fetch, upload-pack: --deepen=N extends shallow boundary by N commitsnd/shallow-deepen

In git-fetch, --depth argument is always relative with the latest
remote refs. This makes it a bit difficult to cover this use case,
where the user wants to make the shallow history, say 3 levels
deeper. It would work if remote refs have not moved yet, but nobody
can guarantee that, especially when that use case is performed a
couple months after the last clone or "git fetch --depth". Also,
modifying shallow boundary using --depth does not work well with
clones created by --since or --not.

This patch fixes that. A new argument --deepen=<N> will add <N> more (*)
parent commits to the current history regardless of where remote refs
are.

Have/Want negotiation is still respected. So if remote refs move, the
server will send two chunks: one between "have" and "want" and another
to extend shallow history. In theory, the client could send no "want"s
in order to get the second chunk only. But the protocol does not allow
that. Either you send no want lines, which means ls-remote; or you
have to send at least one want line that carries deep-relative to the
server..

The main work was done by Dongcan Jiang. I fixed it up here and there.
And of course all the bugs belong to me.

(*) We could even support --deepen=<N> where <N> is negative. In that
case we can cut some history from the shallow clone. This operation
(and --depth=<shorter depth>) does not require interaction with remote
side (and more complicated to implement as a result).

Helped-by: Duy Nguyen <pclouds@gmail.com>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Dongcan Jiang <dongcan.jiang@gmail.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 17 insertions, 1 deletions

diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
index 07570bee2d..82653487f8 100644
--- a/builtin/fetch-pack.c
+++ b/builtin/fetch-pack.c
@@ -113,6 +113,10 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 			string_list_append(&deepen_not, arg);
 			continue;
 		}
+		if (!strcmp(arg, "--deepen-relative")) {
+			args.deepen_relative = 1;
+			continue;
+		}
 		if (!strcmp("--no-progress", arg)) {
 			args.no_progress = 1;
 			continue;
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 147504dd51..7b0ea1c86e 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -34,7 +34,7 @@ static int fetch_prune_config = -1; /* unspecified */
 static int prune = -1; /* unspecified */
 #define PRUNE_BY_DEFAULT 0 /* do we prune by default? */
 
-static int all, append, dry_run, force, keep, multiple, update_head_ok, verbosity;
+static int all, append, dry_run, force, keep, multiple, update_head_ok, verbosity, deepen_relative;
 static int progress = -1, recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 static int tags = TAGS_DEFAULT, unshallow, update_shallow, deepen;
 static int max_children = 1;
@@ -121,6 +121,8 @@ static struct option builtin_fetch_options[] = {
 		   N_("deepen history of shallow repository based on time")),
 	OPT_STRING_LIST(0, "shallow-exclude", &deepen_not, N_("revision"),
 			N_("deepen history of shallow clone by excluding rev")),
+	OPT_INTEGER(0, "deepen", &deepen_relative,
+		    N_("deepen history of shallow clone")),
 	{ OPTION_SET_INT, 0, "unshallow", &unshallow, NULL,
 		   N_("convert to a complete repository"),
 		   PARSE_OPT_NONEG | PARSE_OPT_NOARG, NULL, 1 },
@@ -881,6 +883,8 @@ static struct transport *prepare_transport(struct remote *remote, int deepen)
 	if (deepen && deepen_not.nr)
 		set_option(transport, TRANS_OPT_DEEPEN_NOT,
 			   (const char *)&deepen_not);
+	if (deepen_relative)
+		set_option(transport, TRANS_OPT_DEEPEN_RELATIVE, "yes");
 	if (update_shallow)
 		set_option(transport, TRANS_OPT_UPDATE_SHALLOW, "yes");
 	return transport;
@@ -906,6 +910,7 @@ static void backfill_tags(struct transport *transport, struct ref *ref_map)
 
 	transport_set_option(transport, TRANS_OPT_FOLLOWTAGS, NULL);
 	transport_set_option(transport, TRANS_OPT_DEPTH, "0");
+	transport_set_option(transport, TRANS_OPT_DEEPEN_RELATIVE, NULL);
 	fetch_refs(transport, ref_map);
 
 	if (gsecondary) {
@@ -1177,6 +1182,13 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix,
 			     builtin_fetch_options, builtin_fetch_usage, 0);
 
+	if (deepen_relative) {
+		if (deepen_relative < 0)
+			die(_("Negative depth in --deepen is not supported"));
+		if (depth)
+			die(_("--deepen and --depth are mutually exclusive"));
+		depth = xstrfmt("%d", deepen_relative);
+	}
 	if (unshallow) {
 		if (depth)
 			die(_("--depth and --unshallow cannot be used together"));