[R-pkg-devel] best practices for handling a mixed-licensed package

A collaborator is arguing that it's a good idea to license one small 
component of a package under the MIT license, while the rest of it 
remains GPL >=2.

   Suppose this is feasible.  How do I specify the license?  As far as I 
can tell from 
https://cran.r-project.org/doc/manuals/r-release/R-exts.html#Licensing 
the DESCRIPTION file should have

License: file LICENSE
License_is_FOSS: yes
License_restricts_use: no

   But I can't figure out what should go in the LICENSE file. The one 
file that contains the MIT-licensed components contains the relevant 
license text in its body.

License: GPL (>=2) | MIT + file LICENSE

doesn't seem right, because these are not *alternative* licenses.  Would 
"GPL (>=2) + file LICENSE" be OK? We could explain the situation in 
LICENSE.note (WRE says "To include comments about the licensing rather 
than the body of a license, use a file named something like 
LICENSE.note. ")

   Could file LICENSE contain

The code in this package is licensed under GPL >=2 (see 
https://www.r-project.org/Licenses/GPL-2, 
https://www.r-project.org/Licenses/GPL-3, except for <FILE xxx>, which 
is under the MIT license (see <FILE xxx for details>).

?

  Happy for advice or pointers to other packages that have successfully 
done something similar.

Looks like igraphdata may have heterogeneous licensing? 
https://cran.r-project.org/web/packages/igraphdata/index.html


Related: 
https://stackoverflow.com/questions/4314708/if-an-r-packages-licence-x-is-do-all-the-content-in-that-package-have-to-be-li