verify associated files when checking numcopies

Most of this is just refactoring. But, handleDropsFrom
did not verify that associated files from the keys db were still
accurate, and has now been fixed to.

A minor improvement to this would be to avoid calling catKeyFile
twice on the same file, when getting the numcopies and mincopies value,
in the common case where the same file has the highest value for both.
But, it avoids checking every associated file, so it will scale well to
lots of dups already.

Sponsored-by: Kevin Mueller on Patreon

Annex/Drop.hs

@@ -52,11 +52,7 @@ type Reason = String
 handleDropsFrom :: [UUID] -> [Remote] -> Reason -> Bool -> Key -> AssociatedFile -> SeekInput -> [VerifiedCopy] -> (CommandStart -> CommandCleanup) -> Annex ()
 handleDropsFrom locs rs reason fromhere key afile si preverified runner = do
 	g <- Annex.gitRepo
-	l <- map (`fromTopFilePath` g)
-		<$> Database.Keys.getAssociatedFiles key
-	let fs = case afile of
-		AssociatedFile (Just f) -> f : filter (/= f) l
-		AssociatedFile Nothing -> l
+	fs <- Database.Keys.getAssociatedFilesIncluding afile key
 	n <- getcopies fs
 	void $ if fromhere && checkcopies n Nothing
 		then go fs rs n >>= dropl fs
@@ -64,11 +60,7 @@ handleDropsFrom locs rs reason fromhere key afile si preverified runner = do
   where
 	getcopies fs = do
 		(untrusted, have) <- trustPartition UnTrusted locs
-		(numcopies, mincopies) <- if null fs
-			then (,) <$> getNumCopies <*> getMinCopies
-			else do
-				l <- mapM getFileNumMinCopies fs
-				return (maximum $ map fst l, maximum $ map snd l)
+		(numcopies, mincopies) <- getSafestNumMinCopies' key fs
 		return (length have, numcopies, mincopies, S.fromList untrusted)
 
 	{- Check that we have enough copies still to drop the content.