Hi Junio,
On Thu, 24 Sep 2020, Junio C Hamano wrote:
> While I was auditing the use of get_oid_committish(), I noticed that
> an abbreviated object name is written to rebase-merge/stopped-sha
> only to be read later and expanded to a full object name to be
> passed to record_in_rewritten(). Nobody seems to expose this to the
> end-user and it is unclear if there is a point in keeping it short
> by abbreviating and risking to make it ambiguous as the rebase
> progresses and creates new objects.
>
> The attached patch tries to simplify the logic involved around this
> file, to write and read full object names to/from the file, and the
> result seems to pass testsuite---which in the ideal world would be
> sufficient signal that this change is safe and sane, but it could be
> that original authors thought that a change to stop abbreviating is
> nonsense and not worth protecting the code against, hence RFH here.
>
> Is there something obvious I am not seeing that makes this change a
> bad idea (other than "somebody may be in the middle of a rebase and
> all of a sudden, version of Git gets updated to contain this one,
> which is unable to read abbreviated object name the current version
> left on disk", which I am deliberately ignoring)?
At least in my understanding, you are not missing anything:
- this file is an implementation detail,
- it is not exposed directly via any user-visible interface,
- any reader will _have_ to be prepared for an unabbreviated object ID (in
the highly unlikely case that an object ID would be ambiguous if
abbreviated even by one hex character),
- and most importantly: just like we expand the commit IDs in the todo
list, we actually want to expand them in `stopped-sha` because it _is_
possible that a new object is written that makes the previous
unambiguously abbreviated object ID now ambiguous (e.g. when the user
commits in a separate worktree while the rebase is interrupted, before
continuing the rebase).
In short: ACK
Thank you,
Dscho
>
> Thanks.
>
>
> sequencer.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/sequencer.c b/sequencer.c
> index fd7701c88a..7dc9088d09 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -120,7 +120,7 @@ static GIT_PATH_FUNC(rebase_path_author_script, "rebase-merge/author-script")
> static GIT_PATH_FUNC(rebase_path_amend, "rebase-merge/amend")
> /*
> * When we stop at a given patch via the "edit" command, this file contains
> - * the abbreviated commit name of the corresponding patch.
> + * the commit object name of the corresponding patch.
> */
> static GIT_PATH_FUNC(rebase_path_stopped_sha, "rebase-merge/stopped-sha")
> /*
> @@ -3012,11 +3012,12 @@ static int make_patch(struct repository *r,
> {
> struct strbuf buf = STRBUF_INIT;
> struct rev_info log_tree_opt;
> - const char *subject, *p;
> + const char *subject;
> + char hex[GIT_MAX_HEXSZ + 1];
> int res = 0;
>
> - p = short_commit_name(commit);
> - if (write_message(p, strlen(p), rebase_path_stopped_sha(), 1) < 0)
> + oid_to_hex_r(hex, &commit->object.oid);
> + if (write_message(hex, strlen(hex), rebase_path_stopped_sha(), 1) < 0)
> return -1;
> res |= write_rebase_head(&commit->object.oid);
>
> @@ -4396,7 +4397,7 @@ int sequencer_continue(struct repository *r, struct replay_opts *opts)
>
> if (read_oneliner(&buf, rebase_path_stopped_sha(),
> READ_ONELINER_SKIP_IF_EMPTY) &&
> - !get_oid_committish(buf.buf, &oid))
> + !get_oid_hex(buf.buf, &oid))
> record_in_rewritten(&oid, peek_command(&todo_list, 0));
> strbuf_release(&buf);
> }
>
