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 a3081f4e237747dc858fd105302cbb9a489de41b..9d0b1515c58dc825beef6b4507542572c51ca988 100644 (file)
--- 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 a6a23fa1f3c7782566d7fcfe470dd424b876e4a5..5f038d64da38820ebaa73ff73d1082e17c3c80d2 100644 (file)
--- 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;