[RFC/PATCH 1/2] update-index: add --clear option

[Jeff King <peff@peff.net>]

This just discards existing entries from the index, which
can be useful if you are rewriting all entries with
"--index-info" or similar.

Signed-off-by: Jeff King <peff@peff.net>
---
I tried to make something like:

  git update-index --from-scratch --index-info

work by avoiding reading all entries in the first place. However,
update-index actually processes its arguments sequentially, so we _must_
read the index before we start processing arguments. But because it's
sequential, a "clear" operation makes sense, since you clear, then add
new entries.

 Documentation/git-update-index.txt |    3 +++
 builtin/update-index.c             |   10 ++++++++++
 2 files changed, 13 insertions(+)

diff --git a/Documentation/git-update-index.txt b/Documentation/git-update-index.txt
index a3081f4..47f0ae6 100644
--- a/Documentation/git-update-index.txt
+++ b/Documentation/git-update-index.txt
@@ -71,6 +71,9 @@ OPTIONS
 --cacheinfo <mode> <object> <path>::
 	Directly insert the specified info into the index.
 
+--clear::
+	Discard all existing entries from the index.
+
 --index-info::
         Read index information from stdin.
 
diff --git a/builtin/update-index.c b/builtin/update-index.c
index a6a23fa..559dfae 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -645,6 +645,13 @@ static int cacheinfo_callback(struct parse_opt_ctx_t *ctx,
 	return 0;
 }
 
+static int clear_callback(const struct option *opt,
+			  const char *arg, int unset)
+{
+	discard_cache();
+	return 0;
+}
+
 static int stdin_cacheinfo_callback(struct parse_opt_ctx_t *ctx,
 			      const struct option *opt, int unset)
 {
@@ -774,6 +781,9 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 			"add entries from standard input to the index",
 			PARSE_OPT_NONEG | PARSE_OPT_NOARG,
 			(parse_opt_cb *) stdin_cacheinfo_callback},
+		{OPTION_CALLBACK, 0, "clear", NULL, NULL,
+			"drop all index entries", PARSE_OPT_NONEG | PARSE_OPT_NOARG,
+			clear_callback},
 		{OPTION_LOWLEVEL_CALLBACK, 0, "unresolve", &has_errors, NULL,
 			"repopulate stages #2 and #3 for the listed paths",
 			PARSE_OPT_NONEG | PARSE_OPT_NOARG,
-- 
1.7.9.6.8.g992e5