy finds a problem. It isn't reasonable to include all the details in your violation description or explanation. So please include a DESCRIPTION section in the POD for your Policy. It should succinctly describe the behavior and motivation for your Policy and include a few examples of both good and bad code. Here's an example:
=pod
=head1 NAME
Perl::Critic::Policy::BuiltinFunctions::RequireBlockGrep
=head1 DESCRIPTION
The expression forms of C<grep> and C<map> are awkward and hard to read.
Use the block forms instead.
@matches = grep /pattern/, @list; #not ok
@matches = grep { /pattern/ } @list; #ok
@mapped = map transform($_), @list; #not ok
@mapped = map { transform($_) } @list; #ok
=cut
When your policy has a section like this, users can invoke
perlcritic with a --verbose parameter of 10 or 11 to see
it along with the rest of the output for violations of your policy.
Perl::Critic takes care of gathering configuration information for
your Policy, from whatever source the user specifies. (See
Perl::Critic/"CONFIGURATION" for the details of how a user specifies
the values you're going to receive.) What your Policy ends up
receiving for the value of a parameter is a string with leading and
trailing whitespace removed. By default, you will need to handle
conversion of that string to a useful form yourself. However, if you
provide some metadata about your parameters, the parameter handling
will be taken care of for you. (Additionally, tools that deal with
Policies themselves can use this information to enhance their
functionality. See the perlcritic --profile-proto option for an
example.)
You can look at Perl::Critic::Policy::ControlStructures::ProhibitCascadingIfElse for a simple example of a configurable Policy and Perl::Critic::Policy::Documentation::RequirePodSections for a more complex one.
The initialize_if_enabled() method for a Policy receives one
argument: an instance of Perl::Critic::PolicyConfig. This method
is only called if the user's configuration has enabled the policy. It
returns a boolean stating whether the Policy should continue to be
enabled. Generally, the only reason to return $FALSE is when some
external requirement is missing. For example,
Perl::Critic::Policy::CodeLayout::RequireTidyCode disables itself
if Perl::Tidy is not installed.
A basic, do-nothing implementation of initialize_if_enabled() would
be:
use Perl::Critic::Utils qw< :booleans >;
...
sub initialize_if_enabled {
my ( $self, $config ) = @_;
return $TRUE;
}
As stated above, what you get in $config are trimmed strings. For
example, if the user's .perlcritic contains
[Your::Policy]
foo = bar baz
factor = 5.52
selections = 2 78 92
then $config will contain the equivalent of
my $config = {
foo => 'bar baz',
factor => '5.52',
selections => '2 78 92',
};
To make this available to the violates() method, the values are
usually put into $self under the name of the configuration item
prefixed with an underscore. E.g.
sub initialize_if_enabled {
my ( $self, $config ) = @_;
$self->{_foo} = $config->get{foo};
$self->{_factor} = $config->get{factor};
$self->{_selections} = $config->get{selections};
return $TRUE;
}
Often, you'll want to convert the configuration values into something
more useful. In this example, selections is supposed to be a list
of integers. Perl::Critic::Utils contains a number of functions
that can help you with this. Assuming that violates() wants to
have selections as an array, you'll want to have something like
this:
use Perl::Critic::Utils qw{ :booleans :characters :data_conversion };
sub initialize_if_enabled {
my ( $self, $config ) = @_;
$self->{_foo} = $config->get{foo};
$self->{_factor} = $config->get{factor};
my $selections = $config->get{selections};
$selections = defined $selections ? $selections : $EMPTY_STRING;
$self->{_selections} = [ words_from_string($selections) ];
return $TRUE;
}
Since selections contains numbers, it may be desirable to change
the assignment to look like
$self->{_selections} = [ map { $_ + 0 } words_from_string($selections) ];
If violates() needs to quickly determine whether a particular value
is in selections, you would want to use a hash instead of an array,
like this:
$self->{_selections} = { hashify( words_from_string($selections) ) };
For an example of a Policy that has some simple, but non-standard configuration handling, see Perl::Critic::Policy::CodeLayout::RequireTidyCode.
It used to be the case that Policies handled configuration by
implementing a constructor. However, there was no requirement to call
the base constructor; as long as the Policy ended up being a blessed
hash reference, everything was fine. Unfortunately, this meant that
Policies would be loaded and their prerequisites would be used,
even if the Policy wasn't enabled, slowing things down. Also, this
severely restricted the core of Perl::Critic's ability to enhance
things. Use of constructors is deprecated and is incompatible with
supported_parameters() metadata below. Kindly use
initialize_if_enabled(), instead, to do any sort of set up that you
need.
supported_parameters()
As minimum for a well behaved Policy, you should implement
supported_parameters() in order to tell the rest of Perl::Critic
what configuration values the Policy looks for, even if it is only to say
that the Policy is not configurable. In the simple form, this
function returns a list of the names of the parameters the Policy
supports. So, for an non-configurable Policy, as in the
RequireBlockGrep example above, this looked like
sub supported_parameters { return () }
For the example being used in the initialize_if_enabled() section
above, this would be
sub supported_parameters { return qw< foo factor selections >; }
Given this information, Perl::Critic can tell the user when they
have specified a parameter for a Policy which isn't valid, e.g. when
they've misspelled the name of the parameter, and can emit the
parameter as part of a .perlcritic prototype.
You can provide even more information about your Policy's
configuration by giving each parameter a description and a string
representation of the default value for the parameter. You do this by
having the values in the list returned by supported_parameters() be
hash references instead of strings, with keys of name,
description, and default_string. For example,
sub supported_parameters {
return (
{
name => 'allowed_values',
description =>
'Individual and ranges of values to allow, and/or "all_integers".',
default_string => '0 1 2',
},
{
name => 'allowed_types',
description => 'Kind of literals to allow.',
default_string => 'Float',
},
);
}
Note that use of constructors is incompatible with specifying parameters in this way.
supported_parameters() to Get It Done For You
The supported_parameters() discussion above showed how you could
help others with your Policy, but didn't do anything to make your life
as a Policy author easier; you still need to implement
initialize_if_enabled() to access any configuration that the user
has specified. To have the configuration automatically handled for
you, you need to declare how your parameters act by specifying a value
for their behavior. For example, the following declares that a
parameter allows the user to choose from five specific values and that
the user can select any combination of them:
sub supported_parameters {
return (
{
name => 'allowed_types',
description => 'Kind of literals to allow.',
default_string => 'Float',
behavior => 'enumeration',
enumeration_values => [ qw{ Binary Exp Float Hex Octal } ],
enumeration_allow_multiple_values => 1,
},
);
}
When you specify a behavior, parsing and validation of the
user-specified and default values is done for you and your
violates() method can retrieve the value under the key of the
parameter name prefixed with an underscore, e.g., for the above
declaration, the parsed and validated value can be accessed via
<$self-{_allowed_types}>>.
The behaviors provide additional functionality to Perl::Critic; for
more on this, see Perl::Critic::PolicyParameter and
Perl::Critic::PolicyParameter::Behavior.
The following discusses each of the supported behaviors and the options they support. For the full details of a behavior, see the documentation for the implementing class.
Implemented in Perl::Critic::PolicyParameter::Behavior::String.
The most basic of behaviors, the value of the parameter will be stored in the Policy as a string.
This behavior is not configurable.
supported_parameters() example
sub supported_parameters {
return (
{
name => 'a_string',
description => 'An example string.',
default_string => 'blah blah blah',
behavior => 'string',
},
);
}
sub violates {
my ($self, $element, $document) = @_;
...
my $string = $self->{_a_string};
...
}
Implemented in Perl::Critic::PolicyParameter::Behavior::Boolean.
The value of the parameter will be either Perl::Critic::Utils/$TRUE or Perl::Critic::Utils/$FALSE.
This behavior is not configurable.
supported_parameters() example
sub supported_parameters {
return (
{
name => 'a_boolean',
description => 'An example boolean.',
default_string => '1',
behavior => 'boolean',
},
);
}
sub violates {
my ($self, $element, $document) = @_;
...
my $is_whatever = $self->{_a_boolean};
if ($is_whatever) {
...
}
...
}
Implemented in Perl::Critic::PolicyParameter::Behavior::Integer.
The value is validated against m/ \A [-+]? [1-9] [\d_]* \z /xms
(with an special check for "0"). Notice that this means that
underscores are allowed in input values as with Perl numeric literals.
This takes two options, integer_minimum and
integer_maximum, which specify endpoints of an inclusive range to
restrict the value to. Either, neither, or both may be specified.
supported_parameters() example
sub supported_parameters {
return (
{
name => 'an_integer',
description => 'An example integer.',
default_string => '5',
behavior => 'integer',
integer_minimum => 0,
integer_maximum => 10,
},
);
}
sub violates {
my ($self, $element, $document) = @_;
...
my $integer = $self->{_an_integer};
if ($integer > $TURNING_POINT) {
...
}
...
}
Implemented in Perl::Critic::PolicyParameter::Behavior::StringList.
The values will be derived by splitting the input string on blanks. (See Perl::Critic::Utils/"words_from_string".) The parameter will be stored as a reference to a hash, with the values being the keys.
This takes one optional option, always_present_values, of a
reference to an array of strings that will always be included in the
parameter value, e.g. if the value of this option is
[ qw{ a b c } ] and the user specifies a value of 'c d e', then
the value of the parameter will contain 'a', 'b', 'c',
'd', and 'e'.
supported_parameters() example
sub supported_parameters {
return (
{
name => 'a_string_list',
description => 'An example list.',
default_string => 'red pink blue',
behavior => 'string list',
always_present_values => [ qw{ green purple} ],
},
);
}
sub violates {
my ($self, $element, $document) = @_;
...
my $list = $self->{_a_string_list};
my @list = keys %{$list};
...
return if not $list->{ $element->content() };
...
}
Implemented in Perl::Critic::PolicyParameter::Behavior::Enumeration.
The values will be derived by splitting the input string on blanks.
(See Perl::Critic::Utils/"words_from_string".) Depending upon the
value of the enumeration_allow_multiple_values option, the
parameter will be stored as a string or a reference to a hash, with
the values being the keys.
This behavior takes one required option and one optional one. A value
for enumeration_values of a reference to an array of valid strings
is required. A true value can be specified for
enumeration_allow_multiple_values to allow the user to pick more
than one value, but this defaults to false.
supported_parameters() example
use Perl::Critic::Utils qw{ :characters };
sub supported_parameters {
return (
{
name => 'a_single_valued_enumeration',
description =>
'An example enumeration that can only have a single value.',
default_string => $EMPTY,
behavior => 'enumeration',
enumeration_values => [ qw{ block statement pod operator } ],
enumeration_allow_multiple_values => 0,
},
{
name => 'a_multi_valued_enumeration',
description =>
'An example enumeration that can have multiple values.',
default_string => 'fe',
behavior => 'enumeration',
enumeration_values => [ qw{ fe fi fo fum } ],
enumeration_allow_multiple_values => 1,
},
);
}
sub violates {
my ($self, $element, $document) = @_;
...
my $single_value = $self->{_a_single_valued_enumeration};
...
my $multi_value = $self->{_a_multi_valued_enumeration};
if ( $multi_value->{fum} ) {
...
}
...
}
If none of the behaviors does exactly what you want it to, you can
provide your own parser for a parameter. The reason for doing this as
opposed to using an implementation of initialize_if_enabled() is
that it allows you to use a behavior to provide its extra
functionality and it provides a means for a Perl::Critic
configuration program, e.g. an IDE that integrates Perl::Critic, to
validate your parameter as the user modifies its value.
The way you declare that you have a custom parser is to include a
reference to it in the parameter specification with the parser key.
For example:
sub supported_parameters {
return (
{
name => 'file_name',
description => 'A file for to read a list of values from.',
default_string => undef,
behavior => 'string',
parser => \&_parse_file_name,
},
);
}
A parser is a method on a subclass of Perl::Critic::Policy that
takes two parameters: the Perl::Critic::PolicyParameter that is
being specified and the value string provided by the user. The method
is responsible for dealing with any default value and for saving the
parsed value for later use by the violates() method.
An example parser (without enough error handling) for the above example declaration:
use File::Slurp qw< slurp >;
use Perl::Critic::Exception::Configuration::Option::Policy::ParameterValue
qw{ throw_policy_value };
sub _parse_file_name {
my ($self, $parameter, $config_string) = @_;
my @thingies;
if ($config_string) {
if (not -r $config_string) {
throw_policy_value
policy => $self->get_short_name(),
option_name => $parameter->get_name(),
option_value => $config_string,
message_suffix => 'is not readable.';
}
@thingies = slurp $config_string;
}
$self->{_thingies} = \@thingies;
return;
}
Note that, if the value for the parameter is not valid, an instance of
Perl::Critic::Exception::Configuration::Option::Policy::ParameterValue
is thrown. This allows Perl::Critic to include that problem along
with any other problems found with the user's configuration in a
single error message.
supported_parameters() and initialize_if_enabled()
There are cases where a Policy needs additional initialization beyond
configuration or where the way it acts depends upon the combination of
multiple parameters. In such situations, you will need to create an
implementation of initialize_if_enabled(). If you want to take
advantage of the supplied parameter handling from within
implementation of initialize_if_enabled(), note that the
information from supported_parameters() will already have been
used, with user-supplied parameter values validated and placed into
the Policy by the time initialize_if_enabled() has been called. It
is likely that you will not need to refer the contents of the
$config parameter; just pull the information you need out of
$self. In fact, any value for the parameter values will be gone.
supported_parameters().
Currently, one of:
default_maximum_violations_per_document()
Certain problems that a Policy detects can be endemic to a particular file; if there's one violation, there's likely to be many. A good example of this is Perl::Critic::Policy::TestingAndDebugging::RequireUseStrict; if there's one line before use strict, there's a good chance that the entire file is missing use strict. In such cases, it's not much help to the user to report every single violation. If you've got such a policy, you should override default_maximum_violations_per_document() method to provide a limit. The user can override this value with a value for "maximum_violations_per_document" in their .perlcriticrc.
See the source code for Perl::Critic::Policy::ValuesAndExpressions::ProhibitMagicNumbers and Perl::Critic::Policy::TestingAndDebugging::RequireUseWarnings for examples.
You need to come up with a name for your set of policies. Sets of
add-on policies are generally named Perl::Critic::something,
e.g. Perl::Critic::More.
The module representing the distribution will not actually have any functionality; it's just documentation and a name for users to use when installing via CPAN/CPANPLUS. The important part is that this will include a list of the included policies, with descriptions of each.
A typical implementation will look like:
package Perl::Critic::Example;
use strict;
use warnings;
our $VERSION = '1.000000';
1; # Magic true value required at end of module
__END__
=head1 NAME
Perl::Critic::Example - Policies for Perl::Critic that act as an example.
=head1 AFFILIATION
This module has no functionality, but instead contains documentation
for this distribution and acts as a means of pulling other modules
into a bundle. All of the Policy modules contained herein will have
an "AFFILIATION" section announcing their participation in this
grouping.
=head1 SYNOPSIS
Some L<Perl::Critic> policies that will help you keep your code
nice and compliant.
=head1 DESCRIPTION
The included policies are:
=over
=item L<Perl::Critic::Policy::Documentation::Example>
Complains about some example documentation issues. [Severity: 3]
=item L<Perl::Critic::Policy::Variables::Example>
All modules must have at least one variable. [Severity: 3]
=back
=head1 CONFIGURATION AND ENVIRONMENT
All policies included are in the "example" theme. See the
L<Perl::Critic> documentation for how to make use of this.
Users can choose which policies to enable using themes. You should
implement default_themes() so that users can take advantage of
this. In particular, you should use a theme named after your
distribution in all your policies; this should match the value listed
in the CONFIGURATION AND ENVIRONMENT POD section as shown above.
default_themes { return qw< example math > }
If you're looking for ideas of what themes to do, have a look at the
output of perlcritic --list-themes.
Since all policies have to go somewhere under the
Perl::Critic::Policy:: namespace, it isn't always clear what
distribution a policy came from when browsing through their
documentation. For this reason, you should include an AFFILIATION
section in the POD for all of your policies that state where the
policy comes from. For example:
=head1 AFFILIATION
This policy is part of L<Perl::Critic::Example>.
In order to make it clear what can be done with a policy, you should
always include a CONFIGURATION section in your POD, even if it's
only to say:
=head1 CONFIGURATION
This Policy is not configurable except for the standard options.
When you're trying to figure out what PPI is going to hand you for a chunk of code, there is a tools/ppidump program in the Perl::Critic distribution that will help you. For example, when developing the above RequireBlockGrep example, you might want to try
tools/ppidump '@matches = grep /pattern/, @list;'
and
tools/ppidump '@matches = grep { /pattern/ } @list;'
to see the differences between the two cases.
This is part of Perl::Critic version 1.088.
Jeffrey Ryan Thalhammer <thaljef@cpan.org>
Copyright (c) 2005-2008 Jeffrey Ryan Thalhammer. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of this license can be found in the LICENSE file included with this module.