Bug#1008292: lintian: inconsistent-appstream-metadata-license seems to be a bad rule

[Joao Eriberto Mota Filho <eriberto@debian.org>]

Package: lintian
Version: 2.104.0
Severity: normal

Dear maintainer,

When reviewing the package achilles, I added an AppStream metafile with the MIT
licensing. The lintian said me:

  achilles source: inconsistent-appstream-metadata-license debian/upstream/net.sourceforge.achilles.achilles.metainfo.xml (mit != gpl-2+) [debian/copyright]

So I changed the licensing of the AppStream metafile to GPL-2+. After this, the
tracker.debian.org showed an error 'metainfo-license-invalid' and asked for use
a valid permissive license like FSFAP, CC0-1.0 or MIT. The same message pointed
a link to understand the problem:

  https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-metadata_license

Part of the text in above weblink says:

  The <metadata_license/> tag indicates the content license that you are
  releasing the one metainfo XML file under. This is typically not the same as
  the project license. Omitting the license value will result in the metainfo
  data not being incorporated into metadata collections as used by Linux
  distributions. This tag is required for all metainfo files. [...]  Currently,
  the following licenses have been reviewed and can be used as metadata
  licenses: FSFAP, MIT, 0BSD, CC0-1.0, CC-BY-3.0, CC-BY-4.0, CC-BY-SA-3.0,
  CC-BY-SA-4.0, GFDL-1.1, GFDL-1.2, GFDL-1.3, BSL-1.0, FTL, FSFUL.

Consequently, IMO, this lintian rule is inconsistent and should be dropped.

Regards,

Eriberto