rust-node: handling binary Node prefix Parallel to the inner signatures of the nodetree functions in revlog.c, we'll have to handle prefixes of `Node` in binary form. Another motivation is that it allows to convert from full Node references to `NodePrefixRef` without copy. This is expected to be by far the most common case in practice. There's a slight complication due to the fact that we'll be sometimes interested in prefixes with an odd number of hexadecimal digits, which translates in binary form by a last byte in which only the highest weight 4 bits are considered. This is totally transparent for callers and could be revised once we have proper means to measure performance. The C implementation does the same, passing the length in nybbles as function arguments. Because Rust byte slices already have a length, we carry the even/odd informaton as a boolean, to avoid introducing logical redundancies and the related potential inconsistency bugs. There are a few candidates for inlining here, but we refrain from such premature optimizations, letting the compiler decide. Differential Revision: https://phab.mercurial-scm.org/D7790

rust-revlog: a trait for the revlog index As explained in the doc comment, this is the minimum needed for our immediate concern, which is to implement a nodemap in Rust. The trait will be later implemented in `hg-cpython` by the index Python object implemented in C, thanks to exposition of the corresponding functions as a capsule. The `None` return cases in `node()` match what the `index_node()` C function does. Differential Revision: https://phab.mercurial-scm.org/D7789

pathauditor: drop a redundant call to bytes.lower() `_lowerclean(s)` calls `s.lower()`, so we don't need to do that before calling it. Differential Revision: https://phab.mercurial-scm.org/D8001

merge: replace a repo.lookup('.') by more typical repo['.'].node() The `repo.lookup('.')` form comes from b3311e26f94f (merge: fix --preview to show all nodes that will be merged (issue2043)., 2010-02-15). I don't know why that commit changed from `repo['.']`, but I don't think there's any reason to do that. Note that performance should not be a reason (anymore?), because repo.lookup() is implemented by first creating a context object. Differential Revision: https://phab.mercurial-scm.org/D7998

merge: drop now-unused "abort" argument from hg.merge() Differential Revision: https://phab.mercurial-scm.org/D7997

merge: don't auto-pick destination with `hg merge 'wdir()'` If the user doesn't specify a commit to merge with, we'll have `node==None` in `commands.merge()`. We'll then try to find a good commit to merge with. However, if the user, for some strange reason, runs `hg merge 'wdir()'`, we'll also have `node==None` and we'll do that same. That's clearly not the intent, so let's not do that. It turns out we'd instead crash on that command after this patch, so I added special handling of it too. Differential Revision: https://phab.mercurial-scm.org/D7996

merge: call hg.abortmerge() directly and return early It's seem really weird to go through a lot of unrelated code before we call `hg.merge(..., abort=True)` when we can just call `hg.abortmerge()` and return early. Differential Revision: https://phab.mercurial-scm.org/D7995