Restore old licence acceptance logic for pre-cabal-version:2.2

In 5c06aba the legacy licence enum was
mapped to SPDX licences, thereby implicitly disallowing the use of
`OtherLicence`; this commit avoids mapping legacy licences to SPDX and
restores the original acceptance-check, thereby re-allowing `OtherLicence`s

Distribution/Server/Packages/Unpack.hs

@@ -26,7 +26,7 @@ import Distribution.Package
 import Distribution.PackageDescription
          ( GenericPackageDescription(..), PackageDescription(..)
          , allBuildInfo, allLibraries
-         , mixins, signatures, specVersion, license
+         , mixins, signatures, specVersion, licenseRaw
          )
 import Distribution.PackageDescription.Configuration
          ( flattenPackageDescription )
@@ -39,6 +39,7 @@ import Distribution.Text
          ( Text(..), display, simpleParse )
 import Distribution.Server.Util.ParseSpecVer
 import qualified Distribution.SPDX as SPDX
+import qualified Distribution.License as License
 import qualified Distribution.Compat.ReadP as Parse
 
 import Control.Monad.Except
@@ -515,11 +516,12 @@ startsWithBOM bs = LBS.take 3 bs == LBS.pack [0xEF, 0xBB, 0xBF]
 --   OSI-accepted licenses or CC0
 --
 isAcceptableLicense :: PackageDescription -> Bool
-isAcceptableLicense = go . license
+isAcceptableLicense = either goSpdx goLegacy . licenseRaw
   where
-    go :: SPDX.License -> Bool
-    go SPDX.NONE = False
-    go (SPDX.License expr) = goExpr expr
+    -- `cabal-version: 2.2` and later
+    goSpdx :: SPDX.License -> Bool
+    goSpdx SPDX.NONE = False
+    goSpdx (SPDX.License expr) = goExpr expr
       where
         goExpr (SPDX.EAnd a b)            = goExpr a && goExpr b
         goExpr (SPDX.EOr a b)             = goExpr a || goExpr b
@@ -530,3 +532,7 @@ isAcceptableLicense = go . license
         goSimple (SPDX.ELicenseIdPlus _)   = False -- don't allow + licenses (use GPL-3.0-or-later e.g.)
         goSimple (SPDX.ELicenseId SPDX.CC0_1_0) = True -- CC0 isn't OSI approved, but we allow it as "PublicDomain", this is eg. PublicDomain in http://hackage.haskell.org/package/string-qq-0.0.2/src/LICENSE
         goSimple (SPDX.ELicenseId lid)     = SPDX.licenseIsOsiApproved lid -- allow only OSI approved licenses.
+
+    -- pre `cabal-version: 2.2`
+    goLegacy License.AllRightsReserved = False
+    goLegacy _                         = True