sparse-checkout: add 'cone' mode

The sparse-checkout feature can have quadratic performance as
the number of patterns and number of entries in the index grow.
If there are 1,000 patterns and 1,000,000 entries, this time can
be very significant.

Create a new Boolean config option, core.sparseCheckoutCone, to
indicate that we expect the sparse-checkout file to contain a
more limited set of patterns. This is a separate config setting
from core.sparseCheckout to avoid breaking older clients by
introducing a tri-state option.

The config option does nothing right now, but will be expanded
upon in a later commit.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/cache.h b/cache.h
index 04cabaac11..4980ee198e 100644
--- a/cache.h
+++ b/cache.h
@@ -918,12 +918,14 @@ extern char *git_replace_ref_base;
 
 extern int fsync_object_files;
 extern int core_preload_index;
-extern int core_apply_sparse_checkout;
 extern int precomposed_unicode;
 extern int protect_hfs;
 extern int protect_ntfs;
 extern const char *core_fsmonitor;
 
+int core_apply_sparse_checkout;
+int core_sparse_checkout_cone;
+
 /*
  * Include broken refs in all ref iterations, which will
  * generally choke dangerous operations rather than letting