Distinguish between deprecated and non-preferred versions in the package index

[grayjay]

Hackage shows deprecated and preferred versions on each package page, but it seems to combine the two types of version ranges in the package index. This means that cabal can't distinguish between versions that are deprecated and versions that are only non-preferred. It would be great to add more functionality to cabal related to identifying and avoiding deprecated versions. Here is an example of an issue that could be solved: haskell/cabal#10097

Adding preferred versions to the index:

hackage-server/src/Distribution/Server/Features/PreferredVersions.hs

Lines 344 to 350 in 5b0d3b0

	updateIndexPackagePreferredVersions :: MonadIO m => PackageName -> PreferredInfo -> m ()
	updateIndexPackagePreferredVersions pkgname prefinfo = do
	now <- liftIO getCurrentTime
	let prefEntryName = display pkgname </> "preferred-versions"
	prefContent = fromMaybe "" $
	formatSinglePreferredVersions pkgname prefinfo
	updateArchiveIndexEntry prefEntryName (BS.pack prefContent) now

Formatting deprecated/preferred versions for one package:

hackage-server/src/Distribution/Server/Features/PreferredVersions.hs

Lines 411 to 413 in 5b0d3b0

	formatSinglePreferredVersions :: PackageName -> PreferredInfo -> Maybe String
	formatSinglePreferredVersions pkgname pref =
	display . (\vr -> Dependency pkgname vr mainLibSet) <$> sumRange pref

PreferredInfo, with sumRange field for merged version ranges:

hackage-server/src/Distribution/Server/Features/PreferredVersions/State.hs

Lines 30 to 34 in 5b0d3b0

	data PreferredInfo = PreferredInfo {
	preferredRanges :: [VersionRange],
	deprecatedVersions :: [Version],
	sumRange :: Maybe VersionRange -- cached form of 'consolidateRanges' below
	} deriving (Typeable, Show, Eq)

Merging version ranges:

hackage-server/src/Distribution/Server/Features/PreferredVersions/State.hs

Lines 39 to 44 in 5b0d3b0

	consolidateRanges :: [VersionRange] -> [Version] -> Maybe VersionRange
	consolidateRanges ranges depr =
	let range = simplifyVersionRange $ foldr intersectVersionRanges anyVersion (map notThisVersion depr ++ ranges)
	in if isAnyVersion range || isNoVersion range
	then Nothing
	else Just range