merge(third_party/git): Merge squashed git subtree at v2.23.0 r/373

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+git-bisect(1)
+=============
+
+NAME
+----
+git-bisect - Use binary search to find the commit that introduced a bug
+
+
+SYNOPSIS
+--------
+[verse]
+'git bisect' <subcommand> <options>
+
+DESCRIPTION
+-----------
+The command takes various subcommands, and different options depending
+on the subcommand:
+
+ git bisect start [--term-{old,good}=<term> --term-{new,bad}=<term>]
+		  [--no-checkout] [<bad> [<good>...]] [--] [<paths>...]
+ git bisect (bad|new|<term-new>) [<rev>]
+ git bisect (good|old|<term-old>) [<rev>...]
+ git bisect terms [--term-good | --term-bad]
+ git bisect skip [(<rev>|<range>)...]
+ git bisect reset [<commit>]
+ git bisect (visualize|view)
+ git bisect replay <logfile>
+ git bisect log
+ git bisect run <cmd>...
+ git bisect help
+
+This command uses a binary search algorithm to find which commit in
+your project's history introduced a bug. You use it by first telling
+it a "bad" commit that is known to contain the bug, and a "good"
+commit that is known to be before the bug was introduced. Then `git
+bisect` picks a commit between those two endpoints and asks you
+whether the selected commit is "good" or "bad". It continues narrowing
+down the range until it finds the exact commit that introduced the
+change.
+
+In fact, `git bisect` can be used to find the commit that changed
+*any* property of your project; e.g., the commit that fixed a bug, or
+the commit that caused a benchmark's performance to improve. To
+support this more general usage, the terms "old" and "new" can be used
+in place of "good" and "bad", or you can choose your own terms. See
+section "Alternate terms" below for more information.
+
+Basic bisect commands: start, bad, good
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+As an example, suppose you are trying to find the commit that broke a
+feature that was known to work in version `v2.6.13-rc2` of your
+project. You start a bisect session as follows:
+
+------------------------------------------------
+$ git bisect start
+$ git bisect bad                 # Current version is bad
+$ git bisect good v2.6.13-rc2    # v2.6.13-rc2 is known to be good
+------------------------------------------------
+
+Once you have specified at least one bad and one good commit, `git
+bisect` selects a commit in the middle of that range of history,
+checks it out, and outputs something similar to the following:
+
+------------------------------------------------
+Bisecting: 675 revisions left to test after this (roughly 10 steps)
+------------------------------------------------
+
+You should now compile the checked-out version and test it. If that
+version works correctly, type
+
+------------------------------------------------
+$ git bisect good
+------------------------------------------------
+
+If that version is broken, type
+
+------------------------------------------------
+$ git bisect bad
+------------------------------------------------
+
+Then `git bisect` will respond with something like
+
+------------------------------------------------
+Bisecting: 337 revisions left to test after this (roughly 9 steps)
+------------------------------------------------
+
+Keep repeating the process: compile the tree, test it, and depending
+on whether it is good or bad run `git bisect good` or `git bisect bad`
+to ask for the next commit that needs testing.
+
+Eventually there will be no more revisions left to inspect, and the
+command will print out a description of the first bad commit. The
+reference `refs/bisect/bad` will be left pointing at that commit.
+
+
+Bisect reset
+~~~~~~~~~~~~
+
+After a bisect session, to clean up the bisection state and return to
+the original HEAD, issue the following command:
+
+------------------------------------------------
+$ git bisect reset
+------------------------------------------------
+
+By default, this will return your tree to the commit that was checked
+out before `git bisect start`.  (A new `git bisect start` will also do
+that, as it cleans up the old bisection state.)
+
+With an optional argument, you can return to a different commit
+instead:
+
+------------------------------------------------
+$ git bisect reset <commit>
+------------------------------------------------
+
+For example, `git bisect reset bisect/bad` will check out the first
+bad revision, while `git bisect reset HEAD` will leave you on the
+current bisection commit and avoid switching commits at all.
+
+
+Alternate terms
+~~~~~~~~~~~~~~~
+
+Sometimes you are not looking for the commit that introduced a
+breakage, but rather for a commit that caused a change between some
+other "old" state and "new" state. For example, you might be looking
+for the commit that introduced a particular fix. Or you might be
+looking for the first commit in which the source-code filenames were
+finally all converted to your company's naming standard. Or whatever.
+
+In such cases it can be very confusing to use the terms "good" and
+"bad" to refer to "the state before the change" and "the state after
+the change". So instead, you can use the terms "old" and "new",
+respectively, in place of "good" and "bad". (But note that you cannot
+mix "good" and "bad" with "old" and "new" in a single session.)
+
+In this more general usage, you provide `git bisect` with a "new"
+commit that has some property and an "old" commit that doesn't have that
+property. Each time `git bisect` checks out a commit, you test if that
+commit has the property. If it does, mark the commit as "new";
+otherwise, mark it as "old". When the bisection is done, `git bisect`
+will report which commit introduced the property.
+
+To use "old" and "new" instead of "good" and bad, you must run `git
+bisect start` without commits as argument and then run the following
+commands to add the commits:
+
+------------------------------------------------
+git bisect old [<rev>]
+------------------------------------------------
+
+to indicate that a commit was before the sought change, or
+
+------------------------------------------------
+git bisect new [<rev>...]
+------------------------------------------------
+
+to indicate that it was after.
+
+To get a reminder of the currently used terms, use
+
+------------------------------------------------
+git bisect terms
+------------------------------------------------
+
+You can get just the old (respectively new) term with `git bisect terms
+--term-old` or `git bisect terms --term-good`.
+
+If you would like to use your own terms instead of "bad"/"good" or
+"new"/"old", you can choose any names you like (except existing bisect
+subcommands like `reset`, `start`, ...) by starting the
+bisection using
+
+------------------------------------------------
+git bisect start --term-old <term-old> --term-new <term-new>
+------------------------------------------------
+
+For example, if you are looking for a commit that introduced a
+performance regression, you might use
+
+------------------------------------------------
+git bisect start --term-old fast --term-new slow
+------------------------------------------------
+
+Or if you are looking for the commit that fixed a bug, you might use
+
+------------------------------------------------
+git bisect start --term-new fixed --term-old broken
+------------------------------------------------
+
+Then, use `git bisect <term-old>` and `git bisect <term-new>` instead
+of `git bisect good` and `git bisect bad` to mark commits.
+
+Bisect visualize/view
+~~~~~~~~~~~~~~~~~~~~~
+
+To see the currently remaining suspects in 'gitk', issue the following
+command during the bisection process (the subcommand `view` can be used
+as an alternative to `visualize`):
+
+------------
+$ git bisect visualize
+------------
+
+If the `DISPLAY` environment variable is not set, 'git log' is used
+instead.  You can also give command-line options such as `-p` and
+`--stat`.
+
+------------
+$ git bisect visualize --stat
+------------
+
+Bisect log and bisect replay
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+After having marked revisions as good or bad, issue the following
+command to show what has been done so far:
+
+------------
+$ git bisect log
+------------
+
+If you discover that you made a mistake in specifying the status of a
+revision, you can save the output of this command to a file, edit it to
+remove the incorrect entries, and then issue the following commands to
+return to a corrected state:
+
+------------
+$ git bisect reset
+$ git bisect replay that-file
+------------
+
+Avoiding testing a commit
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If, in the middle of a bisect session, you know that the suggested
+revision is not a good one to test (e.g. it fails to build and you
+know that the failure does not have anything to do with the bug you
+are chasing), you can manually select a nearby commit and test that
+one instead.
+
+For example:
+
+------------
+$ git bisect good/bad			# previous round was good or bad.
+Bisecting: 337 revisions left to test after this (roughly 9 steps)
+$ git bisect visualize			# oops, that is uninteresting.
+$ git reset --hard HEAD~3		# try 3 revisions before what
+					# was suggested
+------------
+
+Then compile and test the chosen revision, and afterwards mark
+the revision as good or bad in the usual manner.
+
+Bisect skip
+~~~~~~~~~~~
+
+Instead of choosing a nearby commit by yourself, you can ask Git to do
+it for you by issuing the command:
+
+------------
+$ git bisect skip                 # Current version cannot be tested
+------------
+
+However, if you skip a commit adjacent to the one you are looking for,
+Git will be unable to tell exactly which of those commits was the
+first bad one.
+
+You can also skip a range of commits, instead of just one commit,
+using range notation. For example:
+
+------------
+$ git bisect skip v2.5..v2.6
+------------
+
+This tells the bisect process that no commit after `v2.5`, up to and
+including `v2.6`, should be tested.
+
+Note that if you also want to skip the first commit of the range you
+would issue the command:
+
+------------
+$ git bisect skip v2.5 v2.5..v2.6
+------------
+
+This tells the bisect process that the commits between `v2.5` and
+`v2.6` (inclusive) should be skipped.
+
+
+Cutting down bisection by giving more parameters to bisect start
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+You can further cut down the number of trials, if you know what part of
+the tree is involved in the problem you are tracking down, by specifying
+path parameters when issuing the `bisect start` command:
+
+------------
+$ git bisect start -- arch/i386 include/asm-i386
+------------
+
+If you know beforehand more than one good commit, you can narrow the
+bisect space down by specifying all of the good commits immediately after
+the bad commit when issuing the `bisect start` command:
+
+------------
+$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
+                   # v2.6.20-rc6 is bad
+                   # v2.6.20-rc4 and v2.6.20-rc1 are good
+------------
+
+Bisect run
+~~~~~~~~~~
+
+If you have a script that can tell if the current source code is good
+or bad, you can bisect by issuing the command:
+
+------------
+$ git bisect run my_script arguments
+------------
+
+Note that the script (`my_script` in the above example) should exit
+with code 0 if the current source code is good/old, and exit with a
+code between 1 and 127 (inclusive), except 125, if the current source
+code is bad/new.
+
+Any other exit code will abort the bisect process. It should be noted
+that a program that terminates via `exit(-1)` leaves $? = 255, (see the
+exit(3) manual page), as the value is chopped with `& 0377`.
+
+The special exit code 125 should be used when the current source code
+cannot be tested. If the script exits with this code, the current
+revision will be skipped (see `git bisect skip` above). 125 was chosen
+as the highest sensible value to use for this purpose, because 126 and 127
+are used by POSIX shells to signal specific error status (127 is for
+command not found, 126 is for command found but not executable--these
+details do not matter, as they are normal errors in the script, as far as
+`bisect run` is concerned).
+
+You may often find that during a bisect session you want to have
+temporary modifications (e.g. s/#define DEBUG 0/#define DEBUG 1/ in a
+header file, or "revision that does not have this commit needs this
+patch applied to work around another problem this bisection is not
+interested in") applied to the revision being tested.
+
+To cope with such a situation, after the inner 'git bisect' finds the
+next revision to test, the script can apply the patch
+before compiling, run the real test, and afterwards decide if the
+revision (possibly with the needed patch) passed the test and then
+rewind the tree to the pristine state.  Finally the script should exit
+with the status of the real test to let the `git bisect run` command loop
+determine the eventual outcome of the bisect session.
+
+OPTIONS
+-------
+--no-checkout::
++
+Do not checkout the new working tree at each iteration of the bisection
+process. Instead just update a special reference named `BISECT_HEAD` to make
+it point to the commit that should be tested.
++
+This option may be useful when the test you would perform in each step
+does not require a checked out tree.
++
+If the repository is bare, `--no-checkout` is assumed.
+
+EXAMPLES
+--------
+
+* Automatically bisect a broken build between v1.2 and HEAD:
++
+------------
+$ git bisect start HEAD v1.2 --      # HEAD is bad, v1.2 is good
+$ git bisect run make                # "make" builds the app
+$ git bisect reset                   # quit the bisect session
+------------
+
+* Automatically bisect a test failure between origin and HEAD:
++
+------------
+$ git bisect start HEAD origin --    # HEAD is bad, origin is good
+$ git bisect run make test           # "make test" builds and tests
+$ git bisect reset                   # quit the bisect session
+------------
+
+* Automatically bisect a broken test case:
++
+------------
+$ cat ~/test.sh
+#!/bin/sh
+make || exit 125                     # this skips broken builds
+~/check_test_case.sh                 # does the test case pass?
+$ git bisect start HEAD HEAD~10 --   # culprit is among the last 10
+$ git bisect run ~/test.sh
+$ git bisect reset                   # quit the bisect session
+------------
++
+Here we use a `test.sh` custom script. In this script, if `make`
+fails, we skip the current commit.
+`check_test_case.sh` should `exit 0` if the test case passes,
+and `exit 1` otherwise.
++
+It is safer if both `test.sh` and `check_test_case.sh` are
+outside the repository to prevent interactions between the bisect,
+make and test processes and the scripts.
+
+* Automatically bisect with temporary modifications (hot-fix):
++
+------------
+$ cat ~/test.sh
+#!/bin/sh
+
+# tweak the working tree by merging the hot-fix branch
+# and then attempt a build
+if	git merge --no-commit hot-fix &&
+	make
+then
+	# run project specific test and report its status
+	~/check_test_case.sh
+	status=$?
+else
+	# tell the caller this is untestable
+	status=125
+fi
+
+# undo the tweak to allow clean flipping to the next commit
+git reset --hard
+
+# return control
+exit $status
+------------
++
+This applies modifications from a hot-fix branch before each test run,
+e.g. in case your build or test environment changed so that older
+revisions may need a fix which newer ones have already. (Make sure the
+hot-fix branch is based off a commit which is contained in all revisions
+which you are bisecting, so that the merge does not pull in too much, or
+use `git cherry-pick` instead of `git merge`.)
+
+* Automatically bisect a broken test case:
++
+------------
+$ git bisect start HEAD HEAD~10 --   # culprit is among the last 10
+$ git bisect run sh -c "make || exit 125; ~/check_test_case.sh"
+$ git bisect reset                   # quit the bisect session
+------------
++
+This shows that you can do without a run script if you write the test
+on a single line.
+
+* Locate a good region of the object graph in a damaged repository
++
+------------
+$ git bisect start HEAD <known-good-commit> [ <boundary-commit> ... ] --no-checkout
+$ git bisect run sh -c '
+	GOOD=$(git for-each-ref "--format=%(objectname)" refs/bisect/good-*) &&
+	git rev-list --objects BISECT_HEAD --not $GOOD >tmp.$$ &&
+	git pack-objects --stdout >/dev/null <tmp.$$
+	rc=$?
+	rm -f tmp.$$
+	test $rc = 0'
+
+$ git bisect reset                   # quit the bisect session
+------------
++
+In this case, when 'git bisect run' finishes, bisect/bad will refer to a commit that
+has at least one parent whose reachable graph is fully traversable in the sense
+required by 'git pack objects'.
+
+* Look for a fix instead of a regression in the code
++
+------------
+$ git bisect start
+$ git bisect new HEAD    # current commit is marked as new
+$ git bisect old HEAD~10 # the tenth commit from now is marked as old
+------------
++
+or:
+------------
+$ git bisect start --term-old broken --term-new fixed
+$ git bisect fixed
+$ git bisect broken HEAD~10
+------------
+
+Getting help
+~~~~~~~~~~~~
+
+Use `git bisect` to get a short usage description, and `git bisect
+help` or `git bisect -h` to get a long usage description.
+
+SEE ALSO
+--------
+link:git-bisect-lk2009.html[Fighting regressions with git bisect],
+linkgit:git-blame[1].
+
+GIT
+---
+Part of the linkgit:git[1] suite