I think `files::merge()` will be a useful place to share code for
resolving conflicting hunks after all. We'll want `MergeHunk` to
support multi-way merges then.
When there are conflicts between different types of tree entries, we
currently materialize them as "Unresolved complex conflict.". This
change makes it so we mention what types were involved and what their
ids were (though we still don't have an easy way of resolving an id).
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.
Merging is currently done with line-level granularity, so it makes
sense to have newlines after the markers. That makes them easier to
edit out when resolving conflicts.
This extracts a bit from `Transaction::check_out()` for taking a
Conflict, materializing it, and writing the resulting plain file to
the store. It will soon be reused.
