add support for fully automatic upgrades

The Upgrader avoids checking for upgrades on startup when it was just
upgraded. This avoids an upgrade loop if something goes wrong. One example
of something going wrong would be if the upgrade info file and the
distribution file get out of sync (or the distribution file is cached in
a proxy), so it thinks it has upgraded to a new version, but has really
not.

Assistant.hs

@@ -153,7 +153,7 @@ startDaemon assistant foreground startdelay cannotrun listenhost startbrowser =
 #endif
 				, assist $ netWatcherThread
 				, assist $ upgraderThread urlrenderer
-				, assist $ upgradWatcherThread urlrenderer
+				, assist $ upgradeWatcherThread urlrenderer
 				, assist $ netWatcherFallbackThread
 				, assist $ transferScannerThread urlrenderer
 				, assist $ cronnerThread urlrenderer

Assistant/Threads/UpgradeWatcher.hs

@@ -8,7 +8,7 @@
 {-# LANGUAGE CPP #-}
 
 module Assistant.Threads.UpgradeWatcher (
-	upgradWatcherThread
+	upgradeWatcherThread
 ) where
 
 import Assistant.Common
@@ -30,9 +30,9 @@ import qualified Data.Text as T
 data WatcherState = InStartupScan | Started | Upgrading
 	deriving (Eq)
 
-upgradWatcherThread :: UrlRenderer -> NamedThread
+upgradeWatcherThread :: UrlRenderer -> NamedThread
-upgradWatcherThread urlrenderer = namedThread "UpgradeWatcher" $ do
+upgradeWatcherThread urlrenderer = namedThread "UpgradeWatcher" $ do
-	whenM (liftIO $ checkSuccessfulUpgrade) $
+	whenM (liftIO checkSuccessfulUpgrade) $
 		showSuccessfulUpgrade urlrenderer
 	go =<< liftIO upgradeFlagFile
   where

Assistant/Threads/Upgrader.hs

@@ -12,6 +12,8 @@ module Assistant.Threads.Upgrader (
 ) where
 
 import Assistant.Common
+import Assistant.Upgrade
+
 import Assistant.Types.UrlRenderer
 import Assistant.DaemonStatus
 import Assistant.Alert
@@ -31,11 +33,14 @@ import Data.Time.Clock
 import qualified Data.Text as T
 
 upgraderThread :: UrlRenderer -> NamedThread
-upgraderThread urlrenderer = namedThread "Upgrader" $ do
+upgraderThread urlrenderer = namedThread "Upgrader" $
-	checkUpgrade urlrenderer
 	when (isJust Build.SysConfig.upgradelocation) $ do
+		{- Check for upgrade on startup, unless it was just
+		 - upgraded. -}
+		unlessM (liftIO checkSuccessfulUpgrade) $
+			checkUpgrade urlrenderer
 		h <- liftIO . newNotificationHandle False . networkConnectedNotifier =<< getDaemonStatus
-		go h Nothing
+		go h =<< liftIO getCurrentTime
   where
   	{- Wait for a network connection event. Then see if it's been
 	 - half a day since the last upgrade check. If so, proceed with
@@ -47,10 +52,10 @@ upgraderThread urlrenderer = namedThread "Upgrader" $ do
 			then go h lastchecked
 			else do
 				now <- liftIO getCurrentTime
-				if maybe True (\t -> diffUTCTime now t > halfday) lastchecked
+				if diffUTCTime now lastchecked > halfday
 					then do
 						checkUpgrade urlrenderer
-						go h =<< Just <$> liftIO getCurrentTime
+						go h =<< liftIO getCurrentTime
 					else go h lastchecked
 	halfday = 12 * 60 * 60
 
@@ -71,13 +76,16 @@ checkUpgrade urlrenderer = do
 				else debug [ "No new version found." ]
 
 canUpgrade :: AlertPriority -> UrlRenderer -> GitAnnexDistribution -> Assistant ()
-canUpgrade urgency urlrenderer d = do
+canUpgrade urgency urlrenderer d = ifM autoUpgradeEnabled
+	( startDistributionDownload d
+	, do
 #ifdef WITH_WEBAPP
-	button <- mkAlertButton True (T.pack "Upgrade") urlrenderer (ConfigStartUpgradeR d)
+		button <- mkAlertButton True (T.pack "Upgrade") urlrenderer (ConfigStartUpgradeR d)
-	void $ addAlert (canUpgradeAlert urgency button)
+		void $ addAlert (canUpgradeAlert urgency button)
 #else
-	noop
+		noop
 #endif
+	)
 
 getDistributionInfo :: Assistant (Maybe GitAnnexDistribution)
 getDistributionInfo = do