[RFC PATCH v6 0/2] diff-files: integrate with sparse index

Did not fix the logic of spare-checkout yet. Leave the spare diff-files with pathspec outside sparse definition as 'test_expect_failure' now. but will fix soon.

Changes since v5:

1. Add space after "definition."

2. Add test case for a pathspec with wildcards or other "magic"

3. Before messing with modified files on disk, add a "baseline" 
of correct behavior when a pathspec points to out-of-cone files.

4. Write the contents of an
existing file inside that sparse directory to disk manually

5. Use 'test_all_match' rather than 'test_sparse_match'. 
wouldn't need the additional 'test_must_be_empty' checks.

Shuqi Liang (2):
  t1092: add tests for `git diff-files`
  diff-files: integrate with sparse index

 builtin/diff-files.c                     |  8 +++
 t/perf/p2000-sparse-operations.sh        |  2 +
 t/t1092-sparse-checkout-compatibility.sh | 73 ++++++++++++++++++++++++
 3 files changed, 83 insertions(+)

base-commit: a38d39a4c50d1275833aba54c4dbdfce9e2e9ca1