appstream-generator doesn't accept dual-licensed metadata

[City-busz]

Evince specifies GPL-2.0+ or GFDL-1.3-only as metadata license, but it's not accepted by appstream-generator as a permissive license. Since the metadata is dual-licensed and one of them is permissive, it should be accepted by appstream-generator.

Tested with appstream 0.14.3 and appstream-generator 0.8.4.

[ximion]

The metadata_license tag does not accept a license expression, and actually even only a list of accepted licenses.
This should likely be made even more clear in the specification (https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-metadata_license) as well as the explanation of the appstream-generator issue tag.

[City-busz]

So it must be fixed in the evince package by removing GPL-2.0+ from metadata_license? I requested it from the developers, but they said that the metainfo file is reported as valid by appstreamcli validate. You can see their comment here:
https://gitlab.gnome.org/GNOME/evince/-/merge_requests/346#note_1135950

[ximion]

Oh, that is indeed not okay - looks like a bug in appstream-generator then...