merge(third_party/git): Merge squashed git subtree at v2.23.0 r/373

Merge commit '1b593e1ea4d2af0f6444d9a7788d5d99abd6fde5' as 'third_party/git'

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+Git v1.8.2 Release Notes
+========================
+
+Backward compatibility notes (this release)
+-------------------------------------------
+
+"git push $there tag v1.2.3" used to allow replacing a tag v1.2.3
+that already exists in the repository $there, if the rewritten tag
+you are pushing points at a commit that is a descendant of a commit
+that the old tag v1.2.3 points at.  This was found to be error prone
+and starting with this release, any attempt to update an existing
+ref under refs/tags/ hierarchy will fail, without "--force".
+
+When "git add -u" and "git add -A" that does not specify what paths
+to add on the command line is run from inside a subdirectory, the
+scope of the operation has always been limited to the subdirectory.
+Many users found this counter-intuitive, given that "git commit -a"
+and other commands operate on the entire tree regardless of where you
+are.  In this release, these commands give a warning message that
+suggests the users to use "git add -u/-A ." when they want to limit
+the scope to the current directory; doing so will squelch the message,
+while training their fingers.
+
+
+Backward compatibility notes (for Git 2.0)
+------------------------------------------
+
+When "git push [$there]" does not say what to push, we have used the
+traditional "matching" semantics so far (all your branches were sent
+to the remote as long as there already are branches of the same name
+over there).  In Git 2.0, the default will change to the "simple"
+semantics that pushes the current branch to the branch with the same
+name, only when the current branch is set to integrate with that
+remote branch.  There is a user preference configuration variable
+"push.default" to change this.  If you are an old-timer who is used
+to the "matching" semantics, you can set it to "matching" to keep the
+traditional behaviour.  If you want to live in the future early,
+you can set it to "simple" today without waiting for Git 2.0.
+
+When "git add -u" and "git add -A", that does not specify what paths
+to add on the command line is run from inside a subdirectory, these
+commands will operate on the entire tree in Git 2.0 for consistency
+with "git commit -a" and other commands. Because there will be no
+mechanism to make "git add -u" behave as if "git add -u .", it is
+important for those who are used to "git add -u" (without pathspec)
+updating the index only for paths in the current subdirectory to start
+training their fingers to explicitly say "git add -u ." when they mean
+it before Git 2.0 comes.
+
+
+Updates since v1.8.1
+--------------------
+
+UI, Workflows & Features
+
+ * Initial ports to QNX and z/OS UNIX System Services have started.
+
+ * Output from the tests is coloured using "green is okay, yellow is
+   questionable, red is bad and blue is informative" scheme.
+
+ * Mention of "GIT/Git/git" in the documentation have been updated to
+   be more uniform and consistent.  The name of the system and the
+   concept it embodies is "Git"; the command the users type is "git".
+   All-caps "GIT" was merely a way to imitate "Git" typeset in small
+   caps in our ASCII text only documentation and to be avoided.
+
+ * The completion script (in contrib/completion) used to let the
+   default completer to suggest pathnames, which gave too many
+   irrelevant choices (e.g. "git add" would not want to add an
+   unmodified path).  It learnt to use a more git-aware logic to
+   enumerate only relevant ones.
+
+ * In bare repositories, "git shortlog" and other commands now read
+   mailmap files from the tip of the history, to help running these
+   tools in server settings.
+
+ * Color specifiers, e.g. "%C(blue)Hello%C(reset)", used in the
+   "--format=" option of "git log" and friends can be disabled when
+   the output is not sent to a terminal by prefixing them with
+   "auto,", e.g. "%C(auto,blue)Hello%C(auto,reset)".
+
+ * Scripts can ask Git that wildcard patterns in pathspecs they give do
+   not have any significance, i.e. take them as literal strings.
+
+ * The patterns in .gitignore and .gitattributes files can have **/,
+   as a pattern that matches 0 or more levels of subdirectory.
+   E.g. "foo/**/bar" matches "bar" in "foo" itself or in a
+   subdirectory of "foo".
+
+ * When giving arguments without "--" disambiguation, object names
+   that come earlier on the command line must not be interpretable as
+   pathspecs and pathspecs that come later on the command line must
+   not be interpretable as object names.  This disambiguation rule has
+   been tweaked so that ":/" (no other string before or after) is
+   always interpreted as a pathspec; "git cmd -- :/" is no longer
+   needed, you can just say "git cmd :/".
+
+ * Various "hint" lines Git gives when it asks the user to edit
+   messages in the editor are commented out with '#' by default. The
+   core.commentchar configuration variable can be used to customize
+   this '#' to a different character.
+
+ * "git add -u" and "git add -A" without pathspec issues warning to
+   make users aware that they are only operating on paths inside the
+   subdirectory they are in.  Use ":/" (everything from the top) or
+   "." (everything from the $cwd) to disambiguate.
+
+ * "git blame" (and "git diff") learned the "--no-follow" option.
+
+ * "git branch" now rejects some nonsense combinations of command line
+   arguments (e.g. giving more than one branch name to rename) with
+   more case-specific error messages.
+
+ * "git check-ignore" command to help debugging .gitignore files has
+   been added.
+
+ * "git cherry-pick" can be used to replay a root commit to an unborn
+   branch.
+
+ * "git commit" can be told to use --cleanup=whitespace by setting the
+   configuration variable commit.cleanup to 'whitespace'.
+
+ * "git diff" and other Porcelain commands can be told to use a
+   non-standard algorithm by setting diff.algorithm configuration
+   variable.
+
+ * "git fetch --mirror" and fetch that uses other forms of refspec
+   with wildcard used to attempt to update a symbolic ref that match
+   the wildcard on the receiving end, which made little sense (the
+   real ref that is pointed at by the symbolic ref would be updated
+   anyway).  Symbolic refs no longer are affected by such a fetch.
+
+ * "git format-patch" now detects more cases in which a whole branch
+   is being exported, and uses the description for the branch, when
+   asked to write a cover letter for the series.
+
+ * "git format-patch" learned "-v $count" option, and prepends a
+   string "v$count-" to the names of its output files, and also
+   automatically sets the subject prefix to "PATCH v$count". This
+   allows patches from rerolled series to be stored under different
+   names and makes it easier to reuse cover letter messages.
+
+ * "git log" and friends can be told with --use-mailmap option to
+   rewrite the names and email addresses of people using the mailmap
+   mechanism.
+
+ * "git log --cc --graph" now shows the combined diff output with the
+   ancestry graph.
+
+ * "git log --grep=<pattern>" honors i18n.logoutputencoding to look
+   for the pattern after fixing the log message to the specified
+   encoding.
+
+ * "git mergetool" and "git difftool" learned to list the available
+   tool backends in a more consistent manner.
+
+ * "git mergetool" is aware of TortoiseGitMerge now and uses it over
+   TortoiseMerge when available.
+
+ * "git push" now requires "-f" to update a tag, even if it is a
+   fast-forward, as tags are meant to be fixed points.
+
+ * Error messages from "git push" when it stops to prevent remote refs
+   from getting overwritten by mistake have been improved to explain
+   various situations separately.
+
+ * "git push" will stop without doing anything if the new "pre-push"
+   hook exists and exits with a failure.
+
+ * When "git rebase" fails to generate patches to be applied (e.g. due
+   to oom), it failed to detect the failure and instead behaved as if
+   there were nothing to do.  A workaround to use a temporary file has
+   been applied, but we probably would want to revisit this later, as
+   it hurts the common case of not failing at all.
+
+ * Input and preconditions to "git reset" has been loosened where
+   appropriate.  "git reset $fromtree Makefile" requires $fromtree to
+   be any tree (it used to require it to be a commit), for example.
+   "git reset" (without options or parameters) used to error out when
+   you do not have any commits in your history, but it now gives you
+   an empty index (to match non-existent commit you are not even on).
+
+ * "git status" says what branch is being bisected or rebased when
+   able, not just "bisecting" or "rebasing".
+
+ * "git submodule" started learning a new mode to integrate with the
+   tip of the remote branch (as opposed to integrating with the commit
+   recorded in the superproject's gitlink).
+
+ * "git upload-pack" which implements the service "ls-remote" and
+   "fetch" talk to can be told to hide ref hierarchies the server
+   side internally uses (and that clients have no business learning
+   about) with transfer.hiderefs configuration.
+
+
+Foreign Interface
+
+ * "git fast-export" has been updated for its use in the context of
+   the remote helper interface.
+
+ * A new remote helper to interact with bzr has been added to contrib/.
+
+ * "git p4" got various bugfixes around its branch handling.  It is
+   also made usable with Python 2.4/2.5.  In addition, its various
+   portability issues for Cygwin have been addressed.
+
+ * The remote helper to interact with Hg in contrib/ has seen a few
+   fixes.
+
+
+Performance, Internal Implementation, etc.
+
+ * "git fsck" has been taught to be pickier about entries in tree
+   objects that should not be there, e.g. ".", ".git", and "..".
+
+ * Matching paths with common forms of pathspecs that contain wildcard
+   characters has been optimized further.
+
+ * We stopped paying attention to $GIT_CONFIG environment that points
+   at a single configuration file from any command other than "git config"
+   quite a while ago, but "git clone" internally set, exported, and
+   then unexported the variable during its operation unnecessarily.
+
+ * "git reset" internals has been reworked and should be faster in
+   general. We tried to be careful not to break any behaviour but
+   there could be corner cases, especially when running the command
+   from a conflicted state, that we may have missed.
+
+ * The implementation of "imap-send" has been updated to reuse xml
+   quoting code from http-push codepath, and lost a lot of unused
+   code.
+
+ * There is a simple-minded checker for the test scripts in t/
+   directory to catch most common mistakes (it is not enabled by
+   default).
+
+ * You can build with USE_WILDMATCH=YesPlease to use a replacement
+   implementation of pattern matching logic used for pathname-like
+   things, e.g. refnames and paths in the repository.  This new
+   implementation is not expected change the existing behaviour of Git
+   in this release, except for "git for-each-ref" where you can now
+   say "refs/**/master" and match with both refs/heads/master and
+   refs/remotes/origin/master.  We plan to use this new implementation
+   in wider places (e.g. "git ls-files '**/Makefile' may find Makefile
+   at the top-level, and "git log '**/t*.sh'" may find commits that
+   touch a shell script whose name begins with "t" at any level) in
+   future versions of Git, but we are not there yet.  By building with
+   USE_WILDMATCH, using the resulting Git daily and reporting when you
+   find breakages, you can help us get closer to that goal.
+
+ * Some reimplementations of Git do not write all the stat info back
+   to the index due to their implementation limitations (e.g. jgit).
+   A configuration option can tell Git to ignore changes to most of
+   the stat fields and only pay attention to mtime and size, which
+   these implementations can reliably update.  This can be used to
+   avoid excessive revalidation of contents.
+
+ * Some platforms ship with old version of expat where xmlparse.h
+   needs to be included instead of expat.h; the build procedure has
+   been taught about this.
+
+ * "make clean" on platforms that cannot compute header dependencies
+   on the fly did not work with implementations of "rm" that do not
+   like an empty argument list.
+
+Also contains minor documentation updates and code clean-ups.
+
+
+Fixes since v1.8.1
+------------------
+
+Unless otherwise noted, all the fixes since v1.8.1 in the maintenance
+track are contained in this release (see release notes to them for
+details).
+
+ * An element on GIT_CEILING_DIRECTORIES list that does not name the
+   real path to a directory (i.e. a symbolic link) could have caused
+   the GIT_DIR discovery logic to escape the ceiling.
+
+ * When attempting to read the XDG-style $HOME/.config/git/config and
+   finding that $HOME/.config/git is a file, we gave a wrong error
+   message, instead of treating the case as "a custom config file does
+   not exist there" and moving on.
+
+ * The behaviour visible to the end users was confusing, when they
+   attempt to kill a process spawned in the editor that was in turn
+   launched by Git with SIGINT (or SIGQUIT), as Git would catch that
+   signal and die.  We ignore these signals now.
+   (merge 0398fc34 pf/editor-ignore-sigint later to maint).
+
+ * A child process that was killed by a signal (e.g. SIGINT) was
+   reported in an inconsistent way depending on how the process was
+   spawned by us, with or without a shell in between.
+
+ * After failing to create a temporary file using mkstemp(), failing
+   pathname was not reported correctly on some platforms.
+
+ * We used to stuff "user@" and then append what we read from
+   /etc/mailname to come up with a default e-mail ident, but a bug
+   lost the "user@" part.
+
+ * The attribute mechanism didn't allow limiting attributes to be
+   applied to only a single directory itself with "path/" like the
+   exclude mechanism does.  The initial implementation of this that
+   was merged to 'maint' and 1.8.1.2 was with a severe performance
+   degradations and needs to merge a fix-up topic.
+
+ * The smart HTTP clients forgot to verify the content-type that comes
+   back from the server side to make sure that the request is being
+   handled properly.
+
+ * "git am" did not parse datestamp correctly from Hg generated patch,
+   when it is run in a locale outside C (or en).
+
+ * "git apply" misbehaved when fixing whitespace breakages by removing
+   excess trailing blank lines.
+
+ * "git apply --summary" has been taught to make sure the similarity
+   value shown in its output is sensible, even when the input had a
+   bogus value.
+
+ * A tar archive created by "git archive" recorded a directory in a
+   way that made NetBSD's implementation of "tar" sometimes unhappy.
+
+ * "git archive" did not record uncompressed size in the header when
+   streaming a zip archive, which confused some implementations of unzip.
+
+ * "git archive" did not parse configuration values in tar.* namespace
+   correctly.
+   (merge b3873c3 jk/config-parsing-cleanup later to maint).
+
+ * Attempt to "branch --edit-description" an existing branch, while
+   being on a detached HEAD, errored out.
+
+ * "git clean" showed what it was going to do, but sometimes end up
+   finding that it was not allowed to do so, which resulted in a
+   confusing output (e.g. after saying that it will remove an
+   untracked directory, it found an embedded git repository there
+   which it is not allowed to remove).  It now performs the actions
+   and then reports the outcome more faithfully.
+
+ * When "git clone --separate-git-dir=$over_there" is interrupted, it
+   failed to remove the real location of the $GIT_DIR it created.
+   This was most visible when interrupting a submodule update.
+
+ * "git cvsimport" mishandled timestamps at DST boundary.
+
+ * We used to have an arbitrary 32 limit for combined diff input,
+   resulting in incorrect number of leading colons shown when showing
+   the "--raw --cc" output.
+
+ * "git fetch --depth" was broken in at least three ways.  The
+   resulting history was deeper than specified by one commit, it was
+   unclear how to wipe the shallowness of the repository with the
+   command, and documentation was misleading.
+   (merge cfb70e1 nd/fetch-depth-is-broken later to maint).
+
+ * "git log --all -p" that walked refs/notes/textconv/ ref can later
+   try to use the textconv data incorrectly after it gets freed.
+
+ * We forgot to close the file descriptor reading from "gpg" output,
+   killing "git log --show-signature" on a long history.
+
+ * The way "git svn" asked for password using SSH_ASKPASS and
+   GIT_ASKPASS was not in line with the rest of the system.
+
+ * The --graph code fell into infinite loop when asked to do what the
+   code did not expect.
+
+ * http transport was wrong to ask for the username when the
+   authentication is done by certificate identity.
+
+ * "git pack-refs" that ran in parallel to another process that
+   created new refs had a nasty race.
+
+ * Rebasing the history of superproject with change in the submodule
+   has been broken since v1.7.12.
+
+ * After "git add -N" and then writing a tree object out of the
+   index, the cache-tree data structure got corrupted.
+
+ * "git clone" used to allow --bare and --separate-git-dir=$there
+   options at the same time, which was nonsensical.
+
+ * "git rebase --preserve-merges" lost empty merges in recent versions
+   of Git.
+
+ * "git merge --no-edit" computed who were involved in the work done
+   on the side branch, even though that information is to be discarded
+   without getting seen in the editor.
+
+ * "git merge" started calling prepare-commit-msg hook like "git
+   commit" does some time ago, but forgot to pay attention to the exit
+   status of the hook.
+
+ * A failure to push due to non-ff while on an unborn branch
+   dereferenced a NULL pointer when showing an error message.
+
+ * When users spell "cc:" in lowercase in the fake "header" in the
+   trailer part, "git send-email" failed to pick up the addresses from
+   there. As e-mail headers field names are case insensitive, this
+   script should follow suit and treat "cc:" and "Cc:" the same way.
+
+ * Output from "git status --ignored" showed an unexpected interaction
+   with "--untracked".
+
+ * "gitweb", when sorting by age to show repositories with new
+   activities first, used to sort repositories with absolutely
+   nothing in it early, which was not very useful.
+
+ * "gitweb"'s code to sanitize control characters before passing it to
+   "highlight" filter lost known-to-be-safe control characters by
+   mistake.
+
+ * "gitweb" pages served over HTTPS, when configured to show picon or
+   gravatar, referred to these external resources to be fetched via
+   HTTP, resulting in mixed contents warning in browsers.
+
+ * When a line to be wrapped has a solid run of non space characters
+   whose length exactly is the wrap width, "git shortlog -w" failed
+   to add a newline after such a line.
+
+ * Command line completion leaked an unnecessary error message while
+   looking for possible matches with paths in <tree-ish>.
+
+ * Command line completion for "tcsh" emitted an unwanted space
+   after completing a single directory name.
+
+ * Command line completion code was inadvertently made incompatible with
+   older versions of bash by using a newer array notation.
+
+ * "git push" was taught to refuse updating the branch that is
+   currently checked out long time ago, but the user manual was left
+   stale.
+   (merge 50995ed wk/man-deny-current-branch-is-default-these-days later to maint).
+
+ * Some shells do not behave correctly when IFS is unset; work it
+   around by explicitly setting it to the default value.
+
+ * Some scripted programs written in Python did not get updated when
+   PYTHON_PATH changed.
+   (cherry-pick 96a4647fca54031974cd6ad1 later to maint).
+
+ * When autoconf is used, any build on a different commit always ran
+   "config.status --recheck" even when unnecessary.
+
+ * A fix was added to the build procedure to work around buggy
+   versions of ccache broke the auto-generation of dependencies, which
+   unfortunately is still relevant because some people use ancient
+   distros.
+
+ * The autoconf subsystem passed --mandir down to generated
+   config.mak.autogen but forgot to do the same for --htmldir.
+   (merge 55d9bf0 ct/autoconf-htmldir later to maint).
+
+ * A change made on v1.8.1.x maintenance track had a nasty regression
+   to break the build when autoconf is used.
+   (merge 7f1b697 jn/less-reconfigure later to maint).
+
+ * We have been carrying a translated and long-unmaintained copy of an
+   old version of the tutorial; removed.
+
+ * t0050 had tests expecting failures from a bug that was fixed some
+   time ago.
+
+ * t4014, t9502 and t0200 tests had various portability issues that
+   broke on OpenBSD.
+
+ * t9020 and t3600 tests had various portability issues.
+
+ * t9200 runs "cvs init" on a directory that already exists, but a
+   platform can configure this fail for the current user (e.g. you
+   need to be in the cvsadmin group on NetBSD 6.0).
+
+ * t9020 and t9810 had a few non-portable shell script construct.
+
+ * Scripts to test bash completion was inherently flaky as it was
+   affected by whatever random things the user may have on $PATH.
+
+ * An element on GIT_CEILING_DIRECTORIES could be a "logical" pathname
+   that uses a symbolic link to point at somewhere else (e.g. /home/me
+   that points at /net/host/export/home/me, and the latter directory
+   is automounted). Earlier when Git saw such a pathname e.g. /home/me
+   on this environment variable, the "ceiling" mechanism did not take
+   effect. With this release (the fix has also been merged to the
+   v1.8.1.x maintenance series), elements on GIT_CEILING_DIRECTORIES
+   are by default checked for such aliasing coming from symbolic
+   links. As this needs to actually resolve symbolic links for each
+   element on the GIT_CEILING_DIRECTORIES, you can disable this
+   mechanism for some elements by listing them after an empty element
+   on the GIT_CEILING_DIRECTORIES. e.g. Setting /home/me::/home/him to
+   GIT_CEILING_DIRECTORIES makes Git resolve symbolic links in
+   /home/me when checking if the current directory is under /home/me,
+   but does not do so for /home/him.
+   (merge 7ec30aa mh/maint-ceil-absolute later to maint).