Re: [GSoC][PATCH v3 06/13] rebase -i: rewrite setup_reflog_action() in C

This rewrites (the misnamed) setup_reflog_action() from shell to C. The
new version is called prepare_branch_to_be_rebased().

A new command is added to rebase--helper.c, “checkout-base”, as well as
a new flag, “verbose”, to avoid silencing the output of the checkout
operation called by checkout_base_commit().

The function `run_git_checkout()` will also be used in the next commit,
therefore its code is not part of `checkout_base_commit()`.

The shell version is then stripped in favour of a call to the helper.

As $GIT_REFLOG_ACTION is no longer set at the first call of
checkout_onto(), a call to comment_for_reflog() is added at the
beginning of this function.

Signed-off-by: Alban Gruin <redacted>
---
 builtin/rebase--helper.c   | 10 ++++++++--
 git-rebase--interactive.sh | 16 ++--------------
 sequencer.c                | 30 ++++++++++++++++++++++++++++++
 sequencer.h                |  2 ++
 4 files changed, 42 insertions(+), 16 deletions(-)

diff --git a/builtin/rebase--helper.c b/builtin/rebase--helper.c
index 731a64971..76bdc6fdb 100644
--- a/builtin/rebase--helper.c
+++ b/builtin/rebase--helper.c

@@ -13,12 +13,12 @@ static const char * const builtin_rebase_helper_usage[] = {
 int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 {
 	struct replay_opts opts = REPLAY_OPTS_INIT;
-	unsigned flags = 0, keep_empty = 0, rebase_merges = 0;
+	unsigned flags = 0, keep_empty = 0, rebase_merges = 0, verbose = 0;

 	struct option options[] = {
 		OPT_BOOL(0, "ff", &opts.allow_ff, N_("allow fast-forward")),

@@ -28,6 +28,7 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 		OPT_BOOL(0, "rebase-merges", &rebase_merges, N_("rebase merge commits")),
 		OPT_BOOL(0, "rebase-cousins", &rebase_cousins,
 			 N_("keep original branch points of cousins")),
+		OPT__VERBOSE(&verbose, N_("be verbose")),

@@ -60,6 +63,7 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 	opts.action = REPLAY_INTERACTIVE_REBASE;
 	opts.allow_ff = 1;
 	opts.allow_empty = 1;
+	opts.verbose = verbose;
 
 	argc = parse_options(argc, argv, NULL, options,
 			builtin_rebase_helper_usage, PARSE_OPT_KEEP_ARGV0);

@@ -94,5 +98,7 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 		return !!append_todo_help(0, keep_empty);
 	if (command == EDIT_TODO && argc == 1)
 		return !!edit_todo_list(flags);
+	if (command == PREPARE_BRANCH && argc == 2)
+		return !!prepare_branch_to_be_rebased(&opts, argv[1]);