[PATCH v2 00/21] Support multiple worktrees

The UI and behavior are taking shape now. On the UI side, you do

  git checkout --to /somewhere -b newbranch origin/master

which will create worktree-only repo at /somewhere. "git prune --repos" could be used to remove cruft in .git/repos.

On the behavior side, you should be able to do everything in /somewhere just like in a normal repository. If a ref is updated (from any repository) that also happens to be your HEAD, it will be detached. "git rev-list --all" is also taught to take repos/.../HEAD into account.

The structure of repos/XXX is documented in 17/21. Known issues

 - naming ($GIT_SUPER_DIR, the name of the shared repo and the
   dependent one, the reuse of "gitdir" in .git files)

 - gc --auto support, support for manually pruning .git/repos

 - should probably support the new .git format in enter_repo() so that
   we can push to it

 - not sure if we need UI for deleting repositories created with
   checkout --to, or just "rm -r" and let "gc --auto" clean
   things up. The thing about "rm -r(f)" is that if .git happens to be
   a real repo, the user is screwed so I don't really like to
   encourage doing it.

 - more tests

Nguyễn Thái Ngọc Duy (21):
  path.c: avoid PATH_MAX as buffer size from get_pathname()
  path.c: rename vsnpath() to git_vsnpath()
  path.c: move git_path() closer to similar functions git_pathdup()
  Make git_path() aware of file relocation in $GIT_DIR
  reflog: use avoid constructing .lock path with git_path
  fast-import: use git_path() for accessing .git dir instead of get_git_dir()
  Add new environment variable $GIT_SUPER_DIR
  setup.c: refactor path manipulation out of read_gitfile()
  setup.c: add split-repo support to .git files
  setup.c: add split-repo support to is_git_directory()
  setup.c: reduce cleanup sites in setup_explicit_git_dir()
  environment.c: support super .git file specified by $GIT_DIR
  setup: support $GIT_SUPER_DIR as well as super .git files
  checkout: support checking out into a new working directory
  checkout: clean up half-prepared directories in --to mode
  setup.c: keep track of the .git file location if read
  prune: strategies for split repositories
  refs: adjust reflog path for repos/<id>/HEAD
  refs: detach split repos' HEAD when the linked ref is updated/deleted
  refs.c: refactor do_head_ref(... to do_one_ref("HEAD", ...
  revision: include repos/../HEAD in --all

 Documentation/config.txt               |   3 +-
 Documentation/git-checkout.txt         |   6 +
 Documentation/git-prune.txt            |   4 +
 Documentation/git.txt                  |   8 ++
 Documentation/gitrepository-layout.txt |  30 ++++
 builtin/checkout.c                     | 173 ++++++++++++++++++++++
 builtin/prune.c                        |  65 +++++++++
 builtin/reflog.c                       |   2 +-
 builtin/rev-parse.c                    |   6 +
 cache.h                                |   5 +
 environment.c                          |  37 ++++-
 fast-import.c                          |   5 +-
 path.c                                 | 140 ++++++++++++++----
 refs.c                                 |  88 ++++++++++--
 refs.h                                 |   1 +
 revision.c                             |   1 +
 setup.c                                | 253 ++++++++++++++++++++++++---------
 t/t0060-path-utils.sh                  | 133 +++++++++++++++++
 t/t1501-worktree.sh                    |  52 +++++++
 t/t1510-repo-setup.sh                  |   1 +
 test-path-utils.c                      |   7 +
 trace.c                                |   1 +
 22 files changed, 904 insertions(+), 117 deletions(-)