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

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+git-check-ref-format(1)
+=======================
+
+NAME
+----
+git-check-ref-format - Ensures that a reference name is well formed
+
+SYNOPSIS
+--------
+[verse]
+'git check-ref-format' [--normalize]
+       [--[no-]allow-onelevel] [--refspec-pattern]
+       <refname>
+'git check-ref-format' --branch <branchname-shorthand>
+
+DESCRIPTION
+-----------
+Checks if a given 'refname' is acceptable, and exits with a non-zero
+status if it is not.
+
+A reference is used in Git to specify branches and tags.  A
+branch head is stored in the `refs/heads` hierarchy, while
+a tag is stored in the `refs/tags` hierarchy of the ref namespace
+(typically in `$GIT_DIR/refs/heads` and `$GIT_DIR/refs/tags`
+directories or, as entries in file `$GIT_DIR/packed-refs`
+if refs are packed by `git gc`).
+
+Git imposes the following rules on how references are named:
+
+. They can include slash `/` for hierarchical (directory)
+  grouping, but no slash-separated component can begin with a
+  dot `.` or end with the sequence `.lock`.
+
+. They must contain at least one `/`. This enforces the presence of a
+  category like `heads/`, `tags/` etc. but the actual names are not
+  restricted.  If the `--allow-onelevel` option is used, this rule
+  is waived.
+
+. They cannot have two consecutive dots `..` anywhere.
+
+. They cannot have ASCII control characters (i.e. bytes whose
+  values are lower than \040, or \177 `DEL`), space, tilde `~`,
+  caret `^`, or colon `:` anywhere.
+
+. They cannot have question-mark `?`, asterisk `*`, or open
+  bracket `[` anywhere.  See the `--refspec-pattern` option below for
+  an exception to this rule.
+
+. They cannot begin or end with a slash `/` or contain multiple
+  consecutive slashes (see the `--normalize` option below for an
+  exception to this rule)
+
+. They cannot end with a dot `.`.
+
+. They cannot contain a sequence `@{`.
+
+. They cannot be the single character `@`.
+
+. They cannot contain a `\`.
+
+These rules make it easy for shell script based tools to parse
+reference names, pathname expansion by the shell when a reference name is used
+unquoted (by mistake), and also avoid ambiguities in certain
+reference name expressions (see linkgit:gitrevisions[7]):
+
+. A double-dot `..` is often used as in `ref1..ref2`, and in some
+  contexts this notation means `^ref1 ref2` (i.e. not in
+  `ref1` and in `ref2`).
+
+. A tilde `~` and caret `^` are used to introduce the postfix
+  'nth parent' and 'peel onion' operation.
+
+. A colon `:` is used as in `srcref:dstref` to mean "use srcref\'s
+  value and store it in dstref" in fetch and push operations.
+  It may also be used to select a specific object such as with
+  'git cat-file': "git cat-file blob v1.3.3:refs.c".
+
+. at-open-brace `@{` is used as a notation to access a reflog entry.
+
+With the `--branch` option, the command takes a name and checks if
+it can be used as a valid branch name (e.g. when creating a new
+branch). But be cautious when using the
+previous checkout syntax that may refer to a detached HEAD state.
+The rule `git check-ref-format --branch $name` implements
+may be stricter than what `git check-ref-format refs/heads/$name`
+says (e.g. a dash may appear at the beginning of a ref component,
+but it is explicitly forbidden at the beginning of a branch name).
+When run with `--branch` option in a repository, the input is first
+expanded for the ``previous checkout syntax''
+`@{-n}`.  For example, `@{-1}` is a way to refer the last thing that
+was checked out using "git switch" or "git checkout" operation.
+This option should be
+used by porcelains to accept this syntax anywhere a branch name is
+expected, so they can act as if you typed the branch name. As an
+exception note that, the ``previous checkout operation'' might result
+in a commit object name when the N-th last thing checked out was not
+a branch.
+
+OPTIONS
+-------
+--[no-]allow-onelevel::
+	Controls whether one-level refnames are accepted (i.e.,
+	refnames that do not contain multiple `/`-separated
+	components).  The default is `--no-allow-onelevel`.
+
+--refspec-pattern::
+	Interpret <refname> as a reference name pattern for a refspec
+	(as used with remote repositories).  If this option is
+	enabled, <refname> is allowed to contain a single `*`
+	in the refspec (e.g., `foo/bar*/baz` or `foo/bar*baz/`
+	but not `foo/bar*/baz*`).
+
+--normalize::
+	Normalize 'refname' by removing any leading slash (`/`)
+	characters and collapsing runs of adjacent slashes between
+	name components into a single slash.  If the normalized
+	refname is valid then print it to standard output and exit
+	with a status of 0, otherwise exit with a non-zero status.
+	(`--print` is a deprecated way to spell `--normalize`.)
+
+
+EXAMPLES
+--------
+
+* Print the name of the previous thing checked out:
++
+------------
+$ git check-ref-format --branch @{-1}
+------------
+
+* Determine the reference name to use for a new branch:
++
+------------
+$ ref=$(git check-ref-format --normalize "refs/heads/$newbranch")||
+{ echo "we do not like '$newbranch' as a branch name." >&2 ; exit 1 ; }
+------------
+
+GIT
+---
+Part of the linkgit:git[1] suite