[PATCH 27/44] builtin/show-index: provide options to determine hash algo

["brian m. carlson" <sandals@crustytoothpaste.net>]

It's possible to use a variety of index formats with show-index, and we
need a way to indicate the hash algorithm which is in use for a
particular index we'd like to show.  Default to using the value for the
repository we're in by calling setup_git_directory_gently, and allow
overriding it by using a --hash argument.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
---
 builtin/show-index.c | 29 ++++++++++++++++++++++++-----
 git.c                |  2 +-
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/builtin/show-index.c b/builtin/show-index.c
index 0826f6a5a2..ebfa2e9abd 100644
--- a/builtin/show-index.c
+++ b/builtin/show-index.c
@@ -1,9 +1,12 @@
 #include "builtin.h"
 #include "cache.h"
 #include "pack.h"
+#include "parse-options.h"
 
-static const char show_index_usage[] =
-"git show-index";
+static const char *const show_index_usage[] = {
+	"git show-index [--hash=HASH]",
+	NULL
+};
 
 int cmd_show_index(int argc, const char **argv, const char *prefix)
 {
@@ -11,10 +14,26 @@ int cmd_show_index(int argc, const char **argv, const char *prefix)
 	unsigned nr;
 	unsigned int version;
 	static unsigned int top_index[256];
-	const unsigned hashsz = the_hash_algo->rawsz;
+	unsigned hashsz;
+	const char *hash_name = NULL;
+	int hash_algo;
+	const struct option show_index_options[] = {
+		OPT_STRING(0, "hash", &hash_name, N_("hash"),
+			   N_("specify the hash algorithm to use")),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, prefix, show_index_options, show_index_usage, 0);
+
+	if (hash_name) {
+		hash_algo = hash_algo_by_name(hash_name);
+		if (hash_algo == GIT_HASH_UNKNOWN)
+			die(_("Unknown hash algorithm"));
+		repo_set_hash_algo(the_repository, hash_algo);
+	}
+
+	hashsz = the_hash_algo->rawsz;
 
-	if (argc != 1)
-		usage(show_index_usage);
 	if (fread(top_index, 2 * 4, 1, stdin) != 1)
 		die("unable to read header");
 	if (top_index[0] == htonl(PACK_IDX_SIGNATURE)) {
diff --git a/git.c b/git.c
index 2e4efb4ff0..e53e8159a2 100644
--- a/git.c
+++ b/git.c
@@ -573,7 +573,7 @@ static struct cmd_struct commands[] = {
 	{ "shortlog", cmd_shortlog, RUN_SETUP_GENTLY | USE_PAGER },
 	{ "show", cmd_show, RUN_SETUP },
 	{ "show-branch", cmd_show_branch, RUN_SETUP },
-	{ "show-index", cmd_show_index },
+	{ "show-index", cmd_show_index, RUN_SETUP_GENTLY },
 	{ "show-ref", cmd_show_ref, RUN_SETUP },
 	{ "sparse-checkout", cmd_sparse_checkout, RUN_SETUP | NEED_WORK_TREE },
 	{ "stage", cmd_add, RUN_SETUP | NEED_WORK_TREE },