vfs: extract 'vfs' class and related code to a new 'vfs' module (API) The 'scmutil' is growing large (1500+ lines) and 2/5 of it is related to vfs. We extract the 'vfs' related code in its own module get both module back to a better scale and clearer contents. We keep all the references available in 'scmutil' for now as many reference needs to be updated.

vfs: replace 'scmutil.opener' usage with 'scmutil.vfs' The 'vfs' class is the first class citizen for years. We remove all usages of the older API. This will let us remove the old API eventually.

fsmonitor: remove use of repo.opener This has been deprecated, so we need to switch to the appropriate vfs apis.

help: align description of 'base rev' with reality [issue5488] The text about revlogs seems to be wrong about -1 being used to indicate the start of a delta chain. Attempt to correct this.

help: fix internals.changegroups Add information about tree manifests, copy edit the text and fix up a few ambiguities. The document also contains a few additional fixes from Siddharth Agarwal <sid0@fb.com>, who used it to build a parser for changegroups in Rust.

share: drop 'relshared' requirement as well

share: fix typo to drop 'shared' requirement on unshare This must be a typo and it seems correct to drop the requirement since the repo is no longer a shared repository.

similar: compare between actual file contents for exact identity Before this patch, similarity detection logic (for addremove and automv) depends entirely on SHA-1 digesting. But this causes incorrect rename detection, if: - removing file A and adding file B occur at same committing, and - SHA-1 hash values of file A and B are same This may prevent security experts from managing sample files for SHAttered issue in Mercurial repository, for example. https://security.googleblog.com/2017/02/announcing-first-sha1-collision.html https://shattered.it/ Hash collision itself isn't so serious for core repository functionality of Mercurial, described by mpm as below, though. https://www.mercurial-scm.org/wiki/mpm/SHA1 This patch compares between actual file contents after hash comparison for exact identity. Even after this patch, SHA-1 is still used, because it is reasonable enough to quickly detect existence of "(almost) same" file. - replacing SHA-1 causes decreasing performance, and - replacement of it has ambiguity, yet Getting content of removed file (= rfctx.data()) at each exact comparison should be cheap enough, even though getting content of added one costs much. ======= ============== ===================== file fctx data() reads from ======= ============== ===================== removed filectx in-memory revlog data added workingfilectx storage ======= ============== =====================

localrepo: handle rename with hardlinks properly In "aftertrans", we rename "journal.*" to "undo.*". We expect "journal.*" files to disappear after renaming. However, if "journal.foo" and "undo.foo" refer to a same file (hardlink), rename may be a no-op, leaving both files on disk, according to Linux manpage [1]: If oldpath and newpath are existing hard links referring to the same file, then rename() does nothing, and returns a suc‐ cess status. The POSIX specification [2] is not very clear about what to do. To be safe, remove "undo.*" before the rename so "journal.*" cannot be left on disk. [1]: http://man7.org/linux/man-pages/man2/rename.2.html [2]: http://pubs.opengroup.org/onlinepubs/9699919799/

dirstate: avoid unnecessary load+dump during backup Previously, dirstate.savebackup unconditionally dumps the dirstate map to disk. It may require loading dirstate first to be able to dump it. Those operations could be expensive if the dirstate is big, and could be avoided if we know the dirstate file is up-to-date. This patch avoids the read and write if the dirstate is clean. In that case, we just do a plain copy without any serialization. This should make commands which use transactions but do not touch dirstate faster. For example, "hg bookmark -r REV NAME".