drop performance improvements

Sped up seeking files to drop by 2x, and also some performance
improvements to checking numcopies.

Interestingly, the seek speedup is not due to precaching, but I think is
due to calling getParsed earlier.

Annex.Drop had to be changed to check inAnnex there, since it was removed
from Command.Drop. All other users of Command.Drop already checked inAnnex
themselves.

This commit was sponsored by Ryan Newton on Patreon.

Command/Drop.hs

@@ -1,6 +1,6 @@
 {- git-annex command
  -
- - Copyright 2010 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2020 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -52,53 +52,55 @@ parseDropFromOption = parseRemoteOption <$> strOption
 	)
 
 seek :: DropOptions -> CommandSeek
-seek o = startConcurrency commandStages $
+seek o = startConcurrency commandStages $ do
+	from <- case dropFrom o of
+		Nothing -> pure Nothing
+		Just f -> getParsed f >>= \remote -> do
+			u <- getUUID
+			if Remote.uuid remote == u
+				then pure Nothing
+				else pure (Just remote)				
+	let seeker = AnnexedFileSeeker
+		{ startAction = start o from
+		, checkContentPresent = case from of
+			Nothing -> Just True
+			Just _ -> Nothing
+		, usesLocationLog = True
+		}
 	case batchOption o of
 		Batch fmt -> batchAnnexedFilesMatching fmt seeker
 		NoBatch -> withKeyOptions (keyOptions o) (autoMode o) seeker
-			(commandAction . startKeys o)
+			(commandAction . startKeys o from)
 			(withFilesInGitAnnex ww seeker)
 			=<< workTreeItems ww (dropFiles o)
   where
 	ww = WarnUnmatchLsFiles
 
-	seeker = AnnexedFileSeeker
-		{ startAction = start o
-		, checkContentPresent = Nothing
-		, usesLocationLog = False
-		}
-
-start :: DropOptions -> RawFilePath -> Key -> CommandStart
-start o file key = start' o key afile ai
+start :: DropOptions -> Maybe Remote -> RawFilePath -> Key -> CommandStart
+start o from file key = start' o from key afile ai
   where
 	afile = AssociatedFile (Just file)
 	ai = mkActionItem (key, afile)
 
-start' :: DropOptions -> Key -> AssociatedFile -> ActionItem -> CommandStart
-start' o key afile ai = do
-	from <- maybe (pure Nothing) (Just <$$> getParsed) (dropFrom o)
+start' :: DropOptions -> Maybe Remote -> Key -> AssociatedFile -> ActionItem -> CommandStart
+start' o from key afile ai = 
 	checkDropAuto (autoMode o) from afile key $ \numcopies ->
-		stopUnless (want from) $
+		stopUnless want $
 			case from of
 				Nothing -> startLocal afile ai numcopies key []
-				Just remote -> do
-					u <- getUUID
-					if Remote.uuid remote == u
-						then startLocal afile ai numcopies key []
-						else startRemote afile ai numcopies key remote
-	  where
-		want from
-			| autoMode o = wantDrop False (Remote.uuid <$> from) (Just key) afile
-			| otherwise = return True
+				Just remote -> startRemote afile ai numcopies key remote
+  where
+	want
+		| autoMode o = wantDrop False (Remote.uuid <$> from) (Just key) afile
+		| otherwise = return True
 
-startKeys :: DropOptions -> (Key, ActionItem) -> CommandStart
-startKeys o (key, ai) = start' o key (AssociatedFile Nothing) ai
+startKeys :: DropOptions -> Maybe Remote -> (Key, ActionItem) -> CommandStart
+startKeys o from (key, ai) = start' o from key (AssociatedFile Nothing) ai
 
 startLocal :: AssociatedFile -> ActionItem -> NumCopies -> Key -> [VerifiedCopy] -> CommandStart
 startLocal afile ai numcopies key preverified =
-	stopUnless (inAnnex key) $
-		starting "drop" (OnlyActionOn key ai) $
-			performLocal key afile numcopies preverified
+	starting "drop" (OnlyActionOn key ai) $
+		performLocal key afile numcopies preverified
 
 startRemote :: AssociatedFile -> ActionItem -> NumCopies -> Key -> Remote -> CommandStart
 startRemote afile ai numcopies key remote =