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From "David E. Wheeler" <da...@kineticode.com>
Subject [lucy-dev] Re: Failed: PAUSE indexer report KARMAN/Lucy-0.3.0.tar.gz
Date Wed, 15 Feb 2012 17:17:57 GMT
On Feb 15, 2012, at 6:43 AM, Peter Karman wrote:

> Status: Decreasing version number
>          =================================
> 
>     module: Lucy::Analysis::Analyzer
>          version: undef
>          in file: lib/Lucy/Analysis/Analyzer.pm
>          status: Not indexed because lib/Lucy/Analysis/Analyzer.pm in
>             D/DW/DWHEELER/Lucy-0.2.2.tar.gz has a higher version number
>             (0)
> 
>     module: Lucy::Anal

You built the distribution with Module::Build version 0.3603, which sets versions in the "provides"
section to `undef` if there is no version.

I built 0.2.2 with Module::Build version 0.38, which sets missing versions in the "provides"
section to 0. From the CPAN indexer’s point of view, 0 != undef.

I argue, however, that *all* Lucy modules should have explicit versions. Why? Let’s say
that I have a module that depends on Lucy::Analysis::Analyzer. So I declare in my Build.PL:

    requires => {
        'Lucy::Analysis::Analyzer' => 0,
    }

So far so good, right? But let’s say that I later realize that I need a new feature in 0.3.0.
Si I change it to:

        'Lucy::Analysis::Analyzer' => '0.3.0',

If someone tries to build, it will fail, because there is no such version. In fact, CPAN cannot
tell the difference between the Lucy::Analysis::Analyzer in 0.3.0 and the Lucy::Analysis::Analyzer
in 0.2.2 or any other release. Because we did not give it a version number. Since the best
practice is for developers to declare requirements on modules they actually `use`, and one
may not actually `use Lucy;`, folks may not then require a specific version of Lucy, but rather
of a module that Lucy packages.

So, IME, it is best for every Perl module in a distribution to have its own version. This
version does not have to change with each release if its contents have not changed, but I
tend to find that a bit complicated (since other modules it depends on may have changed, and
those changes might have side-effects on my module). So better, IME, is to have the same version
in every single module in a distribution. You can see this at work in all of my distributions,
e.g.,

  http://search.cpan.org/dist/DBIx-Connector/

There are two ways to do this. One is to have this line in every .pm file:

    our $VERSION = '0.003001';

Then, before a release (or just after a release, depending on your preferences), you would
change it every file. I do that with something like:

    ack -laiQ 0.003000 | xargs perl -i -pe "s{\QVERSION = '0.003001'}{VERSION = '0.003001}g"

Some might find it a bit annoying, but it’s probably the safest way to manage Perl module
versions. The second way to do it is lazier: Just put this line in every Perl module in a
distribution:

    require Lucy; our $VERSION = eval $Lucy::VERSION;

And yes, it has to be on one line so that Module::Build will parse out the one line and eval
it. I think this would be safe, though I don’t know if you want to load Lucy.pm in every
file.

Anyway, best practice is to have an explicit version in every module and to make sure it’s
properly set for every release.

The upshot for this particular release is that only Lucy.pm is indexed. So if you `cpan Lucy`,
it will install, but if you `cpan Lucy::Analysis::Analyzer`, you’ll get an error:

    Warning: Cannot install Lucy::Analysis::Analyzer, don't know what it is.
    Try the command

        i /Lucy::Analysis::Analyzer/

Best,

David




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