Fix bug importing from a special remote into a subdirectory more than one level deep

Which generated unusual git trees that could confuse git merge,
since they incorrectly had 2 subtrees with the same name.

Root of the bug was a) not testing that at all! but also
b) confusing graftdirs, which contains eg "foo/bar" with
non-recursively read trees, which would contain eg "bar"
when reading a subtree of "foo".

It's worth noting that Annex.Import uses graftTree, but it really
shouldn't have needed to. Eg, when importing into foo/bar from a remote,
it's enough to generate a tree of foo/bar/x, foo/bar/y, and does not
include other files that are at the top of the master branch. It uses
graftTree, so it does include the other files, as well as the foo/bar
tree. git merge will do the same thing for both trees. With that said,
switching it away from graftTree would result in another import
generating a new commit that seems to delete files that were there in a
previous commit, so it probably has to keep using graftTree since it
used it before.

This commit was sponsored by Kevin Mueller on Patreon.

CHANGELOG

@@ -28,6 +28,9 @@ git-annex (8.20210311) UNRELEASED; urgency=medium
   * Improved display of errors when accessing a git http remote fails.
   * borg: Fix a bug that prevented importing keys of type URL and WORM.
   * borg: Support importing files that are hard linked in the borg backup.
+  * Fix bug importing from a special remote into a subdirectory more than
+    one level deep, which generated unusual git trees that could confuse
+    git merge.
 
  -- Joey Hess <id@joeyh.name>  Fri, 12 Mar 2021 12:06:37 -0400
 

Git/Tree.hs

@@ -306,43 +306,43 @@ graftTree'
 	-> Repo
 	-> MkTreeHandle
 	-> IO Sha
-graftTree' subtree graftloc basetree repo hdl = go basetree graftdirs
+graftTree' subtree graftloc basetree repo hdl = go basetree subdirs graftdirs 
   where
-	go tsha (topmostgraphdir:restgraphdirs) = do
+	go tsha (subdir:restsubdirs) (topmostgraphdir:restgraphdirs) = do
 		Tree t <- getTree LsTree.LsTreeNonRecursive tsha repo
-		t' <- case partition isabovegraft t of
+		let abovegraftpoint i = gitPath i == gitPath subdir
+		t' <- case partition abovegraftpoint t of
+			-- the graft point is not already in the tree,
+			-- so graft it in, keeping the existing tree
+			-- content
 			([], _) -> do
 				graft <- graftin (topmostgraphdir:restgraphdirs)
 				return (graft:t)
-			-- normally there can only be one matching item
-			-- in the tree, but it's theoretically possible
-			-- for a git tree to have multiple items with the
-			-- same name, so process them all
 			(matching, rest) -> do
 				newshas <- forM matching $ \case
 					RecordedSubTree tloc tsha' _
 						| null restgraphdirs -> return $
 							RecordedSubTree tloc subtree []
 						| otherwise -> do
-							tsha'' <- go tsha' restgraphdirs
+							tsha'' <- go tsha' restsubdirs restgraphdirs
 							return $ RecordedSubTree tloc tsha'' []
 					_ -> graftin (topmostgraphdir:restgraphdirs)
 				return (newshas ++ rest)
 		mkTree hdl t'
-	go _ [] = return subtree
-
-	isabovegraft i = beneathSubTree i graftloc || gitPath i == gitPath graftloc
+	go _ _ [] = return subtree
 	
 	graftin t = recordSubTree hdl $ graftin' t
 	graftin' [] = RecordedSubTree graftloc subtree []
 	graftin' (d:rest) 
 		| d == graftloc = graftin' []
 		| otherwise = NewSubTree d [graftin' rest]
-	
+
+	subdirs = splitDirectories $ gitPath graftloc
+
 	-- For a graftloc of "foo/bar/baz", this generates
 	-- ["foo", "foo/bar", "foo/bar/baz"]
 	graftdirs = map (asTopFilePath . toInternalGitPath . encodeBS) $
-		mkpaths [] $ splitDirectories $ gitPath graftloc
+		mkpaths [] subdirs
 	mkpaths _ [] = []
 	mkpaths base (d:rest) = (joinPath base </> d) : mkpaths (base ++ [d]) rest
 

doc/bugs/Importing_into_nested_directory_overwrites_files__63__.mdwn

@@ -100,3 +100,5 @@ supported repository versions: 8
 upgrade supported from repository versions: 0 1 2 3 4 5 6 7
 local repository version: 8
 ```
+
+> [[fixed|done]], thanks for an excellent test case. --[[Joey]]

doc/bugs/Importing_into_nested_directory_overwrites_files__63__/comment_4_c555ea6eeab30eeebb5d33988908118a._comment

@@ -0,0 +1,11 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 4"""
+ date="2021-03-26T18:46:19Z"
+ content="""
+Note that level1/level2 is sufficient for git-annex to generate the bad
+tree. I also saw git merge fail at that depth.
+
+I've fixed this, at least the test case given and some other similar ones
+I thought of to try.
+"""]]