optimise adjustTree when adding many TreeItems (take 2)

The old code traversed the list of addtreeitems once per subdirectory in
the tree, so could get quite slow. Converting to Map lookups sped it up
significantly.

In my test case, git-annex import used to take about 2 minutes, when
calling adjustTree to add back excluded files to the imported tree. This
dropped it down to 6 seconds. Of which 4 seconds are the actual
enumeration of the contents of the remote, so really only 2 seconds for
this.

The path prefix map is a bit suboptimal memory-wise, since items get
stored in the map once per subdirectory on the path to the item. It
would perhaps be better to use a tree data structure.

Also it's suboptimal memory-wise that it builds two maps, as well
as retaining a reference to addtreeitems. I could not see a way around
that though.

This is a fixed version of commit 2c86651180.
It fixes a test suite reversion.

Sponsored-by: Jack Hill on Patreon

Git/Tree.hs

@@ -1,11 +1,12 @@
 {- git trees
  -
- - Copyright 2016-2021 Joey Hess <id@joeyh.name>
+ - Copyright 2016-2023 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
 {-# LANGUAGE BangPatterns, TypeSynonymInstances, FlexibleInstances #-}
+{-# LANGUAGE OverloadedStrings #-}
 
 module Git.Tree (
 	Tree(..),
@@ -231,7 +232,7 @@ adjustTree adjusttreeitem addtreeitems resolveaddconflict removefiles r repo =
 	withMkTreeHandle repo $ \h -> do
 		(l, cleanup) <- liftIO $ lsTreeWithObjects LsTree.LsTreeRecursive r repo
 		(l', _, _) <- go h False [] 1 inTopTree l
-		l'' <- adjustlist h 0 inTopTree (const True) l'
+		l'' <- adjustlist h 0 inTopTree topTreePath l'
 		sha <- liftIO $ mkTree h l''
 		void $ liftIO cleanup
 		return sha
@@ -250,7 +251,7 @@ adjustTree adjusttreeitem addtreeitems resolveaddconflict removefiles r repo =
 						in go h modified (blob:c) depth intree is
 			Just TreeObject -> do
 				(sl, modified, is') <- go h False [] (depth+1) (beneathSubTree i) is
-				sl' <- adjustlist h depth (inTree i) (beneathSubTree i) sl
+				sl' <- adjustlist h depth (inTree i) (gitPath i) sl
 				let slmodified = sl' /= sl
 				subtree <- if modified || slmodified
 					then liftIO $ recordSubTree h $ NewSubTree (LsTree.file i) sl'
@@ -268,16 +269,22 @@ adjustTree adjusttreeitem addtreeitems resolveaddconflict removefiles r repo =
 			_ -> giveup ("unexpected object type \"" ++ decodeBS (LsTree.typeobj i) ++ "\"")
 		| otherwise = return (c, wasmodified, i:is)
 
-	adjustlist h depth ishere underhere l = do
-		let (addhere, rest) = partition ishere addtreeitems
+	adjustlist h depth ishere herepath l = do
+		let addhere = fromMaybe [] $ M.lookup herepath addtreeitempathmap
 		let l' = filter (not . removed) $
 			addoldnew l (map treeItemToTreeContent addhere)
 		let inl i = any (\t -> beneathSubTree t i) l'
 		let (Tree addunderhere) = flattenTree depth $ treeItemsToTree $
-			filter (\i -> underhere i && not (inl i)) rest
+			filter (not . inl) $ if herepath == topTreePath
+				then filter (not . ishere) addtreeitems
+				else fromMaybe [] $
+					M.lookup (subTreePrefix herepath) addtreeitemprefixmap
 		addunderhere' <- liftIO $ mapM (recordSubTree h) addunderhere
 		return (addoldnew l' addunderhere')
 
+	addtreeitempathmap = mkPathMap addtreeitems
+	addtreeitemprefixmap = mkSubTreePathPrefixMap addtreeitems
+
 	removeset = S.fromList $ map (P.normalise . gitPath) removefiles
 	removed (TreeBlob f _ _) = S.member (P.normalise (gitPath f)) removeset
 	removed (TreeCommit f _ _) = S.member (P.normalise (gitPath f)) removeset
@@ -355,12 +362,8 @@ graftTree' subtree graftloc basetree repo hdl = go basetree subdirs graftdirs
 
 	subdirs = P.splitDirectories $ gitPath graftloc
 
-	-- For a graftloc of "foo/bar/baz", this generates
-	-- ["foo", "foo/bar", "foo/bar/baz"]
 	graftdirs = map (asTopFilePath . toInternalGitPath) $
-		mkpaths [] subdirs
-	mkpaths _ [] = []
-	mkpaths base (d:rest) = (P.joinPath base P.</> d) : mkpaths (base ++ [d]) rest
+		pathPrefixes subdirs
 
 {- Assumes the list is ordered, with tree objects coming right before their
  - contents. -}
@@ -413,13 +416,50 @@ instance GitPath TreeContent where
 	gitPath (TreeCommit f _ _) = gitPath f
 
 inTopTree :: GitPath t => t -> Bool
-inTopTree = inTree "."
+inTopTree = inTree topTreePath
+
+topTreePath :: RawFilePath
+topTreePath = "."
 
 inTree :: (GitPath t, GitPath f) => t -> f -> Bool
 inTree t f = gitPath t == P.takeDirectory (gitPath f)
 
 beneathSubTree :: (GitPath t, GitPath f) => t -> f -> Bool
-beneathSubTree t f = prefix `B.isPrefixOf` P.normalise (gitPath f)
+beneathSubTree t f = subTreePrefix t `B.isPrefixOf` subTreePath f
+
+subTreePath :: GitPath t => t -> RawFilePath
+subTreePath = P.normalise . gitPath
+
+subTreePrefix :: GitPath t => t -> RawFilePath
+subTreePrefix t
+	| B.null tp = tp
+	| otherwise = P.addTrailingPathSeparator (P.normalise tp)
   where
 	tp = gitPath t
-	prefix = if B.null tp then tp else P.addTrailingPathSeparator (P.normalise tp)
+
+{- Makes a Map where the keys are directories, and the values
+ - are the items located in that directory.
+ -
+ - Values that are not in any subdirectory are placed in
+ - the topTreePath key.
+ -}
+mkPathMap :: GitPath t => [t] -> M.Map RawFilePath [t]
+mkPathMap l = M.fromListWith (++) $
+	map (\ti -> (P.takeDirectory (gitPath ti), [ti])) l
+
+{- Input is eg splitDirectories "foo/bar/baz",
+ - for which it will output ["foo", "foo/bar", "foo/bar/baz"] -}
+pathPrefixes :: [RawFilePath] -> [RawFilePath]
+pathPrefixes = go []
+  where
+	go _ [] = []
+	go base (d:rest) = (P.joinPath base P.</> d) : go (base ++ [d]) rest
+
+{- Makes a Map where the keys are all subtree path prefixes, 
+ - and the values are items with that subtree path prefix.
+ -}
+mkSubTreePathPrefixMap :: GitPath t => [t] -> M.Map RawFilePath [t]
+mkSubTreePathPrefixMap l = M.fromListWith (++) $ concatMap go l
+  where
+	go ti = map (\p -> (p, [ti]))
+		(map subTreePrefix $ pathPrefixes $ P.splitDirectories $ subTreePath ti)