refs: use chdir_notify to update cached relative paths

Commit f57f37e (files-backend: remove the use of
git_path(), 2017-03-26) introduced a regression when a
relative $GIT_DIR is used in a working tree:

  - when we initialize the ref backend, we make a copy of
    get_git_dir(), which may be relative

  - later, we may call setup_work_tree() and chdir to the
    root of the working tree

  - further calls to the ref code will use the stored git
    directory, but relative paths will now point to the
    wrong place

The new test in t1501 demonstrates one such instance (the
bug causes us to write the ref update to the nonsense
"relative/relative/.git").

Since setup_work_tree() now uses chdir_notify, we can just
ask it update our relative paths when necessary.

Reported-by: Rafael Ascensao <[email protected]>
Helped-by: Nguyễn Thái Ngọc Duy <[email protected]>
Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

refs/files-backend.c

@@ -9,6 +9,7 @@
 #include "../lockfile.h"
 #include "../object.h"
 #include "../dir.h"
+#include "../chdir-notify.h"
 
 /*
  * This backend uses the following flags in `ref_update::flags` for
@@ -106,6 +107,11 @@ static struct ref_store *files_ref_store_create(const char *gitdir,
 	refs->packed_ref_store = packed_ref_store_create(sb.buf, flags);
 	strbuf_release(&sb);
 
+	chdir_notify_reparent("files-backend $GIT_DIR",
+			      &refs->gitdir);
+	chdir_notify_reparent("files-backend $GIT_COMMONDIR",
+			      &refs->gitcommondir);
+
 	return ref_store;
 }
 

refs/packed-backend.c

@@ -5,6 +5,7 @@
 #include "packed-backend.h"
 #include "../iterator.h"
 #include "../lockfile.h"
+#include "../chdir-notify.h"
 
 enum mmap_strategy {
 	/*
@@ -202,6 +203,8 @@ struct ref_store *packed_ref_store_create(const char *path,
 	refs->store_flags = store_flags;
 
 	refs->path = xstrdup(path);
+	chdir_notify_reparent("packed-refs", &refs->path);
+
 	return ref_store;
 }
 

t/t1501-work-tree.sh

@@ -431,4 +431,16 @@ test_expect_success 'error out gracefully on invalid $GIT_WORK_TREE' '
 	)
 '
 
+test_expect_success 'refs work with relative gitdir and work tree' '
+	git init relative &&
+	git -C relative commit --allow-empty -m one &&
+	git -C relative commit --allow-empty -m two &&
+
+	GIT_DIR=relative/.git GIT_WORK_TREE=relative git reset HEAD^ &&
+
+	git -C relative log -1 --format=%s >actual &&
+	echo one >expect &&
+	test_cmp expect actual
+'
+
 test_done