wt-status: refactor detached HEAD analysis

wt_status_print() is the only caller of wt_status_get_detached_from().
The latter performs most of the analysis of a detached HEAD, including
finding state->detached_from; the caller checks whether the detached
HEAD is still at state->detached_from or has moved away.

Move that last bit of analysis to wt_status_get_detached_from(), too,
and store the boolean result in state->detached_at.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

wt-status.c

@@ -1222,6 +1222,8 @@ static void wt_status_get_detached_from(struct wt_status_state *state)
 		state->detached_from =
 			xstrdup(find_unique_abbrev(cb.nsha1, DEFAULT_ABBREV));
 	hashcpy(state->detached_sha1, cb.nsha1);
+	state->detached_at = !get_sha1("HEAD", sha1) &&
+			     !hashcmp(sha1, state->detached_sha1);
 
 	free(ref);
 	strbuf_release(&cb.buf);
@@ -1310,10 +1312,8 @@ void wt_status_print(struct wt_status *s)
 				on_what = _("rebase in progress; onto ");
 				branch_name = state.onto;
 			} else if (state.detached_from) {
-				unsigned char sha1[20];
 				branch_name = state.detached_from;
-				if (!get_sha1("HEAD", sha1) &&
+				if (state.detached_at)
-				    !hashcmp(sha1, state.detached_sha1))
 					on_what = _("HEAD detached at ");
 				else
 					on_what = _("HEAD detached from ");

wt-status.h

@@ -84,6 +84,7 @@ struct wt_status_state {
 	int cherry_pick_in_progress;
 	int bisect_in_progress;
 	int revert_in_progress;
+	int detached_at;
 	char *branch;
 	char *onto;
 	char *detached_from;