A Semantic Version Plugin for Dist::Zilla

These days, I try to give a semantic logic to the version numbers of my distributions: bug fixes increment the revision number (e.g., 1.2.3 => 1.2.4, added functionality increments the minor version number (1.2.3 => 1.3.0) and an api change increments a major version number (1.2.3 => 2.0.0).

caveat emptor: last time I checked the general concensus of the greater Perl community was leaning more toward single-dot version notation instead of the double-dot (1.002003 instead of 1.2.3). But for the good of this blog entry, that's only a formatting issue -- the underlaying logic applies to any numbering scheme allowing different levels of incrementation.

Back when I was playing with Dist::Release, I came up with a semi-automated way of incrementing the version number of the distribution, but that fell on the wayside when I switched to Dist::Zilla.
With Dist::Zilla, so far I was manually setting up the new version number in the dist.ini of my distributions. But, as I'm a lazy, lazy man, automating the process was still at the back of my mind. Moreso after CPAN::Changes appeared, as the module makes the whole endeavor much easier by both providing concrete specifications on the format of the changelog, and a clear api to query and modify it.

Well, today I finally found the time to work on this. The result is Dist::Zilla::Plugin::Author::YANICK::NextSemanticVersion, which currently lives in the Dist::Zilla::PluginBundle::YANICK distribution (and, of course, in its GitHub repository).

This new plugin mostly piggyback on Dist::Zilla::Plugin::NextRelease and trails its wake to add the few extra behaviors we want. For a new '{{$NEXT}}' entry, in addition to the version head line it inserts the different types of changes we can have:

{{$NEXT}} 
[API CHANGES]

[BUG FIXES]

[ENHANCEMENTS]

This way, we never have to remember what is our different types, as they all are explicitly given. But, of course, we don't want the visual noise of empty groups in our final changelog, so we also have our plugin strip back empty groups in the built changelog. Thanks to CPAN::Changes, all that juggling is done rather painlessly:

    # triggered after the release step
    sub after_release {
        my $self = shift;

        my $changes = CPAN::Changes->load( 
            $self->filename, 
            next_token => qr/{{\$NEXT}}/ 
        ); 

        # clean empty groups all around
        for my $r ( $changes->releases ) {
            for my $g ( $r->groups ) {
                $r->delete_group($g) unless @{ $r->changes($g) };
            }
        }

        # ... but put back a template for the $NEXT release
        my ( $next ) = reverse $changes->releases;
        $next->add_group( @major_groups, @minor_groups, @revision_groups );

        $self->log_debug([ 'updating contents of %s on disk', $filename ]);

        open my $out_fh, '>', $self->filename or die $!;
        print $out_fh $changes->serialize;
    }

    # triggered at the file munging step
    sub munge_files {
        my $self = shift;

        my ($file) = grep { $_->name eq 'Changes' } @{ $self->zilla->files }
            or return;

        my $changes = CPAN::Changes->load_string( $file->content, 
            next_token => qr/{{\$NEXT}}/
        );

        my ( $next ) = reverse $changes->releases;

        # empty groups only for the work copy
        $next->delete_group(
            grep { !@{$next->changes($_)} } $next->groups 
        );

        $self->log_debug([ 'updating contents of %s in memory', $file->name ]);
        $file->content($changes->serialize);
    }

With that done, the other part of functionality that is missing is the version increment itself. For that, I simply let myself be heavily inspired by Dist::Zilla::Plugin::Git::NextVersion in its implementation of the VersionProvider's role:

    # for the VersionProvider role
    sub provide_version {
        my $self = shift;

        my $git  = Git::Repository->new( work_tree => '.');
        my $regexp = $self->version_regexp;

        # TODO actually, should be after the next stanza
        my @tags = $git->run('tag') or return $self->first_version;

        # find highest version from tags
        my ($last_ver) =  
            sort { version->parse($b) <=> version->parse($a) }
            grep { eval { version->parse($_) }  }
            map  { /$regexp/ ? $1 : ()          } @tags;

        $self->log_fatal("Could not determine last version from tags")
            unless defined $last_ver;

        my $new_ver = $self->next_version($last_ver);

        $self->zilla->version("$new_ver");
    }

    sub next_version {
        my( $self, $last_version ) = @_;

        my ($changes_file) = grep { $_->name eq $self->filename } @{ $self->zilla->files };

        my $changes = CPAN::Changes->load_string( $changes_file->content,
            next_token => qr/{{\$NEXT}}/ ); 

        my ($next) = reverse $changes->releases;

        my $new_ver = $self->inc_version( 
            $last_version, 
            grep { scalar @{ $next->changes($_) } } $next->groups
        );

        $self->log("Bumping version from $last_version to $new_ver");
        return $new_ver;
    }

    sub inc_version {
        my ( $self, $version, @groups ) = @_;

        $version = Perl::Version->new( $version );

        if ( grep { $_ ~~ @groups } @major_groups ) {
            $version->inc_revision;
            return $version
        }
            
        for ( grep { $_ ~~ @groups } @minor_groups ) {
            $version->inc_version;
            return $version
        }

        $version->inc_subversion;
        return $version;
    }

And that's it. All that I'm left to do is to enter my changes under the correct groups, and the plugin will take care of both correctly incrementing the version number and tidying the changelog before the a release.