dirstate-tree: Avoid BTreeMap double-lookup when inserting a dirstate entry The child nodes of a given node in the tree-shaped dirstate are kept in a `BTreeMap` where keys are file names as strings. Finding or inserting a value in the map takes `O(log(n))` string comparisons, which adds up when constructing the tree. The `entry` API allows finding a "spot" in the map that may or may not be occupied and then access that value or insert a new one without doing map lookup again. However the current API is limited in that calling `entry` requires an owned key (and so a memory allocation), even if it ends up not being used in the case where the map already has a value with an equal key. This is still a win, with 4% better end-to-end time for `hg status` measured here with hyperfine: ``` Benchmark #1: ../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1 Time (mean ± σ): 1.337 s ± 0.018 s [User: 892.9 ms, System: 437.5 ms] Range (min … max): 1.316 s … 1.373 s 10 runs Benchmark #2: ./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1 Time (mean ± σ): 1.291 s ± 0.008 s [User: 853.4 ms, System: 431.1 ms] Range (min … max): 1.283 s … 1.309 s 10 runs Summary './hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1' ran 1.04 ± 0.02 times faster than '../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1' ``` * ./hg is this revision * ../hg2/hg is its parent * $REPO is an old snapshot of mozilla-central Differential Revision: https://phab.mercurial-scm.org/D10550

dirstate-tree: Handle I/O errors in status Errors such as insufficient permissions when listing a directory are logged, and the algorithm continues without considering that directory. Differential Revision: https://phab.mercurial-scm.org/D10549

dirstate-tree: Ignore FIFOs etc. in the status algorithm If a filesystem directory contains anything that is not: * a "normal" file * a symbolic link * or a directory … act as if that directory entry was not there. For example, if that path was previously a tracked file, mark it as deleted or removed. Differential Revision: https://phab.mercurial-scm.org/D10548

dirstate-tree: Add the new `status()` algorithm With the dirstate organized in a tree that mirrors the structure of the filesystem tree, we can traverse both trees at the same time in order to compare them. This is hopefully more efficient that building multiple big hashmaps for all of the repository’s contents. Differential Revision: https://phab.mercurial-scm.org/D10547