cabal.config link

Handler/StackageHome.hs

@@ -2,6 +2,7 @@ module Handler.StackageHome where
 
 import Data.BlobStore (storeExists)
 import Import
+import Data.Time (FormatTime)
 
 getStackageHomeR :: PackageSetIdent -> Handler Html
 getStackageHomeR ident = do
@@ -49,4 +50,33 @@ getStackageMetadataR ident = do
         , "\n"
         ]
 
+getStackageCabalConfigR :: PackageSetIdent -> Handler TypedContent
+getStackageCabalConfigR ident = do
+    Entity sid _ <- runDB $ getBy404 $ UniqueStackage ident
+    respondSourceDB typePlain $ stream sid
+  where
+    stream sid =
+        selectSource
+            [ PackageStackage ==. sid
+            , PackageOverwrite ==. False
+            ]
+            [ Asc PackageName'
+            , Asc PackageVersion
+            ] $= (goFirst >> mapC (Chunk . showPackage))
+
+    goFirst = do
+        mx <- await
+        forM_ mx $ \(Entity _ (Package _ name version _)) -> yield $ Chunk $
+            toBuilder (asText "constraints: ") ++
+            toBuilder (toPathPiece name) ++
+            toBuilder (asText " ==") ++
+            toBuilder (toPathPiece version)
+
+    showPackage (Entity _ (Package _ name version _)) =
+        toBuilder (asText ",\n             ") ++
+        toBuilder (toPathPiece name) ++
+        toBuilder (asText " ==") ++
+        toBuilder (toPathPiece version)
+
+yearMonthDay :: FormatTime t => t -> String
 yearMonthDay = formatTime defaultTimeLocale "%Y-%m-%d"

config/routes

@@ -12,6 +12,7 @@
 /upload UploadStackageR GET PUT
 /stackage/#PackageSetIdent StackageHomeR GET
 /stackage/#PackageSetIdent/metadata StackageMetadataR GET
+/stackage/#PackageSetIdent/cabal.config StackageCabalConfigR GET
 /stackage/#PackageSetIdent/00-index.tar.gz StackageIndexR GET
 /stackage/#PackageSetIdent/bundle StackageBundleR GET
 /stackage/#PackageSetIdent/package/#PackageNameVersion StackageSdistR GET

templates/stackage-home.hamlet

@@ -13,6 +13,10 @@ $newline never
            <span>
                <a href=@{StackageBundleR ident} title="This is useful for making modifications to an existing snapshot">
                    \Bundle
+           <span .separator>
+           <span>
+               <a href=@{StackageCabalConfigR ident} title="If you want to stick with upstream Hackage but get a stable package set">
+                   \cabal.config
     <p>
         <pre>
             remote-repo: stackage:@{StackageHomeR ident}