diff-files: integrate with sparse index
Remove full index requirement for `git diff-files`. Refactor the
ensure_expanded and ensure_not_expanded functions by introducing a
common helper function, ensure_index_state. Add test to ensure the index
is no expanded in `git diff-files`.
The `p2000` tests demonstrate a ~96% execution time reduction for 'git
diff-files' and a ~97% execution time reduction for 'git diff-files'
for a file using a sparse index:
Test before after
-----------------------------------------------------------------------
2000.94: git diff-files (full-v3) 0.09 0.08 -11.1%
2000.95: git diff-files (full-v4) 0.09 0.09 +0.0%
2000.96: git diff-files (sparse-v3) 0.52 0.02 -96.2%
2000.97: git diff-files (sparse-v4) 0.51 0.02 -96.1%
2000.98: git diff-files -- f2/f4/a (full-v3) 0.06 0.07 +16.7%
2000.99: git diff-files -- f2/f4/a (full-v4) 0.08 0.08 +0.0%
2000.100: git diff-files -- f2/f4/a (sparse-v3) 0.46 0.01 -97.8%
2000.101: git diff-files -- f2/f4/a (sparse-v4) 0.51 0.02 -96.1%
Signed-off-by: Shuqi Liang <cheskaqiqi@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>