In a comment on my entry about Dist::Zilla pros and cons, Phred says:

I’m not clear on the value Dist::Zilla provides other than some versioning auto-incrementing and syntactic sugar for testing.

This brings a up a good question. What the heck to does dzil do?

Let’s walk through a dist.ini file from a real project. I’ll use the dist.ini from my Markdent distribution. This should answer the “what does it do” question quite well.

Here’s the whole file:

name    = Markdent
author  = Dave Rolsky 
license = Perl_5
copyright_holder = Dave Rolsky
copyright_year   = 2010

version = 0.13

[@Basic]
[InstallGuide]
[MetaJSON]

[MetaResources]
bugtracker.web    = http://rt.cpan.org/NoAuth/Bugs.html?Dist=Markdent
bugtracker.mailto = bug-markdent@rt.cpan.org
repository.url    = http://hg.urth.org/hg/Markdent
repository.web    = http://hg.urth.org/hg/Markdent
repository.type   = hg

[PodWeaver]

[KwaliteeTests]
[NoTabsTests]
[EOLTests]
[Signature]

[CheckChangeLog]

[Prereq]
Digest::SHA1                   = 0
HTML::Stream                   = 0
List::AllUtils                 = 0
Moose                          = 0.92
MooseX::Params::Validate       = 0.12
MooseX::Role::Parameterized    = 0
MooseX::SemiAffordanceAccessor = 0.05
MooseX::StrictConstructor      = 0.08
MooseX::Types                  = 0.20
namespace::autoclean           = 0.09
Tree::Simple                   = 0
Try::Tiny                      = 0

[Prereq / TestRequires]
File::Slurp                          = 0
Test::Deep                           = 0
Test::Differences                    = 0
Test::Exception                      = 0
Test::More                           = 0.88
Tree::Simple::Visitor::ToNestedArray = 0

[@Mercurial]

That’s a mouthful. Let’s step through it in tiny chunks …

name    = Markdent
author  = Dave Rolsky 

Setting these does several things. First, these values will end up in the generated Makefile.PL for the distro. Second, these values are available for plugins which do POD munging, which we’ll look at shortly. In particular, the author will end up in the every module’s POD.

license = Perl_5

The license setting is used for several things. First, the License plugin will use it to add a LICENSE file to the distro. Second, it is also available to POD mungers.

copyright_holder = Dave Rolsky
copyright_year   = 2010

This is another bit for the POD mungers. Together with the license, we’ll end up with this POD section in each module:

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2010 by Dave Rolsky.

This is free software; you can redistribute it and/or modify it under

the same terms as the Perl 5 programming language system itself.

version = 0.13

Again, this ends up in both my Makefile.PL and my POD.

[@Basic]

This is a plugin bundle, which is a name for a pre-defined set of plugins. The Basic bundle contains:

[GatherDir]
[PruneCruft]
[ManifestSkip]
[MetaYAML]
[License]
[Readme]
[ExtraTests]
[ExecDir]
[ShareDir]
[MakeMaker]
[Manifest]
[TestRelease]
[ConfirmRelease]
[UploadToCPAN]

Whoa, that’s a lot. So what do these do?

[GatherDir]

This tells dzil that it should include all the files in the current directory (the root of my distro) in the generated distro. I have to include this, or I won’t end up with a distro at all!

[PruneCruft]

This prunes the gathered files to remove generated files like a Build file, files that start with a dot (.), etc.

[ManifestSkip]

This prunes the gathered files based on the contents of a MANIFEST.SKIP file.

[MetaYAML]

This generates a META.yml file for the distro (using version 1.4 of the CPAN Meta format).

[License]

This plugin generates a LICENSE file, based on the value I set for the license earlier.

[Readme]

This one generates a fairly minimal README. Arguably, it’s so minimal it’s useless. It could probably be improved ;)

[ExtraTests]

This looks for tests under my working copy’s xt directory. This directory can contain subdirectories for three different types of “extra” tests, smoke tests, author tests, and release tests. Each of these directories has its tests rewritten so that they only run under specific circumstances (based on environment variables). The tests are rewritten into the t directory.

Typically, I only use xt/release. The tests in the release directory are run when $ENV{RELEASE_TESTING} is true. The dzil release command makes sure this is true, so my release tests are run before I do a release, but not when the module is installed from CPAN. This is perfect for things like POD tests.

[ExecDir]

This plugin arranges for a directory’s contents to be installed as executables. Well, actually, it just marks the files as executables, and another plugin does something useful with them. By default, it looks for a directory named bin.

[ShareDir]

Just like ExecDir but for “share” files (non-executable content like templates, images, etc).

[MakeMaker]

This generates Makefile.PL for the distro. This plugin is pretty smart, and generates a file with lots of conditionals so that it does the best job it can for the version of ExtUtils::MakeMaker that is available on the installing user’s machine. If you’ve ever written this sort of conditional crap you know how annoying it is to maintain. Now I don’t have to deal with this. As a bonus, future versions of dzil will account for new versions of EUMM, and I’ll get a better Makefile.PL for free.

This plugin makes use of the information provided by the ExecDir and ShareDir plugins we saw earlier. It arranges to have these files installed in the right place via ExtUtils::MakeMaker and File::ShareDir.

There is also a ModuleBuild plugin, but dzil really makes the difference between the two minimal. Unless I want to integrate a custom Module::Build subclass, as I did with Silki, there isn’t much difference between EUMM and MB for a project which uses dzil.

[Manifest]

This plugin creates the MANIFEST.

[TestRelease]

This runs the tests when I run dzil release.

[ConfirmRelease]

This prompts me to ask if I’m really sure I want to upload a distro when I run dzil release.

[UploadToCPAN]

I bet you can figure out what this does.

[InstallGuide]

This generates a nice INSTALL file. This plugin is smart. It generates the right instructions regardless of whether the distro is using EUMM or Module::Build.

[MetaJSON]

This generates a META.json file for the distro (using version 2.0 of the CPAN Meta format).

[MetaResources]
bugtracker.web    = http://rt.cpan.org/NoAuth/Bugs.html?Dist=Markdent
bugtracker.mailto = bug-markdent@rt.cpan.org
repository.url    = http://hg.urth.org/hg/Markdent
repository.web    = http://hg.urth.org/hg/Markdent
repository.type   = hg

This adds a “resources” section to my META.* files. There are some plugins on CPAN which will automate this. For the repository settings, the plugin looks at your working copy to figure out your VCS and remote VCS uris. I might switch over to these plugins in the future, although I think I’d actually have to add Mercurial support first.

[PodWeaver]

I mentioned “POD mungers” several times. Pod::Weaver is a POD rewriting module which does all sorts of fancy stuff, though I’m using just using a subset of its default behavior.

First, it looks in my module files for a comment in the form:

# ABSTRACT: Some text here

It uses this to generate the “NAME” section in the POD.

It also inserts “VERSION”, “AUTHOR”, and “COPYRIGHT AND LICENSE” sections. Pod::Weaver also lets you do even fancier stuff, like use POD dialects, add custom sections, etc. I’ll be investigating this further in the future. Really, this module deserves its own blog entry or three.

[KwaliteeTests]
[NoTabsTests]
[EOLTests]

These add some release tests for various sanity checks. I never need to customize these tests, so I can let the plugins write them out for me.

[Signature]

This signs the distro using Module::Signature.

[CheckChangeLog]

This checks my Changes file to ensure that I have an entry for the version mentioned in my dist.ini. It could be smarter and check for a date as well. I’m sure patches are welcome ;)

[Prereq]
...

This should be obvious. It lists the prerequisites for my distro. There is also an AutoPrereq module. I don’t use this because it generates a lot of prereqs I think are cruft, like core modules, or multiple modules in the same distro.

[Prereq / TestRequires]
...

Again, this is pretty obvious.

[@Mercurial]

Another plugin bundle. I wrote some plugins to automate some release tasks for a Mercurial-using project.

When I run dzil release, it will check to make sure that my repository is in a clean state (no changes that haven’t yet been checked in). After the release is uploaded, it tags my working copy and then pushes the changes back to the remote.

Summary

At a high level, dzil does a couple different tasks.

It ensures that support files like the MANIFEST and LICENSE stay up to date. It also helps improve compatibility by generating a “smart” Makefile.PL. Basically, it takes distribution metadata and generates all the files support files I need. Of course, both EUMM and Module::Build already did that, but dzil takes this several steps further.

The pod munging is similar. It includes standard POD boilerplate that should be in all my modules, but can be annoying to maintain.

It also helps me include various “sanity tests”. Since the plugin writes them out anew each time I build the distro, I don’t have to worry about keeping them up to date with changes to the testing modules, I just have to update the plugin.

Besides automating support, dzil also helps automate the actual release process. It adds some sanity checks like checking the changelog and the working copy state, and after the release it automates tagging and pushing.

Whereas I previously had to maintain various support files and update them as the toolchain changed, I can now update my plugins and get the updated support files “for free” in every distro I maintain. Overall, the number of steps that go into a release has been hugely reduced, and the possibility of error is much lower. That means its easier to make a new release, and the release quality is higher. Faster and better!

At last count, I maintain (for some value of maintain) 66 distros, so anything I can do to reduce busy work is very welcome!