This change teaches `Tree::diff()` to filter by a matcher. It only
filters the result so far; it does not restrict the tree walk to what
`Matcher::visit()` says is necessary yet. It also doesn't teach the
CLI to create a matcher and pass it in.
I had initially hoped that the type-safety provided by the separate
`FileRepoPath` and `DirRepoPath` types would help prevent bugs. I'm
not sure if it has prevented any bugs so far. It has turned out that
there are more cases than I had hoped where it's unknown whether a
path is for a directory or a file. One such example is for the path of
a conflict. Since it can be conflict between a directory and a file,
it doesn't make sense to use either. Instead we end up with quite a
bit of conversion between the types. I feel like they are not worth
the extra complexity. This patch therefore starts simplifying it by
replacing uses of `FileRepoPath` by `RepoPath`. `DirRepoPath` is a
little more complicated because its string form ends with a '/'. I'll
address that in separate patches.
Evolution needs to have fast access to the predecessors. This change
adds that information to the commit index.
Evolution also needs fast access to the change id and the bit saying
whether a commit is pruned. We'll add those soon.
Some tests changed because they previously added commits with
predecessors that were not indexed, which is no longer allowed from
this change. (We'll probably eventually want to allow that again, so
that the user can prune predecessors they no longer care about from
the repo.)
I'm preparing to publish an early version before someone takes the
name(s) on crates.io. "jj" has been taken by a seemingly useless
project, but "jujube" and "jujube-lib" are still available, so let's
use those.
