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

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+gitattributes(5)
+================
+
+NAME
+----
+gitattributes - Defining attributes per path
+
+SYNOPSIS
+--------
+$GIT_DIR/info/attributes, .gitattributes
+
+
+DESCRIPTION
+-----------
+
+A `gitattributes` file is a simple text file that gives
+`attributes` to pathnames.
+
+Each line in `gitattributes` file is of form:
+
+	pattern attr1 attr2 ...
+
+That is, a pattern followed by an attributes list,
+separated by whitespaces. Leading and trailing whitespaces are
+ignored. Lines that begin with '#' are ignored. Patterns
+that begin with a double quote are quoted in C style.
+When the pattern matches the path in question, the attributes
+listed on the line are given to the path.
+
+Each attribute can be in one of these states for a given path:
+
+Set::
+
+	The path has the attribute with special value "true";
+	this is specified by listing only the name of the
+	attribute in the attribute list.
+
+Unset::
+
+	The path has the attribute with special value "false";
+	this is specified by listing the name of the attribute
+	prefixed with a dash `-` in the attribute list.
+
+Set to a value::
+
+	The path has the attribute with specified string value;
+	this is specified by listing the name of the attribute
+	followed by an equal sign `=` and its value in the
+	attribute list.
+
+Unspecified::
+
+	No pattern matches the path, and nothing says if
+	the path has or does not have the attribute, the
+	attribute for the path is said to be Unspecified.
+
+When more than one pattern matches the path, a later line
+overrides an earlier line.  This overriding is done per
+attribute.
+
+The rules by which the pattern matches paths are the same as in
+`.gitignore` files (see linkgit:gitignore[5]), with a few exceptions:
+
+  - negative patterns are forbidden
+
+  - patterns that match a directory do not recursively match paths
+    inside that directory (so using the trailing-slash `path/` syntax is
+    pointless in an attributes file; use `path/**` instead)
+
+When deciding what attributes are assigned to a path, Git
+consults `$GIT_DIR/info/attributes` file (which has the highest
+precedence), `.gitattributes` file in the same directory as the
+path in question, and its parent directories up to the toplevel of the
+work tree (the further the directory that contains `.gitattributes`
+is from the path in question, the lower its precedence). Finally
+global and system-wide files are considered (they have the lowest
+precedence).
+
+When the `.gitattributes` file is missing from the work tree, the
+path in the index is used as a fall-back.  During checkout process,
+`.gitattributes` in the index is used and then the file in the
+working tree is used as a fall-back.
+
+If you wish to affect only a single repository (i.e., to assign
+attributes to files that are particular to
+one user's workflow for that repository), then
+attributes should be placed in the `$GIT_DIR/info/attributes` file.
+Attributes which should be version-controlled and distributed to other
+repositories (i.e., attributes of interest to all users) should go into
+`.gitattributes` files. Attributes that should affect all repositories
+for a single user should be placed in a file specified by the
+`core.attributesFile` configuration option (see linkgit:git-config[1]).
+Its default value is $XDG_CONFIG_HOME/git/attributes. If $XDG_CONFIG_HOME
+is either not set or empty, $HOME/.config/git/attributes is used instead.
+Attributes for all users on a system should be placed in the
+`$(prefix)/etc/gitattributes` file.
+
+Sometimes you would need to override a setting of an attribute
+for a path to `Unspecified` state.  This can be done by listing
+the name of the attribute prefixed with an exclamation point `!`.
+
+
+EFFECTS
+-------
+
+Certain operations by Git can be influenced by assigning
+particular attributes to a path.  Currently, the following
+operations are attributes-aware.
+
+Checking-out and checking-in
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These attributes affect how the contents stored in the
+repository are copied to the working tree files when commands
+such as 'git switch', 'git checkout'  and 'git merge' run.
+They also affect how
+Git stores the contents you prepare in the working tree in the
+repository upon 'git add' and 'git commit'.
+
+`text`
+^^^^^^
+
+This attribute enables and controls end-of-line normalization.  When a
+text file is normalized, its line endings are converted to LF in the
+repository.  To control what line ending style is used in the working
+directory, use the `eol` attribute for a single file and the
+`core.eol` configuration variable for all text files.
+Note that setting `core.autocrlf` to `true` or `input` overrides
+`core.eol` (see the definitions of those options in
+linkgit:git-config[1]).
+
+Set::
+
+	Setting the `text` attribute on a path enables end-of-line
+	normalization and marks the path as a text file.  End-of-line
+	conversion takes place without guessing the content type.
+
+Unset::
+
+	Unsetting the `text` attribute on a path tells Git not to
+	attempt any end-of-line conversion upon checkin or checkout.
+
+Set to string value "auto"::
+
+	When `text` is set to "auto", the path is marked for automatic
+	end-of-line conversion.  If Git decides that the content is
+	text, its line endings are converted to LF on checkin.
+	When the file has been committed with CRLF, no conversion is done.
+
+Unspecified::
+
+	If the `text` attribute is unspecified, Git uses the
+	`core.autocrlf` configuration variable to determine if the
+	file should be converted.
+
+Any other value causes Git to act as if `text` has been left
+unspecified.
+
+`eol`
+^^^^^
+
+This attribute sets a specific line-ending style to be used in the
+working directory.  It enables end-of-line conversion without any
+content checks, effectively setting the `text` attribute.  Note that
+setting this attribute on paths which are in the index with CRLF line
+endings may make the paths to be considered dirty.  Adding the path to
+the index again will normalize the line endings in the index.
+
+Set to string value "crlf"::
+
+	This setting forces Git to normalize line endings for this
+	file on checkin and convert them to CRLF when the file is
+	checked out.
+
+Set to string value "lf"::
+
+	This setting forces Git to normalize line endings to LF on
+	checkin and prevents conversion to CRLF when the file is
+	checked out.
+
+Backwards compatibility with `crlf` attribute
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+For backwards compatibility, the `crlf` attribute is interpreted as
+follows:
+
+------------------------
+crlf		text
+-crlf		-text
+crlf=input	eol=lf
+------------------------
+
+End-of-line conversion
+^^^^^^^^^^^^^^^^^^^^^^
+
+While Git normally leaves file contents alone, it can be configured to
+normalize line endings to LF in the repository and, optionally, to
+convert them to CRLF when files are checked out.
+
+If you simply want to have CRLF line endings in your working directory
+regardless of the repository you are working with, you can set the
+config variable "core.autocrlf" without using any attributes.
+
+------------------------
+[core]
+	autocrlf = true
+------------------------
+
+This does not force normalization of text files, but does ensure
+that text files that you introduce to the repository have their line
+endings normalized to LF when they are added, and that files that are
+already normalized in the repository stay normalized.
+
+If you want to ensure that text files that any contributor introduces to
+the repository have their line endings normalized, you can set the
+`text` attribute to "auto" for _all_ files.
+
+------------------------
+*	text=auto
+------------------------
+
+The attributes allow a fine-grained control, how the line endings
+are converted.
+Here is an example that will make Git normalize .txt, .vcproj and .sh
+files, ensure that .vcproj files have CRLF and .sh files have LF in
+the working directory, and prevent .jpg files from being normalized
+regardless of their content.
+
+------------------------
+*               text=auto
+*.txt		text
+*.vcproj	text eol=crlf
+*.sh		text eol=lf
+*.jpg		-text
+------------------------
+
+NOTE: When `text=auto` conversion is enabled in a cross-platform
+project using push and pull to a central repository the text files
+containing CRLFs should be normalized.
+
+From a clean working directory:
+
+-------------------------------------------------
+$ echo "* text=auto" >.gitattributes
+$ git add --renormalize .
+$ git status        # Show files that will be normalized
+$ git commit -m "Introduce end-of-line normalization"
+-------------------------------------------------
+
+If any files that should not be normalized show up in 'git status',
+unset their `text` attribute before running 'git add -u'.
+
+------------------------
+manual.pdf	-text
+------------------------
+
+Conversely, text files that Git does not detect can have normalization
+enabled manually.
+
+------------------------
+weirdchars.txt	text
+------------------------
+
+If `core.safecrlf` is set to "true" or "warn", Git verifies if
+the conversion is reversible for the current setting of
+`core.autocrlf`.  For "true", Git rejects irreversible
+conversions; for "warn", Git only prints a warning but accepts
+an irreversible conversion.  The safety triggers to prevent such
+a conversion done to the files in the work tree, but there are a
+few exceptions.  Even though...
+
+- 'git add' itself does not touch the files in the work tree, the
+  next checkout would, so the safety triggers;
+
+- 'git apply' to update a text file with a patch does touch the files
+  in the work tree, but the operation is about text files and CRLF
+  conversion is about fixing the line ending inconsistencies, so the
+  safety does not trigger;
+
+- 'git diff' itself does not touch the files in the work tree, it is
+  often run to inspect the changes you intend to next 'git add'.  To
+  catch potential problems early, safety triggers.
+
+
+`working-tree-encoding`
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Git recognizes files encoded in ASCII or one of its supersets (e.g.
+UTF-8, ISO-8859-1, ...) as text files. Files encoded in certain other
+encodings (e.g. UTF-16) are interpreted as binary and consequently
+built-in Git text processing tools (e.g. 'git diff') as well as most Git
+web front ends do not visualize the contents of these files by default.
+
+In these cases you can tell Git the encoding of a file in the working
+directory with the `working-tree-encoding` attribute. If a file with this
+attribute is added to Git, then Git reencodes the content from the
+specified encoding to UTF-8. Finally, Git stores the UTF-8 encoded
+content in its internal data structure (called "the index"). On checkout
+the content is reencoded back to the specified encoding.
+
+Please note that using the `working-tree-encoding` attribute may have a
+number of pitfalls:
+
+- Alternative Git implementations (e.g. JGit or libgit2) and older Git
+  versions (as of March 2018) do not support the `working-tree-encoding`
+  attribute. If you decide to use the `working-tree-encoding` attribute
+  in your repository, then it is strongly recommended to ensure that all
+  clients working with the repository support it.
++
+For example, Microsoft Visual Studio resources files (`*.rc`) or
+PowerShell script files (`*.ps1`) are sometimes encoded in UTF-16.
+If you declare `*.ps1` as files as UTF-16 and you add `foo.ps1` with
+a `working-tree-encoding` enabled Git client, then `foo.ps1` will be
+stored as UTF-8 internally. A client without `working-tree-encoding`
+support will checkout `foo.ps1` as UTF-8 encoded file. This will
+typically cause trouble for the users of this file.
++
+If a Git client that does not support the `working-tree-encoding`
+attribute adds a new file `bar.ps1`, then `bar.ps1` will be
+stored "as-is" internally (in this example probably as UTF-16).
+A client with `working-tree-encoding` support will interpret the
+internal contents as UTF-8 and try to convert it to UTF-16 on checkout.
+That operation will fail and cause an error.
+
+- Reencoding content to non-UTF encodings can cause errors as the
+  conversion might not be UTF-8 round trip safe. If you suspect your
+  encoding to not be round trip safe, then add it to
+  `core.checkRoundtripEncoding` to make Git check the round trip
+  encoding (see linkgit:git-config[1]). SHIFT-JIS (Japanese character
+  set) is known to have round trip issues with UTF-8 and is checked by
+  default.
+
+- Reencoding content requires resources that might slow down certain
+  Git operations (e.g 'git checkout' or 'git add').
+
+Use the `working-tree-encoding` attribute only if you cannot store a file
+in UTF-8 encoding and if you want Git to be able to process the content
+as text.
+
+As an example, use the following attributes if your '*.ps1' files are
+UTF-16 encoded with byte order mark (BOM) and you want Git to perform
+automatic line ending conversion based on your platform.
+
+------------------------
+*.ps1		text working-tree-encoding=UTF-16
+------------------------
+
+Use the following attributes if your '*.ps1' files are UTF-16 little
+endian encoded without BOM and you want Git to use Windows line endings
+in the working directory (use `UTF-16LE-BOM` instead of `UTF-16LE` if
+you want UTF-16 little endian with BOM).
+Please note, it is highly recommended to
+explicitly define the line endings with `eol` if the `working-tree-encoding`
+attribute is used to avoid ambiguity.
+
+------------------------
+*.ps1		text working-tree-encoding=UTF-16LE eol=CRLF
+------------------------
+
+You can get a list of all available encodings on your platform with the
+following command:
+
+------------------------
+iconv --list
+------------------------
+
+If you do not know the encoding of a file, then you can use the `file`
+command to guess the encoding:
+
+------------------------
+file foo.ps1
+------------------------
+
+
+`ident`
+^^^^^^^
+
+When the attribute `ident` is set for a path, Git replaces
+`$Id$` in the blob object with `$Id:`, followed by the
+40-character hexadecimal blob object name, followed by a dollar
+sign `$` upon checkout.  Any byte sequence that begins with
+`$Id:` and ends with `$` in the worktree file is replaced
+with `$Id$` upon check-in.
+
+
+`filter`
+^^^^^^^^
+
+A `filter` attribute can be set to a string value that names a
+filter driver specified in the configuration.
+
+A filter driver consists of a `clean` command and a `smudge`
+command, either of which can be left unspecified.  Upon
+checkout, when the `smudge` command is specified, the command is
+fed the blob object from its standard input, and its standard
+output is used to update the worktree file.  Similarly, the
+`clean` command is used to convert the contents of worktree file
+upon checkin. By default these commands process only a single
+blob and terminate. If a long running `process` filter is used
+in place of `clean` and/or `smudge` filters, then Git can process
+all blobs with a single filter command invocation for the entire
+life of a single Git command, for example `git add --all`. If a
+long running `process` filter is configured then it always takes
+precedence over a configured single blob filter. See section
+below for the description of the protocol used to communicate with
+a `process` filter.
+
+One use of the content filtering is to massage the content into a shape
+that is more convenient for the platform, filesystem, and the user to use.
+For this mode of operation, the key phrase here is "more convenient" and
+not "turning something unusable into usable".  In other words, the intent
+is that if someone unsets the filter driver definition, or does not have
+the appropriate filter program, the project should still be usable.
+
+Another use of the content filtering is to store the content that cannot
+be directly used in the repository (e.g. a UUID that refers to the true
+content stored outside Git, or an encrypted content) and turn it into a
+usable form upon checkout (e.g. download the external content, or decrypt
+the encrypted content).
+
+These two filters behave differently, and by default, a filter is taken as
+the former, massaging the contents into more convenient shape.  A missing
+filter driver definition in the config, or a filter driver that exits with
+a non-zero status, is not an error but makes the filter a no-op passthru.
+
+You can declare that a filter turns a content that by itself is unusable
+into a usable content by setting the filter.<driver>.required configuration
+variable to `true`.
+
+Note: Whenever the clean filter is changed, the repo should be renormalized:
+$ git add --renormalize .
+
+For example, in .gitattributes, you would assign the `filter`
+attribute for paths.
+
+------------------------
+*.c	filter=indent
+------------------------
+
+Then you would define a "filter.indent.clean" and "filter.indent.smudge"
+configuration in your .git/config to specify a pair of commands to
+modify the contents of C programs when the source files are checked
+in ("clean" is run) and checked out (no change is made because the
+command is "cat").
+
+------------------------
+[filter "indent"]
+	clean = indent
+	smudge = cat
+------------------------
+
+For best results, `clean` should not alter its output further if it is
+run twice ("clean->clean" should be equivalent to "clean"), and
+multiple `smudge` commands should not alter `clean`'s output
+("smudge->smudge->clean" should be equivalent to "clean").  See the
+section on merging below.
+
+The "indent" filter is well-behaved in this regard: it will not modify
+input that is already correctly indented.  In this case, the lack of a
+smudge filter means that the clean filter _must_ accept its own output
+without modifying it.
+
+If a filter _must_ succeed in order to make the stored contents usable,
+you can declare that the filter is `required`, in the configuration:
+
+------------------------
+[filter "crypt"]
+	clean = openssl enc ...
+	smudge = openssl enc -d ...
+	required
+------------------------
+
+Sequence "%f" on the filter command line is replaced with the name of
+the file the filter is working on.  A filter might use this in keyword
+substitution.  For example:
+
+------------------------
+[filter "p4"]
+	clean = git-p4-filter --clean %f
+	smudge = git-p4-filter --smudge %f
+------------------------
+
+Note that "%f" is the name of the path that is being worked on. Depending
+on the version that is being filtered, the corresponding file on disk may
+not exist, or may have different contents. So, smudge and clean commands
+should not try to access the file on disk, but only act as filters on the
+content provided to them on standard input.
+
+Long Running Filter Process
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If the filter command (a string value) is defined via
+`filter.<driver>.process` then Git can process all blobs with a
+single filter invocation for the entire life of a single Git
+command. This is achieved by using the long-running process protocol
+(described in technical/long-running-process-protocol.txt).
+
+When Git encounters the first file that needs to be cleaned or smudged,
+it starts the filter and performs the handshake. In the handshake, the
+welcome message sent by Git is "git-filter-client", only version 2 is
+suppported, and the supported capabilities are "clean", "smudge", and
+"delay".
+
+Afterwards Git sends a list of "key=value" pairs terminated with
+a flush packet. The list will contain at least the filter command
+(based on the supported capabilities) and the pathname of the file
+to filter relative to the repository root. Right after the flush packet
+Git sends the content split in zero or more pkt-line packets and a
+flush packet to terminate content. Please note, that the filter
+must not send any response before it received the content and the
+final flush packet. Also note that the "value" of a "key=value" pair
+can contain the "=" character whereas the key would never contain
+that character.
+------------------------
+packet:          git> command=smudge
+packet:          git> pathname=path/testfile.dat
+packet:          git> 0000
+packet:          git> CONTENT
+packet:          git> 0000
+------------------------
+
+The filter is expected to respond with a list of "key=value" pairs
+terminated with a flush packet. If the filter does not experience
+problems then the list must contain a "success" status. Right after
+these packets the filter is expected to send the content in zero
+or more pkt-line packets and a flush packet at the end. Finally, a
+second list of "key=value" pairs terminated with a flush packet
+is expected. The filter can change the status in the second list
+or keep the status as is with an empty list. Please note that the
+empty list must be terminated with a flush packet regardless.
+
+------------------------
+packet:          git< status=success
+packet:          git< 0000
+packet:          git< SMUDGED_CONTENT
+packet:          git< 0000
+packet:          git< 0000  # empty list, keep "status=success" unchanged!
+------------------------
+
+If the result content is empty then the filter is expected to respond
+with a "success" status and a flush packet to signal the empty content.
+------------------------
+packet:          git< status=success
+packet:          git< 0000
+packet:          git< 0000  # empty content!
+packet:          git< 0000  # empty list, keep "status=success" unchanged!
+------------------------
+
+In case the filter cannot or does not want to process the content,
+it is expected to respond with an "error" status.
+------------------------
+packet:          git< status=error
+packet:          git< 0000
+------------------------
+
+If the filter experiences an error during processing, then it can
+send the status "error" after the content was (partially or
+completely) sent.
+------------------------
+packet:          git< status=success
+packet:          git< 0000
+packet:          git< HALF_WRITTEN_ERRONEOUS_CONTENT
+packet:          git< 0000
+packet:          git< status=error
+packet:          git< 0000
+------------------------
+
+In case the filter cannot or does not want to process the content
+as well as any future content for the lifetime of the Git process,
+then it is expected to respond with an "abort" status at any point
+in the protocol.
+------------------------
+packet:          git< status=abort
+packet:          git< 0000
+------------------------
+
+Git neither stops nor restarts the filter process in case the
+"error"/"abort" status is set. However, Git sets its exit code
+according to the `filter.<driver>.required` flag, mimicking the
+behavior of the `filter.<driver>.clean` / `filter.<driver>.smudge`
+mechanism.
+
+If the filter dies during the communication or does not adhere to
+the protocol then Git will stop the filter process and restart it
+with the next file that needs to be processed. Depending on the
+`filter.<driver>.required` flag Git will interpret that as error.
+
+Delay
+^^^^^
+
+If the filter supports the "delay" capability, then Git can send the
+flag "can-delay" after the filter command and pathname. This flag
+denotes that the filter can delay filtering the current blob (e.g. to
+compensate network latencies) by responding with no content but with
+the status "delayed" and a flush packet.
+------------------------
+packet:          git> command=smudge
+packet:          git> pathname=path/testfile.dat
+packet:          git> can-delay=1
+packet:          git> 0000
+packet:          git> CONTENT
+packet:          git> 0000
+packet:          git< status=delayed
+packet:          git< 0000
+------------------------
+
+If the filter supports the "delay" capability then it must support the
+"list_available_blobs" command. If Git sends this command, then the
+filter is expected to return a list of pathnames representing blobs
+that have been delayed earlier and are now available.
+The list must be terminated with a flush packet followed
+by a "success" status that is also terminated with a flush packet. If
+no blobs for the delayed paths are available, yet, then the filter is
+expected to block the response until at least one blob becomes
+available. The filter can tell Git that it has no more delayed blobs
+by sending an empty list. As soon as the filter responds with an empty
+list, Git stops asking. All blobs that Git has not received at this
+point are considered missing and will result in an error.
+
+------------------------
+packet:          git> command=list_available_blobs
+packet:          git> 0000
+packet:          git< pathname=path/testfile.dat
+packet:          git< pathname=path/otherfile.dat
+packet:          git< 0000
+packet:          git< status=success
+packet:          git< 0000
+------------------------
+
+After Git received the pathnames, it will request the corresponding
+blobs again. These requests contain a pathname and an empty content
+section. The filter is expected to respond with the smudged content
+in the usual way as explained above.
+------------------------
+packet:          git> command=smudge
+packet:          git> pathname=path/testfile.dat
+packet:          git> 0000
+packet:          git> 0000  # empty content!
+packet:          git< status=success
+packet:          git< 0000
+packet:          git< SMUDGED_CONTENT
+packet:          git< 0000
+packet:          git< 0000  # empty list, keep "status=success" unchanged!
+------------------------
+
+Example
+^^^^^^^
+
+A long running filter demo implementation can be found in
+`contrib/long-running-filter/example.pl` located in the Git
+core repository. If you develop your own long running filter
+process then the `GIT_TRACE_PACKET` environment variables can be
+very helpful for debugging (see linkgit:git[1]).
+
+Please note that you cannot use an existing `filter.<driver>.clean`
+or `filter.<driver>.smudge` command with `filter.<driver>.process`
+because the former two use a different inter process communication
+protocol than the latter one.
+
+
+Interaction between checkin/checkout attributes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In the check-in codepath, the worktree file is first converted
+with `filter` driver (if specified and corresponding driver
+defined), then the result is processed with `ident` (if
+specified), and then finally with `text` (again, if specified
+and applicable).
+
+In the check-out codepath, the blob content is first converted
+with `text`, and then `ident` and fed to `filter`.
+
+
+Merging branches with differing checkin/checkout attributes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If you have added attributes to a file that cause the canonical
+repository format for that file to change, such as adding a
+clean/smudge filter or text/eol/ident attributes, merging anything
+where the attribute is not in place would normally cause merge
+conflicts.
+
+To prevent these unnecessary merge conflicts, Git can be told to run a
+virtual check-out and check-in of all three stages of a file when
+resolving a three-way merge by setting the `merge.renormalize`
+configuration variable.  This prevents changes caused by check-in
+conversion from causing spurious merge conflicts when a converted file
+is merged with an unconverted file.
+
+As long as a "smudge->clean" results in the same output as a "clean"
+even on files that are already smudged, this strategy will
+automatically resolve all filter-related conflicts.  Filters that do
+not act in this way may cause additional merge conflicts that must be
+resolved manually.
+
+
+Generating diff text
+~~~~~~~~~~~~~~~~~~~~
+
+`diff`
+^^^^^^
+
+The attribute `diff` affects how Git generates diffs for particular
+files. It can tell Git whether to generate a textual patch for the path
+or to treat the path as a binary file.  It can also affect what line is
+shown on the hunk header `@@ -k,l +n,m @@` line, tell Git to use an
+external command to generate the diff, or ask Git to convert binary
+files to a text format before generating the diff.
+
+Set::
+
+	A path to which the `diff` attribute is set is treated
+	as text, even when they contain byte values that
+	normally never appear in text files, such as NUL.
+
+Unset::
+
+	A path to which the `diff` attribute is unset will
+	generate `Binary files differ` (or a binary patch, if
+	binary patches are enabled).
+
+Unspecified::
+
+	A path to which the `diff` attribute is unspecified
+	first gets its contents inspected, and if it looks like
+	text and is smaller than core.bigFileThreshold, it is treated
+	as text. Otherwise it would generate `Binary files differ`.
+
+String::
+
+	Diff is shown using the specified diff driver.  Each driver may
+	specify one or more options, as described in the following
+	section. The options for the diff driver "foo" are defined
+	by the configuration variables in the "diff.foo" section of the
+	Git config file.
+
+
+Defining an external diff driver
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The definition of a diff driver is done in `gitconfig`, not
+`gitattributes` file, so strictly speaking this manual page is a
+wrong place to talk about it.  However...
+
+To define an external diff driver `jcdiff`, add a section to your
+`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:
+
+----------------------------------------------------------------
+[diff "jcdiff"]
+	command = j-c-diff
+----------------------------------------------------------------
+
+When Git needs to show you a diff for the path with `diff`
+attribute set to `jcdiff`, it calls the command you specified
+with the above configuration, i.e. `j-c-diff`, with 7
+parameters, just like `GIT_EXTERNAL_DIFF` program is called.
+See linkgit:git[1] for details.
+
+
+Defining a custom hunk-header
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Each group of changes (called a "hunk") in the textual diff output
+is prefixed with a line of the form:
+
+	@@ -k,l +n,m @@ TEXT
+
+This is called a 'hunk header'.  The "TEXT" portion is by default a line
+that begins with an alphabet, an underscore or a dollar sign; this
+matches what GNU 'diff -p' output uses.  This default selection however
+is not suited for some contents, and you can use a customized pattern
+to make a selection.
+
+First, in .gitattributes, you would assign the `diff` attribute
+for paths.
+
+------------------------
+*.tex	diff=tex
+------------------------
+
+Then, you would define a "diff.tex.xfuncname" configuration to
+specify a regular expression that matches a line that you would
+want to appear as the hunk header "TEXT". Add a section to your
+`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:
+
+------------------------
+[diff "tex"]
+	xfuncname = "^(\\\\(sub)*section\\{.*)$"
+------------------------
+
+Note.  A single level of backslashes are eaten by the
+configuration file parser, so you would need to double the
+backslashes; the pattern above picks a line that begins with a
+backslash, and zero or more occurrences of `sub` followed by
+`section` followed by open brace, to the end of line.
+
+There are a few built-in patterns to make this easier, and `tex`
+is one of them, so you do not have to write the above in your
+configuration file (you still need to enable this with the
+attribute mechanism, via `.gitattributes`).  The following built in
+patterns are available:
+
+- `ada` suitable for source code in the Ada language.
+
+- `bibtex` suitable for files with BibTeX coded references.
+
+- `cpp` suitable for source code in the C and C++ languages.
+
+- `csharp` suitable for source code in the C# language.
+
+- `css` suitable for cascading style sheets.
+
+- `fortran` suitable for source code in the Fortran language.
+
+- `fountain` suitable for Fountain documents.
+
+- `golang` suitable for source code in the Go language.
+
+- `html` suitable for HTML/XHTML documents.
+
+- `java` suitable for source code in the Java language.
+
+- `matlab` suitable for source code in the MATLAB and Octave languages.
+
+- `objc` suitable for source code in the Objective-C language.
+
+- `pascal` suitable for source code in the Pascal/Delphi language.
+
+- `perl` suitable for source code in the Perl language.
+
+- `php` suitable for source code in the PHP language.
+
+- `python` suitable for source code in the Python language.
+
+- `ruby` suitable for source code in the Ruby language.
+
+- `rust` suitable for source code in the Rust language.
+
+- `tex` suitable for source code for LaTeX documents.
+
+
+Customizing word diff
+^^^^^^^^^^^^^^^^^^^^^
+
+You can customize the rules that `git diff --word-diff` uses to
+split words in a line, by specifying an appropriate regular expression
+in the "diff.*.wordRegex" configuration variable.  For example, in TeX
+a backslash followed by a sequence of letters forms a command, but
+several such commands can be run together without intervening
+whitespace.  To separate them, use a regular expression in your
+`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:
+
+------------------------
+[diff "tex"]
+	wordRegex = "\\\\[a-zA-Z]+|[{}]|\\\\.|[^\\{}[:space:]]+"
+------------------------
+
+A built-in pattern is provided for all languages listed in the
+previous section.
+
+
+Performing text diffs of binary files
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Sometimes it is desirable to see the diff of a text-converted
+version of some binary files. For example, a word processor
+document can be converted to an ASCII text representation, and
+the diff of the text shown. Even though this conversion loses
+some information, the resulting diff is useful for human
+viewing (but cannot be applied directly).
+
+The `textconv` config option is used to define a program for
+performing such a conversion. The program should take a single
+argument, the name of a file to convert, and produce the
+resulting text on stdout.
+
+For example, to show the diff of the exif information of a
+file instead of the binary information (assuming you have the
+exif tool installed), add the following section to your
+`$GIT_DIR/config` file (or `$HOME/.gitconfig` file):
+
+------------------------
+[diff "jpg"]
+	textconv = exif
+------------------------
+
+NOTE: The text conversion is generally a one-way conversion;
+in this example, we lose the actual image contents and focus
+just on the text data. This means that diffs generated by
+textconv are _not_ suitable for applying. For this reason,
+only `git diff` and the `git log` family of commands (i.e.,
+log, whatchanged, show) will perform text conversion. `git
+format-patch` will never generate this output. If you want to
+send somebody a text-converted diff of a binary file (e.g.,
+because it quickly conveys the changes you have made), you
+should generate it separately and send it as a comment _in
+addition to_ the usual binary diff that you might send.
+
+Because text conversion can be slow, especially when doing a
+large number of them with `git log -p`, Git provides a mechanism
+to cache the output and use it in future diffs.  To enable
+caching, set the "cachetextconv" variable in your diff driver's
+config. For example:
+
+------------------------
+[diff "jpg"]
+	textconv = exif
+	cachetextconv = true
+------------------------
+
+This will cache the result of running "exif" on each blob
+indefinitely. If you change the textconv config variable for a
+diff driver, Git will automatically invalidate the cache entries
+and re-run the textconv filter. If you want to invalidate the
+cache manually (e.g., because your version of "exif" was updated
+and now produces better output), you can remove the cache
+manually with `git update-ref -d refs/notes/textconv/jpg` (where
+"jpg" is the name of the diff driver, as in the example above).
+
+Choosing textconv versus external diff
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If you want to show differences between binary or specially-formatted
+blobs in your repository, you can choose to use either an external diff
+command, or to use textconv to convert them to a diff-able text format.
+Which method you choose depends on your exact situation.
+
+The advantage of using an external diff command is flexibility. You are
+not bound to find line-oriented changes, nor is it necessary for the
+output to resemble unified diff. You are free to locate and report
+changes in the most appropriate way for your data format.
+
+A textconv, by comparison, is much more limiting. You provide a
+transformation of the data into a line-oriented text format, and Git
+uses its regular diff tools to generate the output. There are several
+advantages to choosing this method:
+
+1. Ease of use. It is often much simpler to write a binary to text
+   transformation than it is to perform your own diff. In many cases,
+   existing programs can be used as textconv filters (e.g., exif,
+   odt2txt).
+
+2. Git diff features. By performing only the transformation step
+   yourself, you can still utilize many of Git's diff features,
+   including colorization, word-diff, and combined diffs for merges.
+
+3. Caching. Textconv caching can speed up repeated diffs, such as those
+   you might trigger by running `git log -p`.
+
+
+Marking files as binary
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Git usually guesses correctly whether a blob contains text or binary
+data by examining the beginning of the contents. However, sometimes you
+may want to override its decision, either because a blob contains binary
+data later in the file, or because the content, while technically
+composed of text characters, is opaque to a human reader. For example,
+many postscript files contain only ASCII characters, but produce noisy
+and meaningless diffs.
+
+The simplest way to mark a file as binary is to unset the diff
+attribute in the `.gitattributes` file:
+
+------------------------
+*.ps -diff
+------------------------
+
+This will cause Git to generate `Binary files differ` (or a binary
+patch, if binary patches are enabled) instead of a regular diff.
+
+However, one may also want to specify other diff driver attributes. For
+example, you might want to use `textconv` to convert postscript files to
+an ASCII representation for human viewing, but otherwise treat them as
+binary files. You cannot specify both `-diff` and `diff=ps` attributes.
+The solution is to use the `diff.*.binary` config option:
+
+------------------------
+[diff "ps"]
+  textconv = ps2ascii
+  binary = true
+------------------------
+
+Performing a three-way merge
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+`merge`
+^^^^^^^
+
+The attribute `merge` affects how three versions of a file are
+merged when a file-level merge is necessary during `git merge`,
+and other commands such as `git revert` and `git cherry-pick`.
+
+Set::
+
+	Built-in 3-way merge driver is used to merge the
+	contents in a way similar to 'merge' command of `RCS`
+	suite.  This is suitable for ordinary text files.
+
+Unset::
+
+	Take the version from the current branch as the
+	tentative merge result, and declare that the merge has
+	conflicts.  This is suitable for binary files that do
+	not have a well-defined merge semantics.
+
+Unspecified::
+
+	By default, this uses the same built-in 3-way merge
+	driver as is the case when the `merge` attribute is set.
+	However, the `merge.default` configuration variable can name
+	different merge driver to be used with paths for which the
+	`merge` attribute is unspecified.
+
+String::
+
+	3-way merge is performed using the specified custom
+	merge driver.  The built-in 3-way merge driver can be
+	explicitly specified by asking for "text" driver; the
+	built-in "take the current branch" driver can be
+	requested with "binary".
+
+
+Built-in merge drivers
+^^^^^^^^^^^^^^^^^^^^^^
+
+There are a few built-in low-level merge drivers defined that
+can be asked for via the `merge` attribute.
+
+text::
+
+	Usual 3-way file level merge for text files.  Conflicted
+	regions are marked with conflict markers `<<<<<<<`,
+	`=======` and `>>>>>>>`.  The version from your branch
+	appears before the `=======` marker, and the version
+	from the merged branch appears after the `=======`
+	marker.
+
+binary::
+
+	Keep the version from your branch in the work tree, but
+	leave the path in the conflicted state for the user to
+	sort out.
+
+union::
+
+	Run 3-way file level merge for text files, but take
+	lines from both versions, instead of leaving conflict
+	markers.  This tends to leave the added lines in the
+	resulting file in random order and the user should
+	verify the result. Do not use this if you do not
+	understand the implications.
+
+
+Defining a custom merge driver
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The definition of a merge driver is done in the `.git/config`
+file, not in the `gitattributes` file, so strictly speaking this
+manual page is a wrong place to talk about it.  However...
+
+To define a custom merge driver `filfre`, add a section to your
+`$GIT_DIR/config` file (or `$HOME/.gitconfig` file) like this:
+
+----------------------------------------------------------------
+[merge "filfre"]
+	name = feel-free merge driver
+	driver = filfre %O %A %B %L %P
+	recursive = binary
+----------------------------------------------------------------
+
+The `merge.*.name` variable gives the driver a human-readable
+name.
+
+The `merge.*.driver` variable's value is used to construct a
+command to run to merge ancestor's version (`%O`), current
+version (`%A`) and the other branches' version (`%B`).  These
+three tokens are replaced with the names of temporary files that
+hold the contents of these versions when the command line is
+built. Additionally, %L will be replaced with the conflict marker
+size (see below).
+
+The merge driver is expected to leave the result of the merge in
+the file named with `%A` by overwriting it, and exit with zero
+status if it managed to merge them cleanly, or non-zero if there
+were conflicts.
+
+The `merge.*.recursive` variable specifies what other merge
+driver to use when the merge driver is called for an internal
+merge between common ancestors, when there are more than one.
+When left unspecified, the driver itself is used for both
+internal merge and the final merge.
+
+The merge driver can learn the pathname in which the merged result
+will be stored via placeholder `%P`.
+
+
+`conflict-marker-size`
+^^^^^^^^^^^^^^^^^^^^^^
+
+This attribute controls the length of conflict markers left in
+the work tree file during a conflicted merge.  Only setting to
+the value to a positive integer has any meaningful effect.
+
+For example, this line in `.gitattributes` can be used to tell the merge
+machinery to leave much longer (instead of the usual 7-character-long)
+conflict markers when merging the file `Documentation/git-merge.txt`
+results in a conflict.
+
+------------------------
+Documentation/git-merge.txt	conflict-marker-size=32
+------------------------
+
+
+Checking whitespace errors
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+`whitespace`
+^^^^^^^^^^^^
+
+The `core.whitespace` configuration variable allows you to define what
+'diff' and 'apply' should consider whitespace errors for all paths in
+the project (See linkgit:git-config[1]).  This attribute gives you finer
+control per path.
+
+Set::
+
+	Notice all types of potential whitespace errors known to Git.
+	The tab width is taken from the value of the `core.whitespace`
+	configuration variable.
+
+Unset::
+
+	Do not notice anything as error.
+
+Unspecified::
+
+	Use the value of the `core.whitespace` configuration variable to
+	decide what to notice as error.
+
+String::
+
+	Specify a comma separate list of common whitespace problems to
+	notice in the same format as the `core.whitespace` configuration
+	variable.
+
+
+Creating an archive
+~~~~~~~~~~~~~~~~~~~
+
+`export-ignore`
+^^^^^^^^^^^^^^^
+
+Files and directories with the attribute `export-ignore` won't be added to
+archive files.
+
+`export-subst`
+^^^^^^^^^^^^^^
+
+If the attribute `export-subst` is set for a file then Git will expand
+several placeholders when adding this file to an archive.  The
+expansion depends on the availability of a commit ID, i.e., if
+linkgit:git-archive[1] has been given a tree instead of a commit or a
+tag then no replacement will be done.  The placeholders are the same
+as those for the option `--pretty=format:` of linkgit:git-log[1],
+except that they need to be wrapped like this: `$Format:PLACEHOLDERS$`
+in the file.  E.g. the string `$Format:%H$` will be replaced by the
+commit hash.
+
+
+Packing objects
+~~~~~~~~~~~~~~~
+
+`delta`
+^^^^^^^
+
+Delta compression will not be attempted for blobs for paths with the
+attribute `delta` set to false.
+
+
+Viewing files in GUI tools
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+`encoding`
+^^^^^^^^^^
+
+The value of this attribute specifies the character encoding that should
+be used by GUI tools (e.g. linkgit:gitk[1] and linkgit:git-gui[1]) to
+display the contents of the relevant file. Note that due to performance
+considerations linkgit:gitk[1] does not use this attribute unless you
+manually enable per-file encodings in its options.
+
+If this attribute is not set or has an invalid value, the value of the
+`gui.encoding` configuration variable is used instead
+(See linkgit:git-config[1]).
+
+
+USING MACRO ATTRIBUTES
+----------------------
+
+You do not want any end-of-line conversions applied to, nor textual diffs
+produced for, any binary file you track.  You would need to specify e.g.
+
+------------
+*.jpg -text -diff
+------------
+
+but that may become cumbersome, when you have many attributes.  Using
+macro attributes, you can define an attribute that, when set, also
+sets or unsets a number of other attributes at the same time.  The
+system knows a built-in macro attribute, `binary`:
+
+------------
+*.jpg binary
+------------
+
+Setting the "binary" attribute also unsets the "text" and "diff"
+attributes as above.  Note that macro attributes can only be "Set",
+though setting one might have the effect of setting or unsetting other
+attributes or even returning other attributes to the "Unspecified"
+state.
+
+
+DEFINING MACRO ATTRIBUTES
+-------------------------
+
+Custom macro attributes can be defined only in top-level gitattributes
+files (`$GIT_DIR/info/attributes`, the `.gitattributes` file at the
+top level of the working tree, or the global or system-wide
+gitattributes files), not in `.gitattributes` files in working tree
+subdirectories.  The built-in macro attribute "binary" is equivalent
+to:
+
+------------
+[attr]binary -diff -merge -text
+------------
+
+
+EXAMPLES
+--------
+
+If you have these three `gitattributes` file:
+
+----------------------------------------------------------------
+(in $GIT_DIR/info/attributes)
+
+a*	foo !bar -baz
+
+(in .gitattributes)
+abc	foo bar baz
+
+(in t/.gitattributes)
+ab*	merge=filfre
+abc	-foo -bar
+*.c	frotz
+----------------------------------------------------------------
+
+the attributes given to path `t/abc` are computed as follows:
+
+1. By examining `t/.gitattributes` (which is in the same
+   directory as the path in question), Git finds that the first
+   line matches.  `merge` attribute is set.  It also finds that
+   the second line matches, and attributes `foo` and `bar`
+   are unset.
+
+2. Then it examines `.gitattributes` (which is in the parent
+   directory), and finds that the first line matches, but
+   `t/.gitattributes` file already decided how `merge`, `foo`
+   and `bar` attributes should be given to this path, so it
+   leaves `foo` and `bar` unset.  Attribute `baz` is set.
+
+3. Finally it examines `$GIT_DIR/info/attributes`.  This file
+   is used to override the in-tree settings.  The first line is
+   a match, and `foo` is set, `bar` is reverted to unspecified
+   state, and `baz` is unset.
+
+As the result, the attributes assignment to `t/abc` becomes:
+
+----------------------------------------------------------------
+foo	set to true
+bar	unspecified
+baz	set to false
+merge	set to string value "filfre"
+frotz	unspecified
+----------------------------------------------------------------
+
+
+SEE ALSO
+--------
+linkgit:git-check-attr[1].
+
+GIT
+---
+Part of the linkgit:git[1] suite