Re-add license field to Cargo.toml

[sdroege]

This was removed in 3a4033e#diff-2e9d962a08321605940b5a657135052fbcef87b5e360662bb527c96d9a615542 and causes automated tooling like cargo deny to fail detecting the license.

It should probably be something like (Apache-2.0 OR MIT) AND BSD-3 but I'm not sure the expression syntax allows parenthesis. If it doesn't then we have a problem and you might want to reconsider if dual-licensing warrants the increased license complexity here. Having to worry about 3 different licenses for a single crate is a bit suboptimal, even if MIT and BSD-3 are approximately the same.

[sdroege]

cargo deny is accepting the following fwiw:

[[licenses.clarify]]
name = "encoding_rs"
version = "*"
expression = "(Apache-2.0 OR MIT) AND BSD-3-Clause"
license-files = [
    { path = "COPYRIGHT", hash = 0x39f8ad31 }
]

[hsivonen]

Indeed, the README says that the right SPDX would be (Apache-2.0 OR MIT) AND BSD-3-Clause and a custom license file is used instead of an expression, because crates.io doesn't support parentheses. FWIW, ICU4X also points to a custom file, because its correct SPDX expression would require parentheses.

What does cargo deny use for parsing SPDX? The issue on the dependency used by crates.io is still open.

[sdroege]

It depends on https://crates.io/crates/spdx/0.7.0, so I assume it's using that.

[hsivonen]

I added the cargo deny clarification recipe to the README. Thanks.

[sdroege]

I assume if you put the same into Cargo.toml then cargo will just explode at this point because the crate it uses doesn't support such complex expressions?

[hsivonen]

Right now, I'm in a situation where I can't handle worse fallout from experimenting with a real create in the next few hours, but later I'll try uploading a bogus crate with metadata that goes against the crates.io documentation to see what happens.

[sdroege]

Sure, no worries :) That's mostly for my own curiosity at this point.

[adam-azarchs]

It's a bit verbose but you can achieve the same effect without requiring changes to cargo by specifying the license as Apache-2.0 AND BSD-3-Clause OR MIT AND BSD-3-Clause.

[lsunsi]

@adam-azarchs Despite being verbose, I think having the field set is worth it

[hsivonen]

crates.io now supports parentheses (thanks to @jqnatividad for the heads-up in #80).

I've now pushed fcf1e10 to git and published on crates.io.

I hope this doesn't break cargo-deny consumers in the short term.