CC0-1.0 in tree-sitter-clojure / tree-sitter-clojure-orchard, previously vendored into rust-difftastic

[Michel Lind]

Dear all,

I maintain the `rust-difftastic` package, a structural diff tool; in a
recent update it has started unbundling the tree-sitter parsers it
used, and as part of the review process for the new crates, this came
up:

https://bugzilla.redhat.com/show_bug.cgi?id=2421761

- difftastic previously used tree-sitter-clojure
- this is CC0-1.0 licensed which is no longer allowed for code in
Fedora (but this usage might be considered grandfathered in -- though
we'd need to file for a retroactive exemption I guess) -
https://lwn.net/Articles/902410/
- tree-sitter-clojure is then forked to tree-sitter-clojure-orchard -
conversation: https://github.com/Wilfred/difftastic/pull/915 - citing
upstream not uploading to crates.io. Apparently there's yet another
fork as well (which requires a newer Rust version)
- the fork difftastic ended up using claims it is MIT licensed:
https://codeberg.org/grammar-orchard/tree-sitter-clojure-orchard/blame/branc...
- but the LICENSE file it bundled is still CC0-1.0 which is how this
issue was surfaced

Any suggestion how to proceed here? I'm temporarily yanking the Clojure
support out of difftastic until this is resolved. Of question:

- is such a relicensing away from CC0-1.0 by a fork allowed? In which
case I will put up a PR to the fork so it carries both license texts
and explain the relicensing
- if not, does the grandfathering of existing CC0-1.0 software cover
forks too?

The difftastic upstream (cc:ed), after I brought this to his attention,
has requested that the original tree-sitter-clojure be dual-licensed
CC0/MIT, which will resolve this too:

https://github.com/sogaiu/tree-sitter-clojure/issues/71

Best regards,