diffcore: add a pickaxe option to find a specific blob

Sometimes users are given a hash of an object and they want to
identify it further (ex.: Use verify-pack to find the largest blobs,
but what are these? or [1])

One might be tempted to extend git-describe to also work with blobs,
such that `git describe <blob-id>` gives a description as
'<commit-ish>:<path>'.  This was implemented at [2]; as seen by the sheer
number of responses (>110), it turns out this is tricky to get right.
The hard part to get right is picking the correct 'commit-ish' as that
could be the commit that (re-)introduced the blob or the blob that
removed the blob; the blob could exist in different branches.

Junio hinted at a different approach of solving this problem, which this
patch implements. Teach the diff machinery another flag for restricting
the information to what is shown. For example:

    $ ./git log --oneline --find-object=v2.0.0:Makefile
    b2feb64309 Revert the whole "ask curl-config" topic for now
    47fbfded53 i18n: only extract comments marked with "TRANSLATORS:"

we observe that the Makefile as shipped with 2.0 was appeared in
v1.9.2-471-g47fbfded53 and in v2.0.0-rc1-5-gb2feb6430b.  The
reason why these commits both occur prior to v2.0.0 are evil
merges that are not found using this new mechanism.

[1] https://stackoverflow.com/questions/223678/which-commit-has-this-blob
[2] https://public-inbox.org/git/20171028004419.10139-1-sbeller@google.com/

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
6 files changed
tree: 7e42bbe8456b5503236458a71abe6ae3827ae6e4
  1. .github/
  2. block-sha1/
  3. builtin/
  4. ci/
  5. compat/
  6. contrib/
  7. Documentation/
  8. ewah/
  9. git-gui/
  10. gitk-git/
  11. gitweb/
  12. mergetools/
  13. perl/
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  20. vcs-svn/
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  43. attr.c
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  45. base85.c
  46. bisect.c
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  48. blame.c
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  54. builtin.h
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  75. config.c
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  79. configure.ac
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  103. diff-no-index.c
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  107. diffcore-delta.c
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  109. diffcore-pickaxe.c
  110. diffcore-rename.c
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  130. git-add--interactive.perl
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  133. git-compat-util.h
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  137. git-difftool--helper.sh
  138. git-filter-branch.sh
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  154. git-send-email.perl
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  184. INSTALL
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  273. README.md
  274. ref-filter.c
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  276. reflog-walk.c
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  278. refs.c
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  280. remote-curl.c
  281. remote-testsvn.c
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  283. remote.h
  284. replace_object.c
  285. repository.c
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  288. rerere.h
  289. resolve-undo.c
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  291. revision.c
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  293. run-command.c
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  295. send-pack.c
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  297. sequencer.c
  298. sequencer.h
  299. server-info.c
  300. setup.c
  301. sh-i18n--envsubst.c
  302. sha1-array.c
  303. sha1-array.h
  304. sha1-lookup.c
  305. sha1-lookup.h
  306. sha1_file.c
  307. sha1_name.c
  308. sha1dc_git.c
  309. sha1dc_git.h
  310. shallow.c
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  312. shortlog.h
  313. show-index.c
  314. sideband.c
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  316. sigchain.c
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  318. split-index.c
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  320. strbuf.c
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  322. streaming.c
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  324. string-list.c
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  326. sub-process.c
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  328. submodule-config.c
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  332. symlinks.c
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  335. tar.h
  336. tempfile.c
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  338. thread-utils.c
  339. thread-utils.h
  340. tmp-objdir.c
  341. tmp-objdir.h
  342. trace.c
  343. trace.h
  344. trailer.c
  345. trailer.h
  346. transport-helper.c
  347. transport.c
  348. transport.h
  349. tree-diff.c
  350. tree-walk.c
  351. tree-walk.h
  352. tree.c
  353. tree.h
  354. unicode_width.h
  355. unimplemented.sh
  356. unix-socket.c
  357. unix-socket.h
  358. unpack-trees.c
  359. unpack-trees.h
  360. upload-pack.c
  361. url.c
  362. url.h
  363. urlmatch.c
  364. urlmatch.h
  365. usage.c
  366. userdiff.c
  367. userdiff.h
  368. utf8.c
  369. utf8.h
  370. varint.c
  371. varint.h
  372. version.c
  373. version.h
  374. versioncmp.c
  375. walker.c
  376. walker.h
  377. wildmatch.c
  378. wildmatch.h
  379. worktree.c
  380. worktree.h
  381. wrap-for-bin.sh
  382. wrapper.c
  383. write_or_die.c
  384. ws.c
  385. wt-status.c
  386. wt-status.h
  387. xdiff-interface.c
  388. xdiff-interface.h
  389. zlib.c
README.md

Git - fast, scalable, distributed revision control system

Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.

Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.

Please read the file INSTALL for installation instructions.

Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.

See Documentation/gittutorial.txt to get started, then see Documentation/giteveryday.txt for a useful minimum set of commands, and Documentation/git-.txt for documentation of each command. If git has been correctly installed, then the tutorial can also be read with man gittutorial or git help tutorial, and the documentation of each command with man git-<commandname> or git help <commandname>.

CVS users may also want to read Documentation/gitcvs-migration.txt (man gitcvs-migration or git help cvs-migration if git is installed).

The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission). To subscribe to the list, send an email with just “subscribe git” in the body to majordomo@vger.kernel.org. The mailing list archives are available at https://public-inbox.org/git/, http://marc.info/?l=git and other archival sites.

The maintainer frequently sends the “What's cooking” reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.

The name “git” was given by Linus Torvalds when he wrote the very first version. He described the tool as “the stupid content tracker” and the name as (depending on your mood):

  • random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of “get” may or may not be relevant.
  • stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
  • “global information tracker”: you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
  • “goddamn idiotic truckload of sh*t”: when it breaks