Perl::Critic::DEVELOPEUser Contributed Perl DocumentPerl::Critic::DEVELOPER(3)NAMEPerl::Critic::DEVELOPER - How to make new Perl::Critic::Policy modules.
DESCRIPTION
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.
BACKGROUND
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.
EXAMPLE POLICY
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::Policy::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
"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 "first_arg" in Perl::Critic::Utils 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 "violation" in Perl::Critic::Policy 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 or with a "%d" escape to see
it along with the rest of the output for violations of your policy.
MAKING YOUR POLICY CONFIGURABLE
Perl::Critic takes care of gathering configuration information for your
Policy, from whatever source the user specifies. (See "CONFIGURATION"
in Perl::Critic 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.
Do It All Yourself
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 used to disable
itself if Perl::Tidy was not installed (that is until we made it no
longer optional for the Perl-Critic distribution).
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.
Note On Constructors
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 "use"d, 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.
Providing Basic Configuration Information Via "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 .perlcriticrc 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.
Using "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
"$self->{_allowed_types}".
The behaviors provide additional functionality to "Perl::Critic"; for
more on this, see Perl::Critic::PolicyParameter and
Perl::Critic::PolicyParameter::Behavior.
The following discusses each of the supported behaviors and the options
they support. For the full details of a behavior, see the
documentation for the implementing class.
"string"
Implemented in Perl::Critic::PolicyParameter::Behavior::String.
The most basic of behaviors, the value of the parameter will be stored
in the Policy as a string.
This behavior is not configurable.
"supported_parameters()" example
sub supported_parameters {
return (
{
name => 'a_string',
description => 'An example string.',
default_string => 'blah blah blah',
behavior => 'string',
},
);
}
Access example
sub violates {
my ($self, $element, $document) = @_;
...
my $string = $self->{_a_string};
...
}
"boolean"
Implemented in Perl::Critic::PolicyParameter::Behavior::Boolean.
The value of the parameter will be either $TRUE or $FALSE.
This behavior is not configurable.
"supported_parameters()" example
sub supported_parameters {
return (
{
name => 'a_boolean',
description => 'An example boolean.',
default_string => '1',
behavior => 'boolean',
},
);
}
Access example
sub violates {
my ($self, $element, $document) = @_;
...
my $is_whatever = $self->{_a_boolean};
if ($is_whatever) {
...
}
...
}
"integer"
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,
},
);
}
Access example
sub violates {
my ($self, $element, $document) = @_;
...
my $integer = $self->{_an_integer};
if ($integer > $TURNING_POINT) {
...
}
...
}
"string list"
Implemented in Perl::Critic::PolicyParameter::Behavior::StringList.
The values will be derived by splitting the input string on blanks.
(See "words_from_string" in Perl::Critic::Utils.) The parameter will be
stored as a reference to a hash, with the values being the keys.
This takes one optional option, "list_always_present_values", of a
reference to an array of strings that will always be included in the
parameter value, e.g. if the value of this option is "[ qw{ a b c } ]"
and the user specifies a value of 'c d e', then the value of the
parameter will contain 'a', 'b', 'c', 'd', and 'e'.
"supported_parameters()" example
sub supported_parameters {
return (
{
name => 'a_string_list',
description => 'An example list.',
default_string => 'red pink blue',
behavior => 'string list',
list_always_present_values => [ qw{ green purple} ],
},
);
}
Access example
sub violates {
my ($self, $element, $document) = @_;
...
my $list = $self->{_a_string_list};
my @list = keys %{$list};
...
return if not $list->{ $element->content() };
...
}
"enumeration"
Implemented in Perl::Critic::PolicyParameter::Behavior::Enumeration.
The values will be derived by splitting the input string on blanks.
(See "words_from_string" in Perl::Critic::Utils.) 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 => $EMPTY,
behavior => 'enumeration',
enumeration_values => [ qw{ block statement pod operator } ],
enumeration_allow_multiple_values => 0,
},
{
name => 'a_multi_valued_enumeration',
description =>
'An example enumeration that can have multiple values.',
default_string => 'fe',
behavior => 'enumeration',
enumeration_values => [ qw{ fe fi fo fum } ],
enumeration_allow_multiple_values => 1,
},
);
}
Access example
sub violates {
my ($self, $element, $document) = @_;
...
my $single_value = $self->{_a_single_valued_enumeration};
...
my $multi_value = $self->{_a_multi_valued_enumeration};
if ( $multi_value->{fum} ) {
...
}
...
}
Using a Custom Parser
If none of the behaviors does exactly what you want it to, you can
provide your own parser for a parameter. The reason for doing this as
opposed to using an implementation of "initialize_if_enabled()" is that
it allows you to use a behavior to provide its extra functionality and
it provides a means for a "Perl::Critic" configuration program, e.g. an
IDE that integrates "Perl::Critic", to validate your parameter as the
user modifies its value.
The way you declare that you have a custom parser is to include a
reference to it in the parameter specification with the "parser" key.
For example:
sub supported_parameters {
return (
{
name => 'file_name',
description => 'A file for to read a list of values from.',
default_string => undef,
behavior => 'string',
parser => \&_parse_file_name,
},
);
}
A parser is a method on a subclass of Perl::Critic::Policy that takes
two parameters: the Perl::Critic::PolicyParameter that is being
specified and the value string provided by the user. The method is
responsible for dealing with any default value and for saving the
parsed value for later use by the "violates()" method.
An example parser (without enough error handling) for the above example
declaration:
use File::Slurp qw< slurp >;
use Perl::Critic::Exception::Configuration::Option::Policy::ParameterValue
qw{ throw_policy_value };
sub _parse_file_name {
my ($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.
Using Both "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.
Summary of permitted hash keys in "supported_parameters()".
All types
- "name" (mandatory)
- "description" (optional)
- "behavior" (optional)
Currently, one of:
"boolean"
"enumeration"
"integer"
"string"
"string list"
- "default_string" (optional)
A string representation of the default value of the parameter.
- "parser" (optional)
A code ref to a custom parser for the parameter.
Enumerations
- "enumeration_values" (mandatory)
A mandatory reference to an array of strings.
- "enumeration_allow_multiple_values" (optional)
Boolean indicating whether or not the user is restricted to a
single value.
Integers
- "integer_minimum" (optional)
Minimum allowed value, inclusive.
- "integer_maximum" (optional)
Maximum allowed value, inclusive.
String lists
- "list_always_present_values" (optional)
A reference to an array of values that should always be included in
the value of the parameter.
ADDITIONAL FEATURES
"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.
"is_safe()"
Most Perl::Critic Policies are purely static. In other words, they
never compile or execute any of the source code that they analyze.
However it is possible to write dynamic Policies that do compile or
execute code, which may result in unsafe operations (see
Perl::Critic::Dynamic for an example). So the "is_safe()" method is
used to indicate whether a Policy can be trusted to not cause mischief.
By default, "is_safe()" returns true. But if you are writing a Policy
that will compile or execute any of the source code that it analyzes,
then you should override the "is_safe()" method to return false.
DISTRIBUTING YOUR POLICIES
Create a Distribution
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|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|Perl::Critic::Policy::Documentation::Example>
Complains about some example documentation issues. [Default severity: 3]
=item L<Perl::Critic::Policy::Variables::Example|Perl::Critic::Policy::Variables::Example>
All modules must have at least one variable. [Default severity: 3]
=back
=head1 CONFIGURATION AND ENVIRONMENT
All policies included are in the "example" theme. See the
L<Perl::Critic|Perl::Critic> documentation for how to make use of this.
Themes
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 use, have a look at the
output of "perlcritic --list-themes".
Documentation
AFFILIATION
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|Perl::Critic::Example>.
CONFIGURATION
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.
TESTING YOUR POLICY
The Perl::Critic distribution also contains a framework for testing
your Policy. See Test::Perl::Critic::Policy for the details.
HINT
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.
Alternatively, see the "ppi_dumper" documentation at
http://search.cpan.org/dist/App-PPI-Dumper/script/ppi_dumper
<http://search.cpan.org/dist/App-PPI-Dumper/script/ppi_dumper> and the
"PPI::Tester" documentation at
http://search.cpan.org/dist/PPI-Tester/lib/PPI/Tester.pm
<http://search.cpan.org/dist/PPI-Tester/lib/PPI/Tester.pm>.
VERSION
This is part of Perl::Critic version 1.116.
SEE ALSO
Chas. Owens has a blog post about developing in-house policies at
http://svok.blogspot.com/2009/09/adding-house-policies-to-perlcritic.html
<http://svok.blogspot.com/2009/09/adding-house-policies-to-
perlcritic.html>.
AUTHOR
Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>
COPYRIGHT
Copyright (c) 2005-2011 Imaginative Software Systems. 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.
perl v5.14.1 2011-07-22 Perl::Critic::DEVELOPER(3)
