sequencer: rewrite update-refs as user edits todo list
An interactive rebase provides opportunities for the user to edit the
todo list. The --update-refs option initializes the list with some
'update-ref <ref>' steps, but the user could add these manually.
Further, the user could add or remove these steps during pauses in the
interactive rebase.
Add a new method, todo_list_filter_update_refs(), that scans a todo_list
and compares it to the stored update-refs file. There are two actions
that can happen at this point:
1. If a '<ref>/<before>/<after>' triple in the update-refs file does not
have a matching 'update-ref <ref>' command in the todo-list _and_ the
<after> value is the null OID, then remove that triple. Here, the
user removed the 'update-ref <ref>' command before it was executed,
since if it was executed then the <after> value would store the
commit at that position.
2. If a 'update-ref <ref>' command in the todo-list does not have a
matching '<ref>/<before>/<after>' triple in the update-refs file,
then insert a new one. Store the <before> value to be the current
OID pointed at by <ref>. This is handled inside of the
init_update_ref_record() helper method.
We can test that this works by rewriting the todo-list several times in
the course of a rebase. Check that each ref is locked or unlocked for
updates after each todo-list update. We can also verify that the ref
update fails if a concurrent process updates one of the refs after the
rebase process records the "locked" ref location.
To help these tests, add a new 'set_replace_editor' helper that will
replace the todo-list with an exact file.
Reported-by: Phillip Wood <phillip.wood123@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>