The commit graph feature is controlled by the new core.commitGraph config
setting. This defaults to 0, so the feature is opt-in.

The intention of core.commitGraph is that a user can always stop checking
for or parsing commit graph files if core.commitGraph=0.
Signed-off-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Teach git-commit-graph to read commit graph files and summarize their contents.

Use the read subcommand to verify the contents of a commit graph file in the
tests.
Signed-off-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Teach git-commit-graph to write graph files. Create new test script to verify
this command succeeds without failure.
Signed-off-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Teach Git to write a commit graph file by checking all packed objects
to see if they are commits, then store the file in the given object
directory.
Helped-by: NJeff King <peff@peff.net>
Signed-off-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Teach git the 'commit-graph' builtin that will be used for writing and
reading packed graph files. The current implementation is mostly
empty, except for an '--object-dir' option.
Signed-off-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Add Documentation/technical/commit-graph.txt with details of the planned
commit graph feature, including future plans.
Signed-off-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Add document specifying the binary format for commit graphs. This
format allows for:

* New versions.
* New hash functions and hash lengths.
* Optional extensions.

Basic header information is followed by a binary table of contents
into "chunks" that include:

* An ordered list of commit object IDs.
* A 256-entry fanout into that list of OIDs.
* A list of metadata for the commits.
* A list of "large edges" to enable octopus merges.

The format automatically includes two parent positions for every
commit. This favors speed over space, since using only one position
per commit would cause an extra level of indirection for every merge
commit. (Octopus merges suffer from this indirection, but they are
very rare.)
Signed-off-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

If we want to use a hashfile on the temporary file for a lockfile, then
we need finalize_hashfile() to fully write the trailing hash but also keep
the file descriptor open.

Do this by adding a new CSUM_HASH_IN_STREAM flag along with a functional
change that checks this flag before writing the checksum to the stream.
This differs from previous behavior since it would be written if either
CSUM_CLOSE or CSUM_FSYNC is provided.
Signed-off-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The hashclose() method behaves very differently depending on the flags
parameter. In particular, the file descriptor is not always closed.

Perform a simple rename of "hashclose()" to "finalize_hashfile()" in
preparation for functional changes.
Signed-off-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

* jk/cached-commit-buffer:
  revision: drop --show-all option
  commit: drop uses of get_cached_commit_buffer()
  Git 2.16.2

* jt/binsearch-with-fanout:
  packfile: refactor hash search with fanout table
  packfile: remove GIT_DEBUG_LOOKUP log statements

This was an undocumented debugging aid that does not seem to
have come in handy in the past decade, judging from its lack
of mentions on the mailing list.

Let's drop it in the name of simplicity. This is morally a
revert of 3131b713 (Add "--show-all" revision walker flag
for debugging, 2008-02-09), but note that I did leave in the
mapping of UNINTERESTING to "^" in get_revision_mark(). I
don't think this would be possible to trigger with the
current code, but it's the only sensible marker.

We'll skip the usual deprecation period because this was
explicitly a debugging aid that was never documented.
Signed-off-by: NJeff King <peff@peff.net>
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The "--show-all" revision option shows UNINTERESTING
commits. Some of these commits may be unparsed when we try
to show them (since we may or may not need to walk their
parents to fulfill the request).

Commit 3131b713 (Add "--show-all" revision walker flag for
debugging, 2008-02-09) resolved this by just skipping
pretty-printing for commits without their object contents
cached, saying:

  Because we now end up listing commits we may not even have been parsed
  at all "show_log" and "show_commit" need to protect against commits
  that don't have a commit buffer entry.

That was the easy fix to avoid the pretty-printer segfaulting,
but:

  1. It doesn't work for all formats. E.g., --oneline
     prints the oid for each such commit but not a trailing
     newline, leading to jumbled output.

  2. It only affects some commits, depending on whether we
     happened to parse them or not (so if they were at the
     tip of an UNINTERESTING starting point, or if we
     happened to traverse over them, you'd see more data).

  3. It unncessarily ties the decision to show the verbose
     header to whether the commit buffer was cached. That
     makes it harder to change the logic around caching
     (e.g., if we could traverse without actually loading
     the full commit objects).

These days it's safe to feed such a commit to the
pretty-print code. Since be5c9fb9 (logmsg_reencode: lazily
load missing commit buffers, 2013-01-26), we'll load it on
demand in such a case. So let's just always show the verbose
headers.

This does change the behavior of plumbing, but:

  a. The --show-all option was explicitly introduced as a
     debugging aid, and was never documented (and has rarely
     even been mentioned on the list by git devs).

  b. Avoiding the commits was already not deterministic due
     to (2) above. So the caller might have seen full
     headers for these commits anyway, and would need to be
     prepared for it.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Doc update.

* ab/doc-cat-file-e-still-shows-errors:
  cat-file doc: document that -e will return some output

Doc update.

* as/read-tree-prefix-doc-fix:
  doc/read-tree: remove obsolete remark

"git add -p" was taught to ignore local changes to submodules as
they do not interfere with the partial addition of regular changes
anyway.

* nd/add-i-ignore-submodules:
  add--interactive: ignore submodule changes except HEAD

"git stash -- <pathspec>" incorrectly blew away untracked files in
the directory that matched the pathspec, which has been corrected.

* tg/stash-with-pathspec-fix:
  stash: don't delete untracked files that match pathspec

"git clone $there $here" is allowed even when here directory exists
as long as it is an empty directory, but the command incorrectly
removed it upon a failure of the operation.

* jk/abort-clone-with-existing-dest:
  clone: do not clean up directories we didn't create
  clone: factor out dir_exists() helper
  t5600: modernize style
  t5600: fix outdated comment about unborn HEAD

"git merge -Xours/-Xtheirs" learned to use our/their version when
resolving a conflicting updates to a symbolic link.

* jc/merge-symlink-ours-theirs:
  merge: teach -Xours/-Xtheirs to symbolic link merge

API clean-up around revision traversal.

* rs/lose-leak-pending:
  commit: remove unused function clear_commit_marks_for_object_array()
  revision: remove the unused flag leak_pending
  checkout: avoid using the rev_info flag leak_pending
  bundle: avoid using the rev_info flag leak_pending
  bisect: avoid using the rev_info flag leak_pending
  object: add clear_commit_marks_all()
  ref-filter: use clear_commit_marks_many() in do_merge_filter()
  commit: use clear_commit_marks_many() in remove_redundant()
  commit: avoid allocation in clear_commit_marks_many()

"git svn dcommit" did not take into account the fact that a
svn+ssh:// URL with a username@ (typically used for pushing) refers
to the same SVN repository without the username@ and failed when
svn.pushmergeinfo option is set.

* jm/svn-pushmergeinfo-fix:
  git-svn: fix svn.pushmergeinfo handling of svn+ssh usernames.

An old regression in "git describe --all $annotated_tag^0" has been
fixed.

* dk/describe-all-output-fix:
  describe: prepend "tags/" when describing tags with embedded name

More perf tests for threaded grep

* ab/perf-grep-threads:
  perf: amend the grep tests to test grep.threads

More abstraction of hash function from the codepath.

* bc/hash-algo:
  hash: update obsolete reference to SHA1_HEADER
  bulk-checkin: abstract SHA-1 usage
  csum-file: abstract uses of SHA-1
  csum-file: rename sha1file to hashfile
  read-cache: abstract away uses of SHA-1
  pack-write: switch various SHA-1 values to abstract forms
  pack-check: convert various uses of SHA-1 to abstract forms
  fast-import: switch various uses of SHA-1 to the_hash_algo
  sha1_file: switch uses of SHA-1 to the_hash_algo
  builtin/unpack-objects: switch uses of SHA-1 to the_hash_algo
  builtin/index-pack: improve hash function abstraction
  hash: create union for hash context allocation
  hash: move SHA-1 macros to hash.h

Doc update.

* nd/ignore-glob-doc-update:
  gitignore.txt: elaborate shell glob syntax

The way "git reset --hard" reports the commit the updated HEAD
points at is made consistent with the way how the commit title is
generated by the other parts of the system.  This matters when the
title is spread across physically multiple lines.

* tg/reset-hard-show-head-with-pretty:
  reset --hard: make use of the pretty machinery

* rs/cocci-strbuf-addf-to-addstr:
  cocci: simplify check for trivial format strings

* nd/trace-index-ops:
  trace: measure where the time is spent in the index-heavy operations

"make perf" enhancement.

* cc/perf-aggregate:
  perf/aggregate: sort JSON fields in output
  perf/aggregate: add --reponame option
  perf/aggregate: add --subsection option

More tests for wildmatch functions.

* ab/wildmatch-tests:
  wildmatch test: mark test as EXPENSIVE_ON_WINDOWS
  test-lib: add an EXPENSIVE_ON_WINDOWS prerequisite
  wildmatch test: create & test files on disk in addition to in-memory
  wildmatch test: perform all tests under all wildmatch() modes
  wildmatch test: use test_must_fail, not ! for test-wildmatch
  wildmatch test: remove dead fnmatch() test code
  wildmatch test: use a paranoia pattern from nul_match()
  wildmatch test: don't try to vertically align our output
  wildmatch test: use more standard shell style
  wildmatch test: indent with tabs, not spaces

Conversion from uchar[20] to struct object_id continues.

* po/object-id:
  sha1_file: rename hash_sha1_file_literally
  sha1_file: convert write_loose_object to object_id
  sha1_file: convert force_object_loose to object_id
  sha1_file: convert write_sha1_file to object_id
  notes: convert write_notes_tree to object_id
  notes: convert combine_notes_* to object_id
  commit: convert commit_tree* to object_id
  match-trees: convert splice_tree to object_id
  cache: clear whole hash buffer with oidclr
  sha1_file: convert hash_sha1_file to object_id
  dir: convert struct sha1_stat to use object_id
  sha1_file: convert pretend_sha1_file to object_id

"git pull --rebase" did not pass verbosity setting down when
recursing into a submodule.

* sb/pull-rebase-submodule:
  builtin/pull: respect verbosity settings in submodules

Avoid mmapping small files while using packed refs (especially ones
with zero size, which would cause later munmap() to fail).

* kg/packed-ref-cache-fix:
  packed_ref_cache: don't use mmap() for small files
  load_contents(): don't try to mmap an empty file
  packed_ref_iterator_begin(): make optimization more general
  find_reference_location(): make function safe for empty snapshots
  create_snapshot(): use `xmemdupz()` rather than a strbuf
  struct snapshot: store `start` rather than `header_len`

Plug recently introduced leaks in fsck.

* jt/fsck-code-cleanup:
  fsck: fix leak when traversing trees

* en/merge-recursive-fixes:
  merge-recursive: add explanation for src_entry and dst_entry
  merge-recursive: fix logic ordering issue
  Tighten and correct a few testcases for merging and cherry-picking

Error message fix.

* jc/worktree-add-short-help:
  worktree: say that "add" takes an arbitrary commit in short-help

Push the submodule version of collision-detecting SHA-1 hash
implementation a bit harder on builders.

* ab/sha1dc-build:
  sha1dc_git.h: re-arrange an ifdef chain for a subsequent change
  Makefile: under "make dist", include the sha1collisiondetection submodule
  Makefile: don't error out under DC_SHA1_EXTERNAL if DC_SHA1_SUBMODULE=auto

Subsequent patches will introduce file formats that make use of a fanout
array and a sorted table containing hashes, just like packfiles.
Refactor the hash search in packfile.c into its own function, so that
those patches can make use of it as well.
Signed-off-by: NJonathan Tan <jonathantanmy@google.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

In commit 628522ec ("sha1-lookup: more memory efficient search in
sorted list of SHA-1", 2008-04-09), a different algorithm for searching
a sorted list was introduced, together with a set of log statements
guarded by GIT_DEBUG_LOOKUP that are invoked both when using that
algorithm and when using the existing binary search. Those log
statements was meant for experiments and debugging, but with the removal
of the aforementioned different algorithm in commit f1068efe
("sha1_file: drop experimental GIT_USE_LOOKUP search", 2017-08-09),
those log statements are probably no longer necessary.

Remove those statements.
Signed-off-by: NJonathan Tan <jonathantanmy@google.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>