On Sun, Apr 01, 2018 at 05:06:50PM +0300, Dan Aloni wrote:
> These commits which have hashes starting with the hex string 'bad',
> always give me the chills. Why should a perfectly good commit be
> jinxed?
>
> Statistically, one of 4096 commits may be 'bad'. This change adds a
> '--prevent-bad' switch to the commit command in order to prevent such
> commit hashes from being generated. Internally, the commit is retried
> with a slight commit meta-data modification - a newline is added to the
> end of the commit message. The meta-data change results in a different
> hash, that if we are lucky enough (4095/4096 chance) may not be 'bad'.
>
> Note that this change does not affect actual software quality maintained
> using Git. Thus, it is recommended keep testing all generated versions
> regardless of commit hash jinxes.
Cute.
A while back we had patches to generate "desirable" commit prefixes, and
they were focused on making the brute-forcing as fast as possible. I
don't think I've seen this reverse case, but it's much easier: we can be
fairly slow since the probability of hitting the bad case repeatedly is
low.
> @@ -1583,12 +1585,34 @@ int cmd_commit(int argc, const char **argv, const
> char *prefix)
> append_merge_tag_headers(parents, &tail);
> }
>
> - if (commit_tree_extended(sb.buf, sb.len, &active_cache_tree->oid,
> - parents, &oid, author_ident.buf, sign_commit,
> - extra)) {
> - rollback_index_files();
> - die(_("failed to write commit object"));
> + for (;;) {
> + char *oid_hex;
> + struct commit_list *copy_parents;
> +
> + copy_parents = copy_commit_list(parents);
> +
> + if (commit_tree_extended(sb.buf, sb.len,
> &active_cache_tree->oid,
> + parents, &oid, author_ident.buf,
> sign_commit,
> + extra)) {
> + rollback_index_files();
> + die(_("failed to write commit object"));
> + }
You could still have a "bad" tree. :)
-Peff
