Action/Server/showFroms: split logic & template

The way the template was filled was rather hard to follow.

This tries to remedy it by splitting the code which infers the data
from the list of targets, and the code which generates the HTML.

The logic should be exactly the same, but we use a sort->groupBy to
stable-sort Targets into their packages.

src/Action/Server.hs

@@ -50,6 +50,9 @@ import Data.Monoid
 import Prelude
 
 import qualified Data.Aeson as JSON
+import Data.Function ((&))
+import Data.Functor ((<&>))
+import Data.Traversable (for)
 
 actionServer :: CmdLine -> IO ()
 actionServer cmd@Server{..} = do
@@ -265,21 +268,39 @@ itemCategories xs =
     [("is","module")  | any ((==) "module"  . targetType) xs] ++
     nubOrd [("package",p) | Just (p,_) <- map targetPackage xs]
 
+-- | Return an alist [(PackageName, PackageUrl, [(TargetUrl, TargetModule)])]
+showFromsLogic :: [Target] -> [(String, URL, [(URL, String)])]
+showFromsLogic targets = do
+    targets
+      & sortOn targetPackage
+      & groupOn targetPackage
+      & mapMaybe genAssocList
+  where
+    genAssocList :: [Target] -> Maybe (String, URL, [(URL, String)])
+    genAssocList targetGroup = do
+        -- all Targets in this targetGroup will have the same pkgName
+        -- due to the sort followed by the group
+        (pkgName, pkgUrl) <- targetGroup <&> targetPackage & headDef Nothing
+        targets' <- for targetGroup $ \Target{..} -> do
+            (moduleName, _) <- targetModule
+            pure (targetURL, moduleName)
+        pure (pkgName, pkgUrl, targets')
+
+
 -- | Display the line under the title of a search result, which contains a list of Modules each target is defined in, ordered by package.
 showFroms :: UrlOpts -> [Target] -> Markup
-showFroms urlOpts targets = mconcat $ intersperse ", " $ flip map pkgs $ \pkg ->
-    let ms = filter ((==) pkg . targetPackage) targets
-    in mconcat $ intersperse " "
-        [(H.a ! H.href (H.stringValue $ showURL urlOpts targetUrl))
-            (H.string pkgName)
-        | (pkgName, targetUrl)
-            <- catMaybes $ pkg : map pkgAndTargetUrlMay ms
-        ]
-    where
-        pkgAndTargetUrlMay Target{targetModule, targetURL} = do
-            (pkgName, _) <- targetModule
-            pure (pkgName, targetURL)
-        pkgs = nubOrd $ map targetPackage targets
+showFroms urlOpts allTargets = do
+    let pkgs = showFromsLogic allTargets
+    mconcat $ intersperse ", " $ flip map pkgs $ \(pkgName, pkgUrl, targets) -> do
+        let link txt url = (H.a ! H.href (H.stringValue $ showURL urlOpts url)) (H.string txt)
+        mconcat $ intersperse " "
+            -- display the list as “pkg Module1 Module2",
+            -- each as links to either the package
+            -- or the target inside the respective module.
+            $ link pkgName pkgUrl
+              : [ link moduleName targetUrl
+                | (targetUrl, moduleName) <- targets
+                ]
 
 showURL :: UrlOpts -> URL -> String
 showURL HaddockUrl x = "haddock/" ++ dropPrefix "file:///" x