fix inversion of control in CommandSeek (no behavior changes)

I've been disliking how the command seek actions were written for some
time, with their inversion of control and ugly workarounds.

The last straw to fix it was sync --content, which didn't fit the
Annex [CommandStart] interface well at all. I have not yet made it take
advantage of the changed interface though.

The crucial change, and probably why I didn't do it this way from the
beginning, is to make each CommandStart action be run with exceptions
caught, and if it fails, increment a failure counter in annex state.
So I finally remove the very first code I wrote for git-annex, which
was before I had exception handling in the Annex monad, and so ran outside
that monad, passing state explicitly as it ran each CommandStart action.

This was a real slog from 1 to 5 am.

Test suite passes.

Memory usage is lower than before, sometimes by a couple of megabytes, and
remains constant, even when running in a large repo, and even when
repeatedly failing and incrementing the error counter. So no accidental
laziness space leaks.

Wall clock speed is identical, even in large repos.

This commit was sponsored by an anonymous bitcoiner.

CmdLine.hs

@@ -23,7 +23,6 @@ import System.Posix.Signals
 
 import Common.Annex
 import qualified Annex
-import qualified Annex.Queue
 import qualified Git
 import qualified Git.AutoCorrect
 import Annex.Content
@@ -41,7 +40,7 @@ dispatch fuzzyok allargs allcmds commonoptions fields header getgitrepo = do
 		Left e -> maybe (throw e) (\a -> a params) (cmdnorepo cmd)
 		Right g -> do
 			state <- Annex.new g
-			(actions, state') <- Annex.run state $ do
+			Annex.eval state $ do
 				checkEnvironment
 				checkfuzzy
 				forM_ fields $ uncurry Annex.setField
@@ -50,8 +49,9 @@ dispatch fuzzyok allargs allcmds commonoptions fields header getgitrepo = do
 				sequence_ flags
 				whenM (annexDebug <$> Annex.getGitConfig) $
 					liftIO enableDebugOutput
-				prepCommand cmd params
-		 	tryRun state' cmd $ [startup] ++ actions ++ [shutdown $ cmdnocommit cmd]
+				startup
+				performCommand cmd params
+				shutdown $ cmdnocommit cmd
   where
 	err msg = msg ++ "\n\n" ++ usage header allcmds
 	cmd = Prelude.head cmds
@@ -92,44 +92,19 @@ getOptCmd argv cmd commonoptions = check $
 		, commandUsage cmd
 		]
 
-{- Runs a list of Annex actions. Catches IO errors and continues
- - (but explicitly thrown errors terminate the whole command).
- -}
-tryRun :: Annex.AnnexState -> Command -> [CommandCleanup] -> IO ()
-tryRun = tryRun' 0
-tryRun' :: Integer -> Annex.AnnexState -> Command -> [CommandCleanup] -> IO ()
-tryRun' errnum _ cmd []
-	| errnum > 0 = error $ cmdname cmd ++ ": " ++ show errnum ++ " failed"
-	| otherwise = noop
-tryRun' errnum state cmd (a:as) = do
-	r <- run
-	handle $! r
-  where
-	run = tryIO $ Annex.run state $ do
-		Annex.Queue.flushWhenFull
-		a
-	handle (Left err) = showerr err >> cont False state
-	handle (Right (success, state')) = cont success state'
-	cont success s = do
-		let errnum' = if success then errnum else errnum + 1
-		(tryRun' $! errnum') s cmd as
-	showerr err = Annex.eval state $ do
-		showErr err
-		showEndFail
-
 {- Actions to perform each time ran. -}
-startup :: Annex Bool
-startup = liftIO $ do
+startup :: Annex ()
+startup =
 #ifndef mingw32_HOST_OS
-	void $ installHandler sigINT Default Nothing
+	liftIO $ void $ installHandler sigINT Default Nothing
+#else
+	return ()
 #endif
-	return True
 
 {- Cleanup actions. -}
-shutdown :: Bool -> Annex Bool
+shutdown :: Bool -> Annex ()
 shutdown nocommit = do
 	saveState nocommit
 	sequence_ =<< M.elems <$> Annex.getState Annex.cleanup
 	liftIO reapZombies -- zombies from long-running git processes
 	sshCleanup -- ssh connection caching
-	return True