From 69dec66b2f6ab5c8138cca37e74bd405c541318a Mon Sep 17 00:00:00 2001
From: Junio C Hamano <gitster@pobox.com>
Date: Wed, 4 Apr 2012 09:37:02 -0700
Subject: update-index: upgrade/downgrade on-disk index version

With the "--index-version <n>" parameter, write the index out in the
specified version.  With this, an index file that is written in newer
format (say v4) can be downgraded to be read by older versions of Git.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-update-index.txt b/Documentation/git-update-index.txt
index a3081f4..9d0b151 100644
--- a/Documentation/git-update-index.txt
+++ b/Documentation/git-update-index.txt
@@ -19,7 +19,7 @@ SYNOPSIS
 	     [--ignore-submodules]
 	     [--really-refresh] [--unresolve] [--again | -g]
 	     [--info-only] [--index-info]
-	     [-z] [--stdin]
+	     [-z] [--stdin] [--index-version <n>]
 	     [--verbose]
 	     [--] [<file>...]
 
@@ -143,6 +143,10 @@ you will need to handle the situation manually.
 --verbose::
         Report what is being added and removed from index.
 
+--index-version <n>::
+	Write the resulting index out in the named on-disk format version.
+	The current default version is 2.
+
 -z::
 	Only meaningful with `--stdin` or `--index-info`; paths are
 	separated with NUL character instead of LF.
diff --git a/builtin/update-index.c b/builtin/update-index.c
index a6a23fa..5f038d6 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -708,6 +708,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	int newfd, entries, has_errors = 0, line_termination = '\n';
 	int read_from_stdin = 0;
 	int prefix_length = prefix ? strlen(prefix) : 0;
+	int preferred_index_format = 0;
 	char set_executable_bit = 0;
 	struct refresh_params refresh_args = {0, &has_errors};
 	int lock_error = 0;
@@ -791,6 +792,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 			"(for porcelains) forget saved unresolved conflicts",
 			PARSE_OPT_NOARG | PARSE_OPT_NONEG,
 			resolve_undo_clear_callback},
+		OPT_INTEGER(0, "index-version", &preferred_index_format,
+			    "write index in this format"),
 		OPT_END()
 	};
 
@@ -851,6 +854,17 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		}
 	}
 	argc = parse_options_end(&ctx);
+	if (preferred_index_format) {
+		if (preferred_index_format < INDEX_FORMAT_LB ||
+		    INDEX_FORMAT_UB < preferred_index_format)
+			die("index-version %d not in range: %d..%d",
+			    preferred_index_format,
+			    INDEX_FORMAT_LB, INDEX_FORMAT_UB);
+
+		if (the_index.version != preferred_index_format)
+			active_cache_changed = 1;
+		the_index.version = preferred_index_format;
+	}
 
 	if (read_from_stdin) {
 		struct strbuf buf = STRBUF_INIT, nbuf = STRBUF_INIT;
-- 
cgit v0.10.2-6-g49f6