wt-status: show sparse checkout status as well

Some of the early feedback of folks trying out sparse-checkouts at
$dayjob is that sparse checkouts can sometimes be disorienting; users
can forget that they had a sparse-checkout and then wonder where files
went.  Add some output to 'git status' in the form of a simple line that
states:

    You are in a sparse checkout with 35% of files present.

where, obviously, the exact figure changes depending on what percentage
of files from the index do not have the SKIP_WORKTREE bit set.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/wt-status.h b/wt-status.h
index 73ab5d4..f1fa0ec 100644
--- a/wt-status.h
+++ b/wt-status.h
@@ -79,6 +79,7 @@ enum wt_status_format {
 
 #define HEAD_DETACHED_AT _("HEAD detached at ")
 #define HEAD_DETACHED_FROM _("HEAD detached from ")
+#define SPARSE_CHECKOUT_DISABLED -1
 
 struct wt_status_state {
 	int merge_in_progress;
@@ -90,6 +91,7 @@ struct wt_status_state {
 	int bisect_in_progress;
 	int revert_in_progress;
 	int detached_at;
+	int sparse_checkout_percentage; /* SPARSE_CHECKOUT_DISABLED if not sparse */
 	char *branch;
 	char *onto;
 	char *detached_from;