builtin rebase: support keep-empty option

The `--keep-empty` option can be used to keep the commits that do not
change anything from its parents in the result.

While the scripted version uses `interactive_rebase=implied` to indicate
that the rebase needs to use the `git-rebase--interactive` backend in
non-interactive mode as fallback when figuring out which backend to use,
the C version needs to use a different route because the backend will
already be chosen during the `parse_options()` call.

Signed-off-by: Pratik Karki <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: prertik

builtin/rebase.c

@@ -95,6 +95,7 @@ struct rebase_options {
 	const char *action;
 	int signoff;
 	int allow_rerere_autoupdate;
+	int keep_empty;
 };
 
 static int is_interactive(struct rebase_options *opts)
@@ -103,6 +104,23 @@ static int is_interactive(struct rebase_options *opts)
 		opts->type == REBASE_PRESERVE_MERGES;
 }
 
+static void imply_interactive(struct rebase_options *opts, const char *option)
+{
+	switch (opts->type) {
+	case REBASE_AM:
+		die(_("%s requires an interactive rebase"), option);
+		break;
+	case REBASE_INTERACTIVE:
+	case REBASE_PRESERVE_MERGES:
+		break;
+	case REBASE_MERGE:
+		/* we silently *upgrade* --merge to --interactive if needed */
+	default:
+		opts->type = REBASE_INTERACTIVE; /* implied */
+		break;
+	}
+}
+
 /* Returns the filename prefixed by the state_dir */
 static const char *state_dir_path(const char *filename, struct rebase_options *opts)
 {
@@ -276,6 +294,7 @@ static int run_specific_rebase(struct rebase_options *opts)
 		opts->allow_rerere_autoupdate < 0 ? "" :
 		opts->allow_rerere_autoupdate ?
 		"--rerere-autoupdate" : "--no-rerere-autoupdate");
+	add_var(&script_snippet, "keep_empty", opts->keep_empty ? "yes" : "");
 
 	switch (opts->type) {
 	case REBASE_AM:
@@ -588,6 +607,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			 &options.allow_rerere_autoupdate,
 			 N_("allow rerere to update index  with resolved "
 			    "conflict")),
+		OPT_BOOL('k', "keep-empty", &options.keep_empty,
+			 N_("preserve empty commits during rebase")),
 		OPT_END(),
 	};
 
@@ -787,6 +808,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		options.flags |= REBASE_FORCE;
 	}
 
+	if (options.keep_empty)
+		imply_interactive(&options, "--keep-empty");
+
 	switch (options.type) {
 	case REBASE_MERGE:
 	case REBASE_INTERACTIVE: