[PATCH 02/11] builtin rebase: support `git rebase --onto A...B`

[Pratik Karki <predatoramigo@gmail.com>]

This commit implements support for an --onto argument that is actually a
"symmetric range" i.e. `<rev1>...<rev2>`.

The equivalent shell script version of the code offers two different
error messages for the cases where there is no merge base vs more than
one merge base. Though following the similar approach would be nice,
this would create more complexity than it is of current. Currently, for
simple convenience, the `get_oid_mb()` function is used whose return
value does not discern between those two error conditions.

Signed-off-by: Pratik Karki <predatoramigo@gmail.com>
---
 builtin/rebase.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 742ed31498..38c496dd10 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -17,6 +17,7 @@
 #include "unpack-trees.h"
 #include "lockfile.h"
 #include "parse-options.h"
+#include "commit.h"
 
 static char const * const builtin_rebase_usage[] = {
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
@@ -311,6 +312,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	int ret, flags;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
+	struct object_id merge_base;
 	struct option builtin_rebase_options[] = {
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
@@ -387,7 +389,11 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		die("TODO");
+		if (get_oid_mb(options.onto_name, &merge_base) < 0)
+			die(_("'%s': need exactly one merge base"),
+			    options.onto_name);
+		options.onto = lookup_commit_or_die(&merge_base,
+						    options.onto_name);
 	} else {
 		options.onto = peel_committish(options.onto_name);
 		if (!options.onto)
-- 
2.18.0