[RFC PATCH 00/12] Sparse checkout

I have not looked at non-builtin commands yet, but I think it's not
a big deal. We have several rounds before this series is good enough ;)
So in short, sparse prefix will be stored in config, core.sparsecheckout.
you have three new commands to enter/update/leave sparse checkout:

git clone --path=prefix       # clone with sparse checkout
git checkout --path=prefix    # limit/update checkout paths
git checkout --full           # stop sparse checkout

Other operations should be normal. User attempts to do anything outside
sparse checkout will get flagged. Git itself should not touch anything
outside sparse checkout.

One more thing. As files outside sparse checkout will not be checking
out, .gitignore and .gitattributes from parent directories (outside
sparse checkout) will be gone too. This may lead to surprise.

Comments are welcome.

Nguyễn Thái Ngọc Duy (12):
  git-grep: read config
  git-grep: support --no-external-grep
  Introduce sparse prefix
  Protect index with sparse prefix
  tests for sparse checkout, index protection
  Avoid accessing working directory outside sparse prefix
  tests for sparse checkout, worktree protection
  git-clone: support --path to do sparse clone
  tests for sparse clone
  git-checkout: support --full and --path to manipulate sparse checkout
  tests for checkout [--full|--path]
  git-status: print sparse checkout status

 builtin-add.c                              |    4 +-
 builtin-apply.c                            |    5 +
 builtin-checkout-index.c                   |    2 +
 builtin-checkout.c                         |   46 ++++++-
 builtin-clean.c                            |    3 +
 builtin-clone.c                            |   13 ++
 builtin-commit.c                           |   13 ++-
 builtin-grep.c                             |   36 +++--
 builtin-ls-files.c                         |    6 +-
 builtin-ls-tree.c                          |    2 +-
 builtin-merge-recursive.c                  |    6 +-
 builtin-mv.c                               |    2 +-
 builtin-read-tree.c                        |    5 +
 builtin-rev-parse.c                        |    4 +
 builtin-rm.c                               |    7 +-
 builtin-update-index.c                     |   37 ++++-
 cache.h                                    |   19 +++
 config.c                                   |    7 +
 diff-lib.c                                 |    5 +-
 diff.c                                     |    3 +-
 entry.c                                    |    3 +
 environment.c                              |  221 ++++++++++++++++++++++++++
 read-cache.c                               |  112 +++++++++++++-
 setup.c                                    |   90 +++++++++++-
 sha1_file.c                                |    3 +
 t/t2010-checkout-sparse.sh                 |   71 +++++++++
 t/t2300-sparse-index.sh                    |  156 +++++++++++++++++++
 t/t2300/diff-index-sub.expected            |    3 +
 t/t2300/log.expected                       |   64 ++++++++
 t/t2301-sparse-index-merge-recursive.sh    |  226 +++++++++++++++++++++++++++
 t/t2302-sparse-worktree.sh                 |  113 ++++++++++++++
 t/t2302/add-u.expected                     |    1 +
 t/t2302/add.expected                       |    2 +
 t/t2302/commit.expected                    |   14 ++
 t/t2302/diff-1.expected                    |    7 +
 t/t2302/diff-cc.expected                   |    9 +
 t/t2302/grep-work.expected                 |    2 +
 t/t2302/grep.expected                      |    2 +
 t/t2302/ls-files.expected                  |    2 +
 t/t2303-sparse-worktree-apply.sh           |   62 ++++++++
 t/t2303/apply-initial.patch                |   14 ++
 t/t2303/apply-inside.patch                 |    7 +
 t/t2303/apply-leading-dirs.patch           |    3 +
 t/t2303/apply-outside.patch                |    7 +
 t/t2303/apply-remove.patch                 |    7 +
 t/t2303/apply-rename.expected              |   13 ++
 t/t2303/apply-rename.patch                 |    4 +
 t/t2304-sparse-worktree-merge-recursive.sh |  233 ++++++++++++++++++++++++++++
 t/t5703-clone-sparse.sh                    |   40 +++++
 unpack-trees.c                             |  152 +++++++++++++++++--
 unpack-trees.h                             |    4 +-
 wt-status.c                                |   12 +-
 52 files changed, 1831 insertions(+), 53 deletions(-)
 create mode 100755 t/t2010-checkout-sparse.sh
 create mode 100755 t/t2300-sparse-index.sh
 create mode 100644 t/t2300/diff-index-sub.expected
 create mode 100644 t/t2300/log.expected
 create mode 100755 t/t2301-sparse-index-merge-recursive.sh
 create mode 100755 t/t2302-sparse-worktree.sh
 create mode 100644 t/t2302/add-u.expected
 create mode 100644 t/t2302/add.expected
 create mode 100644 t/t2302/commit.expected
 create mode 100644 t/t2302/diff-1.expected
 create mode 100644 t/t2302/diff-cc.expected
 create mode 100644 t/t2302/grep-work.expected
 create mode 100644 t/t2302/grep.expected
 create mode 100644 t/t2302/ls-files.expected
 create mode 100755 t/t2303-sparse-worktree-apply.sh
 create mode 100644 t/t2303/apply-initial.patch
 create mode 100644 t/t2303/apply-inside.patch
 create mode 100644 t/t2303/apply-leading-dirs.patch
 create mode 100644 t/t2303/apply-outside.patch
 create mode 100644 t/t2303/apply-remove.patch
 create mode 100644 t/t2303/apply-rename.expected
 create mode 100644 t/t2303/apply-rename.patch
 create mode 100755 t/t2304-sparse-worktree-merge-recursive.sh
 create mode 100755 t/t5703-clone-sparse.sh