merge(3p/git): Merge git subtree at v2.29.2 r/1890

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

1 files changed, 525 insertions, 0 deletions

diff --git a/third_party/git/Documentation/RelNotes/2.27.0.txt b/third_party/git/Documentation/RelNotes/2.27.0.txt
new file mode 100644
index 0000000000..15518d06c1
--- /dev/null
+++ b/third_party/git/Documentation/RelNotes/2.27.0.txt
@@ -0,0 +1,525 @@
+Git 2.27 Release Notes
+======================
+
+Updates since v2.26
+-------------------
+
+Backward compatibility notes
+
+ * When "git describe C" finds that commit C is pointed by a signed or
+   annotated tag, which records T as its tagname in the object, the
+   command gives T as its answer.  Even if the user renames or moves
+   such a tag from its natural location in the "refs/tags/" hierarchy,
+   "git describe C" would still give T as the answer, but in such a
+   case "git show T^0" would no longer work as expected.  There may be
+   nothing at "refs/tags/T" or even worse there may be a different tag
+   instead.
+
+   Starting from this version, "git describe" will always use the
+   "long" version, as if the "--long" option were given, when giving
+   its output based on such a misplaced tag to work around the problem.
+
+ * "git pull" issues a warning message until the pull.rebase
+   configuration variable is explicitly given, which some existing
+   users may find annoying---those who prefer not to rebase need to
+   set the variable to false to squelch the warning.
+
+ * The transport protocol version 2, which was promoted to the default
+   in Git 2.26 release, turned out to have some remaining rough edges,
+   so it has been demoted from the default.
+
+
+UI, Workflows & Features
+
+ * A handful of options to configure SSL when talking to proxies have
+   been added.
+
+ * Smudge/clean conversion filters are now given more information
+   (e.g. the object of the tree-ish in which the blob being converted
+   appears, in addition to its path, which has already been given).
+
+ * When "git describe C" finds an annotated tag with tagname A to be
+   the best name to explain commit C, and the tag is stored in a
+   "wrong" place in the refs/tags hierarchy, e.g. refs/tags/B, the
+   command gave a warning message but used A (not B) to describe C.
+   If C is exactly at the tag, the describe output would be "A", but
+   "git rev-parse A^0" would not be equal as "git rev-parse C^0".  The
+   behavior of the command has been changed to use the "long" form
+   i.e. A-0-gOBJECTNAME, which is correctly interpreted by rev-parse.
+
+ * "git pull" learned to warn when no pull.rebase configuration
+   exists, and neither --[no-]rebase nor --ff-only is given (which
+   would result a merge).
+
+ * "git p4" learned four new hooks and also "--no-verify" option to
+   bypass them (and the existing "p4-pre-submit" hook).
+
+ * "git pull" shares many options with underlying "git fetch", but
+   some of them were not documented and some of those that would make
+   sense to pass down were not passed down.
+
+ * "git rebase" learned the "--no-gpg-sign" option to countermand
+   commit.gpgSign the user may have.
+
+ * The output from "git format-patch" uses RFC 2047 encoding for
+   non-ASCII letters on From: and Subject: headers, so that it can
+   directly be fed to e-mail programs.  A new option has been added
+   to produce these headers in raw.
+
+ * "git log" learned "--show-pulls" that helps pathspec limited
+   history views; a merge commit that takes the whole change from a
+   side branch, which is normally omitted from the output, is shown
+   in addition to the commits that introduce real changes.
+
+ * The interactive input from various codepaths are consolidated and
+   any prompt possibly issued earlier are fflush()ed before we read.
+
+ * Allow "git rebase" to reapply all local commits, even if the may be
+   already in the upstream, without checking first.
+
+ * The 'pack.useSparse' configuration variable now defaults to 'true',
+   enabling an optimization that has been experimental since Git 2.21.
+
+ * "git rebase" happens to call some hooks meant for "checkout" and
+   "commit" by this was not a designed behaviour than historical
+   accident.  This has been documented.
+
+ * "git merge" learns the "--autostash" option.
+
+ * "sparse-checkout" UI improvements.
+
+ * "git update-ref --stdin" learned a handful of new verbs to let the
+   user control ref update transactions more explicitly, which helps
+   as an ingredient to implement two-phase commit-style atomic
+   ref-updates across multiple repositories.
+
+ * "git commit-graph write" learned different ways to write out split
+   files.
+
+ * Introduce an extension to the commit-graph to make it efficient to
+   check for the paths that were modified at each commit using Bloom
+   filters.
+
+ * The approxidate parser learns to parse seconds with fraction and
+   ignore fractional part.
+
+ * The userdiff patterns for Markdown documents have been added.
+
+ * The sparse-checkout patterns have been forbidden from excluding all
+   paths, leaving an empty working tree, for a long time.  This
+   limitation has been lifted.
+
+ * "git restore --staged --worktree" now defaults to take the contents
+   out of "HEAD", instead of erring out.
+
+ * "git p4" learned to recover from a (broken) state where a directory
+   and a file are recorded at the same path in the Perforce repository
+   the same way as their clients do.
+
+ * "git multi-pack-index repack" has been taught to honor some
+   repack.* configuration variables.
+
+
+Performance, Internal Implementation, Development Support etc.
+
+ * The advise API has been revamped to allow more systematic enumeration of
+   advice knobs in the future.
+
+ * SHA-256 transition continues.
+
+ * The code to interface with GnuPG has been refactored.
+
+ * "git stash" has kept an escape hatch to use the scripted version
+   for a few releases, which got stale.  It has been removed.
+
+ * Enable tests that require GnuPG on Windows.
+
+ * Minor test usability improvement.
+
+ * Trace2 enhancement to allow logging of the environment variables.
+
+ * Test clean-up continues.
+
+ * Perf-test update.
+
+ * A Windows-specific test element has been made more robust against
+   misuse from both user's environment and programmer's errors.
+
+ * Various tests have been updated to work around issues found with
+   shell utilities that come with busybox etc.
+
+ * The config API made mixed uses of int and size_t types to represent
+   length of various pieces of text it parsed, which has been updated
+   to use the correct type (i.e. size_t) throughout.
+
+ * The "--decorate-refs" and "--decorate-refs-exclude" options "git
+   log" takes have learned a companion configuration variable
+   log.excludeDecoration that sits at the lowest priority in the
+   family.
+
+ * A new CI job to build and run test suite on linux with musl libc
+   has been added.
+
+ * Update the CI configuration to use GitHub Actions, retiring the one
+   based on Azure Pipelines.
+
+ * The directory traversal code had redundant recursive calls which
+   made its performance characteristics exponential with respect to
+   the depth of the tree, which was corrected.
+
+ * "git blame" learns to take advantage of the "changed-paths" Bloom
+   filter stored in the commit-graph file.
+
+ * The "bugreport" tool has been added.
+
+ * The object walk with object filter "--filter=tree:0" can now take
+   advantage of the pack bitmap when available.
+
+ * Instead of always building all branches at GitHub via Actions,
+   users can specify which branches to build.
+
+ * Codepaths that show progress meter have been taught to also use the
+   start_progress() and the stop_progress() calls as a "region" to be
+   traced.
+
+ * Instead of downloading Windows SDK for CI jobs for windows builds
+   from an external site (wingit.blob.core.windows.net), use the one
+   created in the windows-build job, to work around quota issues at
+   the external site.
+
+
+Fixes since v2.26
+-----------------
+
+ * The real_path() convenience function can easily be misused; with a
+   bit of code refactoring in the callers' side, its use has been
+   eliminated.
+   (merge 49d3c4b481 am/real-path-fix later to maint).
+
+ * Update "git p4" to work with Python 3.
+   (merge 6bb40ed20a yz/p4-py3 later to maint).
+
+ * The mechanism to prevent "git commit" from making an empty commit
+   or amending during an interrupted cherry-pick was broken during the
+   rewrite of "git rebase" in C, which has been corrected.
+   (merge 430b75f720 pw/advise-rebase-skip later to maint).
+
+ * Fix "git checkout --recurse-submodules" of a nested submodule
+   hierarchy.
+   (merge 846f34d351 pb/recurse-submodules-fix later to maint).
+
+ * The "--fork-point" mode of "git rebase" regressed when the command
+   was rewritten in C back in 2.20 era, which has been corrected.
+   (merge f08132f889 at/rebase-fork-point-regression-fix later to maint).
+
+ * The import-tars importer (in contrib/fast-import/) used to create
+   phony files at the top-level of the repository when the archive
+   contains global PAX headers, which made its own logic to detect and
+   omit the common leading directory ineffective, which has been
+   corrected.
+   (merge c839fcff65 js/import-tars-do-not-make-phony-files-from-pax-headers later to maint).
+
+ * Simplify the commit ancestry connectedness check in a partial clone
+   repository in which "promised" objects are assumed to be obtainable
+   lazily on-demand from promisor remote repositories.
+   (merge 2b98478c6f jt/connectivity-check-optim-in-partial-clone later to maint).
+
+ * The server-end of the v2 protocol to serve "git clone" and "git
+   fetch" was not prepared to see a delim packets at unexpected
+   places, which led to a crash.
+   (merge cacae4329f jk/harden-protocol-v2-delim-handling later to maint).
+
+ * When fed a midx that records no objects, some codepaths tried to
+   loop from 0 through (num_objects-1), which, due to integer
+   arithmetic wrapping around, made it nonsense operation with out of
+   bounds array accesses.  The code has been corrected to reject such
+   an midx file.
+   (merge 796d61cdc0 dr/midx-avoid-int-underflow later to maint).
+
+ * Utitiles run via the run_command() API were not spawned correctly
+   on Cygwin, when the paths to them are given as a full path with
+   backslashes.
+   (merge 05ac8582bc ak/run-command-on-cygwin-fix later to maint).
+
+ * "git pull --rebase" tried to run a rebase even after noticing that
+   the pull results in a fast-forward and no rebase is needed nor
+   sensible, for the past few years due to a mistake nobody noticed.
+   (merge fbae70ddc6 en/pull-do-not-rebase-after-fast-forwarding later to maint).
+
+ * "git rebase" with the merge backend did not work well when the
+   rebase.abbreviateCommands configuration was set.
+   (merge de9f1d3ef4 ag/rebase-merge-allow-ff-under-abbrev-command later to maint).
+
+ * The logic to auto-follow tags by "git clone --single-branch" was
+   not careful to avoid lazy-fetching unnecessary tags, which has been
+   corrected.
+   (merge 167a575e2d jk/use-quick-lookup-in-clone-for-tag-following later to maint).
+
+ * "git rebase -i" did not leave the reflog entries correctly.
+   (merge 1f6965f994 en/sequencer-reflog-action later to maint).
+
+ * The more aggressive updates to remote-tracking branches we had for
+   the past 7 years or so were not reflected in the documentation,
+   which has been corrected.
+   (merge a44088435c pb/pull-fetch-doc later to maint).
+
+ * We've left the command line parsing of "git log :/a/b/" broken for
+   about a full year without anybody noticing, which has been
+   corrected.
+   (merge 0220461071 jc/missing-ref-store-fix later to maint).
+
+ * Misc fixes for Windows.
+   (merge 3efc128cd5 js/mingw-fixes later to maint).
+
+ * "git rebase" (again) learns to honor "--no-keep-empty", which lets
+   the user to discard commits that are empty from the beginning (as
+   opposed to the ones that become empty because of rebasing).  The
+   interactive rebase also marks commits that are empty in the todo.
+   (merge 50ed76148a en/rebase-no-keep-empty later to maint).
+
+ * Parsing the host part out of URL for the credential helper has been corrected.
+   (merge 4c5971e18a jk/credential-parsing-end-of-host-in-URL later to maint).
+
+ * Document the recommended way to abort a failing test early (e.g. by
+   exiting a loop), which is to say "return 1".
+   (merge 7cc112dc95 jc/doc-test-leaving-early later to maint).
+
+ * The code that refreshes the last access and modified time of
+   on-disk packfiles and loose object files have been updated.
+   (merge 312cd76130 lr/freshen-file-fix later to maint).
+
+ * Validation of push certificate has been made more robust against
+   timing attacks.
+   (merge 719483e547 bc/constant-memequal later to maint).
+
+ * The custom hash function used by "git fast-import" has been
+   replaced with the one from hashmap.c, which gave us a nice
+   performance boost.
+   (merge d8410a816b jk/fast-import-use-hashmap later to maint).
+
+ * The "git submodule" command did not initialize a few variables it
+   internally uses and was affected by variable settings leaked from
+   the environment.
+   (merge 65d100c4dd lx/submodule-clear-variables later to maint).
+
+ * Raise the minimum required version of docbook-xsl package to 1.74,
+   as 1.74.0 was from late 2008, which is more than 10 years old, and
+   drop compatibility cruft from our documentation suite.
+   (merge 3c255ad660 ma/doc-discard-docbook-xsl-1.73 later to maint).
+
+ * "git log" learns "--[no-]mailmap" as a synonym to "--[no-]use-mailmap"
+   (merge 88acccda38 jc/log-no-mailmap later to maint).
+
+ * "git commit-graph write --expire-time=<timestamp>" did not use the
+   given timestamp correctly, which has been corrected.
+   (merge b09b785c78 ds/commit-graph-expiry-fix later to maint).
+
+ * Tests update to use "test-chmtime" instead of "touch -t".
+   (merge e892a56845 ds/t5319-touch-fix later to maint).
+
+ * "git diff" in a partial clone learned to avoid lazy loading blob
+   objects in more casese when they are not needed.
+   (merge 95acf11a3d jt/avoid-prefetch-when-able-in-diff later to maint).
+
+ * "git push --atomic" used to show failures for refs that weren't
+   even pushed, which has been corrected.
+   (merge dfe1b7f19c jx/atomic-push later to maint).
+
+ * Code in builtin/*, i.e. those can only be called from within
+   built-in subcommands, that implements bulk of a couple of
+   subcommands have been moved to libgit.a so that they could be used
+   by others.
+   (merge 9460fd48b5 dl/libify-a-few later to maint).
+
+ * Allowing the user to split a patch hunk while "git stash -p" does
+   not work well; a band-aid has been added to make this (partially)
+   work better.
+
+ * "git diff-tree --pretty --notes" used to hit an assertion failure,
+   as it forgot to initialize the notes subsystem.
+   (merge 5778b22b3d tb/diff-tree-with-notes later to maint).
+
+ * "git range-diff" fixes.
+   (merge 8d1675eb7f vd/range-diff-with-custom-pretty-format-fix later to maint).
+
+ * "git grep" did not quote a path with unusual character like other
+   commands (like "git diff", "git status") do, but did quote when run
+   from a subdirectory, both of which has been corrected.
+   (merge 45115d8490 mt/grep-cquote-path later to maint).
+
+ * GNU/Hurd is also among the ones that need the fopen() wrapper.
+   (merge 274a1328fb jc/gnu-hurd-lets-fread-read-dirs later to maint).
+
+ * Those fetching over protocol v2 from linux-next and other kernel
+   repositories are reporting that v2 often fetches way too much than
+   needed.
+   (merge 11c7f2a30b jn/demote-proto2-from-default later to maint).
+
+ * The upload-pack protocol v2 gave up too early before finding a
+   common ancestor, resulting in a wasteful fetch from a fork of a
+   project.  This has been corrected to match the behaviour of v0
+   protocol.
+   (merge 2f0a093dd6 jt/v2-fetch-nego-fix later to maint).
+
+ * The build procedure did not use the libcurl library and its include
+   files correctly for a custom-built installation.
+   (merge 0573831950 jk/build-with-right-curl later to maint).
+
+ * Tighten "git mailinfo" to notice and error out when decoded result
+   contains NUL in it.
+   (merge 3919997447 dd/mailinfo-with-nul later to maint).
+
+ * Fix in-core inconsistency after fetching into a shallow repository
+   that broke the code to write out commit-graph.
+   (merge 37b9dcabfc tb/reset-shallow later to maint).
+
+ * The commit-graph code exhausted file descriptors easily when it
+   does not have to.
+   (merge c8828530b7 tb/commit-graph-fd-exhaustion-fix later to maint).
+
+ * The multi-pack-index left mmapped file descriptors open when it
+   does not have to.
+   (merge 6c7ff7cf7f ds/multi-pack-index later to maint).
+
+ * Recent update to Homebrew used by macOS folks breaks build by
+   moving gettext library and necessary headers.
+   (merge a0b3108618 ds/build-homebrew-gettext-fix later to maint).
+
+ * Incompatible options "--root" and "--fork-point" of "git rebase"
+   have been marked and documented as being incompatible.
+   (merge a35413c378 en/rebase-root-and-fork-point-are-incompatible later to maint).
+
+ * Error and verbose trace messages from "git push" did not redact
+   credential material embedded in URLs.
+   (merge d192fa5006 js/anonymise-push-url-in-errors later to maint).
+
+ * Update the parser used for credential.<URL>.<variable>
+   configuration, to handle <URL>s with '/' in them correctly.
+   (merge b44d0118ac bc/wildcard-credential later to maint).
+
+ * Recent updates broke parsing of "credential.<url>.<key>" where
+   <url> is not a full URL (e.g. [credential "https://"] helper = ...)
+   stopped working, which has been corrected.
+   (merge 9a121b0d22 js/partial-urlmatch-2.17 later to maint).
+   (merge cd93e6c029 js/partial-urlmatch later to maint).
+
+ * Some of the files commit-graph subsystem keeps on disk did not
+   correctly honor the core.sharedRepository settings and some were
+   left read-write.
+
+ * In error messages that "git switch" mentions its option to create a
+   new branch, "-b/-B" options were shown, where "-c/-C" options
+   should be, which has been corrected.
+   (merge 7c16ef7577 dl/switch-c-option-in-error-message later to maint).
+
+ * With the recent tightening of the code that is used to parse
+   various parts of a URL for use in the credential subsystem, a
+   hand-edited credential-store file causes the credential helper to
+   die, which is a bit too harsh to the users.  Demote the error
+   behaviour to just ignore and keep using well-formed lines instead.
+   (merge c03859a665 cb/credential-store-ignore-bogus-lines later to maint).
+
+ * The samples in the credential documentation has been updated to
+   make it clear that we depict what would appear in the .git/config
+   file, by adding appropriate quotes as needed..
+   (merge 177681a07e jk/credential-sample-update later to maint).
+
+ * "git branch" and other "for-each-ref" variants accepted multiple
+   --sort=<key> options in the increasing order of precedence, but it
+   had a few breakages around "--ignore-case" handling, and tie-breaking
+   with the refname, which have been fixed.
+   (merge 7c5045fc18 jk/for-each-ref-multi-key-sort-fix later to maint).
+
+ * The coding guideline for shell scripts instructed to refer to a
+   variable with dollar-sign inside arithmetic expansion to work
+   around a bug in old versions of dash, which is a thing of the past.
+   Now we are not forbidden from writing $((var+1)).
+   (merge 32b5fe7f0e jk/arith-expansion-coding-guidelines later to maint).
+
+ * The <stdlib.h> header on NetBSD brings in its own definition of
+   hmac() function (eek), which conflicts with our own and unrelated
+   function with the same name.  Our function has been renamed to work
+   around the issue.
+   (merge 3013118eb8 cb/avoid-colliding-with-netbsd-hmac later to maint).
+
+ * The basic test did not honor $TEST_SHELL_PATH setting, which has
+   been corrected.
+   (merge 0555e4af58 cb/t0000-use-the-configured-shell later to maint).
+
+ * Minor in-code comments and documentation updates around credential
+   API.
+   (merge 1aed817f99 cb/credential-doc-fixes later to maint).
+
+ * Teach "am", "commit", "merge" and "rebase", when they are run with
+   the "--quiet" option, to pass "--quiet" down to "gc --auto".
+   (merge 7c3e9e8cfb jc/auto-gc-quiet later to maint).
+
+ * The code to skip unmerged paths in the index when sparse checkout
+   is in use would have made out-of-bound access of the in-core index
+   when the last path was unmerged, which has been corrected.
+
+ * Serving a "git fetch" client over "git://" and "ssh://" protocols
+   using the on-wire protocol version 2 was buggy on the server end
+   when the client needs to make a follow-up request to
+   e.g. auto-follow tags.
+   (merge 08450ef791 cc/upload-pack-v2-fetch-fix later to maint).
+
+ * "git bisect replay" had trouble with input files when they used
+   CRLF line ending, which has been corrected.
+   (merge 6c722cbe5a cw/bisect-replay-with-dos later to maint).
+
+ * "rebase -i" segfaulted when rearranging a sequence that has a
+   fix-up that applies another fix-up (which may or may not be a
+   fix-up of yet another step).
+   (merge 02471e7e20 js/rebase-autosquash-double-fixup-fix later to maint).
+
+ * "git fsck" ensures that the paths recorded in tree objects are
+   sorted and without duplicates, but it failed to notice a case where
+   a blob is followed by entries that sort before a tree with the same
+   name.  This has been corrected.
+   (merge 9068cfb20f rs/fsck-duplicate-names-in-trees later to maint).
+
+ * Code clean-up by removing a compatibility implementation of a
+   function we no longer use.
+   (merge 84b0115f0d cb/no-more-gmtime later to maint).
+
+ * When a binary file gets modified and renamed on both sides of history
+   to different locations, both files would be written to the working
+   tree but both would have the contents from "ours".  This has been
+   corrected so that the path from each side gets their original content.
+
+ * Fix for a copy-and-paste error introduced during 2.20 era.
+   (merge e68a5272b1 ds/multi-pack-verify later to maint).
+
+ * Update an unconditional use of "grep -a" with a perl script in a test.
+   (merge 1eb7371236 dd/t5703-grep-a-fix later to maint).
+
+ * Other code cleanup, docfix, build fix, etc.
+   (merge 564956f358 jc/maintain-doc later to maint).
+   (merge 7422b2a0a1 sg/commit-slab-clarify-peek later to maint).
+   (merge 9c688735f6 rs/doc-passthru-fetch-options later to maint).
+   (merge 757c2ba3e2 en/oidset-uninclude-hashmap later to maint).
+   (merge 8312aa7d74 jc/config-tar later to maint).
+   (merge d00a5bdd50 ss/submodule-foreach-cb later to maint).
+   (merge 64d1022e14 ar/test-style-fixes later to maint).
+   (merge 4a465443a6 ds/doc-clone-filter later to maint).
+   (merge bb2dbe301b jk/t3419-drop-expensive-tests later to maint).
+   (merge d3507cc712 js/test-junit-finalization-fix later to maint).
+   (merge 2149b6748f bc/faq later to maint).
+   (merge 12dc0879f1 jk/test-cleanup later to maint).
+   (merge 344420bf0f pb/rebase-doc-typofix later to maint).
+   (merge 7cd54d37dc dl/wrapper-fix-indentation later to maint).
+   (merge 78725ebda9 jc/allow-strlen-substitution-in-shell-scripts later to maint).
+   (merge 2ecfcdecc6 jm/gitweb-fastcgi-utf8 later to maint).
+   (merge 0740d0a5d3 jk/oid-array-cleanups later to maint).
+   (merge a1aba0c95c js/t0007-typofix later to maint).
+   (merge 76ba7fa225 ma/config-doc-fix later to maint).
+   (merge 826f0c0df2 js/subtree-doc-update-to-asciidoctor-2 later to maint).
+   (merge 88eaf361e0 eb/mboxrd-doc later to maint).
+   (merge 051cc54941 tm/zsh-complete-switch-restore later to maint).
+   (merge 39102cf4fe ms/doc-revision-illustration-fix later to maint).
+   (merge 4d9378bfad eb/gitweb-more-trailers later to maint).
+   (merge bdccbf7047 mt/doc-worktree-ref later to maint).
+   (merge ce9baf234f dl/push-recurse-submodules-fix later to maint).
+   (merge 4153274052 bc/doc-credential-helper-value later to maint).
+   (merge 5c7bb0146e jc/codingstyle-compare-with-null later to maint).