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Perl::Critic::CORE_DEVELOPER(3)User Contributed Perl DocumentationPerl::Critic::CORE_DEVELOPER(3)

NAME
       Perl::Critic::CORE_DEVELOPER - Hints for working on the Perl::Critic core.

DESCRIPTION
       This document is a grab-bag of notes for those who are working on the underpinnings of
       Perl::Critic. They are intended to be informative, but unfortunately can not really be
       considered authoritative. It is in the nature of the task being described that the user of
       this document will end up working out the details for him- or herself based on the actual
       work being performed. Caveat lector.

BECOMING A CORE DEVELOPER
       Here are my thoughts on how to get started. Note that the steps are not numbered because
       I'm not sure there is a clear order to them. The items with two stars in front of them are
       from the mailing list; the ones with one star are my opinion. Although sometimes I have
       felt it helpful to comment on the two-star items, just to make things thoroughly unclear.

       * If you're unsure of yourself, install Perl::Critic, then download the source and rummage
       around in it.

       ** Subscribe to the developers' mailing list. There are instructions in "EXTENDING THE
       CRITIC" in Perl::Critic. The commits mailing list is another good one.

       ** You will need to be registered as a developer before you can actually change code.
       <http://perlcritic.tigris.org/> only lets you register as an observer. I got promoted on
       registration, but if that doesn't happen, a note to the developers' mailing list might
       help.

       ** If you are working on an RT ticket, you should update the ticket to say that you are,
       to keep other people from duplicating your effort.

       * I personally would update RT at the point I was reasonably confident I could hack it,
       just to prevent myself from having to update RT again in a week or so saying "oops, bit
       off more than I could chew."  But that's me talking.

       * Subversion (also known as svn, which is the command name) is a version control system.
       It provides a repository for the code being worked on. Developers check out the code into
       a local directory, work on that, and and then commit changes back to the repository.  Any
       previous version of the code is available from the repository - a bad change can be backed
       out, though the longer the bad change hangs around the harder it may be to deal with.

       * Install Subversion if you don't already have it. You can get it from
       <http://subversion.tigris.org/>. The current version is Subversion 1.6, but as of
       mid-2009, the 1.4.4 client seems to be adequate. The O'Reilly book, "Version Control with
       Subversion", is available online at <http://svnbook.red-bean.com/>. The English version of
       the 1.4 documentation may be still available at
       <http://svnbook.red-bean.com/en/1.4/index.html>.

       * Branching is essentially pulling off your own managed copy of the code to develop on. It
       is creating a "sandbox", if you will. You can commit changes back to the repository
       without affecting the main line of development (the "trunk"). The entire branch can be
       abandoned without affecting the trunk. The down side of branches is that it is a bit of a
       pain to merge them back into the trunk.

       Consult the developers' mailing list on whether you should branch or work directly against
       the trunk.

       ** The Perl Critic subversion repository on Tigris contains a bunch of stuff other than
       Perl::Critic. You probably do not need it all. But if you execute the 'svn checkout'
       command given on Tigris you get it all.	This is not recommended.

       * Here is my "branch and checkout" cookbook:

	   Name the branch after the ticket you are working on (e.g. rt25046).
	   Issue the following commands (we assume '$ ' is your system prompt):

	   $ svn copy
	       http://perlcritic.tigris.org/svn/perlcritic/trunk/distributions/Perl-Critic
	       http://perlcritic.tigris.org/svn/perlcritic/branches/rt25046
	       -m "Put your comment here" --username your_username

	   $ svn checkout http://perlcritic.tigris.org/svn/perlcritic/branches/rt25046
	       --username your_username

       The 'svn copy' command is the one that does the branch. Each 'svn' command is one line,
       though sometimes (e.g. the 'branch') it's a huge one. The "svn" commands above have been
       wrapped. A checkout from the trunk is also done with the "svn checkout" command, but
       specifying the trunk's URL. You can also specify, as a second argument to "svn checkout",
       the directory you want the code to go into.

       ** Development requires using Module::Build rather than ExtUtils::MakeMaker.  In other
       words,

	   $ perl Build.PL
	   $ ./Build
	   $ ./Build test

       ** You need to run the suite of author tests by running

	   $ ./Build authortest

       (but not 'make authortest', which is one of the reasons you should start with Build.PL
       rather than Makefile.PL) These should run cleanly before you declare your work done. My
       advice, though, is not to worry about them until your code is functionally correct.

   Modules required for authortest
       The authortest requires a bunch of modules above and beyond those required to run
       "Perl::Critic". The list probably depends on which "Perl::Critic" you are testing, so the
       following should not be considered definitive.  You need the following in addition to all
       optional modules for Perl::Critic itself.

	   Devel::EnforceEncapsulation
	   Perl::Critic::More
	   Test::Kwalitee
	   Test::Memory::Cycle
	   Test::Perl::Critic
	   Test::Pod
	   Test::Pod::Coverage
	   Test::Without::Module

       You can find out what the optional modules are by looking at
       "recommended_module_versions()" in inc/Perl/Critic/BuildUtilities.pm.

       In the absence of "Test::Memory::Cycle", the relevant tests are simply skipped.	In the
       absence of the other modules, the tests die horribly.  Of course, either way they do not
       get run, so the difference is mainly one of aesthetics.

       Under Perl 5.12 and above, Devel::Cycle 1.11 needs to be patched to handle a "Regexp" as a
       first-class Perl object. See <https://rt.cpan.org/Public/Bug/Display.html?id=56681> for
       the details.

ADDING A GLOBAL CONFIGURATION ITEM
       Perlcritic handles global configuration items and command line options in very similar
       ways. These notes will cover adding both a global configuration item and a corresponding,
       same-named command option.  These notes can not, of course, cover implementing the
       functionality of the new item, just the mechanics of getting the item into Perl::Critic.

   Naming Conventions
       All names are lower-case, except for the names of constants (if any), which are upper-
       case. When a name contains multiple words, dashes will be used to separate the words in
       the configuration item name and the command line option, and underscores will be used in
       the accessor and attribute value names, and constant names if any.

       For example, if "new item" is being added, the configuration item is "new-item", the
       command option is "--new-item", the accessors are "new_item()", and the value of the
       attribute will be stored in "$self->{_new_item}". If there are constants involved, their
       names will start with "NEW_ITEM_". These names will be used in the following discussion.

   Implementation
       There are several files that must be modified to get your new configuation item and/or
       command line option.

       lib/Perl/Critic/Utils/Constants.pm

       If there are manifest constants connected with your implementation they go here. You may
       well at least have a

	   $NEW_ITEM_DEFAULT

       to define. All the constants for your new item must be exported, and should be exported
       not only individually but all together with export tag

	   new_item

       lib/Perl/Critic/Command.pm

       If your new item is a command option, its Getopt::Long specification must be defined in
       "_get_option_specification()". If your new configuration item does not have a
       corresponding command option, you do not need to make any changes to this file.

       lib/Perl/Critic/OptionsProcessor.pm

       If your new item is a global configuration item, you need to add the code to handle it
       here. Specifically:

       You must add code to the "_init()" method to store the value of your item as an attribute
       value, defaulting it if necessary. Using our naming convention, a single-valued item would
       be stored like this:

	   $self->{_new_item} = dor(delete $args{'new-item'},
	       $NEW_ITEM_DEFAULT);

       If the item has synonyms (e.g. both 'color' and 'colour' meaning the same thing), the
       "dor()" call must check for all of them. If the item took a list of values, they would be
       parsed apart and stored as an array reference.

       You must also add and document an accessor for your new item. This would look something
       like this:

	   sub new_item {
	       my ($self) = @_;
	       return $self->{_new_item};
	   }

       In the case of multi-valued items, the accessor must return the array reference, so the
       above specimen code works in that case also.

       Note that no validation is done here -- this class is simply a bridge between the physical
       .perlcriticrc file and Perl::Critic::Config, which is where the action is.

       If your new item is a command option without a corresponding global configuration item,
       you do not need to modify this file.

       lib/Perl/Critic/Config.pm

       You must write a "_validate_and_store_new_item()" method to validate and store the value
       of the new item. The signature of this method depends on the details of your new item, but
       it must include at least the value of the item, even if there is no corresponding global
       configuration item. If it is possible to get validation failures, it will also need an
       errors object to add the validation exception to.  Because the details vary, the best way
       to proceed is probably to find a method similar to the one you want to write, and
       implement from there. The "_validate_and_store_top()" method is a reasonable starting
       point for an item having a single value. The validated value needs to be stored in
       "$self->{_new_item}".

       You must call "_validate_and_store_new_item()" in the "_init()" method.

       You must write and document an accessor method for the value of the new item. The typical
       accessor method for a single-valued item is

	   sub new_item {
	       my ($self) = @_;
	       return $self->{_new_item};
	   }

       but the accessor for a multi-valued item must return a list:

	   sub new_item {
	       my ($self) = @_;
	       return @{ $self->{_new_item} };
	   }

       Last, you must document the item iteself.

       lib/Perl/Critic/ProfilePrototype.pm

       If your new item has a corresponding global configuration item, you must update the
       "to_string()" method to include the item in the string. Your implementation of the item
       must be such that the generated string is the same as the input string for the item,
       except for whitespace.

       If your new item has no corresponding global configuration item, you do not need to change
       this file.

       bin/perlcriticrc

       If your new item has a corresponding command option, you must document it here. If it does
       not, you do not need to change this file.

       examples/perlcriticrc

       If your new item has a corresponding global configuration item, you must add it here. If
       it does not, you do not need to change this file.

   Testing
       The following test files must be considered for modification:

	   t/00_modules.t
	   t/01_config.t
	   t/01_config_bad_perlcritic.t
	   t/04_options_processor.t
	   t/07_command.t
	   t/10_user_profile.t
	   t/16_roundtrip_defaults.t

       Depending on your new item, you may not need to change all of these, but you should at
       least review them. Depending on what your new item actually does, other test files may
       need to be modified as well.

DEPRECATING AND REMOVING A PUBLIC SUBROUTINE OR METHOD
       This is something to be done cautiously. The code in question may only exist to serve
       Perl::Critic, but if it is documented as public it may well be in use "in the wild",
       either in add-ons to Perl::Critic or by users of Perl::Critic.

       Before deprecating public code, the potential deprecator must discuss the issues on the
       Perl::Critic developers' mailing list. There are instructions on how to subscribe to this
       list in "EXTENDING THE CRITIC" in Perl::Critic.

       Once agreement is reached, the technical details of the deprecation are fairly simple.

       You must insert something like the following in the code to be deprecated:

	   warnings::warnif(
	       'deprecated',
	       'Perl::Critic::Utils::foo() deprecated, use blah::foo() instead.',
	   );

       You should have the deprecated subroutine delegate its functionality to the new
       subroutine, if that is practical (it may not be).

       You must update the documentation to say that the old code is deprecated, and what the
       replacement is.

       After the old code has been deprecated for a couple production releases, it can be
       removed.

AUTHOR
       Thomas R. Wyant, III wyant at cpan dot org

COPYRIGHT
       Copyright (c) 2009-2011 Thomas R. Wyant, III

       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 v5.16.3				    2014-06-09		  Perl::Critic::CORE_DEVELOPER(3)
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