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

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diff --git a/third_party/git/Documentation/git-checkout.txt b/third_party/git/Documentation/git-checkout.txt
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+git-checkout(1)
+===============
+
+NAME
+----
+git-checkout - Switch branches or restore working tree files
+
+SYNOPSIS
+--------
+[verse]
+'git checkout' [-q] [-f] [-m] [<branch>]
+'git checkout' [-q] [-f] [-m] --detach [<branch>]
+'git checkout' [-q] [-f] [-m] [--detach] <commit>
+'git checkout' [-q] [-f] [-m] [[-b|-B|--orphan] <new_branch>] [<start_point>]
+'git checkout' [-f|--ours|--theirs|-m|--conflict=<style>] [<tree-ish>] [--] <paths>...
+'git checkout' [<tree-ish>] [--] <pathspec>...
+'git checkout' (-p|--patch) [<tree-ish>] [--] [<paths>...]
+
+DESCRIPTION
+-----------
+Updates files in the working tree to match the version in the index
+or the specified tree.  If no paths are given, 'git checkout' will
+also update `HEAD` to set the specified branch as the current
+branch.
+
+'git checkout' [<branch>]::
+	To prepare for working on `<branch>`, switch to it by updating
+	the index and the files in the working tree, and by pointing
+	`HEAD` at the branch. Local modifications to the files in the
+	working tree are kept, so that they can be committed to the
+	`<branch>`.
++
+If `<branch>` is not found but there does exist a tracking branch in
+exactly one remote (call it `<remote>`) with a matching name and
+`--no-guess` is not specified, treat as equivalent to
++
+------------
+$ git checkout -b <branch> --track <remote>/<branch>
+------------
++
+You could omit `<branch>`, in which case the command degenerates to
+"check out the current branch", which is a glorified no-op with
+rather expensive side-effects to show only the tracking information,
+if exists, for the current branch.
+
+'git checkout' -b|-B <new_branch> [<start point>]::
+
+	Specifying `-b` causes a new branch to be created as if
+	linkgit:git-branch[1] were called and then checked out.  In
+	this case you can use the `--track` or `--no-track` options,
+	which will be passed to 'git branch'.  As a convenience,
+	`--track` without `-b` implies branch creation; see the
+	description of `--track` below.
++
+If `-B` is given, `<new_branch>` is created if it doesn't exist; otherwise, it
+is reset. This is the transactional equivalent of
++
+------------
+$ git branch -f <branch> [<start point>]
+$ git checkout <branch>
+------------
++
+that is to say, the branch is not reset/created unless "git checkout" is
+successful.
+
+'git checkout' --detach [<branch>]::
+'git checkout' [--detach] <commit>::
+
+	Prepare to work on top of `<commit>`, by detaching `HEAD` at it
+	(see "DETACHED HEAD" section), and updating the index and the
+	files in the working tree.  Local modifications to the files
+	in the working tree are kept, so that the resulting working
+	tree will be the state recorded in the commit plus the local
+	modifications.
++
+When the `<commit>` argument is a branch name, the `--detach` option can
+be used to detach `HEAD` at the tip of the branch (`git checkout
+<branch>` would check out that branch without detaching `HEAD`).
++
+Omitting `<branch>` detaches `HEAD` at the tip of the current branch.
+
+'git checkout' [<tree-ish>] [--] <pathspec>...::
+
+	Overwrite paths in the working tree by replacing with the
+	contents in the index or in the `<tree-ish>` (most often a
+	commit).  When a `<tree-ish>` is given, the paths that
+	match the `<pathspec>` are updated both in the index and in
+	the working tree.
++
+The index may contain unmerged entries because of a previous failed merge.
+By default, if you try to check out such an entry from the index, the
+checkout operation will fail and nothing will be checked out.
+Using `-f` will ignore these unmerged entries.  The contents from a
+specific side of the merge can be checked out of the index by
+using `--ours` or `--theirs`.  With `-m`, changes made to the working tree
+file can be discarded to re-create the original conflicted merge result.
+
+'git checkout' (-p|--patch) [<tree-ish>] [--] [<pathspec>...]::
+	This is similar to the "check out paths to the working tree
+	from either the index or from a tree-ish" mode described
+	above, but lets you use the interactive interface to show
+	the "diff" output and choose which hunks to use in the
+	result.  See below for the description of `--patch` option.
+
+
+OPTIONS
+-------
+-q::
+--quiet::
+	Quiet, suppress feedback messages.
+
+--progress::
+--no-progress::
+	Progress status is reported on the standard error stream
+	by default when it is attached to a terminal, unless `--quiet`
+	is specified. This flag enables progress reporting even if not
+	attached to a terminal, regardless of `--quiet`.
+
+-f::
+--force::
+	When switching branches, proceed even if the index or the
+	working tree differs from `HEAD`.  This is used to throw away
+	local changes.
++
+When checking out paths from the index, do not fail upon unmerged
+entries; instead, unmerged entries are ignored.
+
+--ours::
+--theirs::
+	When checking out paths from the index, check out stage #2
+	('ours') or #3 ('theirs') for unmerged paths.
++
+Note that during `git rebase` and `git pull --rebase`, 'ours' and
+'theirs' may appear swapped; `--ours` gives the version from the
+branch the changes are rebased onto, while `--theirs` gives the
+version from the branch that holds your work that is being rebased.
++
+This is because `rebase` is used in a workflow that treats the
+history at the remote as the shared canonical one, and treats the
+work done on the branch you are rebasing as the third-party work to
+be integrated, and you are temporarily assuming the role of the
+keeper of the canonical history during the rebase.  As the keeper of
+the canonical history, you need to view the history from the remote
+as `ours` (i.e. "our shared canonical history"), while what you did
+on your side branch as `theirs` (i.e. "one contributor's work on top
+of it").
+
+-b <new_branch>::
+	Create a new branch named `<new_branch>` and start it at
+	`<start_point>`; see linkgit:git-branch[1] for details.
+
+-B <new_branch>::
+	Creates the branch `<new_branch>` and start it at `<start_point>`;
+	if it already exists, then reset it to `<start_point>`. This is
+	equivalent to running "git branch" with "-f"; see
+	linkgit:git-branch[1] for details.
+
+-t::
+--track::
+	When creating a new branch, set up "upstream" configuration. See
+	"--track" in linkgit:git-branch[1] for details.
++
+If no `-b` option is given, the name of the new branch will be
+derived from the remote-tracking branch, by looking at the local part of
+the refspec configured for the corresponding remote, and then stripping
+the initial part up to the "*".
+This would tell us to use `hack` as the local branch when branching
+off of `origin/hack` (or `remotes/origin/hack`, or even
+`refs/remotes/origin/hack`).  If the given name has no slash, or the above
+guessing results in an empty name, the guessing is aborted.  You can
+explicitly give a name with `-b` in such a case.
+
+--no-track::
+	Do not set up "upstream" configuration, even if the
+	`branch.autoSetupMerge` configuration variable is true.
+
+--guess::
+--no-guess::
+	If `<branch>` is not found but there does exist a tracking
+	branch in exactly one remote (call it `<remote>`) with a
+	matching name, treat as equivalent to
++
+------------
+$ git checkout -b <branch> --track <remote>/<branch>
+------------
++
+If the branch exists in multiple remotes and one of them is named by
+the `checkout.defaultRemote` configuration variable, we'll use that
+one for the purposes of disambiguation, even if the `<branch>` isn't
+unique across all remotes. Set it to
+e.g. `checkout.defaultRemote=origin` to always checkout remote
+branches from there if `<branch>` is ambiguous but exists on the
+'origin' remote. See also `checkout.defaultRemote` in
+linkgit:git-config[1].
++
+Use `--no-guess` to disable this.
+
+-l::
+	Create the new branch's reflog; see linkgit:git-branch[1] for
+	details.
+
+--detach::
+	Rather than checking out a branch to work on it, check out a
+	commit for inspection and discardable experiments.
+	This is the default behavior of `git checkout <commit>` when
+	`<commit>` is not a branch name.  See the "DETACHED HEAD" section
+	below for details.
+
+--orphan <new_branch>::
+	Create a new 'orphan' branch, named `<new_branch>`, started from
+	`<start_point>` and switch to it.  The first commit made on this
+	new branch will have no parents and it will be the root of a new
+	history totally disconnected from all the other branches and
+	commits.
++
+The index and the working tree are adjusted as if you had previously run
+`git checkout <start_point>`.  This allows you to start a new history
+that records a set of paths similar to `<start_point>` by easily running
+`git commit -a` to make the root commit.
++
+This can be useful when you want to publish the tree from a commit
+without exposing its full history. You might want to do this to publish
+an open source branch of a project whose current tree is "clean", but
+whose full history contains proprietary or otherwise encumbered bits of
+code.
++
+If you want to start a disconnected history that records a set of paths
+that is totally different from the one of `<start_point>`, then you should
+clear the index and the working tree right after creating the orphan
+branch by running `git rm -rf .` from the top level of the working tree.
+Afterwards you will be ready to prepare your new files, repopulating the
+working tree, by copying them from elsewhere, extracting a tarball, etc.
+
+--ignore-skip-worktree-bits::
+	In sparse checkout mode, `git checkout -- <paths>` would
+	update only entries matched by `<paths>` and sparse patterns
+	in `$GIT_DIR/info/sparse-checkout`. This option ignores
+	the sparse patterns and adds back any files in `<paths>`.
+
+-m::
+--merge::
+	When switching branches,
+	if you have local modifications to one or more files that
+	are different between the current branch and the branch to
+	which you are switching, the command refuses to switch
+	branches in order to preserve your modifications in context.
+	However, with this option, a three-way merge between the current
+	branch, your working tree contents, and the new branch
+	is done, and you will be on the new branch.
++
+When a merge conflict happens, the index entries for conflicting
+paths are left unmerged, and you need to resolve the conflicts
+and mark the resolved paths with `git add` (or `git rm` if the merge
+should result in deletion of the path).
++
+When checking out paths from the index, this option lets you recreate
+the conflicted merge in the specified paths.
++
+When switching branches with `--merge`, staged changes may be lost.
+
+--conflict=<style>::
+	The same as `--merge` option above, but changes the way the
+	conflicting hunks are presented, overriding the
+	`merge.conflictStyle` configuration variable.  Possible values are
+	"merge" (default) and "diff3" (in addition to what is shown by
+	"merge" style, shows the original contents).
+
+-p::
+--patch::
+	Interactively select hunks in the difference between the
+	`<tree-ish>` (or the index, if unspecified) and the working
+	tree.  The chosen hunks are then applied in reverse to the
+	working tree (and if a `<tree-ish>` was specified, the index).
++
+This means that you can use `git checkout -p` to selectively discard
+edits from your current working tree. See the ``Interactive Mode''
+section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
++
+Note that this option uses the no overlay mode by default (see also
+`--overlay`), and currently doesn't support overlay mode.
+
+--ignore-other-worktrees::
+	`git checkout` refuses when the wanted ref is already checked
+	out by another worktree. This option makes it check the ref
+	out anyway. In other words, the ref can be held by more than one
+	worktree.
+
+--overwrite-ignore::
+--no-overwrite-ignore::
+	Silently overwrite ignored files when switching branches. This
+	is the default behavior. Use `--no-overwrite-ignore` to abort
+	the operation when the new branch contains ignored files.
+
+--recurse-submodules::
+--no-recurse-submodules::
+	Using `--recurse-submodules` will update the content of all initialized
+	submodules according to the commit recorded in the superproject. If
+	local modifications in a submodule would be overwritten the checkout
+	will fail unless `-f` is used. If nothing (or `--no-recurse-submodules`)
+	is used, the work trees of submodules will not be updated.
+	Just like linkgit:git-submodule[1], this will detach `HEAD` of the
+	submodule.
+
+--overlay::
+--no-overlay::
+	In the default overlay mode, `git checkout` never
+	removes files from the index or the working tree.  When
+	specifying `--no-overlay`, files that appear in the index and
+	working tree, but not in `<tree-ish>` are removed, to make them
+	match `<tree-ish>` exactly.
+
+<branch>::
+	Branch to checkout; if it refers to a branch (i.e., a name that,
+	when prepended with "refs/heads/", is a valid ref), then that
+	branch is checked out. Otherwise, if it refers to a valid
+	commit, your `HEAD` becomes "detached" and you are no longer on
+	any branch (see below for details).
++
+You can use the `@{-N}` syntax to refer to the N-th last
+branch/commit checked out using "git checkout" operation. You may
+also specify `-` which is synonymous to `@{-1}`.
++
+As a special case, you may use `A...B` as a shortcut for the
+merge base of `A` and `B` if there is exactly one merge base. You can
+leave out at most one of `A` and `B`, in which case it defaults to `HEAD`.
+
+<new_branch>::
+	Name for the new branch.
+
+<start_point>::
+	The name of a commit at which to start the new branch; see
+	linkgit:git-branch[1] for details. Defaults to `HEAD`.
++
+As a special case, you may use `"A...B"` as a shortcut for the
+merge base of `A` and `B` if there is exactly one merge base. You can
+leave out at most one of `A` and `B`, in which case it defaults to `HEAD`.
+
+<tree-ish>::
+	Tree to checkout from (when paths are given). If not specified,
+	the index will be used.
+
+
+
+DETACHED HEAD
+-------------
+`HEAD` normally refers to a named branch (e.g. `master`). Meanwhile, each
+branch refers to a specific commit. Let's look at a repo with three
+commits, one of them tagged, and with branch `master` checked out:
+
+------------
+           HEAD (refers to branch 'master')
+            |
+            v
+a---b---c  branch 'master' (refers to commit 'c')
+    ^
+    |
+  tag 'v2.0' (refers to commit 'b')
+------------
+
+When a commit is created in this state, the branch is updated to refer to
+the new commit. Specifically, 'git commit' creates a new commit `d`, whose
+parent is commit `c`, and then updates branch `master` to refer to new
+commit `d`. `HEAD` still refers to branch `master` and so indirectly now refers
+to commit `d`:
+
+------------
+$ edit; git add; git commit
+
+               HEAD (refers to branch 'master')
+                |
+                v
+a---b---c---d  branch 'master' (refers to commit 'd')
+    ^
+    |
+  tag 'v2.0' (refers to commit 'b')
+------------
+
+It is sometimes useful to be able to checkout a commit that is not at
+the tip of any named branch, or even to create a new commit that is not
+referenced by a named branch. Let's look at what happens when we
+checkout commit `b` (here we show two ways this may be done):
+
+------------
+$ git checkout v2.0  # or
+$ git checkout master^^
+
+   HEAD (refers to commit 'b')
+    |
+    v
+a---b---c---d  branch 'master' (refers to commit 'd')
+    ^
+    |
+  tag 'v2.0' (refers to commit 'b')
+------------
+
+Notice that regardless of which checkout command we use, `HEAD` now refers
+directly to commit `b`. This is known as being in detached `HEAD` state.
+It means simply that `HEAD` refers to a specific commit, as opposed to
+referring to a named branch. Let's see what happens when we create a commit:
+
+------------
+$ edit; git add; git commit
+
+     HEAD (refers to commit 'e')
+      |
+      v
+      e
+     /
+a---b---c---d  branch 'master' (refers to commit 'd')
+    ^
+    |
+  tag 'v2.0' (refers to commit 'b')
+------------
+
+There is now a new commit `e`, but it is referenced only by `HEAD`. We can
+of course add yet another commit in this state:
+
+------------
+$ edit; git add; git commit
+
+	 HEAD (refers to commit 'f')
+	  |
+	  v
+      e---f
+     /
+a---b---c---d  branch 'master' (refers to commit 'd')
+    ^
+    |
+  tag 'v2.0' (refers to commit 'b')
+------------
+
+In fact, we can perform all the normal Git operations. But, let's look
+at what happens when we then checkout `master`:
+
+------------
+$ git checkout master
+
+               HEAD (refers to branch 'master')
+      e---f     |
+     /          v
+a---b---c---d  branch 'master' (refers to commit 'd')
+    ^
+    |
+  tag 'v2.0' (refers to commit 'b')
+------------
+
+It is important to realize that at this point nothing refers to commit
+`f`. Eventually commit `f` (and by extension commit `e`) will be deleted
+by the routine Git garbage collection process, unless we create a reference
+before that happens. If we have not yet moved away from commit `f`,
+any of these will create a reference to it:
+
+------------
+$ git checkout -b foo   <1>
+$ git branch foo        <2>
+$ git tag foo           <3>
+------------
+
+<1> creates a new branch `foo`, which refers to commit `f`, and then
+    updates `HEAD` to refer to branch `foo`. In other words, we'll no longer
+    be in detached `HEAD` state after this command.
+
+<2> similarly creates a new branch `foo`, which refers to commit `f`,
+    but leaves `HEAD` detached.
+
+<3> creates a new tag `foo`, which refers to commit `f`,
+    leaving `HEAD` detached.
+
+If we have moved away from commit `f`, then we must first recover its object
+name (typically by using git reflog), and then we can create a reference to
+it. For example, to see the last two commits to which `HEAD` referred, we
+can use either of these commands:
+
+------------
+$ git reflog -2 HEAD # or
+$ git log -g -2 HEAD
+------------
+
+ARGUMENT DISAMBIGUATION
+-----------------------
+
+When there is only one argument given and it is not `--` (e.g. `git
+checkout abc`), and when the argument is both a valid `<tree-ish>`
+(e.g. a branch `abc` exists) and a valid `<pathspec>` (e.g. a file
+or a directory whose name is "abc" exists), Git would usually ask
+you to disambiguate.  Because checking out a branch is so common an
+operation, however, `git checkout abc` takes "abc" as a `<tree-ish>`
+in such a situation.  Use `git checkout -- <pathspec>` if you want
+to checkout these paths out of the index.
+
+EXAMPLES
+--------
+
+. The following sequence checks out the `master` branch, reverts
+  the `Makefile` to two revisions back, deletes `hello.c` by
+  mistake, and gets it back from the index.
++
+------------
+$ git checkout master             <1>
+$ git checkout master~2 Makefile  <2>
+$ rm -f hello.c
+$ git checkout hello.c            <3>
+------------
++
+<1> switch branch
+<2> take a file out of another commit
+<3> restore `hello.c` from the index
++
+If you want to check out _all_ C source files out of the index,
+you can say
++
+------------
+$ git checkout -- '*.c'
+------------
++
+Note the quotes around `*.c`.  The file `hello.c` will also be
+checked out, even though it is no longer in the working tree,
+because the file globbing is used to match entries in the index
+(not in the working tree by the shell).
++
+If you have an unfortunate branch that is named `hello.c`, this
+step would be confused as an instruction to switch to that branch.
+You should instead write:
++
+------------
+$ git checkout -- hello.c
+------------
+
+. After working in the wrong branch, switching to the correct
+  branch would be done using:
++
+------------
+$ git checkout mytopic
+------------
++
+However, your "wrong" branch and correct `mytopic` branch may
+differ in files that you have modified locally, in which case
+the above checkout would fail like this:
++
+------------
+$ git checkout mytopic
+error: You have local changes to 'frotz'; not switching branches.
+------------
++
+You can give the `-m` flag to the command, which would try a
+three-way merge:
++
+------------
+$ git checkout -m mytopic
+Auto-merging frotz
+------------
++
+After this three-way merge, the local modifications are _not_
+registered in your index file, so `git diff` would show you what
+changes you made since the tip of the new branch.
+
+. When a merge conflict happens during switching branches with
+  the `-m` option, you would see something like this:
++
+------------
+$ git checkout -m mytopic
+Auto-merging frotz
+ERROR: Merge conflict in frotz
+fatal: merge program failed
+------------
++
+At this point, `git diff` shows the changes cleanly merged as in
+the previous example, as well as the changes in the conflicted
+files.  Edit and resolve the conflict and mark it resolved with
+`git add` as usual:
++
+------------
+$ edit frotz
+$ git add frotz
+------------
+
+SEE ALSO
+--------
+linkgit:git-switch[1],
+linkgit:git-restore[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite