rust-nodemap: abstracting the indexing In the forthcoming mutable implementation, we'll have to visit node trees that are more complex than a single slice, although the algorithm will still be expressed in simple indexing terms. We still refrain using `#[inline]` indications as being premature optimizations, but we strongly hope the compiler will indeed inline most of the glue. Differential Revision: https://phab.mercurial-scm.org/D7792

rust-nodemap: NodeMap trait with simplest implementation We're defining here only a small part of the immutable methods it will have at the end. This is so we can focus in the following changesets on the needed abstractions for a mutable append-only serializable version. The first implementor exposes the actual lookup algorithm in its simplest form. It will have to be expanded to account for the missing methods, and the special cases related to NULL_NODE. Differential Revision: https://phab.mercurial-scm.org/D7791

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