Catalyst::Upgrading - Instructions for upgrading to the latest Catalyst

Upgrading to Catalyst 5.9

The major change is that Plack, a toolkit for using the PSGI specification, now replaces most of the subclasses of Catalyst::Engine. If you are using one of the standard subclasses of Catalyst::Engine this should be a straightforward upgrade for you. It was a design goal for this release to preserve as much backwards compatibility as possible. However, since Plack is different from Catalyst::Engine, it is possible that differences exist for edge cases. Therefore, we recommend that care be taken with this upgrade and that testing should be greater than would be the case with a minor point update. Please inform the Catalyst developers of any problems so that we can fix them and incorporate tests.

It is highly recommended that you become familiar with the Plack ecosystem and documentation. Being able to take advantage of Plack development and middleware is a major bonus to this upgrade. Documentation about how to take advantage of Plack::Middleware by writing your own .psgi file is contained in Catalyst::PSGI.

If you have created a custom subclass of Catalyst:Engine, you will need to convert it to be a subclass of Plack::Handler.

If you are using the Plack engine, Catalyst::Engine::PSGI, this new release supersedes that code.

If you are using a subclass of Catalyst::Engine that is aimed at nonstandard or internal/testing uses, such as Catalyst::Engine::Embeddable, you should still be able to continue using that engine.

Advice for specific subclasses of Catalyst::Engine follows:

Upgrading the FastCGI Engine

No upgrade is needed if your script is already upgraded to use Catalyst::Script::FastCGI.

Upgrading the mod_perl / Apache Engines

The engines that are built upon the various iterations of mod_perl, Catalyst::Engine::Apache::MP13 (for mod_perl 1, and Apache 1.x) and Catalyst::Engine::Apache2::MP20 (for mod_perl 2, and Apache 2.x), should be seamless upgrades and will work using using Plack::Handler::Apache1 or Plack::Handler::Apache2 as required.

Catalyst::Engine::Apache2::MP19, however, is no longer supported, as Plack does not support mod_perl version 1.99. This is unlikely to be a problem for anyone, as 1.99 was a brief beta-test release for mod_perl 2, and all users of mod_perl 1.99 are encouraged to upgrade to a supported release of Apache 2 and mod_perl 2.

Upgrading the HTTP Engine

The default development server that comes with the Catalyst distribution should continue to work as expected with no changes as long as your myapp_server script is upgraded to use Catalyst::Script::HTTP.

Upgrading the CGI Engine

If you were using Catalyst::Engine::CGI there is no upgrade needed if your script is already upgraded to use Catalyst::Script::CGI.

Upgrading Catalyst::Engine::HTTP::Prefork

If you were using Catalyst::Engine::HTTP::Prefork then Starman is automatically loaded. You should (at least) change your Makefile.PL to depend on Starman.

You can regenerate your script with and implement a MyApp::Script::Server class that looks like this:

    package MyApp::Script::Server;
    use Moose;
    use namespace::autoclean;

    extends 'CatalystX::Script::Server::Starman';


This takes advantage of the new script system, and will add a number of options to the standard server script as extra options are added by Starman.

More information about these options can be seen at "SYNOPSIS" in CatalystX::Script::Server::Starman.

An alternate route to implement this functionality is to write a simple .psgi file for your application, and then use the plackup utility to start the server.

Upgrading the PSGI Engine

If you were using Catalyst::Engine::PSGI, this new release supersedes this engine in supporting Plack. By default the Engine is now always Plack. As a result, you can remove the dependency on Catalyst::Engine::PSGI in your Makefile.PL.

Applications that were using Catalyst::Engine::PSGI previously should entirely continue to work in this release with no changes.

However, if you have an app.psgi script, then you no longer need to specify the PSGI engine. Instead, the Catalyst application class now has a new method psgi_app which returns a PSGI compatible coderef which you can wrap in the middleware of your choice.

Catalyst will use the .psgi for your application if it is located in the home directory of the application.

For example, if you were using Catalyst::Engine::PSGI in the past, you will have written (or generated) a script/myapp.psgi file similar to this one:

    use Plack::Builder;
    use MyCatalytApp;


    builder {
        enable ... # enable your desired middleware
        sub { MyCatalystApp->run(@_) };

Instead, you now say:

    use Plack::Builder;
    use MyCatalystApp;

    builder {
        enable ... #enable your desired middleware

In the simplest case:

    my $app = sub { MyCatalystApp->run(@_) }


    my $app = MyCatalystApp->psgi_app(@_);


    my $app = sub { MyCatalystApp->psgi_app(@_) };
    # If you make ^^ this mistake, your app won't work, and will confuse the hell out of you!

You can now move script/myapp.psgi to myapp.psgi, and the built-in Catalyst scripts and your test suite will start using your .psgi file.

NOTE: If you rename your .psgi file without these modifications, then any tests run via Catalyst::Test will not be compatible with the new release, and will result in the development server starting, rather than the expected test running.

NOTE: If you are directly accessing $c->req->env to get the PSGI environment then this accessor is moved to $c->engine->env, you will need to update your code.

Engines which are known to be broken

The following engines DO NOT work as of Catalyst version 5.9. The core team will be happy to work with the developers and/or users of these engines to help them port to the new Plack/Engine system, but for now, applications which are currently using these engines WILL NOT run without modification to the engine code.


Engines with unknown status

The following engines are untested or have unknown compatibility. Reports are highly encouraged:

Catalyst::Engine::Server (marked as Deprecated)
Catalyst::Engine::HTTP::POE (marked as Deprecated)

Plack functionality

See Catalyst::PSGI.

Tests in 5.9

Tests should generally work the same in Catalyst 5.9, but there are some differences.

Previously, if using Catalyst::Test and doing local requests (against a local server), if the application threw an exception then this exception propagated into the test.

This behavior has been removed, and now a 500 response will be returned to the test. This change standardizes behavior, so that local test requests behave similarly to remote requests.

Upgrading to Catalyst 5.80

Most applications and plugins should run unaltered on Catalyst 5.80.

However, a lot of refactoring work has taken place, and several changes have been made which could cause incompatibilities. If your application or plugin is using deprecated code, or relying on side effects, then you could have issues upgrading to this release.

Most issues found with existing components have been easy to solve. This document provides a complete description of behavior changes which may cause compatibility issues, and of new Catalyst warnings which might be unclear.

If you think you have found an upgrade-related issue which is not covered in this document, please email the Catalyst list to discuss the problem.

Moose features

Application class roles

You can only apply method modifiers after the application's ->setup method has been called. This means that modifiers will not work with methods run during the call to ->setup.

See Catalyst::Manual::ExtendingCatalyst for more information about using Moose in your applications.

Controller actions in Moose roles

You can use MooseX::MethodAttributes::Role if you want to declare actions inside Moose roles.

Using Moose in Components

The correct way to use Moose in a component in a both forward and backwards compatible way is:

    package TestApp::Controller::Root;
    use Moose;
    BEGIN { extends 'Catalyst::Component' }; # Or ::Controller, or whatever

See "Components which inherit from Moose::Object before Catalyst::Component".

Known backwards compatibility breakages

Applications in a single file

Applications must be in their own file, and loaded at compile time. This issue generally only affects the tests of CPAN distributions. Your application will fail if you try to define an application inline in a block, and use plugins which supply a new method, then use that application latter in tests within the same file.

This is due to the fact that Catalyst is inlining a new method on your application class allowing it to be compatible with Moose. The method used to do this changed in 5.80004 to avoid the possibility of reporting an 'Unknown Error' if your application failed to compile.

Issues with Class::C3

Catalyst 5.80 uses the Algorithm::C3 method dispatch order. This is built into Perl 5.10, and comes via Class::C3 for Perl 5.8. This replaces NEXT with Class::C3::Adopt::NEXT, forcing all components to resolve methods using C3, rather than the unpredictable dispatch order of NEXT.

This issue manifests itself by your application failing to start due to an error message about having a non-linear @ISA.

The Catalyst plugin most often causing this is Catalyst::Plugin::Session::Store::FastMmap - if you are using this plugin and see issues, then please upgrade your plugins, as it has been fixed. Note that Makefile.PL in the distribution will warn about known incompatible components.

This issue can, however, be found in your own application - the only solution is to go through each base class of the class the error was reported against, until you identify the ones in conflict, and resolve them.

To be able to generate a linear @ISA, the list of superclasses for each class must be resolvable using the C3 algorithm. Unfortunately, when superclasses are being used as mixins (to add functionality used in your class), and with multiple inheritance, it is easy to get this wrong.

Most common is the case of:

    package Component1; # Note, this is the common case
    use base qw/Class::Accessor::Fast Class::Data::Inheritable/;

    package Component2; # Accidentally saying it this way causes a failure
    use base qw/Class::Data::Inheritable Class::Accessor::Fast/;

    package GoesBang;
    use base qw/Component1 Component2/;

Any situation like this will cause your application to fail to start.

For additional documentation about this issue, and how to resolve it, see Class::C3::Adopt::NEXT.

Components which inherit from Moose::Object before Catalyst::Component

Moose components which say:

    package TestApp::Controller::Example;
    use Moose;
    extends qw/Moose::Object Catalyst::Component/;

to use the constructor provided by Moose, while working (if you do some hacks with the BUILDARGS method), will not work with Catalyst 5.80 as Catalyst::Component inherits from Moose::Object, and so @ISA fails to linearize.

The correct way to use Moose in a component in a both forward and backwards compatible way is:

    package TestApp::Controller::Root;
    use Moose;
    BEGIN { extends 'Catalyst::Component' }; # Or ::Controller, or whatever

Note that the extends declaration needs to occur in a begin block for attributes to operate correctly.

This way you do not inherit directly from Moose::Object yourself. Having components which do not inherit their constructor from Catalyst::Component is unsupported, and has never been recommended, therefore you're on your own if you're using this technique. You'll need to detect the version of Catalyst your application is running, and deal with it appropriately.

You also don't get the Moose::Object constructor, and therefore attribute initialization will not work as normally expected. If you want to use Moose attributes, then they need to be made lazy to correctly initialize.

Note that this only applies if your component needs to maintain component backwards compatibility for Catalyst versions before 5.71001 - in 5.71001 attributes work as expected, and the BUILD method is called normally (although BUILDARGS is not).

If you depend on Catalyst 5.8, then all Moose features work as expected.

You will also see this issue if you do the following:

    package TestApp::Controller::Example;
    use Moose;
    use base 'Catalyst::Controller';

as use base appends to @ISA.

use Moose in MyApp

Similar to the above, this will also fail:

    package MyApp;
    use Moose;
    use Catalyst qw/

If you need to use Moose in your application class (e.g. for method modifiers etc.) then the correct technique is:

    package MyApp;
    use Moose;
    use Catalyst;

    extends 'Catalyst';

    __PACKAGE__->config( name => 'MyApp' );

Anonymous closures installed directly into the symbol table

If you have any code which installs anonymous subroutine references directly into the symbol table, you may encounter breakages. The simplest solution is to use Sub::Name to name the subroutine. Example:

    # Original code, likely to break:
    my $full_method_name = join('::', $package_name, $method_name);
    *$full_method_name = sub { ... };

    # Fixed Code
    use Sub::Name 'subname';
    my $full_method_name = join('::',$package_name, $method_name);
    *$full_method_name = subname $full_method_name, sub { ... };

Additionally, you can take advantage of Catalyst's use of Class::MOP and install the closure using the appropriate metaclass. Example:

    use Class::MOP;
    my $metaclass = Moose::Meta::Class->initialize($package_name);
    $metaclass->add_method($method_name => sub { ... });

Hooking into application setup

To execute code during application start-up, the following snippet in used to work:

    sub setup {
        my ($class, @args) = @_;
        ... # things to do after the actual setup

With Catalyst 5.80 this won't work anymore, because Catalyst no longer uses for method resolution. The functionality was only ever originally operational as NEXT remembers what methods have already been called, and will not call them again.

Using this now causes infinite recursion between MyApp::setup and Catalyst::setup, due to other backwards compatibility issues related to how plugin setup works. Moose method modifiers like before|after|around setup => sub { ... }; also will not operate correctly on the setup method.

The right way to do it is this:

    after setup_finalize => sub {
        ... # things to do after the actual setup

The setup_finalize hook was introduced as a way to avoid this issue.

Components with a new method which returns false

Previously, if you had a component which inherited from Catalyst::COMPONENT, but overrode the new method to return false, then your class's configuration would be blessed into a hash on your behalf, and this would be returned from the COMPONENT method.

This behavior makes no sense, and so has been removed. Implementing your own new method in components is highly discouraged. Instead, you should inherit the new method from Catalyst::Component, and use Moose's BUILD functionality and/or Moose attributes to perform any construction work necessary for your class.


Won't work due to a limitation of Moose. This is currently being fixed inside Moose.

Class::Data::Inheritable side effects

Previously, writing to a class data accessor would copy the accessor method down into your package.

This behavior has been removed. While the class data is still stored per-class, it is stored on the metaclass of the class defining the accessor.

Therefore anything relying on the side effect of the accessor being copied down will be broken.

The following test demonstrates the problem:

        package BaseClass;
        use base qw/Class::Data::Inheritable/;

        package Child;
        use base qw/BaseClass/;

    BaseClass->foo('base class');
    Child->foo('sub class');

    use Test::More;
    isnt(BaseClass->can('foo'), Child->can('foo'));

Extending Catalyst::Request or other classes in an ad hoc manner using mk_accessors

Previously, it was possible to add additional accessors to Catalyst::Request (or other classes) by calling the mk_accessors class method.

This is no longer supported - users should make a subclass of the class whose behavior they would like to change, rather than globally polluting the Catalyst objects.

Confused multiple inheritance with Catalyst::Component::COMPONENT

Previously, Catalyst's COMPONENT method would delegate to the method on the right hand side, which could then delegate back again with NEXT. This is poor practice, and in addition, makes no sense with C3 method dispatch order, and is therefore no longer supported.

If a COMPONENT method is detected in the inheritance hierarchy to the right hand side of Catalyst::Component::COMPONENT, then the following warning message will be emitted:

    There is a COMPONENT method resolving after Catalyst::Component
    in ${next_package}.

The correct fix is to re-arrange your class's inheritance hierarchy so that the COMPONENT method you would like to inherit is the first (left-hand most) COMPONENT method in your @ISA.

Development server relying on environment variables

Previously, the development server would allow propagation of system environment variables into the request environment, this has changed with the adoption of Plack. You can use Plack::Middleware::ForceEnv to achieve the same effect.


Actions in your application class

Having actions in your application class will now emit a warning at application startup as this is deprecated. It is highly recommended that these actions are moved into a MyApp::Controller::Root (as demonstrated by the scaffold application generated by

This warning, also affects tests. You should move actions in your test, creating a myTest::Controller::Root, like the following example:

    package MyTest::Controller::Root;

    use strict;
    use warnings;

    use parent 'Catalyst::Controller';

    __PACKAGE__->config(namespace => '');

    sub action : Local {
        my ( $self, $c ) = @_;


::[MVC]:: naming scheme

Having packages called MyApp::[MVC]::XX is deprecated and can no longer be generated by

This is still supported, but it is recommended that you rename your application components to Model/View/Controller.

A warning will be issued at application startup if the ::[MVC]:: naming scheme is in use.


Any code using Catalyst::Base will now emit a warning; this module will be removed in a future release.

Methods in Catalyst::Dispatcher

The following methods in Catalyst::Dispatcher are implementation details, which may change in the 5.8X release series, and therefore their use is highly deprecated.


The first time one of these methods is called, a warning will be emitted:

    Class $class is calling the deprecated method Catalyst::Dispatcher::$public_method_name,
    this will be removed in Catalyst 5.9

You should NEVER be calling any of these methods from application code.

Plugin authors and maintainers whose plugins currently call these methods should change to using the public API, or, if you do not feel the public API adequately supports your use case, please email the development list to discuss what API features you need so that you can be appropriately supported.

Class files with names that don't correspond to the packages they define

In this version of Catalyst, if a component is loaded from disk, but no symbols are defined in that component's name space after it is loaded, this warning will be issued:

    require $class was successful but the package is not defined.

This is to protect against confusing bugs caused by mistyping package names, and will become a fatal error in a future version.

Please note that 'inner packages' (via Devel::InnerPackage) are still fully supported; this warning is only issued when component file naming does not map to any of the packages defined within that component.

$c->plugin method

Calling the plugin method is deprecated, and calling it at run time is highly deprecated.

Instead you are recommended to use Catalyst::Model::Adaptor or similar to compose the functionality you need outside of the main application name space.

Calling the plugin method will not be supported past Catalyst 5.81.