1 files changed, 50 insertions, 0 deletions
diff --git a/builtin-diff-index.c b/builtin-diff-index.c
new file mode 100644
index 0000000000..04837494fe
--- /dev/null
+++ b/builtin-diff-index.c
@@ -0,0 +1,50 @@
+#include "cache.h"
+#include "diff.h"
+#include "commit.h"
+#include "revision.h"
+#include "builtin.h"
+
+static const char diff_cache_usage[] =
+"git diff-index [-m] [--cached] "
+"[<common diff options>] <tree-ish> [<path>...]"
+COMMON_DIFF_OPTIONS_HELP;
+
+int cmd_diff_index(int argc, const char **argv, const char *prefix)
+{
+	struct rev_info rev;
+	int cached = 0;
+	int i;
+	int result;
+
+	init_revisions(&rev, prefix);
+	git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
+	rev.abbrev = 0;
+
+	argc = setup_revisions(argc, argv, &rev, NULL);
+	for (i = 1; i < argc; i++) {
+		const char *arg = argv[i];
+
+		if (!strcmp(arg, "--cached"))
+			cached = 1;
+		else
+			usage(diff_cache_usage);
+	}
+	if (!rev.diffopt.output_format)
+		rev.diffopt.output_format = DIFF_FORMAT_RAW;
+
+	/*
+	 * Make sure there is one revision (i.e. pending object),
+	 * and there is no revision filtering parameters.
+	 */
+	if (rev.pending.nr != 1 ||
+	    rev.max_count != -1 || rev.min_age != -1 || rev.max_age != -1)
+		usage(diff_cache_usage);
+	if (!cached)
+		setup_work_tree();
+	if (read_cache() < 0) {
+		perror("read_cache");
+		return -1;
+	}
+	result = run_diff_index(&rev, cached);
+	return diff_result_code(&rev.diffopt, result);
+}