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 2.7 Release Notes
+=====================
+
+Updates since v2.6
+------------------
+
+UI, Workflows & Features
+
+ * The appearance of "gitk", particularly on high DPI monitors, have
+   been improved.  "gitk" also comes with an undated translation for
+   Swedish and Japanese.
+
+ * "git remote" learned "get-url" subcommand to show the URL for a
+   given remote name used for fetching and pushing.
+
+ * There was no way to defeat a configured rebase.autostash variable
+   from the command line, as "git rebase --no-autostash" was missing.
+
+ * "git log --date=local" used to only show the normal (default)
+   format in the local timezone.  The command learned to take 'local'
+   as an instruction to use the local timezone with other formats,
+
+ * The refs used during a "git bisect" session is now per-worktree so
+   that independent bisect sessions can be done in different worktrees
+   created with "git worktree add".
+
+ * Users who are too busy to type three extra keystrokes to ask for
+   "git stash show -p" can now set stash.showPatch configuration
+   variable to true to always see the actual patch, not just the list
+   of paths affected with feel for the extent of damage via diffstat.
+
+ * "quiltimport" allows to specify the series file by honoring the
+   $QUILT_SERIES environment and also --series command line option.
+
+ * The use of 'good/bad' in "git bisect" made it confusing to use when
+   hunting for a state change that is not a regression (e.g. bugfix).
+   The command learned 'old/new' and then allows the end user to
+   say e.g. "bisect start --term-old=fast --term-new=slow" to find a
+   performance regression.
+
+ * "git interpret-trailers" can now run outside of a Git repository.
+
+ * "git p4" learned to reencode the pathname it uses to communicate
+   with the p4 depot with a new option.
+
+ * Give progress meter to "git filter-branch".
+
+ * Allow a later "!/abc/def" to override an earlier "/abc" that
+   appears in the same .gitignore file to make it easier to express
+   "everything in /abc directory is ignored, except for ...".
+
+ * Teach "git p4" to send large blobs outside the repository by
+   talking to Git LFS.
+
+ * Prepare for Git on-disk repository representation to undergo
+   backward incompatible changes by introducing a new repository
+   format version "1", with an extension mechanism.
+
+ * "git worktree" learned a "list" subcommand.
+
+ * "git clone --dissociate" learned that it can be used even when
+   "--reference" was not used at the same time.
+
+ * "git blame" learnt to take "--first-parent" and "--reverse" at the
+   same time when it makes sense.
+
+ * "git checkout" did not follow the usual "--[no-]progress"
+   convention and implemented only "--quiet" that is essentially
+   a superset of "--no-progress".  Extend the command to support the
+   usual "--[no-]progress".
+
+ * The semantics of transfer.hideRefs configuration variable have been
+   extended to work better with the ref "namespace" feature that lets
+   you throw unrelated bunches of repositories in a single physical
+   repository and virtually serve them as separate ones.
+
+ * send-email config variables whose values are pathnames now go
+   through the ~username/ expansion.
+
+ * bash completion learnt to TAB-complete recipient addresses given
+   to send-email.
+
+ * The credential-cache daemon can be told to ignore SIGHUP to work
+   around issue when running Git from inside emacs.
+
+ * "git push" learned new configuration for doing "--recurse-submodules"
+   on each push.
+
+ * "format-patch" has learned a new option to zero-out the commit
+   object name on the mbox "From " line.
+
+
+Performance, Internal Implementation, Development Support etc.
+
+ * The infrastructure to rewrite "git submodule" in C is being built
+   incrementally.  Let's polish these early parts well enough and make
+   them graduate to 'next' and 'master', so that the more involved
+   follow-up can start cooking on a solid ground.
+
+ * Some features from "git tag -l" and "git branch -l" have been made
+   available to "git for-each-ref" so that eventually the unified
+   implementation can be shared across all three.  The version merged
+   to the 'master' branch earlier had a performance regression in "tag
+   --contains", which has since been corrected.
+
+ * Because "test_when_finished" in our test framework queues the
+   clean-up tasks to be done in a shell variable, it should not be
+   used inside a subshell.  Add a mechanism to allow 'bash' to catch
+   such uses, and fix the ones that were found.
+
+ * The debugging infrastructure for pkt-line based communication has
+   been improved to mark the side-band communication specifically.
+
+ * Update "git branch" that list existing branches, using the
+   ref-filter API that is shared with "git tag" and "git
+   for-each-ref".
+
+ * The test for various line-ending conversions has been enhanced.
+
+ * A few test scripts around "git p4" have been improved for
+   portability.
+
+ * Many allocations that is manually counted (correctly) that are
+   followed by strcpy/sprintf have been replaced with a less error
+   prone constructs such as xstrfmt.
+
+ * The internal stripspace() function has been moved to where it
+   logically belongs to, i.e. strbuf API, and the command line parser
+   of "git stripspace" has been updated to use the parse_options API.
+
+ * "git am" used to spawn "git mailinfo" via run_command() API once
+   per each patch, but learned to make a direct call to mailinfo()
+   instead.
+
+ * The implementation of "git mailinfo" was refactored so that a
+   mailinfo() function can be directly called from inside a process.
+
+ * With a "debug" helper, debugging of a single "git" invocation in
+   our test scripts has become a lot easier.
+
+ * The "configure" script did not test for -lpthread correctly, which
+   upset some linkers.
+
+ * Cross completed task off of subtree project's todo list.
+
+ * Test cleanups for the subtree project.
+
+ * Clean up style in an ancient test t9300.
+
+ * Work around some test flakiness with p4d.
+
+ * Fsck did not correctly detect a NUL-truncated header in a tag.
+
+ * Use a safer behavior when we hit errors verifying remote certificates.
+
+ * Speed up filter-branch for cases where we only care about rewriting
+   commits, not tree data.
+
+ * The parse-options API has been updated to make "-h" command line
+   option work more consistently in all commands.
+
+ * "git svn rebase/mkdirs" got optimized by keeping track of empty
+   directories better.
+
+ * Fix some racy client/server tests by treating SIGPIPE the same as a
+   normal non-zero exit.
+
+ * The necessary infrastructure to build topics using the free Travis
+   CI has been added. Developers forking from this topic (and enabling
+   Travis) can do their own builds, and we can turn on auto-builds for
+   git/git (including build-status for pull requests that people
+   open).
+
+ * The write(2) emulation for Windows learned to set errno to EPIPE
+   when necessary.
+
+
+Also contains various documentation updates and code clean-ups.
+
+
+Fixes since v2.6
+----------------
+
+Unless otherwise noted, all the fixes since v2.6 in the maintenance
+track are contained in this release (see the maintenance releases'
+notes for details).
+
+ * Very small number of options take a parameter that is optional
+   (which is not a great UI element as they can only appear at the end
+   of the command line).  Add notice to documentation of each and
+   every one of them.
+
+ * "git blame --first-parent v1.0..v2.0" was not rejected but did not
+   limit the blame to commits on the first parent chain.
+
+ * "git subtree" (in contrib/) now can take whitespaces in the
+   pathnames, not only in the in-tree pathname but the name of the
+   directory that the repository is in.
+
+ * The ssh transport, just like any other transport over the network,
+   did not clear GIT_* environment variables, but it is possible to
+   use SendEnv and AcceptEnv to leak them to the remote invocation of
+   Git, which is not a good idea at all.  Explicitly clear them just
+   like we do for the local transport.
+
+ * Correct "git p4 --detect-labels" so that it does not fail to create
+   a tag that points at a commit that is also being imported.
+
+ * The Makefile always runs the library archiver with hardcoded "crs"
+   options, which was inconvenient for exotic platforms on which
+   people want to use programs with totally different set of command
+   line options.
+
+ * Customization to change the behaviour with "make -w" and "make -s"
+   in our Makefile was broken when they were used together.
+
+ * Allocation related functions and stdio are unsafe things to call
+   inside a signal handler, and indeed killing the pager can cause
+   glibc to deadlock waiting on allocation mutex as our signal handler
+   tries to free() some data structures in wait_for_pager().  Reduce
+   these unsafe calls.
+
+ * The way how --ref/--notes to specify the notes tree reference are
+   DWIMmed was not clearly documented.
+
+ * "git gc" used to barf when a symbolic ref has gone dangling
+   (e.g. the branch that used to be your upstream's default when you
+   cloned from it is now gone, and you did "fetch --prune").
+
+ * "git clone --dissociate" runs a big "git repack" process at the
+   end, and it helps to close file descriptors that are open on the
+   packs and their idx files before doing so on filesystems that
+   cannot remove a file that is still open.
+
+ * Description of the "log.follow" configuration variable in "git log"
+   documentation is now also copied to "git config" documentation.
+
+ * "git rebase -i" had a minor regression recently, which stopped
+   considering a line that begins with an indented '#' in its insn
+   sheet not a comment. Further, the code was still too picky on
+   Windows where CRLF left by the editor is turned into a trailing CR
+   on the line read via the "read" built-in command of bash.  Both of
+   these issues are now fixed.
+
+ * After "git checkout --detach", "git status" reported a fairly
+   useless "HEAD detached at HEAD", instead of saying at which exact
+   commit.
+
+ * When "git send-email" wanted to talk over Net::SMTP::SSL,
+   Net::Cmd::datasend() did not like to be fed too many bytes at the
+   same time and failed to send messages.  Send the payload one line
+   at a time to work around the problem.
+
+ * When "git am" was rewritten as a built-in, it stopped paying
+   attention to user.signingkey, which was fixed.
+
+ * It was not possible to use a repository-lookalike created by "git
+   worktree add" as a local source of "git clone".
+
+ * On a case insensitive filesystems, setting GIT_WORK_TREE variable
+   using a random cases that does not agree with what the filesystem
+   thinks confused Git that it wasn't inside the working tree.
+
+ * Performance-measurement tests did not work without an installed Git.
+
+ * A test script for the HTTP service had a timing dependent bug,
+   which was fixed.
+
+ * There were some classes of errors that "git fsck" diagnosed to its
+   standard error that did not cause it to exit with non-zero status.
+
+ * Work around "git p4" failing when the P4 depot records the contents
+   in UTF-16 without UTF-16 BOM.
+
+ * When "git gc --auto" is backgrounded, its diagnosis message is
+   lost.  Save it to a file in $GIT_DIR and show it next time the "gc
+   --auto" is run.
+
+ * The submodule code has been taught to work better with separate
+   work trees created via "git worktree add".
+
+ * "git gc" is safe to run anytime only because it has the built-in
+   grace period to protect young objects.  In order to run with no
+   grace period, the user must make sure that the repository is
+   quiescent.
+
+ * A recent "filter-branch --msg-filter" broke skipping of the commit
+   object header, which is fixed.
+
+ * The normalize_ceiling_entry() function does not muck with the end
+   of the path it accepts, and the real world callers do rely on that,
+   but a test insisted that the function drops a trailing slash.
+
+ * A test for interaction between untracked cache and sparse checkout
+   added in Git 2.5 days were flaky.
+
+ * A couple of commands still showed "[options]" in their usage string
+   to note where options should come on their command line, but we
+   spell that "[<options>]" in most places these days.
+
+ * The synopsis text and the usage string of subcommands that read
+   list of things from the standard input are often shown as if they
+   only take input from a file on a filesystem, which was misleading.
+
+ * "git am -3" had a small regression where it is aborted in its error
+   handling codepath when underlying merge-recursive failed in certain
+   ways, as it assumed that the internal call to merge-recursive will
+   never die, which is not the case (yet).
+
+ * The linkage order of libraries was wrong in places around libcurl.
+
+ * The name-hash subsystem that is used to cope with case insensitive
+   filesystems keeps track of directories and their on-filesystem
+   cases for all the paths in the index by holding a pointer to a
+   randomly chosen cache entry that is inside the directory (for its
+   ce->ce_name component).  This pointer was not updated even when the
+   cache entry was removed from the index, leading to use after free.
+   This was fixed by recording the path for each directory instead of
+   borrowing cache entries and restructuring the API somewhat.
+
+ * "git merge-file" tried to signal how many conflicts it found, which
+   obviously would not work well when there are too many of them.
+
+ * The error message from "git blame --contents --reverse" incorrectly
+   talked about "--contents --children".
+
+ * "git imap-send" did not compile well with older version of cURL library.
+
+ * Merging a branch that removes a path and another that changes the
+   mode bits on the same path should have conflicted at the path, but
+   it didn't and silently favoured the removal.
+
+ * "git --literal-pathspecs add -u/-A" without any command line
+   argument misbehaved ever since Git 2.0.
+
+ * "git daemon" uses "run_command()" without "finish_command()", so it
+   needs to release resources itself, which it forgot to do.
+
+ * "git status --branch --short" accessed beyond the constant string
+   "HEAD", which has been corrected.
+
+ * We peek objects from submodule's object store by linking it to the
+   list of alternate object databases, but the code to do so forgot to
+   correctly initialize the list.
+
+ * The code to prepare the working tree side of temporary directory
+   for the "dir-diff" feature forgot that symbolic links need not be
+   copied (or symlinked) to the temporary area, as the code already
+   special cases and overwrites them.  Besides, it was wrong to try
+   computing the object name of the target of symbolic link, which may
+   not even exist or may be a directory.
+
+ * A Range: request can be responded with a full response and when
+   asked properly libcurl knows how to strip the result down to the
+   requested range.  However, we were hand-crafting a range request
+   and it did not kick in.
+
+ * Having a leftover .idx file without corresponding .pack file in
+   the repository hurts performance; "git gc" learned to prune them.
+
+ * Apple's common crypto implementation of SHA1_Update() does not take
+   more than 4GB at a time, and we now have a compile-time workaround
+   for it.
+
+ * Produce correct "dirty" marker for shell prompts, even when we
+   are on an orphan or an unborn branch.
+
+ * A build without NO_IPv6 used to use gethostbyname() when guessing
+   user's hostname, instead of getaddrinfo() that is used in other
+   codepaths in such a build.
+
+ * The exit code of git-fsck did not reflect some types of errors
+   found in packed objects, which has been corrected.
+
+ * The helper used to iterate over loose object directories to prune
+   stale objects did not closedir() immediately when it is done with a
+   directory--a callback such as the one used for "git prune" may want
+   to do rmdir(), but it would fail on open directory on platforms
+   such as WinXP.
+
+ * "git p4" used to import Perforce CLs that touch only paths outside
+   the client spec as empty commits.  It has been corrected to ignore
+   them instead, with a new configuration git-p4.keepEmptyCommits as a
+   backward compatibility knob.
+
+ * The completion script (in contrib/) used to list "git column"
+   (which is not an end-user facing command) as one of the choices
+   (merge 160fcdb sg/completion-no-column later to maint).
+
+ * The error reporting from "git send-email", when SMTP TLS fails, has
+   been improved.
+   (merge 9d60524 jk/send-email-ssl-errors later to maint).
+
+ * When getpwuid() on the system returned NULL (e.g. the user is not
+   in the /etc/passwd file or other uid-to-name mappings), the
+   codepath to find who the user is to record it in the reflog barfed
+   and died.  Loosen the check in this codepath, which already accepts
+   questionable ident string (e.g. host part of the e-mail address is
+   obviously bogus), and in general when we operate fmt_ident() function
+   in non-strict mode.
+   (merge 92bcbb9 jk/ident-loosen-getpwuid later to maint).
+
+ * "git symbolic-ref" forgot to report a failure with its exit status.
+   (merge f91b273 jk/symbolic-ref-maint later to maint).
+
+ * History traversal with "git log --source" that starts with an
+   annotated tag failed to report the tag as "source", due to an
+   old regression in the command line parser back in v2.2 days.
+   (merge 728350b jk/pending-keep-tag-name later to maint).
+
+ * "git p4" when interacting with multiple depots at the same time
+   used to incorrectly drop changes.
+
+ * Code clean-up, minor fixes etc.