clang/docs/ClangFormatStyleOptions.rst

==========================
Clang-Format Style Options
==========================

:doc:`ClangFormatStyleOptions` describes configurable formatting style options
supported by :doc:`LibFormat` and :doc:`ClangFormat`.

When using :program:`clang-format` command line utility or
``clang::format::reformat(...)`` functions from code, one can either use one of
the predefined styles (LLVM, Google, Chromium, Mozilla, WebKit) or create a
custom style by configuring specific style options.


Configuring Style with clang-format
===================================

:program:`clang-format` supports two ways to provide custom style options:
directly specify style configuration in the ``-style=`` command line option or
use ``-style=file`` and put style configuration in the ``.clang-format`` or
``_clang-format`` file in the project directory.

When using ``-style=file``, :program:`clang-format` for each input file will
try to find the ``.clang-format`` file located in the closest parent directory
of the input file. When the standard input is used, the search is started from
the current directory.

The ``.clang-format`` file uses YAML format:

.. code-block:: yaml

  key1: value1
  key2: value2
  # A comment.
  ...

The configuration file can consist of several sections each having different
``Language:`` parameter denoting the programming language this section of the
configuration is targeted at. See the description of the **Language** option
below for the list of supported languages. The first section may have no
language set, it will set the default style options for all lanugages.
Configuration sections for specific language will override options set in the
default section.

When :program:`clang-format` formats a file, it auto-detects the language using
the file name. When formatting standard input or a file that doesn't have the
extension corresponding to its language, ``-assume-filename=`` option can be
used to override the file name :program:`clang-format` uses to detect the
language.

An example of a configuration file for multiple languages:

.. code-block:: yaml

  ---
  # We'll use defaults from the LLVM style, but with 4 columns indentation.
  BasedOnStyle: LLVM
  IndentWidth: 4
  ---
  Language: Cpp
  # Force pointers to the type for C++.
  DerivePointerAlignment: false
  PointerAlignment: Left
  ---
  Language: JavaScript
  # Use 100 columns for JS.
  ColumnLimit: 100
  ---
  Language: Proto
  # Don't format .proto files.
  DisableFormat: true
  ...

An easy way to get a valid ``.clang-format`` file containing all configuration
options of a certain predefined style is:

.. code-block:: console

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

When specifying configuration in the ``-style=`` option, the same configuration
is applied for all input files. The format of the configuration is:

.. code-block:: console

  -style='{key1: value1, key2: value2, ...}'


Disabling Formatting on a Piece of Code
=======================================

Clang-format understands also special comments that switch formatting in a
delimited range. The code between a comment ``// clang-format off`` or
``/* clang-format off */`` up to a comment ``// clang-format on`` or
``/* clang-format on */`` will not be formatted. The comments themselves
will be formatted (aligned) normally.

.. code-block:: c++

  int formatted_code;
  // clang-format off
      void    unformatted_code  ;
  // clang-format on
  void formatted_code_again;


Configuring Style in Code
=========================

When using ``clang::format::reformat(...)`` functions, the format is specified
by supplying the `clang::format::FormatStyle
<http://clang.llvm.org/doxygen/structclang_1_1format_1_1FormatStyle.html>`_
structure.


Configurable Format Style Options
=================================

This section lists the supported style options. Value type is specified for
each option. For enumeration types possible values are specified both as a C++
enumeration member (with a prefix, e.g. ``LS_Auto``), and as a value usable in
the configuration (without a prefix: ``Auto``).


**BasedOnStyle** (``string``)
  The style used for all options not specifically set in the configuration.

  This option is supported only in the :program:`clang-format` configuration
  (both within ``-style='{...}'`` and the ``.clang-format`` file).

  Possible values:

  * ``LLVM``
    A style complying with the `LLVM coding standards
    <http://llvm.org/docs/CodingStandards.html>`_
  * ``Google``
    A style complying with `Google's C++ style guide
    <http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml>`_
  * ``Chromium``
    A style complying with `Chromium's style guide
    <http://www.chromium.org/developers/coding-style>`_
  * ``Mozilla``
    A style complying with `Mozilla's style guide
    <https://developer.mozilla.org/en-US/docs/Developer_Guide/Coding_Style>`_
  * ``WebKit``
    A style complying with `WebKit's style guide
    <http://www.webkit.org/coding/coding-style.html>`_

.. START_FORMAT_STYLE_OPTIONS

**AccessModifierOffset** (``int``)
  The extra indent or outdent of access modifiers, e.g. ``public:``.

**AlignAfterOpenBracket** (``bool``)
  If ``true``, horizontally aligns arguments after an open bracket.

  This applies to round brackets (parentheses), angle brackets and square
  brackets. This will result in formattings like
  \code
  someLongFunction(argument1,
  argument2);
  \endcode

**AlignConsecutiveAssignments** (``bool``)
  If ``true``, aligns consecutive assignments.

  This will align the assignment operators of consecutive lines. This
  will result in formattings like
  \code
  int aaaa = 12;
  int b    = 23;
  int ccc  = 23;
  \endcode

**AlignEscapedNewlinesLeft** (``bool``)
  If ``true``, aligns escaped newlines as far left as possible.
  Otherwise puts them into the right-most column.

**AlignOperands** (``bool``)
  If ``true``, horizontally align operands of binary and ternary
  expressions.

**AlignTrailingComments** (``bool``)
  If ``true``, aligns trailing comments.

**AllowAllParametersOfDeclarationOnNextLine** (``bool``)
  Allow putting all parameters of a function declaration onto
  the next line even if ``BinPackParameters`` is ``false``.

**AllowShortBlocksOnASingleLine** (``bool``)
  Allows contracting simple braced statements to a single line.

  E.g., this allows ``if (a) { return; }`` to be put on a single line.

**AllowShortCaseLabelsOnASingleLine** (``bool``)
  If ``true``, short case labels will be contracted to a single line.

**AllowShortFunctionsOnASingleLine** (``ShortFunctionStyle``)
  Dependent on the value, ``int f() { return 0; }`` can be put
  on a single line.

  Possible values:

  * ``SFS_None`` (in configuration: ``None``)
    Never merge functions into a single line.
  * ``SFS_Empty`` (in configuration: ``Empty``)
    Only merge empty functions.
  * ``SFS_Inline`` (in configuration: ``Inline``)
    Only merge functions defined inside a class. Implies "empty".
  * ``SFS_All`` (in configuration: ``All``)
    Merge all functions fitting on a single line.


**AllowShortIfStatementsOnASingleLine** (``bool``)
  If ``true``, ``if (a) return;`` can be put on a single
  line.

**AllowShortLoopsOnASingleLine** (``bool``)
  If ``true``, ``while (true) continue;`` can be put on a
  single line.

**AlwaysBreakAfterDefinitionReturnType** (``DefinitionReturnTypeBreakingStyle``)
  The function definition return type breaking style to use.

  Possible values:

  * ``DRTBS_None`` (in configuration: ``None``)
    Break after return type automatically.
    ``PenaltyReturnTypeOnItsOwnLine`` is taken into account.
  * ``DRTBS_All`` (in configuration: ``All``)
    Always break after the return type.
  * ``DRTBS_TopLevel`` (in configuration: ``TopLevel``)
    Always break after the return types of top level functions.


**AlwaysBreakBeforeMultilineStrings** (``bool``)
  If ``true``, always break before multiline string literals.

  This flag is mean to make cases where there are multiple multiline strings
  in a file look more consistent. Thus, it will only take effect if wrapping
  the string at that point leads to it being indented
  ``ContinuationIndentWidth`` spaces from the start of the line.

**AlwaysBreakTemplateDeclarations** (``bool``)
  If ``true``, always break after the ``template<...>`` of a
  template declaration.

**BinPackArguments** (``bool``)
  If ``false``, a function call's arguments will either be all on the
  same line or will have one line each.

**BinPackParameters** (``bool``)
  If ``false``, a function declaration's or function definition's
  parameters will either all be on the same line or will have one line each.

**BraceWrapping** (``BraceWrappingFlags``)
  Control of individual brace wrapping cases.

  If ``BreakBeforeBraces`` is set to ``custom``, use this to specify how each
  individual brace case should be handled. Otherwise, this is ignored.

  Nested configuration flags:

  * ``bool AfterClass`` Wrap class definitions.
  * ``bool AfterControlStatement`` Wrap control statements (if/for/while/switch/..).
  * ``bool AfterEnum`` Wrap enum definitions.
  * ``bool AfterFunction`` Wrap function definitions.
  * ``bool AfterNamespace`` Wrap namespace definitions.
  * ``bool AfterObjCDeclaration`` Wrap ObjC definitions (@autoreleasepool, interfaces, ..).
  * ``bool AfterStruct`` Wrap struct definitions.
  * ``bool AfterUnion`` Wrap union definitions.
  * ``bool BeforeCatch`` Wrap before ``catch``.
  * ``bool BeforeElse`` Wrap before ``else``.
  * ``bool IndentBraces`` Indent the wrapped braces themselves.


**BreakBeforeBinaryOperators** (``BinaryOperatorStyle``)
  The way to wrap binary operators.

  Possible values:

  * ``BOS_None`` (in configuration: ``None``)
    Break after operators.
  * ``BOS_NonAssignment`` (in configuration: ``NonAssignment``)
    Break before operators that aren't assignments.
  * ``BOS_All`` (in configuration: ``All``)
    Break before operators.


**BreakBeforeBraces** (``BraceBreakingStyle``)
  The brace breaking style to use.

  Possible values:

  * ``BS_Attach`` (in configuration: ``Attach``)
    Always attach braces to surrounding context.
  * ``BS_Linux`` (in configuration: ``Linux``)
    Like ``Attach``, but break before braces on function, namespace and
    class definitions.
  * ``BS_Mozilla`` (in configuration: ``Mozilla``)
    Like ``Attach``, but break before braces on enum, function, and record
    definitions.
  * ``BS_Stroustrup`` (in configuration: ``Stroustrup``)
    Like ``Attach``, but break before function definitions, 'catch', and 'else'.
  * ``BS_Allman`` (in configuration: ``Allman``)
    Always break before braces.
  * ``BS_GNU`` (in configuration: ``GNU``)
    Always break before braces and add an extra level of indentation to
    braces of control statements, not to those of class, function
    or other definitions.
  * ``BS_WebKit`` (in configuration: ``WebKit``)
    Like ``Attach``, but break before functions.
  * ``BS_Custom`` (in configuration: ``Custom``)
    Configure each individual brace in ``BraceWrapping``.


**BreakBeforeTernaryOperators** (``bool``)
  If ``true``, ternary operators will be placed after line breaks.

**BreakConstructorInitializersBeforeComma** (``bool``)
  Always break constructor initializers before commas and align
  the commas with the colon.

**ColumnLimit** (``unsigned``)
  The column limit.

  A column limit of ``0`` means that there is no column limit. In this case,
  clang-format will respect the input's line breaking decisions within
  statements unless they contradict other rules.

**CommentPragmas** (``std::string``)
  A regular expression that describes comments with special meaning,
  which should not be split into lines or otherwise changed.

**ConstructorInitializerAllOnOneLineOrOnePerLine** (``bool``)
  If the constructor initializers don't fit on a line, put each
  initializer on its own line.

**ConstructorInitializerIndentWidth** (``unsigned``)
  The number of characters to use for indentation of constructor
  initializer lists.

**ContinuationIndentWidth** (``unsigned``)
  Indent width for line continuations.

**Cpp11BracedListStyle** (``bool``)
  If ``true``, format braced lists as best suited for C++11 braced
  lists.

  Important differences:
  - No spaces inside the braced list.
  - No line break before the closing brace.
  - Indentation with the continuation indent, not with the block indent.

  Fundamentally, C++11 braced lists are formatted exactly like function
  calls would be formatted in their place. If the braced list follows a name
  (e.g. a type or variable name), clang-format formats as if the ``{}`` were
  the parentheses of a function call with that name. If there is no name,
  a zero-length name is assumed.

**DerivePointerAlignment** (``bool``)
  If ``true``, analyze the formatted file for the most common
  alignment of & and \*. ``PointerAlignment`` is then used only as fallback.

**DisableFormat** (``bool``)
  Disables formatting completely.

**ExperimentalAutoDetectBinPacking** (``bool``)
  If ``true``, clang-format detects whether function calls and
  definitions are formatted with one parameter per line.

  Each call can be bin-packed, one-per-line or inconclusive. If it is
  inconclusive, e.g. completely on one line, but a decision needs to be
  made, clang-format analyzes whether there are other bin-packed cases in
  the input file and act accordingly.

  NOTE: This is an experimental flag, that might go away or be renamed. Do
  not use this in config files, etc. Use at your own risk.

**ForEachMacros** (``std::vector<std::string>``)
  A vector of macros that should be interpreted as foreach loops
  instead of as function calls.

  These are expected to be macros of the form:
  \code
  FOREACH(<variable-declaration>, ...)
  <loop-body>
  \endcode

  For example: BOOST_FOREACH.

**IncludeCategories** (``std::vector<std::pair<std::string, unsigned>>``)
  Regular expressions denoting the different #include categories used
  for ordering #includes.

  These regular expressions are matched against the filename of an include
  (including the <> or "") in order. The value belonging to the first
  matching regular expression is assigned and #includes are sorted first
  according to increasing category number and then alphabetically within
  each category.

  If none of the regular expressions match, UINT_MAX is assigned as
  category. The main header for a source file automatically gets category 0,
  so that it is kept at the beginning of the #includes
  (http://llvm.org/docs/CodingStandards.html#include-style).

**IndentCaseLabels** (``bool``)
  Indent case labels one level from the switch statement.

  When ``false``, use the same indentation level as for the switch statement.
  Switch statement body is always indented one level more than case labels.

**IndentWidth** (``unsigned``)
  The number of columns to use for indentation.

**IndentWrappedFunctionNames** (``bool``)
  Indent if a function definition or declaration is wrapped after the
  type.

**KeepEmptyLinesAtTheStartOfBlocks** (``bool``)
  If true, empty lines at the start of blocks are kept.

**Language** (``LanguageKind``)
  Language, this format style is targeted at.

  Possible values:

  * ``LK_None`` (in configuration: ``None``)
    Do not use.
  * ``LK_Cpp`` (in configuration: ``Cpp``)
    Should be used for C, C++, ObjectiveC, ObjectiveC++.
  * ``LK_Java`` (in configuration: ``Java``)
    Should be used for Java.
  * ``LK_JavaScript`` (in configuration: ``JavaScript``)
    Should be used for JavaScript.
  * ``LK_Proto`` (in configuration: ``Proto``)
    Should be used for Protocol Buffers
    (https://developers.google.com/protocol-buffers/).


**MacroBlockBegin** (``std::string``)
  A regular expression matching macros that start a block.

**MacroBlockEnd** (``std::string``)
  A regular expression matching macros that end a block.

**MaxEmptyLinesToKeep** (``unsigned``)
  The maximum number of consecutive empty lines to keep.

**NamespaceIndentation** (``NamespaceIndentationKind``)
  The indentation used for namespaces.

  Possible values:

  * ``NI_None`` (in configuration: ``None``)
    Don't indent in namespaces.
  * ``NI_Inner`` (in configuration: ``Inner``)
    Indent only in inner namespaces (nested in other namespaces).
  * ``NI_All`` (in configuration: ``All``)
    Indent in all namespaces.


**ObjCBlockIndentWidth** (``unsigned``)
  The number of characters to use for indentation of ObjC blocks.

**ObjCSpaceAfterProperty** (``bool``)
  Add a space after ``@property`` in Objective-C, i.e. use
  ``\@property (readonly)`` instead of ``\@property(readonly)``.

**ObjCSpaceBeforeProtocolList** (``bool``)
  Add a space in front of an Objective-C protocol list, i.e. use
  ``Foo <Protocol>`` instead of ``Foo<Protocol>``.

**PenaltyBreakBeforeFirstCallParameter** (``unsigned``)
  The penalty for breaking a function call after "call(".

**PenaltyBreakComment** (``unsigned``)
  The penalty for each line break introduced inside a comment.

**PenaltyBreakFirstLessLess** (``unsigned``)
  The penalty for breaking before the first ``<<``.

**PenaltyBreakString** (``unsigned``)
  The penalty for each line break introduced inside a string literal.

**PenaltyExcessCharacter** (``unsigned``)
  The penalty for each character outside of the column limit.

**PenaltyReturnTypeOnItsOwnLine** (``unsigned``)
  Penalty for putting the return type of a function onto its own
  line.

**PointerAlignment** (``PointerAlignmentStyle``)
  Pointer and reference alignment style.

  Possible values:

  * ``PAS_Left`` (in configuration: ``Left``)
    Align pointer to the left.
  * ``PAS_Right`` (in configuration: ``Right``)
    Align pointer to the right.
  * ``PAS_Middle`` (in configuration: ``Middle``)
    Align pointer in the middle.


**SpaceAfterCStyleCast** (``bool``)
  If ``true``, a space may be inserted after C style casts.

**SpaceBeforeAssignmentOperators** (``bool``)
  If ``false``, spaces will be removed before assignment operators.

**SpaceBeforeParens** (``SpaceBeforeParensOptions``)
  Defines in which cases to put a space before opening parentheses.

  Possible values:

  * ``SBPO_Never`` (in configuration: ``Never``)
    Never put a space before opening parentheses.
  * ``SBPO_ControlStatements`` (in configuration: ``ControlStatements``)
    Put a space before opening parentheses only after control statement
    keywords (``for/if/while...``).
  * ``SBPO_Always`` (in configuration: ``Always``)
    Always put a space before opening parentheses, except when it's
    prohibited by the syntax rules (in function-like macro definitions) or
    when determined by other style rules (after unary operators, opening
    parentheses, etc.)


**SpaceInEmptyParentheses** (``bool``)
  If ``true``, spaces may be inserted into '()'.

**SpacesBeforeTrailingComments** (``unsigned``)
  The number of spaces before trailing line comments
  (``//`` - comments).

  This does not affect trailing block comments (``/**/`` - comments) as those
  commonly have different usage patterns and a number of special cases.

**SpacesInAngles** (``bool``)
  If ``true``, spaces will be inserted after '<' and before '>' in
  template argument lists

**SpacesInCStyleCastParentheses** (``bool``)
  If ``true``, spaces may be inserted into C style casts.

**SpacesInContainerLiterals** (``bool``)
  If ``true``, spaces are inserted inside container literals (e.g.
  ObjC and Javascript array and dict literals).

**SpacesInParentheses** (``bool``)
  If ``true``, spaces will be inserted after '(' and before ')'.

**SpacesInSquareBrackets** (``bool``)
  If ``true``, spaces will be inserted after '[' and before ']'.

**Standard** (``LanguageStandard``)
  Format compatible with this standard, e.g. use
  ``A<A<int> >`` instead of ``A<A<int>>`` for LS_Cpp03.

  Possible values:

  * ``LS_Cpp03`` (in configuration: ``Cpp03``)
    Use C++03-compatible syntax.
  * ``LS_Cpp11`` (in configuration: ``Cpp11``)
    Use features of C++11 (e.g. ``A<A<int>>`` instead of
    ``A<A<int> >``).
  * ``LS_Auto`` (in configuration: ``Auto``)
    Automatic detection based on the input.


**TabWidth** (``unsigned``)
  The number of columns used for tab stops.

**UseTab** (``UseTabStyle``)
  The way to use tab characters in the resulting file.

  Possible values:

  * ``UT_Never`` (in configuration: ``Never``)
    Never use tab.
  * ``UT_ForIndentation`` (in configuration: ``ForIndentation``)
    Use tabs only for indentation.
  * ``UT_Always`` (in configuration: ``Always``)
    Use tabs whenever we need to fill whitespace that spans at least from
    one tab stop to the next one.


.. END_FORMAT_STYLE_OPTIONS

Adding additional style options
===============================

Each additional style option adds costs to the clang-format project. Some of
these costs affect the clang-format developement itself, as we need to make
sure that any given combination of options work and that new features don't
break any of the existing options in any way. There are also costs for end users
as options become less discoverable and people have to think about and make a
decision on options they don't really care about.

The goal of the clang-format project is more on the side of supporting a
limited set of styles really well as opposed to supporting every single style
used by a codebase somewhere in the wild. Of course, we do want to support all
major projects and thus have established the following bar for adding style
options. Each new style option must ..

  * be used in a project of significant size (have dozens of contributors)
  * have a publicly accessible style guide
  * have a person willing to contribute and maintain patches

Examples
========

A style similar to the `Linux Kernel style
<https://www.kernel.org/doc/Documentation/CodingStyle>`_:

.. code-block:: yaml

  BasedOnStyle: LLVM
  IndentWidth: 8
  UseTab: Always
  BreakBeforeBraces: Linux
  AllowShortIfStatementsOnASingleLine: false
  IndentCaseLabels: false

The result is (imagine that tabs are used for indentation here):

.. code-block:: c++

  void test()
  {
          switch (x) {
          case 0:
          case 1:
                  do_something();
                  break;
          case 2:
                  do_something_else();
                  break;
          default:
                  break;
          }
          if (condition)
                  do_something_completely_different();

          if (x == y) {
                  q();
          } else if (x > y) {
                  w();
          } else {
                  r();
          }
  }

A style similar to the default Visual Studio formatting style:

.. code-block:: yaml

  UseTab: Never
  IndentWidth: 4
  BreakBeforeBraces: Allman
  AllowShortIfStatementsOnASingleLine: false
  IndentCaseLabels: false
  ColumnLimit: 0

The result is:

.. code-block:: c++

  void test()
  {
      switch (suffix)
      {
      case 0:
      case 1:
          do_something();
          break;
      case 2:
          do_something_else();
          break;
      default:
          break;
      }
      if (condition)
          do_somthing_completely_different();

      if (x == y)
      {
          q();
      }
      else if (x > y)
      {
          w();
      }
      else
      {
          r();
      }
  }