the license in *.cabal is not parsed correctly by cabal for some servant packages

[teto]

while running cabal2nix on servant (to be able to reference the master version from nix), I hit the following issue:

cabal2nix: Distribution.Nixpkgs.Haskell.FromCabal.License.fromCabalLicense: unknown licenseUnknownLicense "BSD-3"
Choose one of: GPL, GPL-2, GPL-3, LGPL, LGPL-2.1, LGPL-3, AGPL, AGPL-3, BSD2, BSD3, MIT, ISC, MPL-2.0, Apache, Apache-2.0, PublicDomain, AllRightsReserved, OtherLicense
CallStack (from HasCallStack):
  error, called at src/Distribution/Nixpkgs/Haskell/FromCabal/License.hs:46:62 in cabal2nix-2.18.0-inplace:Distribution.Nixpkgs.Haskell.FromCabal.License

I first thought this was a cabal2nix issue but a few debug statements later, I think it's servant that incorrectly specifies its license. Cabal supports two types of licenses, native and SPDX, which can be seen here https://hackage.haskell.org/package/Cabal-3.6.2.0/docs/Distribution-Types-PackageDescription.html#v:licenseRaw

Several packages use BSD-3-Clause as a license, in conjonction with cabal-version: >=1.10 which cabal parses as Right (UnknownLicense "BSD-3").
If I change teh cabal-version to cabal-version: 2.2 , cabal correctly identifdies the license License (ELicense (ELicenseId BSD_3_Clause)).

Remediation:

• either update cabal-version from >= 1.1. to 2.2
• or change BSD-3-Clause to BSD3

My preference goes to the first solution (because SPDX is good) but the second doesn't need a bump in cabal-version.

I can provide a PR once a consensus is reached.

[tchoutri]

@teto Hi, and thank for reporting this!
As a co-maintainer, my opinion is to specify 2.2 as the minimum version for Cabal files, but I'll ask the other @haskell-servant/maintainers for their opinion.

[alpmestan]

I think it's reasonable.

[tchoutri]

Fantastic.
@teto You may proceed with a PR, thank you very much for having noticed this.