Git 2.18 Release Notes
======================

Updates since v2.17
-------------------

UI, Workflows & Features

 * Rename detection logic in "diff" family that is used in "merge" has
   learned to guess when all of x/a, x/b and x/c have moved to z/a,
   z/b and z/c, it is likely that x/d added in the meantime would also
   want to move to z/d by taking the hint that the entire directory
   'x' moved to 'z'.  A bug causing dirty files involved in a rename
   to be overwritten during merge has also been fixed as part of this
   work.

 * "git filter-branch" learned to use a different exit code to allow
   the callers to tell the case where there was no new commits to
   rewrite from other error cases.

 * When built with more recent cURL, GIT_SSL_VERSION can now specify
   "tlsv1.3" as its value.


Performance, Internal Implementation, Development Support etc.

 * A "git fetch" from a repository with insane number of refs into a
   repository that is already up-to-date still wasted too many cycles
   making many lstat(2) calls to see if these objects at the tips
   exist as loose objects locally.  These lstat(2) calls are optimized
   away by enumerating all loose objects beforehand.
   It is unknown if the new strategy negatively affects existing use
   cases, fetching into a repository with many loose objects from a
   repository with small number of refs.

 * Git can be built to use either v1 or v2 of the PCRE library, and so
   far, the build-time configuration USE_LIBPCRE=YesPlease instructed
   the build procedure to use v1, but now it means v2.  USE_LIBPCRE1
   and USE_LIBPCRE2 can be used to explicitly choose which version to
   use, as before.

 * The build procedure learned to optionally use symbolic links
   (instead of hardlinks and copies) to install "git-foo" for built-in
   commands, whose binaries are all identical.

 * Conversion from uchar[20] to struct object_id continues.

 * The way "git worktree prune" worked internally has been simplified,
   by assuming how "git worktree move" moves an existing worktree to a
   different place.

 * Code clean-up for the "repository" abstraction.
   (merge 00a3da2a13 nd/remove-ignore-env-field later to maint).

 * Code to find the length to uniquely abbreviate object names based
   on packfile content, which is a relatively recent addtion, has been
   optimized to use the same fan-out table.

 * The mechanism to use parse-options API to automate the command line
   completion continues to get extended and polished.

 * Copies of old scripted Porcelain commands in contrib/examples/ have
   been removed.

 * Some tests that rely on the exact hardcoded values of object names
   have been updated in preparation for hash function migration.

 * Perf-test update.

 * Test helper update.

 * The effort continues to refactor the internal global data structure
   to make it possible to open multiple repositories, work with and
   then close them,

 * Small test-helper programs have been consolidated into a single
   binary.

Also contains various documentation updates and code clean-ups.


Fixes since v2.17
-----------------

 * "git shortlog cruft" aborted with a BUG message when run outside a
   Git repository.  The command has been taught to complain about
   extra and unwanted arguments on its command line instead in such a
   case.
   (merge 4aa0161e83 ma/shortlog-revparse later to maint).

 * "git stash push -u -- <pathspec>" gave an unnecessary and confusing
   error message when there was no tracked files that match the
   <pathspec>, which has been fixed.
   (merge 353278687e tg/stash-untracked-with-pathspec-fix later to maint).

 * "git tag --contains no-such-commit" gave a full list of options
   after giving an error message.
   (merge 3bb0923f06 ps/contains-id-error-message later to maint).

 * "diff-highlight" filter (in contrib/) learned to undertand "git log
   --graph" output better.
   (merge 4551fbba14 jk/diff-highlight-graph-fix later to maint).

 * when refs that do not point at committish are given, "git
   filter-branch" gave a misleading error messages.  This has been
   corrected.
   (merge f78ab355e7 yk/filter-branch-non-committish-refs later to maint).

 * "git submodule status" misbehaved on a submodule that has been
   removed from the working tree.
   (merge 74b6bda32f rs/status-with-removed-submodule later to maint).

 * When credential helper exits very quickly without reading its
   input, it used to cause Git to die with SIGPIPE, which has been
   fixed.
   (merge a0d51e8d0e eb/cred-helper-ignore-sigpipe later to maint).

 * Other minor doc, test and build updates and code cleanups.
   (merge 248f66ed8e nd/trace-with-env later to maint).
   (merge 14ced5562c ys/bisect-object-id-missing-conversion-fix later to maint).
   (merge 5988eb631a ab/doc-hash-brokenness later to maint).
   (merge a4d4e32a70 pk/test-avoid-pipe-hiding-exit-status later to maint).