Add --verbose arg and show how package dependency is being solved

elm-package.cabal

@@ -48,6 +48,7 @@ Library
         Install.Fetch,
         Install.Plan,
         Install.Solver,
+        Logger,
         Manager,
         Paths_elm_package,
         Store,
@@ -63,6 +64,7 @@ Library
         directory >= 1.0 && < 2.0,
         elm-compiler >= 0.16 && < 0.17,
         filepath >= 1 && < 2.0,
+        hslogger >= 1.2.9 && < 1.3,
         HTTP >= 4000.2.5 && < 4000.3,
         http-client >= 0.4.15 && < 0.5,
         http-client-tls >= 0.2 && < 0.3,
@@ -105,6 +107,7 @@ Executable elm-package
         Install.Fetch,
         Install.Plan,
         Install.Solver,
+        Logger,
         Manager,
         Publish,
         Store,
@@ -123,6 +126,7 @@ Executable elm-package
         directory >= 1.0 && < 2.0,
         elm-compiler >= 0.16 && < 0.17,
         filepath >= 1 && < 2.0,
+        hslogger >= 1.2.9 && < 1.3,
         HTTP >= 4000.2.5 && < 4000.3,
         http-client >= 0.3 && < 0.5,
         http-client-tls >= 0.2 && < 0.3,

src/CommandLine/Arguments.hs

@@ -88,18 +88,18 @@ installInfo =
     Opt.info args infoModifier
   where
     args =
-        installWith <$> optional package <*> optional version <*> yes
+        installWith <$> optional package <*> optional version <*> yes <*> verbose
 
-    installWith maybeName maybeVersion autoYes =
+    installWith maybeName maybeVersion autoYes verbose =
         case (maybeName, maybeVersion) of
           (Nothing, Nothing) ->
-              Install.install autoYes Install.Everything
+              Install.install verbose autoYes Install.Everything
 
           (Just name, Nothing) ->
-              Install.install autoYes (Install.Latest name)
+              Install.install verbose autoYes (Install.Latest name)
 
           (Just name, Just version) ->
-              Install.install autoYes (Install.Exactly name version)
+              Install.install verbose autoYes (Install.Exactly name version)
 
           (Nothing, Just version) ->
               throwError $
@@ -152,6 +152,15 @@ yes =
         ]
 
 
+verbose :: Opt.Parser Bool
+verbose =
+    Opt.switch $
+        mconcat
+        [ Opt.long "verbose"
+        , Opt.help "Print out detailed log so that you can trace back what went wrong at which point."
+        ]
+
+
 customReader :: String -> (String -> Either String a) -> Opt.ReadM a
 customReader argType fromString =
   let reader arg =

src/Elm/Package/Initialize.hs

@@ -11,20 +11,21 @@ import qualified Install
 import qualified Manager
 
 
-solution :: (MonadError String m, MonadIO m) => Bool -> m S.Solution
-solution autoYes =
-    runInstall autoYes Install.Everything
+solution :: (MonadError String m, MonadIO m) => Bool -> Bool -> m S.Solution
+solution verbose autoYes =
+    runInstall verbose autoYes Install.Everything
 
 
 runInstall
     :: (MonadError String m, MonadIO m)
     => Bool
+    -> Bool
     -> Install.Args
     -> m S.Solution
-runInstall autoYes args =
+runInstall verbose autoYes args =
   do  either <- liftIO $ do
           env <- Manager.defaultEnvironment
-          Manager.run env (Install.install autoYes args)
+          Manager.run env (Install.install verbose autoYes args)
 
       case either of
         Left err -> throwError err

src/Install.hs

@@ -19,6 +19,7 @@ import qualified Install.Plan as Plan
 import qualified Install.Solver as Solver
 import qualified Manager
 import qualified Store
+import qualified Logger
 
 
 data Args
@@ -27,9 +28,10 @@ data Args
     | Exactly Package.Name Package.Version
 
 
-install :: Bool -> Args -> Manager.Manager ()
-install autoYes args =
-  do  exists <- liftIO (doesFileExist Path.description)
+install :: Bool -> Bool -> Args -> Manager.Manager ()
+install verbose autoYes args =
+  do  liftIO (Logger.configure verbose)
+      exists <- liftIO (doesFileExist Path.description)
 
       description <-
           case exists of

src/Install/Solver.hs

@@ -11,6 +11,7 @@ import qualified Elm.Package as Package
 import qualified Elm.Package.Solution as S
 import qualified Manager
 import qualified Store
+import Logger
 
 
 solve :: [(Package.Name, C.Constraint)] -> Manager.Manager S.Solution
@@ -70,7 +71,9 @@ exploreVersion name version solution remainingPackages =
   do  (elmVersion, constraints) <- Store.getConstraints name version
       if C.isSatisfied elmVersion Compiler.version
         then explore constraints
-        else return Nothing
+        else
+          do  infoM $ (displayNameAndVersion name version) ++ " requires Elm version " ++ (C.toString elmVersion) ++ " but we are on " ++ (Package.versionToString Compiler.version)
+              return Nothing
 
   where
     explore constraints =
@@ -80,7 +83,12 @@ exploreVersion name version solution remainingPackages =
           case all (satisfiedBy solution) overlappingConstraints of
             False -> return Nothing
             True ->
-              do  maybePackages <- addConstraints remainingPackages newConstraints
+              do  case newConstraints of
+                    [] -> return Nothing
+                    someConstraints ->
+                        do  infoM $ (displayNameAndVersion name version) ++ " depends on " ++ (displayConstraints someConstraints)
+                            return Nothing
+                  maybePackages <- addConstraints remainingPackages newConstraints
                   case maybePackages of
                     Nothing -> return Nothing
                     Just extendedPackages ->
@@ -102,5 +110,46 @@ addConstraints packages constraints =
       (name, constraint) : rest ->
           do  versions <- Store.getVersions name
               case filter (C.isSatisfied constraint) versions of
-                [] -> return Nothing
-                vs -> addConstraints (Map.insert name vs packages) rest
+                [] ->
+                  do  infoM $ (Package.toString name) ++ " (" ++ (displayVersions versions) ++ ") has no package version that satisfies " ++ (C.toString constraint)
+                      return Nothing
+                vs ->
+                  do  infoM $ (Package.toString name) ++ " = " ++ (displayVersions vs) ++ (displayNewerVersions (head vs) versions)
+                      addConstraints (Map.insert name vs packages) rest
+
+
+-- LOGGING
+
+
+displayNamedConstraint :: (Package.Name, C.Constraint) -> String
+displayNamedConstraint (name, constraint) =
+  (Package.toString name) ++ ": " ++ (C.toString constraint)
+
+
+displayNameAndVersion :: Package.Name -> Package.Version -> String
+displayNameAndVersion name version =
+  (Package.toString name) ++ " = " ++ (Package.versionToString version)
+
+
+displayConstraints :: [(Package.Name, C.Constraint)] -> String
+displayConstraints constraints =
+  List.intercalate ", " (map displayNamedConstraint constraints)
+
+
+displayVersions :: [Package.Version] -> String
+displayVersions versions =
+  List.intercalate ", " (map Package.versionToString versions)
+
+
+displayNewerVersions :: Package.Version -> [Package.Version] -> String
+displayNewerVersions current versions =
+  do  case newerVersions of
+        [] ->
+          ""
+
+        versions ->
+          " < " ++ (displayVersions versions)
+
+  where
+    newerVersions =
+      filter (\v -> v > current) versions

src/Logger.hs

@@ -0,0 +1,21 @@
+module Logger where
+
+import Control.Monad.Trans (MonadIO(..), liftIO)
+import System.Log.Logger (updateGlobalLogger,
+                          Priority(..),
+                          rootLoggerName,
+                          setLevel)
+import qualified System.Log.Logger as L
+
+
+configure :: Bool -> IO ()
+configure verbose =
+  do liftIO $ updateGlobalLogger rootLoggerName (setLevel logLevel)
+  where logLevel = if verbose
+                   then DEBUG
+                   else WARNING
+
+
+infoM :: MonadIO m => String -> m ()
+infoM message =
+  liftIO $ L.infoM rootLoggerName message