clang/docs/ClangFormat.rst

===========
ClangFormat
===========

`ClangFormat` describes a set of tools that are built on top of
:doc:`LibFormat`. It can support your workflow in a variety of ways including a
standalone tool and editor integrations.


Standalone Tool
===============

:program:`clang-format` is located in `clang/tools/clang-format` and can be used
to format C/C++/Java/JavaScript/JSON/Objective-C/Protobuf/C# code.

.. START_FORMAT_HELP

.. code-block:: console

  $ clang-format --help
  OVERVIEW: A tool to format C/C++/Java/JavaScript/JSON/Objective-C/Protobuf/C# code.

  If no arguments are specified, it formats the code from standard input
  and writes the result to the standard output.
  If <file>s are given, it reformats the files. If -i is specified
  together with <file>s, the files are edited in-place. Otherwise, the
  result is written to the standard output.

  USAGE: clang-format [options] [@<file>] [<file> ...]

  OPTIONS:

  Clang-format options:

    --Werror                       - If set, changes formatting warnings to errors
    --Wno-error=<value>            - If set, don't error out on the specified warning type.
      =unknown                     -   If set, unknown format options are only warned about.
                                       This can be used to enable formatting, even if the
                                       configuration contains unknown (newer) options.
                                       Use with caution, as this might lead to dramatically
                                       differing format depending on an option being
                                       supported or not.
    --assume-filename=<string>     - Set filename used to determine the language and to find
                                     .clang-format file.
                                     Only used when reading from stdin.
                                     If this is not passed, the .clang-format file is searched
                                     relative to the current working directory when reading stdin.
                                     Unrecognized filenames are treated as C++.
                                     supported:
                                       CSharp: .cs
                                       Java: .java
                                       JavaScript: .js .mjs .cjs .ts
                                       Json: .json .ipynb
                                       Objective-C: .m .mm
                                       Proto: .proto .protodevel
                                       TableGen: .td
                                       TextProto: .txtpb .textpb .pb.txt .textproto .asciipb
                                       Verilog: .sv .svh .v .vh
    --cursor=<uint>                - The position of the cursor when invoking
                                     clang-format from an editor integration
    --dry-run                      - If set, do not actually make the formatting changes
    --dump-config                  - Dump configuration options to stdout and exit.
                                     Can be used with -style option.
    --fail-on-incomplete-format    - If set, fail with exit code 1 on incomplete format.
    --fallback-style=<string>      - The name of the predefined style used as a
                                     fallback in case clang-format is invoked with
                                     -style=file, but can not find the .clang-format
                                     file to use. Defaults to 'LLVM'.
                                     Use -fallback-style=none to skip formatting.
    --ferror-limit=<uint>          - Set the maximum number of clang-format errors to emit
                                     before stopping (0 = no limit).
                                     Used only with --dry-run or -n
    --files=<filename>             - A file containing a list of files to process, one per line.
    -i                             - Inplace edit <file>s, if specified.
    --length=<uint>                - Format a range of this length (in bytes).
                                     Multiple ranges can be formatted by specifying
                                     several -offset and -length pairs.
                                     When only a single -offset is specified without
                                     -length, clang-format will format up to the end
                                     of the file.
                                     Can only be used with one input file.
    --lines=<string>               - <start line>:<end line> - format a range of
                                     lines (both 1-based).
                                     Multiple ranges can be formatted by specifying
                                     several -lines arguments.
                                     Can't be used with -offset and -length.
                                     Can only be used with one input file.
    -n                             - Alias for --dry-run
    --offset=<uint>                - Format a range starting at this byte offset.
                                     Multiple ranges can be formatted by specifying
                                     several -offset and -length pairs.
                                     Can only be used with one input file.
    --output-replacements-xml      - Output replacements as XML.
    --qualifier-alignment=<string> - If set, overrides the qualifier alignment style
                                     determined by the QualifierAlignment style flag
    --sort-includes                - If set, overrides the include sorting behavior
                                     determined by the SortIncludes style flag
    --style=<string>               - Set coding style. <string> can be:
                                     1. A preset: LLVM, GNU, Google, Chromium, Microsoft,
                                        Mozilla, WebKit.
                                     2. 'file' to load style configuration from a
                                        .clang-format file in one of the parent directories
                                        of the source file (for stdin, see --assume-filename).
                                        If no .clang-format file is found, falls back to
                                        --fallback-style.
                                        --style=file is the default.
                                     3. 'file:<format_file_path>' to explicitly specify
                                        the configuration file.
                                     4. "{key: value, ...}" to set specific parameters, e.g.:
                                        --style="{BasedOnStyle: llvm, IndentWidth: 8}"
    --verbose                      - If set, shows the list of processed files

  Generic Options:

    --help                         - Display available options (--help-hidden for more)
    --help-list                    - Display list of available options (--help-list-hidden for more)
    --version                      - Display the version of this program


.. END_FORMAT_HELP

When the desired code formatting style is different from the available options,
the style can be customized using the ``-style="{key: value, ...}"`` option or
by putting your style configuration in the ``.clang-format`` or ``_clang-format``
file in your project's directory and using ``clang-format -style=file``.

An easy way to create the ``.clang-format`` file is:

.. code-block:: console

  clang-format -style=llvm -dump-config > .clang-format

Available style options are described in :doc:`ClangFormatStyleOptions`.

.clang-format-ignore
====================

You can create ``.clang-format-ignore`` files to make ``clang-format`` ignore
certain files. A ``.clang-format-ignore`` file consists of patterns of file path
names. It has the following format:

* A blank line is skipped.
* Leading and trailing spaces of a line are trimmed.
* A line starting with a hash (``#``) is a comment.
* A non-comment line is a single pattern.
* The slash (``/``) is used as the directory separator.
* A pattern is relative to the directory of the ``.clang-format-ignore`` file
  (or the root directory if the pattern starts with a slash). Patterns
  containing drive names (e.g. ``C:``) are not supported.
* Patterns follow the rules specified in `POSIX 2.13.1, 2.13.2, and Rule 1 of
  2.13.3 <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/
  V3_chap02.html#tag_18_13>`_.
* Bash globstar (``**``) is supported.
* A pattern is negated if it starts with a bang (``!``).

To match all files in a directory, use e.g. ``foo/bar/*``. To match all files in
the directory of the ``.clang-format-ignore`` file, use ``*``.
Multiple ``.clang-format-ignore`` files are supported similar to the
``.clang-format`` files, with a lower directory level file voiding the higher
level ones.

Vim Integration
===============

There is an integration for :program:`vim` which lets you run the
:program:`clang-format` standalone tool on your current buffer, optionally
selecting regions to reformat. The integration has the form of a `python`-file
which can be found under `clang/tools/clang-format/clang-format.py`.

This can be integrated by adding the following to your `.vimrc`:

.. code-block:: vim

  if has('python')
    map <C-K> :pyf <path-to-this-file>/clang-format.py<cr>
    imap <C-K> <c-o>:pyf <path-to-this-file>/clang-format.py<cr>
  elseif has('python3')
    map <C-K> :py3f <path-to-this-file>/clang-format.py<cr>
    imap <C-K> <c-o>:py3f <path-to-this-file>/clang-format.py<cr>
  endif

The first line enables :program:`clang-format` for NORMAL and VISUAL mode, the
second line adds support for INSERT mode. Change "C-K" to another binding if
you need :program:`clang-format` on a different key (C-K stands for Ctrl+k).

With this integration you can press the bound key and clang-format will
format the current line in NORMAL and INSERT mode or the selected region in
VISUAL mode. The line or region is extended to the next bigger syntactic
entity.

It operates on the current, potentially unsaved buffer and does not create
or save any files. To revert a formatting, just undo.

An alternative option is to format changes when saving a file and thus to
have a zero-effort integration into the coding workflow. To do this, add this to
your `.vimrc`:

.. code-block:: vim

  function! Formatonsave()
    let l:formatdiff = 1
    pyf <path-to-this-file>/clang-format.py
  endfunction
  autocmd BufWritePre *.h,*.cc,*.cpp call Formatonsave()


Emacs Integration
=================

Similar to the integration for :program:`vim`, there is an integration for
:program:`emacs`. It can be found at `clang/tools/clang-format/clang-format.el`
and used by adding this to your `.emacs`:

.. code-block:: common-lisp

  (load "<path-to-clang>/tools/clang-format/clang-format.el")
  (global-set-key [C-M-tab] 'clang-format-region)

This binds the function `clang-format-region` to C-M-tab, which then formats the
current line or selected region.


BBEdit Integration
==================

:program:`clang-format` cannot be used as a text filter with BBEdit, but works
well via a script. The AppleScript to do this integration can be found at
`clang/tools/clang-format/clang-format-bbedit.applescript`; place a copy in
`~/Library/Application Support/BBEdit/Scripts`, and edit the path within it to
point to your local copy of :program:`clang-format`.

With this integration you can select the script from the Script menu and
:program:`clang-format` will format the selection. Note that you can rename the
menu item by renaming the script, and can assign the menu item a keyboard
shortcut in the BBEdit preferences, under Menus & Shortcuts.


CLion Integration
=================

:program:`clang-format` is integrated into `CLion <https://www.jetbrains
.com/clion/>`_ as an alternative code formatter. CLion turns it on
automatically when there is a ``.clang-format`` file under the project root.
Code style rules are applied as you type, including indentation,
auto-completion, code generation, and refactorings.

:program:`clang-format` can also be enabled without a ``.clang-format`` file.
In this case, CLion prompts you to create one based on the current IDE settings
or the default LLVM style.


Visual Studio Integration
=========================

Download the latest Visual Studio extension from the `alpha build site
<https://llvm.org/builds/>`_. The default key-binding is Ctrl-R,Ctrl-F.


Visual Studio Code Integration
==============================

Get the latest Visual Studio Code extension from the `Visual Studio Marketplace <https://marketplace.visualstudio.com/items?itemName=xaver.clang-format>`_. The default key-binding is Alt-Shift-F.

Git integration
===============

The script `clang/tools/clang-format/git-clang-format` can be used to
format just the lines touched in git commits:

.. code-block:: console

  % git clang-format -h
  usage: git clang-format [OPTIONS] [<commit>] [<commit>|--staged] [--] [<file>...]

  If zero or one commits are given, run clang-format on all lines that differ
  between the working directory and <commit>, which defaults to HEAD.  Changes are
  only applied to the working directory, or in the stage/index.

  Examples:
    To format staged changes, i.e everything that's been `git add`ed:
      git clang-format

    To also format everything touched in the most recent commit:
      git clang-format HEAD~1

    If you're on a branch off main, to format everything touched on your branch:
      git clang-format main

  If two commits are given (requires --diff), run clang-format on all lines in the
  second <commit> that differ from the first <commit>.

  The following git-config settings set the default of the corresponding option:
    clangFormat.binary
    clangFormat.commit
    clangFormat.extensions
    clangFormat.style

  positional arguments:
    <commit>              revision from which to compute the diff
    <file>...             if specified, only consider differences in these files

  optional arguments:
    -h, --help            show this help message and exit
    --binary BINARY       path to clang-format
    --commit COMMIT       default commit to use if none is specified
    --diff                print a diff instead of applying the changes
    --diffstat            print a diffstat instead of applying the changes
    --extensions EXTENSIONS
                          comma-separated list of file extensions to format, excluding the period and case-insensitive
    -f, --force           allow changes to unstaged files
    -p, --patch           select hunks interactively
    -q, --quiet           print less information
    --staged, --cached    format lines in the stage instead of the working dir
    --style STYLE         passed to clang-format
    -v, --verbose         print extra information


Script for patch reformatting
=============================

The python script `clang/tools/clang-format/clang-format-diff.py` parses the
output of a unified diff and reformats all contained lines with
:program:`clang-format`.

.. code-block:: console

  usage: clang-format-diff.py [-h] [-i] [-p NUM] [-regex PATTERN] [-iregex PATTERN] [-sort-includes] [-v] [-style STYLE]
                              [-fallback-style FALLBACK_STYLE] [-binary BINARY]

  This script reads input from a unified diff and reformats all the changed
  lines. This is useful to reformat all the lines touched by a specific patch.
  Example usage for git/svn users:

    git diff -U0 --no-color --relative HEAD^ | clang-format-diff.py -p1 -i
    svn diff --diff-cmd=diff -x-U0 | clang-format-diff.py -i

  It should be noted that the filename contained in the diff is used unmodified
  to determine the source file to update. Users calling this script directly
  should be careful to ensure that the path in the diff is correct relative to the
  current working directory.

  optional arguments:
    -h, --help            show this help message and exit
    -i                    apply edits to files instead of displaying a diff
    -p NUM                strip the smallest prefix containing P slashes
    -regex PATTERN        custom pattern selecting file paths to reformat (case sensitive, overrides -iregex)
    -iregex PATTERN       custom pattern selecting file paths to reformat (case insensitive, overridden by -regex)
    -sort-includes        let clang-format sort include blocks
    -v, --verbose         be more verbose, ineffective without -i
    -style STYLE          formatting style to apply (LLVM, GNU, Google, Chromium, Microsoft, Mozilla, WebKit)
    -fallback-style FALLBACK_STYLE
                          The name of the predefined style used as a fallback in case clang-format is invoked with-style=file, but can not
                          find the .clang-formatfile to use.
    -binary BINARY        location of binary to use for clang-format

To reformat all the lines in the latest Mercurial/:program:`hg` commit, do:

.. code-block:: console

  hg diff -U0 --color=never | clang-format-diff.py -i -p1

The option `-U0` will create a diff without context lines (the script would format
those as well).

These commands use the file paths shown in the diff output
so they will only work from the root of the repository.