checkout: inform the user when removing branch state

After a successful switch, if a merge, cherry-pick or revert is ongoing,
it is canceled. This behavior has been with us from the very early
beginning, soon after git-merge was created but never actually
documented [1]. It may be a good idea to be transparent and tell the
user if some operation is canceled.

I consider this a better way of telling the user than just adding a
sentence or two in git-checkout.txt, which will be mostly ignored
anyway.

PS. Originally I wanted to print more details like

    warning: cancelling an in-progress merge from <SHA-1>

which may allow some level of undo if the user wants to. But that seems
a lot more work. Perhaps it can be improved later if people still want
that.

[1] ... and I will try not to argue whether it is a sensible behavior.
There is some more discussion here if people are interested:
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, 1 insertions, 1 deletions

diff --git a/builtin/am.c b/builtin/am.c
index 4fb107a9d1..99b66508fd 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1957,7 +1957,7 @@ static int clean_index(const struct object_id *head, const struct object_id *rem
 	if (merge_tree(remote_tree))
 		return -1;
 
-	remove_branch_state(the_repository);
+	remove_branch_state(the_repository, 0);
 
 	return 0;
 }