switch: reject if some operation is in progress

Unless you know what you're doing, switching to another branch to do
something then switching back could be confusing. Worse, you may even
forget that you're in the middle of something. By the time you realize,
you may have done a ton of work and it gets harder to go back.

A new option --ignore-in-progress was considered but dropped because it
was not exactly clear what should happen. Sometimes you can switch away
and get back safely and resume the operation. Sometimes not. And the
git-checkout behavior is automatically clear merge/revert/cherry-pick,
which makes it a bit even more confusing [1].

We may revisit and add this option in the future. But for now play it
safe and not allow it (you can't even skip this check with --force). The
user is suggested to cancel the operation by themselves (and hopefully
they do consider the consequences, not blindly type the command), or to
create a separate worktree instead of switching. The third option is
the good old "git checkout", but it's not mentioned.

[1] CACsJy8Axa5WsLSjiscjnxVK6jQHkfs-gH959=YtUvQkWriAk5w@mail.gmail.com

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/builtin/checkout.c b/builtin/checkout.c
index f7967cd..5f100c1 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -24,6 +24,7 @@
 #include "tree.h"
 #include "tree-walk.h"
 #include "unpack-trees.h"
+#include "wt-status.h"
 #include "xdiff-interface.h"
 
 static const char * const checkout_usage[] = {
@@ -56,6 +57,7 @@ struct checkout_opts {
 	int accept_pathspec;
 	int switch_branch_doing_nothing_is_ok;
 	int only_merge_on_switching_branches;
+	int can_switch_when_in_progress;
 
 	const char *new_branch;
 	const char *new_branch_force;
@@ -1202,6 +1204,39 @@ static void die_expecting_a_branch(const struct branch_info *branch_info)
 	die(_("a branch is expected, got '%s'"), branch_info->name);
 }
 
+static void die_if_some_operation_in_progress(void)
+{
+	struct wt_status_state state;
+
+	memset(&state, 0, sizeof(state));
+	wt_status_get_state(the_repository, &state, 0);
+
+	if (state.merge_in_progress)
+		die(_("cannot switch branch while merging\n"
+		      "Consider \"git merge --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.am_in_progress)
+		die(_("cannot switch branch in the middle of an am session\n"
+		      "Consider \"git am --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.rebase_interactive_in_progress || state.rebase_in_progress)
+		die(_("cannot switch branch while rebasing\n"
+		      "Consider \"git rebase --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.cherry_pick_in_progress)
+		die(_("cannot switch branch while cherry-picking\n"
+		      "Consider \"git cherry-pick --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.revert_in_progress)
+		die(_("cannot switch branch while reverting\n"
+		      "Consider \"git revert --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.bisect_in_progress)
+		die(_("cannot switch branch while bisecting\n"
+		      "Consider \"git bisect reset HEAD\" "
+		      "or \"git worktree add\"."));
+}
+
 static int checkout_branch(struct checkout_opts *opts,
 			   struct branch_info *new_branch_info)
 {
@@ -1257,6 +1292,9 @@ static int checkout_branch(struct checkout_opts *opts,
 	    !new_branch_info->path)
 		die_expecting_a_branch(new_branch_info);
 
+	if (!opts->can_switch_when_in_progress)
+		die_if_some_operation_in_progress();
+
 	if (new_branch_info->path && !opts->force_detach && !opts->new_branch &&
 	    !opts->ignore_other_worktrees) {
 		int flag;
@@ -1514,6 +1552,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	opts.only_merge_on_switching_branches = 0;
 	opts.accept_pathspec = 1;
 	opts.implicit_detach = 1;
+	opts.can_switch_when_in_progress = 1;
 
 	options = parse_options_dup(checkout_options);
 	options = add_common_options(&opts, options);
@@ -1549,6 +1588,7 @@ int cmd_switch(int argc, const char **argv, const char *prefix)
 	opts.switch_branch_doing_nothing_is_ok = 0;
 	opts.only_merge_on_switching_branches = 1;
 	opts.implicit_detach = 0;
+	opts.can_switch_when_in_progress = 0;
 
 	options = parse_options_dup(switch_options);
 	options = add_common_options(&opts, options);