update-index: add a new --force-write-index option

At times, it makes sense to avoid the cost of writing out the index
when the only changes can easily be recomputed on demand. This causes
problems when trying to write test cases to verify that state as they
can't guarantee the state has been persisted to disk.

Add a new option (--force-write-index) to update-index that will
ensure the index is written out even if the cache_changed flag is not
set.

Signed-off-by: Ben Peart <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: benpeart

builtin/update-index.c

@@ -915,6 +915,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	struct refresh_params refresh_args = {0, &has_errors};
 	int lock_error = 0;
 	int split_index = -1;
+	int force_write = 0;
 	struct lock_file *lock_file;
 	struct parse_opt_ctx_t ctx;
 	strbuf_getline_fn getline_fn;
@@ -1006,6 +1007,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 			    N_("test if the filesystem supports untracked cache"), UC_TEST),
 		OPT_SET_INT(0, "force-untracked-cache", &untracked_cache,
 			    N_("enable untracked cache without testing the filesystem"), UC_FORCE),
+		OPT_SET_INT(0, "force-write-index", &force_write,
+			N_("write out the index even if is not flagged as changed"), 1),
 		OPT_END()
 	};
 
@@ -1147,7 +1150,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		die("BUG: bad untracked_cache value: %d", untracked_cache);
 	}
 
-	if (active_cache_changed) {
+	if (active_cache_changed || force_write) {
 		if (newfd < 0) {
 			if (refresh_args.flags & REFRESH_QUIET)
 				exit(128);