Software::LicenseUtils->guess_license_from_meta doesn't work on META.json

[Graham Knop]

Software::LicenseUtils->guess_license_from_meta is documented as working on META.json, it uses a regex to find the license which only accounts for a single string value. license in meta v2 is an array, so it is unable to match properly.

[Karen Etheridge]

Agreed, it should use CPAN::Meta to parse the meta file properly and extract the data using the API, rather than using a regex on the file.

[Andrew Grangaard]

Incoming #hacktober #cpan-prc PR.

[Andrew Grangaard]

CPAN::Meta does a lossy conversion when importing meta v1 licenses, specifically it
punts on gpl, lgpl, and mozilla, since it isn't clear which exact version was specified in older Module::Build.

From CPAN::Meta::Converter:

# The "old" values were defined by Module::Build, and were often vague.  I have
# made the decisions below based on reading Module::Build::API and how clearly
# it specifies the version of the license.
my %license_map_2 = (
  (map { $_ => $_ } @valid_licenses_2),
  apache      => 'apache_2_0',  # clearly stated as 2.0
  artistic    => 'artistic_1',  # clearly stated as 1
  artistic2   => 'artistic_2',  # clearly stated as 2
  gpl         => 'open_source', # we don't know which GPL; punt
  lgpl        => 'open_source', # we don't know which LGPL; punt
  mozilla     => 'open_source', # we don't know which MPL; punt
  perl        => 'perl_5',      # clearly Perl 5
  restrictive => 'restricted',
);

In Software::License
'open_source' is mapped in Software::License to Software::License::Mozilla_2_0 and Software::License::PostgreSQL.

A naive conversion of guess_license_from_meta to use CPAN::Meta for parsing will thus convert a 1.x META file containing license: gpl to [ 'Software::License::Mozilla_2_0", "Software::License::PostgreSQL"] rather than the current value of ['Software::License::GPL_1', Software::License::GPL_2', 'Software::License::GPL_3'].

Would we be sad to change to this result?

I can keep the current behavior while using the CPAN::Meta toolbox, but it'll require more juggling. E.g. using Parse::CPAN::Meta and CPAN::Meta::Convert manually to get the original license and meta version before upgrading.