Change GPL-2 to GPL-2.0-only instead of GPL-2.0-or-later

[cbrueffer]

R packages have the license key "GPL (>= 2)" for GPL-2.0-or-later (see https://r-pkgs.org/license.html#key-files). Nothing indicates that "GPL-2" should include later versions of the GPL.

[cbrueffer]

Thanks @bgruening , could you merge as well?

[bgruening]

Sure. Thanks @cbrueffer

[jdblischak]

The problem is that the string GPL-2 that the regex is matching comes from conda skeleton.

conda_r_skeleton_helper/run.py

Lines 106 to 107 in 9059db9

	# Changing GPL-2 to GPL-2.0-only
	line = re.sub('license: GPL-2$', 'license: GPL-2.0-only', line)

conda_r_skeleton_helper/run.R

Lines 91 to 92 in 9059db9

	# Changing GPL-2 to GPL-2.0-only
	meta_new <- str_replace(meta_new, "license: GPL-2$", "license: GPL-2.0-only")

Thus even R packages that specify GPL (>= 2), eg {nanotime}, are assigned GPL-2.0-only when they should be GPL-2.0-or-later. The only way to get it right for both license strings would be to parse the field License in DESCRIPTION, but that seems like way too much for this hacky script to handle robustly.

Ideally the CRAN skeleton would be updated to use the SPDX identifiers, but I don't have the bandwidth to implement this (nor the clout to get it merged). Issues about migrating to SPDX have been open for years (conda/conda-build#2015, conda/conda#5280).

Unfortunately grayskull doesn't get it right either

grayskull --version
## 2.5.3
grayskull cran r-nanotime
grep license r-nanotime/meta.yaml
##   license: NGPL