$GIT_COMMON_DIR: a new environment variable

This variable is intended to support multiple working directories
attached to a repository. Such a repository may have a main working
directory, created by either "git init" or "git clone" and one or more
linked working directories. These working directories and the main
repository share the same repository directory.

In linked working directories, $GIT_COMMON_DIR must be defined to point
to the real repository directory and $GIT_DIR points to an unused
subdirectory inside $GIT_COMMON_DIR. File locations inside the
repository are reorganized from the linked worktree view point:

 - worktree-specific such as HEAD, logs/HEAD, index, other top-level
   refs and unrecognized files are from $GIT_DIR.

 - the rest like objects, refs, info, hooks, packed-refs, shallow...
   are from $GIT_COMMON_DIR (except info/sparse-checkout, but that's
   a separate patch)

Scripts are supposed to retrieve paths in $GIT_DIR with "git rev-parse
--git-path", which will take care of "$GIT_DIR vs $GIT_COMMON_DIR"
business.

The redirection is done by git_path(), git_pathdup() and
strbuf_git_path(). The selected list of paths goes to $GIT_COMMON_DIR,
not the other way around in case a developer adds a new
worktree-specific file and it's accidentally promoted to be shared
across repositories (this includes unknown files added by third party
commands)

The list of known files that belong to $GIT_DIR are:

ADD_EDIT.patch BISECT_ANCESTORS_OK BISECT_EXPECTED_REV BISECT_LOG
BISECT_NAMES CHERRY_PICK_HEAD COMMIT_MSG FETCH_HEAD HEAD MERGE_HEAD
MERGE_MODE MERGE_RR NOTES_EDITMSG NOTES_MERGE_WORKTREE ORIG_HEAD
REVERT_HEAD SQUASH_MSG TAG_EDITMSG fast_import_crash_* logs/HEAD
next-index-* rebase-apply rebase-merge rsync-refs-* sequencer/*
shallow_*

Path mapping is NOT done for git_path_submodule(). Multi-checkouts are
not supported as submodules.

Helped-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index 33d2818d02..f5d6f80d66 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -262,5 +262,21 @@ test_expect_success 'setup fake objects directory foo' 'mkdir foo'
 test_git_path GIT_OBJECT_DIRECTORY=foo objects foo
 test_git_path GIT_OBJECT_DIRECTORY=foo objects/foo foo/foo
 test_git_path GIT_OBJECT_DIRECTORY=foo objects2 .git/objects2
+test_expect_success 'setup common repository' 'git --git-dir=bar init'
+test_git_path GIT_COMMON_DIR=bar index                    .git/index
+test_git_path GIT_COMMON_DIR=bar HEAD                     .git/HEAD
+test_git_path GIT_COMMON_DIR=bar logs/HEAD                .git/logs/HEAD
+test_git_path GIT_COMMON_DIR=bar objects                  bar/objects
+test_git_path GIT_COMMON_DIR=bar objects/bar              bar/objects/bar
+test_git_path GIT_COMMON_DIR=bar info/exclude             bar/info/exclude
+test_git_path GIT_COMMON_DIR=bar info/grafts              bar/info/grafts
+test_git_path GIT_COMMON_DIR=bar remotes/bar              bar/remotes/bar
+test_git_path GIT_COMMON_DIR=bar branches/bar             bar/branches/bar
+test_git_path GIT_COMMON_DIR=bar logs/refs/heads/master   bar/logs/refs/heads/master
+test_git_path GIT_COMMON_DIR=bar refs/heads/master        bar/refs/heads/master
+test_git_path GIT_COMMON_DIR=bar hooks/me                 bar/hooks/me
+test_git_path GIT_COMMON_DIR=bar config                   bar/config
+test_git_path GIT_COMMON_DIR=bar packed-refs              bar/packed-refs
+test_git_path GIT_COMMON_DIR=bar shallow                  bar/shallow
 
 test_done