Fix haskell#4251

cabal-install-solver/src/Distribution/Solver/Modular/Message.hs

@@ -77,37 +77,36 @@ displayMessage (LogUnknownPackage qpn gr) = "unknown package" ++ showQPN qpn ++
 displayMessage LogSuccessMsg = "done"
 displayMessage (LogFailureMsg c fr) = "fail: " ++ showFR c fr
 displayMessage (LogSkipMany _ _ cs) = "skipping: " ++ showConflicts cs
--- TODO: Instead of displaying `aeson-1.0.2.1, aeson-1.0.2.0, aeson-1.0.1.0, ...`,
+-- Instead of displaying `aeson-1.0.2.1, aeson-1.0.2.0, aeson-1.0.1.0, ...`,
 -- the following line aim to display `aeson: 1.0.2.1, 1.0.2.0, 1.0.1.0, ...`.
 --
--- displayMessage (RejectMany qpn is c fr) = "rejecting: " ++ fmtPkgsGroupedByName (map (showQPNPOpt qpn) (reverse is)) ++ showFR c fr
-displayMessage (LogRejectMany qpn is c fr) = "rejecting: " ++ L.intercalate ", " (map (showQPNPOpt qpn) (reverse is)) ++ showFR c fr
+displayMessage (LogRejectMany qpn is c fr) = "rejecting: " ++ fmtPkgsGroupedByName (map (showQPNPOpt qpn) (reverse is)) ++ showFR c fr
 
 -- TODO: This function should take as input the Index? So even without calling the solver, We can say things as
 -- "There is no version in the Hackage index that match the given constraints".
 --
 -- Alternatively, by passing this to the solver, we could get a more semantic output like:
 -- `all versions of aeson available are in conflict with ...`. Isn't already what `tryToMinimizeConflictSet` is doing?
--- fmtPkgsGroupedByName :: [String] -> String
--- fmtPkgsGroupedByName pkgs = L.intercalate " " $ fmtPkgGroup (groupByName pkgs)
---   where
---     groupByName :: [String] -> Map.Map String [String]
---     groupByName = foldr f Map.empty
---       where
---         f versionString m = let (pkg, ver) = splitOnLastHyphen versionString
---                             in Map.insertWith (++) pkg [ver] m
---         -- FIXME: This is not a very robust way to split the package name and version.
---         -- I should rather retrieve the package name and version from the QPN ...
---         splitOnLastHyphen :: String -> (String, String)
---         splitOnLastHyphen s =
---             case reverse (L.elemIndices '-' s) of
---                 (x:_)  -> (take x s, drop (x + 1) s)
---                 _ -> error "splitOnLastHyphen: no hyphen found"
-
---     fmtPkgGroup :: Map.Map String [String] -> [String]
---     fmtPkgGroup = map formatEntry . Map.toList
---       where
---         formatEntry (pkg, versions) = pkg ++ ": " ++ L.intercalate ", " versions
+fmtPkgsGroupedByName :: [String] -> String
+fmtPkgsGroupedByName pkgs = L.intercalate " " $ fmtPkgGroup (groupByName pkgs)
+  where
+    groupByName :: [String] -> M.Map String [String]
+    groupByName = foldr f M.empty
+      where
+        f versionString m = let (pkg, ver) = splitOnLastHyphen versionString
+                            in M.insertWith (++) pkg [ver] m
+        -- FIXME: This is not a very robust way to split the package name and version.
+        -- I should rather retrieve the package name and version from the QPN ...
+        splitOnLastHyphen :: String -> (String, String)
+        splitOnLastHyphen s =
+            case reverse (L.elemIndices '-' s) of
+                (x:_)  -> (take x s, drop (x + 1) s)
+                _ -> error "splitOnLastHyphen: no hyphen found"
+
+    fmtPkgGroup :: M.Map String [String] -> [String]
+    fmtPkgGroup = map formatEntry . M.toList
+      where
+        formatEntry (pkg, versions) = pkg ++ ": " ++ L.intercalate ", " versions
 
 -- | Transforms the structured message type to actual messages (SummarizedMsg s).
 --