Include latest LTS by GHC version (fixes #210)

Handler/Home.hs

@@ -31,6 +31,7 @@ getHomeR = track "Handler.Snapshots.getAllSnapshotsR" $ do
         getSnapshots Nothing snapshotsPerPage
                              ((fromIntegral currentPage - 1) * snapshotsPerPage)
     let groups = groupUp now' snapshots
+    latestLtsByGhc <- getLatestLtsByGhc
     defaultLayout $ do
         setTitle "Stackage Server"
         $(widgetFile "home")

Stackage/Database.hs

@@ -39,6 +39,7 @@ module Stackage.Database
     , last5Lts5Nightly
     , snapshotsJSON
     , getPackageCount
+    , getLatestLtsByGhc
     ) where
 
 import Database.Sqlite (SqliteException)
@@ -783,3 +784,15 @@ getPackageCount :: GetStackageDatabase m
                 => SnapshotId
                 -> m Int
 getPackageCount sid = run $ count [SnapshotPackageSnapshot ==. sid]
+
+getLatestLtsByGhc :: GetStackageDatabase m
+                  => m [(Int, Int, Text)]
+getLatestLtsByGhc = run $ fmap (map toTuple) $ do
+    E.select $ E.from $ \(lts `E.InnerJoin` snapshot) -> do
+        E.on $ lts E.^. LtsSnap E.==. snapshot E.^. SnapshotId
+        E.orderBy [E.desc (lts E.^. LtsMajor), E.desc (lts E.^. LtsMinor)]
+        E.groupBy (snapshot E.^. SnapshotGhc)
+        return (lts, snapshot)
+  where
+    toTuple (Entity _ lts, Entity _ snapshot) =
+        (ltsMajor lts, ltsMinor lts, snapshotGhc snapshot)

templates/home.hamlet

@@ -46,6 +46,13 @@
                 on
                 <a href="https://haskell-lang.org/">
                   haskell-lang.org
+
+            <h3>
+                Latest LTS per GHC version
+            <ul>
+                $forall (major, minor, ghc) <- latestLtsByGhc
+                  <li>
+                    <a href=@{SnapshotR (SNLts major minor) StackageHomeR}>LTS #{major}.#{minor} for GHC #{ghc}
       <div .span6>
         <h3>Snapshots
         $forall stackages <- groups