[GRASS-dev] Compatibility of GPL v.2/3 and EUPL v1.2 licenses

[Nikos Alexandris]

Dear GRASS GIS team,

does publishing a GRASS GIS add-on, in the official GRASS GIS Addon SVN
repository [0] or else in any other git-based source code repository,
under the EUPL v1.2 license [1], constitute a breach of the GPL v.2/3
license(s) [3], under which GRASS GIS is published?

[0] https://trac.osgeo.org/grass/browser/grass-addons
[1] https://eupl.eu/1.2/en/
[2] https://www.gnu.org/licenses/old-licenses/gpl-2.0.html /
https://www.gnu.org/licenses/gpl-3.0.en.html


The GPL license is a "strong copyleft" license. However, it is not downstream
compatible with the EUPL license. The latter is a "flexible copyleft" license,
as it includes a "compatibility clause" that references, among others, the GPL
license(s).

Does the "at arm's length" case apply for GRASS GIS and GRASS GIS
addons? Do GRASS GIS core and GRASS GIS addons considered to operate as
one?

If yes,

1. this would mean that the GPL and the EUPL cannot be combined, in
the case of GRASS GIS addons.

2. would the GRASS GIS team consider to add a similar "compatibility
clause" to effectively make both licenses 100% cross-compatible?


The specific case is an addon that:

- is a Python script (or more Python scripts)

- uses the following Python librairies: os, sys, subprocess, datetime,
  time, csv, math, atexit

- uses the following PyGRASS librairies: grass.script, grass.exceptions,
  grass.pygrass.modules.shortcuts

- a `Makefile` that points to the following GRASS GIS' source code
  files, at compile time to generate a GUI and an HTML file (the
  manual):
    - `$(MODULE_TOPDIR)/include/Make/Script.make` and
    - `$(MODULE_TOPDIR)/include/Make/Python.make`

- uses GRASS GIS data base and modules (binaries and not their source
  code) to perform raster and/or vector processing operations


Note also,

- the page https://grass.osgeo.org/home/copyright/ states:

    "Geographic Resources Analysis Support System (GRASS) is Copyright,
    1999-2018 GRASS Development Team, and licensed under terms of the
    GNU General Public License (GPL). This includes all software,
    documentation, and associated materials."

- `g.version -c`, returns, among other text:

    "Parts of GRASS are not copyright by the GRASS development team.
    The original authors hold the copyrights and you have to abide
    to their licensing terms where noted.
    (Keep in mind that code linking into GRASS can only be distributed
    if compatible with the GPL.)"


Is, effectively, the compilation of a GRASS GIS addon, using the above
mentioned source code files, considered as "linking into GRASS"?


Thank you, Nikos

ps- Please note that the link to
https://grass.osgeo.org/grass77/source/COPYING
under
https://grass.osgeo.org/download/software/sources/
is broken.
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