After hiding the Perl Critic issues reported by the CPAN Testers I wanted to check what were those?

One of them was Private Member Data shouldn't be accessed directly and the other one Three-argument form of open used and it is not available until perl 5.6.

The second policy lead me to the Compatibility::PerlMinimumVersionAndWhy policy which seemed to be useful. It analyzes the source code and reports features that are only available in recent versions of perl. For example the defined-or (//) appeared in perl 5.10.

The policy requires us to explicitly state the minimal version of perl in each one of our files.

I know, I've removed the use use 5.005 statement earlier and now I am adding similar use-statements. I am not really convinced that adding the minimum version to every file is that useful, but that allows me to use this policy.

The question:

How to use the Compatibility::PerlMinimumVersionAndWhy policy?

After installing the Perl-Critic-Pulp distribution I could run: 

perlcritic --single-policy Compatibility::PerlMinimumVersionAndWhy .

that generated quite a few lines, but all of them were versions of these lines: 

[Compatibility::PerlMinimumVersionAndWhy] _perl_5006_pragmas requires 5.006 at line 2, column 1.
[Compatibility::PerlMinimumVersionAndWhy] _Pulp__for_loop_variable_using_my requires 5.004 at line 13, column 1.
[Compatibility::PerlMinimumVersionAndWhy] _Pulp__open_my_filehandle requires 5.006 at line 52, column 2.
[Compatibility::PerlMinimumVersionAndWhy] _three_argument_open requires 5.006 at line 52, column 2.

That means adding use 5.006; to all the files will silence this policy, but before we do that, let's see how can we convince perlcritic to use this policy.

In the .perlcriticrc file we need to enable the compatibility theme as well: 

theme = core + compatibility

That's not enough because the severity level of this specific policy was quite low. I think it was 2. We had to tell perlcritic to use a higher severity: 

[Compatibility::PerlMinimumVersionAndWhy]
severity = 5

that's fine, and now perlcritic . already started to report the validations, but now it also reported about other violations. I had to turn the one I found off: 

[-Compatibility::ProhibitThreeArgumentOpen]

Lastly, in order to get Travis-CI run these tests too I had to add 

  - cpanm --notest Perl::Critic::Policy::Compatibility::PerlMinimumVersionAndWhy

to the .travis.yml file which I've actually failed at first, hence I had to make a second commit fixing .travis.yml.

commit: set minimum version number in every perl file

commit: proper module name (in travis.yml file)