Commit Graph

14689 Commits

Author SHA1 Message Date
Junio C Hamano
2fc9e9ca3c The twelfth batch
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-30 14:24:32 -08:00
Junio C Hamano
a5eaa76b30 Merge branch 'ar/markup-em-dash'
Doc mark-up updates.

* ar/markup-em-dash:
  Documentation: render dash correctly
2023-01-30 14:24:24 -08:00
Junio C Hamano
4ac326f64f Merge branch 'po/pretty-format-columns-doc'
Clarify column-padding operators in the pretty format string.

* po/pretty-format-columns-doc:
  doc: pretty-formats note wide char limitations, and add tests
  doc: pretty-formats describe use of ellipsis in truncation
  doc: pretty-formats document negative column alignments
  doc: pretty-formats: delineate `%<|(` parameter values
  doc: pretty-formats: separate parameters from placeholders
2023-01-30 14:24:22 -08:00
Junio C Hamano
06f2b5fb70 Merge branch 'jc/doc-checkout-b'
Clarify how "checkout -b/-B" and "git branch [-f]" are similar but
different in the documentation.

* jc/doc-checkout-b:
  checkout: document -b/-B to highlight the differences from "git branch"
2023-01-30 14:24:21 -08:00
Junio C Hamano
5cc9858f1b The eleventh batch
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-27 08:51:41 -08:00
Junio C Hamano
8f82904caf Merge branch 'jc/doc-branch-update-checked-out-branch'
Document that "branch -f <branch>" disables only the safety to
avoid recreating an existing branch.

* jc/doc-branch-update-checked-out-branch:
  branch: document `-f` and linked worktree behaviour
2023-01-27 08:51:41 -08:00
Junio C Hamano
3e6417681c Merge branch 'sa/cat-file-mailmap--batch-check'
Docfix.

* sa/cat-file-mailmap--batch-check:
  git-cat-file.txt: fix list continuations rendering literally
2023-01-27 08:51:40 -08:00
Junio C Hamano
5dec958dcf The tenth batch
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-23 13:39:52 -08:00
Junio C Hamano
577bff3a81 Merge branch 'kn/attr-from-tree'
"git check-attr" learned to take an optional tree-ish to read the
.gitattributes file from.

* kn/attr-from-tree:
  attr: add flag `--source` to work with tree-ish
  t0003: move setup for `--all` into new block
2023-01-23 13:39:51 -08:00
Andrei Rybak
70661d288b Documentation: render dash correctly
Three hyphens are rendered verbatim in documentation, so "--" has to be
used to produce a dash.  Fix asciidoc output for dashes.  This is
similar to previous commits f0b922473e (Documentation: render special
characters correctly, 2021-07-29) and de82095a95 (doc
hash-function-transition: fix asciidoc output, 2021-02-05).

Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-23 09:40:14 -08:00
Junio C Hamano
56c8fb1e95 The ninth batch
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-21 17:22:01 -08:00
Junio C Hamano
86ccd39a74 Merge branch 'yc/doc-fetch-fix'
Doc fix.

* yc/doc-fetch-fix:
  doc: fix non-existent config name
2023-01-21 17:22:01 -08:00
Junio C Hamano
9c2003a6cb Merge branch 'pb/doc-orig-head'
Document ORIG_HEAD a bit more.

* pb/doc-orig-head:
  git-rebase.txt: add a note about 'ORIG_HEAD' being overwritten
  revisions.txt: be explicit about commands writing 'ORIG_HEAD'
  git-merge.txt: mention 'ORIG_HEAD' in the Description
  git-reset.txt: mention 'ORIG_HEAD' in the Description
  git-cherry-pick.txt: do not use 'ORIG_HEAD' in example
2023-01-21 17:22:00 -08:00
Junio C Hamano
b106341d57 Merge branch 'yo/doc-use-more-switch-c'
Doc update.

* yo/doc-use-more-switch-c:
  doc: add "git switch -c" as another option on detached HEAD
2023-01-21 17:22:00 -08:00
Junio C Hamano
f2744aa37e Merge branch 'ar/bisect-doc-update'
Doc update.

* ar/bisect-doc-update:
  git-bisect-lk2009: update nist report link
  git-bisect-lk2009: update java code conventions link
2023-01-21 17:21:59 -08:00
Junio C Hamano
c253d61137 Merge branch 'jc/doc-diff-patch.txt'
Doc update.

* jc/doc-diff-patch.txt:
  docs: link generating patch sections
2023-01-21 17:21:58 -08:00
Junio C Hamano
fc2735f427 Merge branch 'es/hooks-and-local-env'
Doc update for environment variables set when hooks are invoked.

* es/hooks-and-local-env:
  githooks: discuss Git operations in foreign repositories
2023-01-21 17:21:58 -08:00
Junio C Hamano
904d404274 The eighth batch
The cURL one hasn't cooked for a week in 'next', but let's fast
track it so that linux-musl CI job would be happy.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-20 15:36:22 -08:00
Philip Oakley
540e7bc477 doc: pretty-formats note wide char limitations, and add tests
The previous commits added clarifications to the column alignment
placeholders, note that the spaces are optional around the parameters.

Also, a proposed extension [1] to allow hard truncation (without
ellipsis '..') highlighted that the existing code does not play well
with wide characters, such as Asian fonts and emojis.

For example, N wide characters take 2N columns so won't fit an odd number
column width, causing misalignment somewhere.

Further analysis also showed that decomposed characters, e.g. separate
`a` + `umlaut` Unicode code-points may also be mis-counted, in some cases
leaving multiple loose `umlauts` all combined together.

Add some notes about these limitations, and add basic tests to demonstrate
them.

The chosen solution for the tests is to substitute any wide character
that overlaps a splitting boundary for the unicode vertical ellipsis
code point as a rare but 'obvious' substitution.

An alternative could be the substitution with a single dot '.' which
matches regular expression usage, and our two dot ellipsis, and further
in scenarios where the bulk of the text is wide characters, would be
obvious. In mainly 'ascii' scenarios a singleton emoji being substituted
by a dot could be confusing.

It is enough that the tests fail cleanly. The final choice for the
substitute character can be deferred.

[1]
https://lore.kernel.org/git/20221030185614.3842-1-philipoakley@iee.email/

Signed-off-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-19 14:35:15 -08:00
Philip Oakley
b5cd634d7a doc: pretty-formats describe use of ellipsis in truncation
Commit a7f01c6b4d (pretty: support truncating in %>, %< and %><,
2013-04-19) added the use of ellipsis when truncating placeholder
values.

Show our 'two dot' ellipsis, and examples for the left, middle and
right truncation to avoid any confusion as to which end of the string
is adjusted. (cf justification and sub-string).

Signed-off-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-19 14:35:15 -08:00
Philip Oakley
63792c564c doc: pretty-formats document negative column alignments
Commit 066790d7cb (pretty.c: support <direction>|(<negative number>) forms,
2016-06-16) added the option for right justified column alignment without
updating the documentation.

Add an explanation of its use of negative column values.

Signed-off-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-19 14:35:15 -08:00
Philip Oakley
8bcb8f8e22 doc: pretty-formats: delineate %<|( parameter values
Commit a57523428b (pretty: support padding placeholders, %< %> and %><,
2013-04-19) introduced column width place holders. It also added
separate column position `%<|(` placeholders for display screen based
placement.

Change the display screen parameter reference from 'N' to 'M' and
corresponding descriptives to make the distinction clearer.

Signed-off-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-19 14:35:15 -08:00
Philip Oakley
d664a7ad20 doc: pretty-formats: separate parameters from placeholders
Commit a57523428b (pretty: support padding placeholders, %< %> and %><,
2013-04-19) introduced columnated place holders. These placeholders
can be confusing as they contain `<` and `>` characters as part
of their placeholders adjacent to the `<N>` parameters.

Add spaces either side of the `<N>` parameters in the title line.
The code (strtol) will consume any spaces around the number values
(assuming they are passed as a quoted string with spaces).
Note that the spaces are optional.

Subsequent commits will clarify other confusions.

Signed-off-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-19 14:35:15 -08:00
Junio C Hamano
fedb8ea2df checkout: document -b/-B to highlight the differences from "git branch"
The existing text read as if "git checkout -b/-B name" were
equivalent to "git branch [-f] name", which clearly was not
what we wanted to say.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-19 09:44:08 -08:00
Junio C Hamano
bf08abac56 branch: document -f and linked worktree behaviour
"git branch -f name start" forces to recreate the named branch, but
the forcing does not defeat the "do not touch a branch that is
checked out elsewhere" safety valve.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-18 23:48:11 -08:00
Martin Ågren
8534bb4cb1 git-cat-file.txt: fix list continuations rendering literally
With Asciidoctor, all of the '+' introduced in a797c0ea04 ("cat-file:
add mailmap support to --batch-check option", 2022-12-20) render
literally rather than functioning as list continuations. With asciidoc,
this renders just fine. It's not too surprising that there is room for
ambiguity and surprises here, since we have lists within lists.

Simply replacing all of these '+' with empty lines makes this render
fine using both tools. Except, in the third hunk, where after this inner
'*' list ends, we want to continue with more contents of the outer list
item (`--batch-command=<format>`). We can solve any ambiguity here and
make this clear to both tools by wrapping the inner list in an open
block (using "--").

For consistency, let's wrap all three of these inner lists from
a797c0ea04 in open blocks. This also future-proofs us a little -- if we
ever gain more contents after any of those first two lists, as we did
already in a797c0ea04 for the third list, we're prepared and should
render fine with both asciidoc and Asciidoctor from the start.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-18 08:24:39 -08:00
Junio C Hamano
a7caae2729 Sync with 'maint' 2023-01-17 06:59:22 -08:00
Junio C Hamano
508386c6c5 Sync with 2.39.1 2023-01-16 12:11:58 -08:00
Junio C Hamano
262c45b6a1 The seventh batch
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-16 12:07:47 -08:00
Junio C Hamano
3ed618f28f Merge branch 'ar/dup-words-fixes'
Typofixes.

* ar/dup-words-fixes:
  *: fix typos which duplicate a word
2023-01-16 12:07:47 -08:00
Junio C Hamano
ffd9238685 Merge branch 'ds/omit-trailing-hash-in-index'
Introduce an optional configuration to allow the trailing hash that
protects the index file from bit flipping.

* ds/omit-trailing-hash-in-index:
  features: feature.manyFiles implies fast index writes
  test-lib-functions: add helper for trailing hash
  read-cache: add index.skipHash config option
  hashfile: allow skipping the hash function
2023-01-16 12:07:47 -08:00
Junio C Hamano
b242e89dff Merge branch 'tr/am--no-verify'
Conditionally skip the pre-applypatch and applypatch-msg hooks when
applying patches with 'git am'.

* tr/am--no-verify:
  am: allow passing --no-verify flag
2023-01-16 12:07:46 -08:00
Johannes Schindelin
c6ab91335a fsck: document the new gitattributes message IDs
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-16 12:03:14 -08:00
Karthik Nayak
47cfc9bd7d attr: add flag --source to work with tree-ish
The contents of the .gitattributes files may evolve over time, but "git
check-attr" always checks attributes against them in the working tree
and/or in the index. It may be beneficial to optionally allow the users
to check attributes taken from a commit other than HEAD against paths.

Add a new flag `--source` which will allow users to check the
attributes against a commit (actually any tree-ish would do). When the
user uses this flag, we go through the stack of .gitattributes files but
instead of checking the current working tree and/or in the index, we
check the blobs from the provided tree-ish object. This allows the
command to also be used in bare repositories.

Since we use a tree-ish object, the user can pass "--source
HEAD:subdirectory" and all the attributes will be looked up as if
subdirectory was the root directory of the repository.

We cannot simply use the `<rev>:<path>` syntax without the `--source`
flag, similar to how it is used in `git show` because any non-flag
parameter before `--` is treated as an attribute and any parameter after
`--` is treated as a pathname.

The change involves creating a new function `read_attr_from_blob`, which
given the path reads the blob for the path against the provided source and
parses the attributes line by line. This function is plugged into
`read_attr()` function wherein we go through the stack of attributes
files.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Toon Claes <toon@iotcl.com>
Co-authored-by: toon@iotcl.com
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-14 08:49:55 -08:00
Yukai Chou
ca554bf36c doc: fix non-existent config name
Replace non-existent `branch.<name>.fetch` to `remote.<repository>.fetch`, in
the first example in `git-fetch` doc, which was introduced in
d504f6975d (modernize fetch/merge/pull examples, 2009-10-21).

Rename placeholder `<name>` to `<repository>`, to be consistent with all other
uses in git docs, except that `git-config.txt` uses `remote.<name>.fetch` in
its "Variables" section.

Also add missing monospace markups.

Signed-off-by: Yukai Chou <muzimuzhi@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 17:33:32 -08:00
John Cai
ebdc46c242 docs: link generating patch sections
Currently, in the git-log documentation, the reference to generating
patches does not match the section title. This can make the section
"Generating patch text with -p" hard to find, since typically readers of
the documentation will copy and paste to search the page.

Let's make this more convenient for readers by linking it directly to
the section.

Since git-log pulls in diff-generate-patch.txt, we can provide a direct
link to the section. Otherwise, change the verbiage to match exactly
what the section title is, to at least make searching for it an easier
task.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 12:55:14 -08:00
Andrei Rybak
f5156f1885 git-bisect-lk2009: update nist report link
Commit d656218a83 (docs/bisect-lk2009: update nist report link,
2017-04-20) replaced a dead link to news release on nist.gov.  However,
this might be confusing to the reader (like myself) because the article
git-bisect-lk2009.txt quotes from the news release but the exact quote
cannot be found in the full report.  In addition to that, the link added
in 2017 is also dead in 2023.

Replace the reference to nist.gov with an version of the original NIST
news release archived to the Wayback Machine.  Include also an updated
link to a live version of the full report.

Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 11:58:51 -08:00
Andrei Rybak
18ecb23c4b git-bisect-lk2009: update java code conventions link
A reference to Java Code Conventions in git-bisect-lk2009.txt uses an
outdated URL that redirects to table of contents for the conventions.
The actual claim about "80%" that this reference backs up is on the
first page of the conventions:

  https://www.oracle.com/java/technologies/javase/codeconventions-introduction.html

Use this newer URL and its title in the reference.

Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 11:58:51 -08:00
Eric Sunshine
772f8ff826 githooks: discuss Git operations in foreign repositories
Hook authors are periodically caught off-guard by difficult-to-diagnose
errors when their hook invokes Git commands in a repository other than
the local one. In particular, Git environment variables, such as GIT_DIR
and GIT_WORK_TREE, which reference the local repository cause the Git
commands to operate on the local repository rather than on the
repository which the author intended. This is true whether the
environment variables have been set manually by the user or
automatically by Git itself. The same problem crops up when a hook
invokes Git commands in a different worktree of the same repository, as
well.

Recommended best-practice[1,2,3,4,5,6] for avoiding this problem is for
the hook to ensure that Git variables are unset before invoking Git
commands in foreign repositories or other worktrees:

    unset $(git rev-parse --local-env-vars)

However, this advice is not documented anywhere. Rectify this
shortcoming by mentioning it in githooks.txt documentation.

[1]: https://lore.kernel.org/git/YFuHd1MMlJAvtdzb@coredump.intra.peff.net/
[2]: https://lore.kernel.org/git/20200228190218.GC1408759@coredump.intra.peff.net/
[3]: https://lore.kernel.org/git/20190516221702.GA11784@sigill.intra.peff.net/
[4]: https://lore.kernel.org/git/20190422162127.GC9680@sigill.intra.peff.net/
[5]: https://lore.kernel.org/git/20180716183942.GB22298@sigill.intra.peff.net/
[6]: https://lore.kernel.org/git/20150203163235.GA9325@peff.net/

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 09:59:26 -08:00
Yutaro Ohno
9e37969e4b doc: add "git switch -c" as another option on detached HEAD
In the "DETACHED HEAD" section in the git-checkout doc, it suggests
using "git checkout -b <branch-name>" to create a new branch on the
detached head.

On the other hand, when you checkout a commit that is not at the tip of
any named branch (e.g., when you checkout a tag), git suggests using
"git switch -c <branch-name>".

Add "git switch -c" as another option and mitigate this inconsistency.

Signed-off-by: Yutaro Ohno <yutaro.ono.418@gmail.com>
Acked-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 09:57:40 -08:00
Philippe Blain
f1c9243fc5 git-rebase.txt: add a note about 'ORIG_HEAD' being overwritten
'ORIG_HEAD' is written at the start of the rebase, but is not guaranteed
to still point to the original branch tip at the end of the rebase.

Indeed, using other commands that write 'ORIG_HEAD' during the rebase,
like splitting a commit using 'git reset HEAD^', will lead to 'ORIG_HEAD'
being overwritten. This causes confusion for some users [1].

Add a note about that in the 'Description' section, and mention the more
robust alternative of using the branch's reflog.

[1] https://lore.kernel.org/git/28ebf03b-e8bb-3769-556b-c9db17e43dbb@gmail.com/T/#m827179c5adcfb504d67f76d03c8e6942b55e5ed0

Reported-by: Erik Cervin Edin <erik@cervined.in>
Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Acked-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 09:55:46 -08:00
Philippe Blain
c6eec9cb36 revisions.txt: be explicit about commands writing 'ORIG_HEAD'
When mentioning 'ORIG_HEAD', be explicit about which command write that
pseudo-ref, namely 'git am', 'git merge', 'git rebase' and 'git reset'.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Acked-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 09:55:46 -08:00
Philippe Blain
0c514d5766 git-merge.txt: mention 'ORIG_HEAD' in the Description
The fact that 'git merge' writes 'ORIG_HEAD' before performing the merge
is missing from the documentation of the command.

Mention it in the 'Description' section.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Acked-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 09:55:46 -08:00
Philippe Blain
d03c773cf6 git-reset.txt: mention 'ORIG_HEAD' in the Description
The fact that 'git reset' writes 'ORIG_HEAD' before changing HEAD is
mentioned in an example, but is missing from the 'Description' section.

Mention it in the discussion of the "'git reset' [<mode>] [<commit>]"
form of the command.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Acked-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 09:55:45 -08:00
Philippe Blain
e29678bb7c git-cherry-pick.txt: do not use 'ORIG_HEAD' in example
Commit 67ac1e1d57 (cherry-pick/revert: add support for
-X/--strategy-option, 2010-12-10) added an example to the documentation
of 'git cherry-pick'. This example mentions how to abort a failed
cherry-pick and retry with an additional merge strategy option.

The command used in the example to abort the cherry-pick is 'git reset
--merge ORIG_HEAD', but cherry-pick does not write 'ORIG_HEAD' before
starting its operation. So this command would checkout a commit
unrelated to what was at HEAD when the user invoked cherry-pick.

Use 'git cherry-pick --abort' instead.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Acked-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-13 09:55:45 -08:00
Junio C Hamano
a38d39a4c5 The sixth batch
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-08 13:25:20 +09:00
Andrei Rybak
b39a84185e *: fix typos which duplicate a word
Fix typos in code comments which repeat various words.  Most of the
cases are simple in that they repeat a word that usually cannot be
repeated in a grammatically correct sentence.  Just remove the
incorrectly duplicated word in these cases and rewrap text, if needed.

A tricky case is usage of "that that", which is sometimes grammatically
correct.  However, an instance of this in "t7527-builtin-fsmonitor.sh"
doesn't need two words "that", because there is only one daemon being
discussed, so replace the second "that" with "the".

Reword code comment "entries exist on on-disk index" in function
update_one in file cache-tree.c, by replacing incorrect preposition "on"
with "in".

Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-08 10:28:34 +09:00
Derrick Stolee
17194b195d features: feature.manyFiles implies fast index writes
The recent addition of the index.skipHash config option allows index
writes to speed up by skipping the hash computation for the trailing
checksum. This is particularly critical for repositories with many files
at HEAD, so add this config option to two cases where users in that
scenario may opt-in to such behavior:

 1. The feature.manyFiles config option enables some options that are
    helpful for repositories with many files at HEAD.

 2. 'scalar register' and 'scalar reconfigure' set config options that
    optimize for large repositories.

In both of these cases, set index.skipHash=true to gain this
speedup. Add tests that demonstrate the proper way that
index.skipHash=true can override feature.manyFiles=true.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-07 07:46:14 +09:00
Derrick Stolee
ee1f0c242e read-cache: add index.skipHash config option
The previous change allowed skipping the hashing portion of the
hashwrite API, using it instead as a buffered write API. Disabling the
hashwrite can be particularly helpful when the write operation is in a
critical path.

One such critical path is the writing of the index. This operation is so
critical that the sparse index was created specifically to reduce the
size of the index to make these writes (and reads) faster.

This trade-off between file stability at rest and write-time performance
is not easy to balance. The index is an interesting case for a couple
reasons:

1. Writes block users. Writing the index takes place in many user-
   blocking foreground operations. The speed improvement directly
   impacts their use. Other file formats are typically written in the
   background (commit-graph, multi-pack-index) or are super-critical to
   correctness (pack-files).

2. Index files are short lived. It is rare that a user leaves an index
   for a long time with many staged changes. Outside of staged changes,
   the index can be completely destroyed and rewritten with minimal
   impact to the user.

Following a similar approach to one used in the microsoft/git fork [1],
add a new config option (index.skipHash) that allows disabling this
hashing during the index write. The cost is that we can no longer
validate the contents for corruption-at-rest using the trailing hash.

[1] 21fed2d914

We load this config from the repository config given by istate->repo,
with a fallback to the_repository if it is not set.

While older Git versions will not recognize the null hash as a special
case, the file format itself is still being met in terms of its
structure. Using this null hash will still allow Git operations to
function across older versions.

The one exception is 'git fsck' which checks the hash of the index file.
This used to be a check on every index read, but was split out to just
the index in a33fc72fe9 (read-cache: force_verify_index_checksum,
2017-04-14) and released first in Git 2.13.0. Document the versions that
relaxed these restrictions, with the optimistic expectation that this
change will be included in Git 2.40.0.

Here, we disable this check if the trailing hash is all zeroes. We add a
warning to the config option that this may cause undesirable behavior
with older Git versions.

As a quick comparison, I tested 'git update-index --force-write' with
and without index.skipHash=true on a copy of the Linux kernel
repository.

Benchmark 1: with hash
  Time (mean ± σ):      46.3 ms ±  13.8 ms    [User: 34.3 ms, System: 11.9 ms]
  Range (min … max):    34.3 ms …  79.1 ms    82 runs

Benchmark 2: without hash
  Time (mean ± σ):      26.0 ms ±   7.9 ms    [User: 11.8 ms, System: 14.2 ms]
  Range (min … max):    16.3 ms …  42.0 ms    69 runs

Summary
  'without hash' ran
    1.78 ± 0.76 times faster than 'with hash'

These performance benefits are substantial enough to allow users the
ability to opt-in to this feature, even with the potential confusion
with older 'git fsck' versions.

Test this new config option, both at a command-line level and within a
submodule. The confirmation is currently limited to confirm that 'git
fsck' does not complain about the index. Future updates will make this
test more robust.

It is critical that this test is placed before the test_index_version
tests, since those tests obliterate the .git/config file and hence lose
the setting from GIT_TEST_DEFAULT_HASH, if set.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-07 07:46:14 +09:00
Junio C Hamano
4dbebc36b0 The fifth batch
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-01-05 15:07:23 +09:00