Support git remotes where .git is a file, not a directory

Eg when --separate-git-dir was used, and core.symlinks=false.

This commit was sponsored by Brock Spratlen on Patreon.

CHANGELOG

@@ -16,6 +16,8 @@ git-annex (8.20200815) UNRELEASED; urgency=medium
     held by another process.
   * test: Stop gpg-agent daemons that are started for the test framework's
     gpg key.
+  * Support git remotes where .git is a file, not a directory,
+    eg when --separate-git-dir was used.
 
  -- Joey Hess <id@joeyh.name>  Fri, 14 Aug 2020 14:57:45 -0400
 

Git/Construct.hs

@@ -1,6 +1,6 @@
 {- Construction of Git Repo objects
  -
- - Copyright 2010-2012 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2020 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -73,7 +73,7 @@ fromAbsPath dir
 				, ret (takeDirectory canondir)
 				)
 		| otherwise = ifM (doesDirectoryExist dir)
-			( ret dir
+			( gitDirFile dir >>= maybe (ret dir) (pure . newFrom)
 			-- git falls back to dir.git when dir doesn't
 			-- exist, as long as dir didn't end with a
 			-- path separator
@@ -198,7 +198,7 @@ expandTilde = expandt True
 checkForRepo :: FilePath -> IO (Maybe RepoLocation)
 checkForRepo dir = 
 	check isRepo $
-		check gitDirFile $
+		check (gitDirFile dir) $
 			check isBareRepo $
 				return Nothing
   where
@@ -217,9 +217,14 @@ checkForRepo dir =
 		gitSignature (".git" </> "gitdir")
 	isBareRepo = checkdir $ gitSignature "config"
 		<&&> doesDirectoryExist (dir </> "objects")
-	gitDirFile = do
-		-- git-submodule, git-worktree, and --separate-git-dir
-		-- make .git be a file pointing to the real git directory.
+	gitSignature file = doesFileExist $ dir </> file
+
+-- git-submodule, git-worktree, and --separate-git-dir
+-- make .git be a file pointing to the real git directory.
+-- Detect that, and return a RepoLocation with gitdir pointing 
+-- to the real git directory.
+gitDirFile :: FilePath -> IO (Maybe RepoLocation)
+gitDirFile dir = do
 	c <- firstLine <$>
 		catchDefaultIO "" (readFile $ dir </> ".git")
 	return $ if gitdirprefix `isPrefixOf` c
@@ -231,7 +236,6 @@ checkForRepo dir =
 		else Nothing
  where
 	gitdirprefix = "gitdir: "
-	gitSignature file = doesFileExist $ dir </> file
 
 newFrom :: RepoLocation -> Repo
 newFrom l = Repo

doc/bugs/separate-git-dir_OK_under_Linux_FAIL_under_Windows.mdwn

@@ -178,3 +178,5 @@ shaddy@jazz-debian:~/slaveproj$ ls -lL services
 ### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)
 
 This issue is not a show stopper. I otherwise love the concepts behind git-annex very much.
+
+> [[fixed|done]] --[[Joey]]

doc/bugs/separate-git-dir_OK_under_Linux_FAIL_under_Windows/comment_1_97ab8d245680e23a9e4b471796db2119._comment

@@ -0,0 +1,35 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 1"""
+ date="2020-08-28T18:03:46Z"
+ content="""
+--separate-git-dir makes eg, masterproj/.git be a file that contains the
+path to the git dir.
+
+git-annex init converts such a .git file to a symlink. That is necessary
+for git-annex symlinks to be resolved, since they always link to files
+inside .git, and if it's a file, the symlinks won't point to the object
+files.
+
+On windows, since core.symlinks is false, it does not make that change.
+
+So, I think the problem might be that, when .git is a file rather
+than a symlink, git-annex in the clone doesn't read the .git file to determine
+the real git repo location, and so can't find annexed files in its remote.
+
+Seem to have found a way to produce the same problem on linux:
+
+* git init --separate-git-dir masterproj.git masterproj
+* cd masterproj; git config core.symlinks false
+* git-annex init
+* add file, commit, make clone
+
+git-annex get in the clone then fails
+
+	openat(AT_FDCWD, "../masterproj/.git/annex/objects/3f/3K/SHA256E-s30--32a7ec5a2905bbeda54a699ed797c96c1fea7b5bc31a6cc104b2ddefe65a95bb/SHA256E-s30--32a7ec5a2905bbeda54a699ed797c96c1fea7b5bc31a6cc104b2ddefe65a95bb", O_RDONLY) = -1 ENOTDIR (Not a directory)
+
+So, I think it would make sense for git-annex to notice when
+a remote's .git is a file rather than a directory, and adjust the remote
+accordingly, so it uses its actual git directory. That will solve
+this situation.
+"""]]