A new hook "post-index-change" is called when the on-disk index
file changes, which can help e.g. a virtualized working tree
implementation.

* bp/post-index-change-hook:
  read-cache: add post-index-change hook

CFLAGS now can be tweaked when invoking Make while using
DEVELOPER=YesPlease; this did not work well before.

* ab/makefile-help-devs-more:
  Makefile: allow for combining DEVELOPER=1 and CFLAGS="..."
  Makefile: move the setting of *FLAGS closer to "include"
  Makefile: Move *_LIBS assignment into its own section
  Makefile: add/remove comments at top and tweak whitespace
  Makefile: move "strip" assignment down from flags
  Makefile: remove an out-of-date comment

The final report from "git bisect" used to show the suspected
culprit using a raw "diff-tree", with which there is no output for
a merge commit.  This has been updated to use a more modern and
human readable output that still is concise enough.

* jk/bisect-final-output:
  bisect: make diff-tree output prettier
  bisect: fix internal diff-tree config loading
  bisect: use string arguments to feed internal diff-tree

"git rebase" that was reimplemented in C did not set ORIG_HEAD
correctly, which has been corrected.

* js/rebase-orig-head-fix:
  built-in rebase: set ORIG_HEAD just once, before the rebase
  built-in rebase: demonstrate that ORIG_HEAD is not set correctly
  built-in rebase: use the correct reflog when switching branches
  built-in rebase: no need to check out `onto` twice

Dev support.

* js/stress-test-ui-tweak:
  tests: introduce --stress-jobs=<N>
  tests: let --stress-limit=<N> imply --stress

"git fsck --connectivity-only" omits computation necessary to sift
the objects that are not reachable from any of the refs into
unreachable and dangling.  This is now enabled when dangling
objects are requested (which is done by default, but can be
overridden with the "--no-dangling" option).

* jk/fsck-doc:
  fsck: always compute USED flags for unreachable objects
  doc/fsck: clarify --connectivity-only behavior

On platforms where "git fetch" is killed with SIGPIPE (e.g. OSX),
the upload-pack that runs on the other end that hangs up after
detecting an error could cause "git fetch" to die with a signal,
which led to a flakey test.  "git fetch" now ignores SIGPIPE during
the network portion of its operation (this is not a problem as we
check the return status from our write(2)s).

* jk/no-sigpipe-during-network-transport:
  fetch: ignore SIGPIPE during network operation
  fetch: avoid calling write_or_die()

A recent update broke "is this object available to us?" check for
well-known objects like an empty tree (which should yield "yes",
even when there is no on-disk object for an empty tree), which has
been corrected.

* jk/virtual-objects-do-exist:
  rev-list: allow cached objects in existence check

"git stash" rewritten in C.

* ps/stash-in-c: (28 commits)
  tests: add a special setup where stash.useBuiltin is off
  stash: optionally use the scripted version again
  stash: add back the original, scripted `git stash`
  stash: convert `stash--helper.c` into `stash.c`
  stash: replace all `write-tree` child processes with API calls
  stash: optimize `get_untracked_files()` and `check_changes()`
  stash: convert save to builtin
  stash: make push -q quiet
  stash: convert push to builtin
  stash: convert create to builtin
  stash: convert store to builtin
  stash: convert show to builtin
  stash: convert list to builtin
  stash: convert pop to builtin
  stash: convert branch to builtin
  stash: convert drop and clear to builtin
  stash: convert apply to builtin
  stash: mention options in `show` synopsis
  stash: add tests for `git stash show` config
  stash: rename test cases to be more descriptive
  ...

The setup code has been cleaned up to avoid leaks around the
repository_format structure.

* ma/clear-repository-format:
  setup: fix memory leaks with `struct repository_format`
  setup: free old value before setting `work_tree`

The command line parser of "git commit-tree" has been rewritten to
use the parse-options API.

* br/commit-tree-parseopt:
  commit-tree: utilize parse-options api

"git config --type=color ..." is meant to replace "git config --get-color"
but there is a slight difference that wasn't documented, which is
now fixed.

* jk/config-type-color-ends-with-lf:
  config: document --type=color output is a complete line

* master:
  gitk: Update Bulgarian translation (317t)

Doc update.

* dl/reset-doc-no-wrt-abbrev:
  git-reset.txt: clarify documentation

Doc update.

* ja/dir-rename-doc-markup-fix:
  Doc: fix misleading asciidoc formating

A GSoC micro.

* ra/t3600-test-path-funcs:
  t3600: use helpers to replace test -d/f/e/s <path>
  t3600: modernize style
  test functions: add function `test_file_not_empty`

Third batch to teach the diff machinery to use the parse-options
API.

* nd/diff-parseopt-3:
  diff-parseopt: convert --submodule
  diff-parseopt: convert --ignore-submodules
  diff-parseopt: convert --textconv
  diff-parseopt: convert --ext-diff
  diff-parseopt: convert --quiet
  diff-parseopt: convert --exit-code
  diff-parseopt: convert --color-words
  diff-parseopt: convert --word-diff-regex
  diff-parseopt: convert --word-diff
  diff-parseopt: convert --[no-]color
  diff-parseopt: convert --[no-]follow
  diff-parseopt: convert -R
  diff-parseopt: convert -a|--text
  diff-parseopt: convert --full-index
  diff-parseopt: convert --binary
  diff-parseopt: convert --anchored
  diff-parseopt: convert --diff-algorithm
  diff-parseopt: convert --histogram
  diff-parseopt: convert --patience
  diff-parseopt: convert --[no-]indent-heuristic

Help developers by making it easier to run most of the tests under
different versions of over-the-wire protocols.

* jt/test-protocol-version:
  t5552: compensate for v2 filtering ref adv.
  tests: fix protocol version for overspecifications
  t5700: only run with protocol version 1
  t5512: compensate for v0 only sending HEAD symrefs
  t5503: fix overspecification of trace expectation
  tests: always test fetch of unreachable with v0
  t5601: check ssh command only with protocol v0
  tests: define GIT_TEST_PROTOCOL_VERSION

"git log -L<from>,<to>:<path>" with "-s" did not suppress the patch
output as it should.  This has been corrected.

* jk/line-log-with-patch:
  line-log: detect unsupported formats
  line-log: suppress diff output with "-s"

When the "clean" filter can reduce the size of a huge file in the
working tree down to a small "token" (a la Git LFS), there is no
point in allocating a huge scratch area upfront, but the buffer is
sized based on the original file size.  The convert mechanism now
allocates very minimum and reallocates as it receives the output
from the clean filter process.

* jh/resize-convert-scratch-buffer:
  convert: avoid malloc of original file size

Doc update.

* dl/ignore-docs:
  docs: move core.excludesFile from git-add to gitignore
  git-clean.txt: clarify ignore pattern files

Further fixes to "git stash" reimplemented in C.

* js/stash-in-c-pathspec-fix:
  stash: pass pathspec as pointer
  built-in stash: handle :(glob) pathspecs again
  legacy stash: fix "rudimentary backport of -q"

"git rebase" uses the refs/rewritten/ hierarchy to store its
intermediate states, which inherently makes the hierarchy per
worktree, but it didn't quite work well.

* nd/rewritten-ref-is-per-worktree:
  Make sure refs/rewritten/ is per-worktree
  files-backend.c: reduce duplication in add_per_worktree_entries_to_dir()
  files-backend.c: factor out per-worktree code in loose_fill_ref_dir()

"git rebase --rebase-merges" replaces its old "--preserve-merges"
option; the latter is now marked as deprecated.

* js/rebase-deprecate-preserve-merges:
  rebase: deprecate --preserve-merges

Code clean-up.

* tb/stash-in-c-unused-param-fix:
  stash: drop unused parameter

"git worktree add" used to do a "find an available name with stat
and then mkdir", which is race-prone.  This has been fixed by using
mkdir and reacting to EEXIST in a loop.

* ms/worktree-add-atomic-mkdir:
  worktree: fix worktree add race

Swap submitGit with GitGitGadget as a way to submit patches based
on GitHub PR to us.

* jk/promote-ggg:
  point pull requesters to GitGitGadget

Error message update.

* jt/submodule-fetch-errmsg:
  submodule: explain first attempt failure clearly

Test cleanup.

* ar/t4150-remove-cruft:
  t4150: remove unused variable

Build update for SHA-1 with collision detection.

* jk/sha1dc:
  Makefile: fix unaligned loads in sha1dc with UBSan

* master:
  The third batch

Build fix around use of asciidoctor instead of asciidoc

* ma/asciidoctor-fixes:
  asciidoctor-extensions: fix spurious space after linkgit
  Documentation/Makefile: add missing dependency on asciidoctor-extensions
  Documentation/Makefile: add missing xsl dependencies for manpages

Documentation mark-up fixes.

* ma/asciidoctor-fixes-more:
  Documentation: turn middle-of-line tabs into spaces
  git-svn.txt: drop escaping '\' that ends up being rendered
  git.txt: remove empty line before list continuation
  config/fsck.txt: avoid starting line with dash
  config/diff.txt: drop spurious backtick

remote-http transport did not anonymize URLs reported in its error
messages at places.

* js/anonymize-remote-curl-diag:
  curl: anonymize URLs in error messages and warnings

Error messages given from the http transport have been updated so
that they can be localized.

* js/remote-curl-i18n:
  remote-curl: mark all error messages for translation

"git init" forgot to read platform-specific repository
configuration, which made Windows port to ignore settings of
core.hidedotfiles, for example.

* js/init-db-update-for-mingw:
  mingw: respect core.hidedotfiles = false in git-init again

"git subtree" (in contrib/) update.

* dl/subtree-limit-to-one-rev:
  contrib/subtree: ensure only one rev is provided

A corner-case object name ambiguity while the sequencer machinery
is working (e.g. "rebase -i -x") has been (half) fixed.

* js/get-short-oid-drop-cache:
  get_oid(): when an object was not found, try harder
  sequencer: move stale comment into correct location
  sequencer: improve error message when an OID could not be parsed
  rebase -i: demonstrate obscure loose object cache bug

"git format-patch" used overwrite an existing patch/cover-letter
file.  A new "--no-clobber" option stops it.

* jc/format-patch-error-check:
  format-patch: notice failure to open cover letter for writing
  builtin/log: downcase the beginning of error messages

The scripted version of "git rebase -i" wrote and rewrote the todo
list many times during a single step of its operation, and the
recent C-rewrite made a faithful conversion of the logic to C.  The
implementation has been updated to carry necessary information
around in-core to avoid rewriting the same file over and over
unnecessarily.

* ag/sequencer-reduce-rewriting-todo:
  rebase--interactive: move transform_todo_file()
  sequencer: use edit_todo_list() in complete_action()
  rebase-interactive: rewrite edit_todo_list() to handle the initial edit
  rebase-interactive: append_todo_help() changes
  rebase-interactive: use todo_list_write_to_file() in edit_todo_list()
  sequencer: refactor skip_unnecessary_picks() to work on a todo_list
  rebase--interactive: move rearrange_squash_in_todo_file()
  rebase--interactive: move sequencer_add_exec_commands()
  sequencer: change complete_action() to use the refactored functions
  sequencer: make sequencer_make_script() write its script to a strbuf
  sequencer: refactor rearrange_squash() to work on a todo_list
  sequencer: refactor sequencer_add_exec_commands() to work on a todo_list
  sequencer: refactor check_todo_list() to work on a todo_list
  sequencer: introduce todo_list_write_to_file()
  sequencer: refactor transform_todos() to work on a todo_list
  sequencer: remove the 'arg' field from todo_item
  sequencer: make the todo_list structure public
  sequencer: changes in parse_insn_buffer()

Doc updates.

* pw/rerere-autoupdate:
  merge: tweak --rerere-autoupdate documentation
  am/cherry-pick/rebase/revert: document --rerere-autoupdate

Test framework update to more robustly clean up leftover files and
processes after tests are done.

* sg/test-atexit:
  t9811-git-p4-label-import: fix pipeline negation
  git p4 test: disable '-x' tracing in the p4d watchdog loop
  git p4 test: simplify timeout handling
  git p4 test: clean up the p4d cleanup functions
  git p4 test: use 'test_atexit' to kill p4d and the watchdog process
  t0301-credential-cache: use 'test_atexit' to stop the credentials helper
  tests: use 'test_atexit' to stop httpd
  git-daemon: use 'test_atexit` to stop 'git-daemon'
  test-lib: introduce 'test_atexit'
  t/lib-git-daemon: make sure to kill the 'git-daemon' process
  test-lib: fix interrupt handling with 'dash' and '--verbose-log -x'

"git checkout -f <branch>" while the index has an unmerged path
incorrectly left some paths in an unmerged state, which has been
corrected.

* nd/checkout-f-while-conflicted-fix:
  unpack-trees: fix oneway_merge accidentally carry over stage index

Doc update.

* tg/glossary-overlay:
  glossary: add definition for overlay

Docfix.

* mh/pack-protocol-doc-fix:
  fix pack protocol example client/server communication

Typofixes.

* ab/doc-misc-typofixes:
  doc: fix typos in man pages

Code cleanup in the test framework.

* jk/perf-lib-tee:
  perf-lib.sh: rely on test-lib.sh for --tee handling

Retire scripted "git rebase" implementation.

* ab/drop-scripted-rebase:
  rebase: remove the rebase.useBuiltin setting

Work-around extra warning from bash in our tests.

* tz/t4038-bash-redirect-target-workaround:
  t4038-diff-combined: quote paths with whitespace

Dev support update to make it easier to compare two formatted
results from our documentation.

* ma/doc-diff-doc-vs-doctor-comparison:
  doc-diff: add `--cut-header-footer`
  doc-diff: support diffing from/to AsciiDoc(tor)
  doc-diff: let `render_tree()` take an explicit directory name
  Doc: auto-detect changed build flags

The completion helper code now pays attention to repository-local
configuration (when available), which allows --list-cmds to honour
a repository specific setting of completion.commands, for example.

* tz/completion:
  completion: use __git when calling --list-cmds
  completion: fix multiple command removals
  t9902: test multiple removals via completion.commands
  git: read local config in --list-cmds

Fix some code that passed a NULL when a va_list was expected.

* tb/trace2-va-list-fix:
  trace2: NULL is not allowed for va_list

A regression fix.

* tg/stash-in-c-show-default-to-p-fix:
  stash: setup default diff output format if necessary

Code cleanup

* jk/unused-params-even-more:
  parse_opt_ref_sorting: always use with NONEG flag
  pretty: drop unused strbuf from parse_padding_placeholder()
  pretty: drop unused "type" parameter in needs_rfc2047_encoding()
  parse-options: drop unused ctx parameter from show_gitcomp()
  fetch_pack(): drop unused parameters
  report_path_error(): drop unused prefix parameter
  unpack-trees: drop unused error_type parameters
  unpack-trees: drop name_entry from traverse_by_cache_tree()
  test-date: drop unused "now" parameter from parse_dates()
  update-index: drop unused prefix_length parameter from do_reupdate()
  log: drop unused "len" from show_tagger()
  log: drop unused rev_info from early output
  revision: drop some unused "revs" parameters

Doc about the above.

* nd/checkout-m-doc-update:
  checkout.txt: note about losing staged changes with --merge

Fourth batch to teach the diff machinery to use the parse-options
API.

* nd/diff-parseopt-4:
  am: avoid diff_opt_parse()
  diff --no-index: use parse_options() instead of diff_opt_parse()
  range-diff: use parse_options() instead of diff_opt_parse()
  diff.c: allow --no-color-moved-ws
  diff-parseopt: convert --color-moved-ws
  diff-parseopt: convert --[no-]color-moved
  diff-parseopt: convert --inter-hunk-context
  diff-parseopt: convert --no-prefix
  diff-parseopt: convert --line-prefix
  diff-parseopt: convert --[src|dst]-prefix
  diff-parseopt: convert --[no-]abbrev
  diff-parseopt: convert --diff-filter
  diff-parseopt: convert --find-object
  diff-parseopt: convert -O
  diff-parseopt: convert --pickaxe-all|--pickaxe-regex
  diff-parseopt: convert -S|-G
  diff-parseopt: convert -l
  diff-parseopt: convert -z
  diff-parseopt: convert --ita-[in]visible-in-index
  diff-parseopt: convert --ws-error-highlight

A corner case bug in the refs API has been corrected.

* jk/refs-double-abort:
  refs/files-backend: don't look at an aborted transaction
  refs/files-backend: handle packed transaction prepare failure

Unicode update.

* bb/unicode-12:
  unicode: update the width tables to Unicode 12

"git multi-pack-index verify" did not scale well with the number of
packfiles, which is being improved.

* jh/midx-verify-too-many-packs:
  midx: during verify group objects by packfile to speed verification
  midx: add progress indicators in multi-pack-index verify
  trace2:data: add trace2 data to midx
  progress: add sparse mode to force 100% complete message

dumb-http walker has been updated to share more error recovery
strategy with the normal codepath.

* jk/http-walker-status-fix:
  http: use normalize_curl_result() instead of manual conversion
  http: normalize curl results for dumb loose and alternates fetches
  http: factor out curl result code normalization

Test update.

* jt/t5551-protocol-v2-does-not-have-half-auth:
  t5551: mark half-auth no-op fetch test as v0-only

Code cleanup.

* sg/t5318-cleanup:
  t5318-commit-graph: remove unused variable

Code clean-up around a much-less-important-than-it-used-to-be
update_server_info() funtion.

* jk/server-info-rabbit-hole:
  update_info_refs(): drop unused force parameter
  server-info: drop objdirlen pointer arithmetic
  server-info: drop nr_alloc struct member
  server-info: use strbuf to read old info/packs file
  server-info: simplify cleanup in parse_pack_def()
  server-info: fix blind pointer arithmetic
  http: simplify parsing of remote objects/info/packs
  packfile: fix pack basename computation
  midx: check both pack and index names for containment
  t5319: drop useless --buffer from cat-file
  t5319: fix bogus cat-file argument
  pack-revindex: open index if necessary
  packfile.h: drop extern from function declarations

The message given when "git commit -a <paths>" errors out has been
updated.

* nd/commit-a-with-paths-msg-update:
  commit: improve error message in "-a <paths>" case

Clean-up markup in the documentation suite.

* cb/doco-mono:
  doc: format pathnames and URLs as monospace.
  doc/CodingGuidelines: URLs and paths as monospace

"git cherry-pick --options A..B", after giving control back to the
user to ask help resolving a conflicted step, did not honor the
options it originally received, which has been corrected.

* pw/cherry-pick-continue:
  cherry-pick --continue: remember options
  cherry-pick: demonstrate option amnesia
  sequencer: break some long lines

"git difftool" can now run outside a repository.

* js/difftool-no-index:
  difftool: allow running outside Git worktrees with --no-index
  parse-options: make OPT_ARGUMENT() more useful
  difftool: remove obsolete (and misleading) comment

"git checkout -m <other>" was about carrying the differences
between HEAD and the working-tree files forward while checking out
another branch, and ignored the differences between HEAD and the
index.  The command has been taught to abort when the index and the
HEAD are different.

* nd/checkout-m:
  checkout: prevent losing staged changes with --merge
  read-tree: add --quiet
  unpack-trees: rename "gently" flag to "quiet"
  unpack-trees: keep gently check inside add_rejected_path

Fix various glitches in "git gc" around reflog handling.

* ab/gc-reflog:
  gc: handle & check gc.reflogExpire config
  reflog tests: assert lack of early exit with expiry="never"
  reflog tests: test for the "points nowhere" warning
  reflog tests: make use of "test_config" idiom
  gc: refactor a "call me once" pattern
  gc: convert to using the_hash_algo
  gc: remove redundant check for gc_auto_threshold

Code cleanup with more careful error checking before using data
read from the commit-graph file.

* ab/commit-graph-fixes:
  commit-graph: improve & i18n error messages
  commit-graph write: don't die if the existing graph is corrupt
  commit-graph verify: detect inability to read the graph
  commit-graph: don't pass filename to load_commit_graph_one_fd_st()
  commit-graph: don't early exit(1) on e.g. "git status"
  commit-graph: fix segfault on e.g. "git status"
  commit-graph tests: test a graph that's too small
  commit-graph tests: split up corrupt_graph_and_verify()

A buglet in configuration parser has been fixed.

* nd/include-if-wildmatch:
  config: correct '**' matching in includeIf patterns

Dev support update.

* js/check-docs-exe:
  check-docs: fix for setups where executables have an extension
  check-docs: do not expect guide pages to correspond to commands
  check-docs: really look at the documented commands again
  docs: do not document the `git remote-testgit` command
  docs: move gitremote-helpers into section 7

Doc updates.

* tz/asciidoctor-fixes:
  Documentation/git-status: fix titles in porcelain v2 section
  Documentation/rev-list-options: wrap --date=<format> block with "--"

Update our support to format documentation in the CI environment,
either with AsciiDoc ro Asciidoctor.

* sg/asciidoctor-in-ci:
  ci: fix AsciiDoc/Asciidoctor stderr check in the documentation build job
  ci: stick with Asciidoctor v1.5.8 for now
  ci: install Asciidoctor in 'ci/install-dependencies.sh'
  Documentation/technical/protocol-v2.txt: fix formatting
  Documentation/technical/api-config.txt: fix formatting
  Documentation/git-diff-tree.txt: fix formatting

A progress indicator has been added to the "index-pack" step, which
often makes users wait for completion during "git clone".

* sg/index-pack-progress:
  index-pack: show progress while checking objects

Allow tracing of Git executable while running out tests.

* ab/test-lib-pass-trace2-env:
  test-lib: whitelist GIT_TR2_* in the environment

Performance fix around "git fetch" that grabs many refs.

* jt/fetch-pack-wanted-refs-optim:
  fetch-pack: binary search when storing wanted-refs

Doc update.

* nd/interpret-trailers-docfix:
  interpret-trailers.txt: start the desc line with a capital letter

Fix for protocol v2 support in "git fetch-pack" of shallow clones.

* jt/fetch-no-update-shallow-in-proto-v2:
  fetch-pack: respect --no-update-shallow in v2
  fetch-pack: call prepare_shallow_info only if v0

"git fast-import" update.

* en/fast-import-parsing-fix:
  fast-import: fix erroneous handling of get-mark with empty orphan commits
  fast-import: only allow cat-blob requests where it makes sense
  fast-import: check most prominent commands first
  git-fast-import.txt: fix wording about where ls command can appear
  t9300: demonstrate bug with get-mark and empty orphan commits

The documentation for "git read-tree --reset -u" has been updated.

* nd/read-tree-reset-doc:
  read-tree.txt: clarify --reset and worktree changes

The tests have been updated not to rely on the abbreviated option
names the parse-options API offers, to protect us from an
abbreviated form of an option that used to be unique within the
command getting non-unique when a new option that share the same
prefix is added.

* js/spell-out-options-in-tests:
  tests: disallow the use of abbreviated options (by default)
  tests (pack-objects): use the full, unabbreviated `--revs` option
  tests (status): spell out the `--find-renames` option in full
  tests (push): do not abbreviate the `--follow-tags` option
  t5531: avoid using an abbreviated option
  t7810: do not abbreviate `--no-exclude-standard` nor `--invert-match`
  tests (rebase): spell out the `--force-rebase` option
  tests (rebase): spell out the `--keep-empty` option

Conversion from unsigned char[20] to struct object_id continues.

* bc/hash-transition-16: (35 commits)
  gitweb: make hash size independent
  Git.pm: make hash size independent
  read-cache: read data in a hash-independent way
  dir: make untracked cache extension hash size independent
  builtin/difftool: use parse_oid_hex
  refspec: make hash size independent
  archive: convert struct archiver_args to object_id
  builtin/get-tar-commit-id: make hash size independent
  get-tar-commit-id: parse comment record
  hash: add a function to lookup hash algorithm by length
  remote-curl: make hash size independent
  http: replace sha1_to_hex
  http: compute hash of downloaded objects using the_hash_algo
  http: replace hard-coded constant with the_hash_algo
  http-walker: replace sha1_to_hex
  http-push: remove remaining uses of sha1_to_hex
  http-backend: allow 64-character hex names
  http-push: convert to use the_hash_algo
  builtin/pull: make hash-size independent
  builtin/am: make hash size independent
  ...

Performance fix around "git blame", especially in a linear history
(which is the norm we should optimize for).

* dk/blame-keep-origin-blob:
  blame.c: don't drop origin blobs as eagerly

Code clean-up.

* dl/flex-str-cocci:
  cocci: FLEX_ALLOC_MEM to FLEX_ALLOC_STR
  midx.c: convert FLEX_ALLOC_MEM to FLEX_ALLOC_STR

Performance fix for "rev-list --parents -- pathspec".

* jk/revision-rewritten-parents-in-prio-queue:
  revision: use a prio_queue to hold rewritten parents

"git mergetool" learned to offer Sublime Merge (smerge) as one of
its backends.

* da/smerge:
  contrib/completion: add smerge to the mergetool completion candidates
  mergetools: add support for smerge (Sublime Merge)

"git submodule" learns "set-branch" subcommand that allows the
submodule.*.branch settings to be modified.

* dl/submodule-set-branch:
  submodule: teach set-branch subcommand
  submodule--helper: teach config subcommand --unset
  git-submodule.txt: "--branch <branch>" option defaults to 'master'

Update docs around "gc".

* ab/gc-docs:
  gc docs: remove incorrect reference to gc.auto=0
  gc docs: clarify that "gc" doesn't throw away referenced objects
  gc docs: note "gc --aggressive" in "fast-import"
  gc docs: downplay the usefulness of --aggressive
  gc docs: note how --aggressive impacts --window & --depth
  gc docs: fix formatting for "gc.writeCommitGraph"
  gc docs: re-flow the "gc.*" section in "config"
  gc docs: include the "gc.*" section from "config" in "gc"
  gc docs: clean grammar for "gc.bigPackThreshold"
  gc docs: stop noting "repack" flags
  gc docs: modernize the advice for manually running "gc"

While running "git diff" in a lazy clone, we can upfront know which
missing blobs we will need, instead of waiting for the on-demand
machinery to discover them one by one.  Aim to achieve better
performance by batching the request for these promised blobs.

* jt/batch-fetch-blobs-in-diff:
  diff: batch fetching of missing blobs
  sha1-file: support OBJECT_INFO_FOR_PREFETCH

Updating the display with progress message has been cleaned up to
deal better with overlong messages.

* sg/overlong-progress-fix:
  progress: break too long progress bar lines
  progress: clear previous progress update dynamically
  progress: assemble percentage and counters in a strbuf before printing
  progress: make display_progress() return void

Docfix.

* po/rerere-doc-fmt:
  rerere doc: quote `rerere.enabled`

Docfix.

* po/describe-not-necessarily-7:
  describe doc: remove '7-char' abbreviation reference

Debugging code fix.

* tg/ls-files-debug-format-fix:
  ls-files: use correct format string

"git blame -- path" in a non-bare repository starts blaming from
the working tree, and the same command in a bare repository errors
out because there is no working tree by definition.  The command
has been taught to instead start blaming from the commit at HEAD,
which is more useful.

* sg/blame-in-bare-start-at-head:
  blame: default to HEAD in a bare repo when no start commit is given

Doc formatting fix.

* tz/doc-apostrophe-no-longer-needed:
  Documentation/git-show-branch: avoid literal {apostrophe}

Test fix.

* js/t3301-unbreak-notes-test:
  t3301: fix false negative

An underallocation in the code to read the untracked cache
extension has been corrected.

* js/untracked-cache-allocfix:
  untracked cache: fix off-by-one

A test update.

* km/t3000-retitle:
  t3000 (ls-files -o): widen description to reflect current tests