opensense-docs/source/development/guidelines/psr2.rst

========================
PSR-2 Coding Style Guide
========================

.. Note::

  | The PSR1 and PSR2 Coding Standards are provided by FIG under a MIT license.
  | See license details: http://www.php-fig.org/bylaws/licensing-policies/
  | The original content of this page can be found at `php-fig <http://www.php-fig.org/psr/psr-2/>`__

This guide extends and expands on
`PSR-1 <https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-1-basic-coding-standard.md>`__,
the basic coding standard.

The intent of this guide is to reduce cognitive friction when scanning code from
different authors. It does so by enumerating a shared set of rules and expectations
about how to format PHP code.

The style rules herein are derived from commonalities among the various member
projects. When various authors collaborate across multiple projects, it helps to
have one set of guidelines to be used among all those projects. Thus, the benefit
of this guide is not in the rules themselves, but in the sharing of those rules.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in `RFC
2119 <http://www.ietf.org/rfc/rfc2119.txt>`__.

-----------
1. Overview
-----------

-  Code MUST follow a "coding style guide" PSR
   [`PSR-1 <https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-1-basic-coding-standard.md>`__].

-  Code MUST use 4 spaces for indenting, not tabs.

-  There MUST NOT be a hard limit on line length; the soft limit MUST be
   120 characters; lines SHOULD be 80 characters or less.

-  There MUST be one blank line after the ``namespace`` declaration, and
   there MUST be one blank line after the block of ``use`` declarations.

-  Opening braces for classes MUST go on the next line, and closing
   braces MUST go on the next line after the body.

-  Opening braces for methods MUST go on the next line, and closing
   braces MUST go on the next line after the body.

-  Visibility MUST be declared on all properties and methods;
   ``abstract`` and ``final`` MUST be declared before the visibility;
   ``static`` MUST be declared after the visibility.

-  Control structure keywords MUST have one space after them; method and
   function calls MUST NOT.

-  Opening braces for control structures MUST go on the same line, and
   closing braces MUST go on the next line after the body.

-  Opening parentheses for control structures MUST NOT have a space
   after them, and closing parentheses for control structures MUST NOT
   have a space before.

1.1. Example
------------

This example encompasses some of the rules below as a quick overview:

.. code-block:: php

    <?php
    namespace Vendor\Package;

    use FooInterface;
    use BarClass as Bar;
    use OtherVendor\OtherPackage\BazClass;

    class Foo extends Bar implements FooInterface
    {
        public function sampleFunction($a, $b = null)
        {
            if ($a === $b) {
                bar();
            } elseif ($a > $b) {
                $foo->bar($arg1);
            } else {
                BazClass::bar($arg2, $arg3);
            }
        }

        final public static function bar()
        {
            // method body
        }
    }

----------
2. General
----------

2.1 Basic Coding Standard
-------------------------

Code MUST follow all rules outlined in
`PSR-1 <https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-1-basic-coding-standard.md>`__.

2.2 Files
---------

All PHP files MUST use the Unix LF (linefeed) line ending.
All PHP files MUST end with a single blank line.

The closing ``?>`` tag MUST be omitted from files containing only PHP.

2.3. Lines
----------

There MUST NOT be a hard limit on line length.

The soft limit on line length MUST be 120 characters; automated style
checkers MUST warn but MUST NOT error at the soft limit.

Lines SHOULD NOT be longer than 80 characters; lines longer than that
SHOULD be split into multiple subsequent lines of no more than 80
characters each.

There MUST NOT be trailing whitespace at the end of non-blank lines.

Blank lines MAY be added to improve readability and to indicate related
blocks of code.

There MUST NOT be more than one statement per line.

2.4. Indenting
--------------

Code MUST use an indent of 4 spaces, and MUST NOT use tabs for
indenting.

.. Note::

    N.b.: Using only spaces, and not mixing spaces with tabs, helps to
    avoid problems with diffs, patches, history, and annotations. The
    use of spaces also makes it easy to insert fine-grained
    sub-indentation for inter-line alignment.

2.5. Keywords and True/False/Null
---------------------------------

PHP `keywords <http://php.net/manual/en/reserved.keywords.php>`__ MUST
be in lower case.

The PHP constants ``true``, ``false``, and ``null`` MUST be in lower
case.

---------------------------------
3. Namespace and Use Declarations
---------------------------------

When present, there MUST be one blank line after the ``namespace``
declaration.

When present, all ``use`` declarations MUST go after the ``namespace``
declaration.

There MUST be one ``use`` keyword per declaration.

There MUST be one blank line after the ``use`` block.

For example:

.. code-block:: php

    <?php
    namespace Vendor\Package;

    use FooClass;
    use BarClass as Bar;
    use OtherVendor\OtherPackage\BazClass;

    // ... additional PHP code ...

-----------------------------------
4. Classes, Properties, and Methods
-----------------------------------

The term "class" refers to all classes, interfaces, and traits.

4.1. Extends and Implements
---------------------------

The ``extends`` and ``implements`` keywords MUST be declared on the same
line as the class name.

The opening brace for the class MUST go on its own line; the closing
brace for the class MUST go on the next line after the body.

.. code-block:: php

    <?php
    namespace Vendor\Package;

    use FooClass;
    use BarClass as Bar;
    use OtherVendor\OtherPackage\BazClass;

    class ClassName extends ParentClass implements \ArrayAccess, \Countable
    {
        // constants, properties, methods
    }


Lists of ``implements`` MAY be split across multiple lines, where each
subsequent line is indented once. When doing so, the first item in the
list MUST be on the next line, and there MUST be only one interface per
line.


.. code-block:: php

    <?php
    namespace Vendor\Package;

    use FooClass;
    use BarClass as Bar;
    use OtherVendor\OtherPackage\BazClass;

    class ClassName extends ParentClass implements
        \ArrayAccess,
        \Countable,
        \Serializable
    {
        // constants, properties, methods
    }

4.2. Properties
---------------

Visibility MUST be declared on all properties.

The ``var`` keyword MUST NOT be used to declare a property.

There MUST NOT be more than one property declared per statement.

Property names SHOULD NOT be prefixed with a single underscore to
indicate protected or private visibility.

A property declaration looks like the following.

.. code-block:: php

    <?php
    namespace Vendor\Package;

    class ClassName
    {
        public $foo = null;
    }

4.3. Methods
------------

Visibility MUST be declared on all methods.

Method names SHOULD NOT be prefixed with a single underscore to indicate
protected or private visibility.

Method names MUST NOT be declared with a space after the method name.
The opening brace MUST go on its own line, and the closing brace MUST go
on the next line following the body. There MUST NOT be a space after the
opening parenthesis, and there MUST NOT be a space before the closing
parenthesis.

A method declaration looks like the following. Note the placement of
parentheses, commas, spaces, and braces:

.. code-block:: php

    <?php
    namespace Vendor\Package;

    class ClassName
    {
        public function fooBarBaz($arg1, &$arg2, $arg3 = [])
        {
            // method body
        }
    }

4.4. Method Arguments
---------------------

In the argument list, there MUST NOT be a space before each comma, and
there MUST be one space after each comma.

Method arguments with default values MUST go at the end of the argument
list.

.. code-block:: php

    <?php
    namespace Vendor\Package;

    class ClassName
    {
        public function foo($arg1, &$arg2, $arg3 = [])
        {
            // method body
        }
    }

Argument lists MAY be split across multiple lines, where each subsequent
line is indented once. When doing so, the first item in the list MUST be
on the next line, and there MUST be only one argument per line.

When the argument list is split across multiple lines, the closing
parenthesis and opening brace MUST be placed together on their own line
with one space between them.

.. code-block:: php

    <?php
    namespace Vendor\Package;

    class ClassName
    {
        public function aVeryLongMethodName(
            ClassTypeHint $arg1,
            &$arg2,
            array $arg3 = []
        ) {
            // method body
        }
    }

4.5. ``abstract``, ``final``, and ``static``
--------------------------------------------

When present, the ``abstract`` and ``final`` declarations MUST precede
the visibility declaration.

When present, the ``static`` declaration MUST come after the visibility
declaration.

.. code-block:: php

    <?php
    namespace Vendor\Package;

    abstract class ClassName
    {
        protected static $foo;

        abstract protected function zim();

        final public static function bar()
        {
            // method body
        }
    }

4.6. Method and Function Calls
------------------------------

When making a method or function call, there MUST NOT be a space between
the method or function name and the opening parenthesis, there MUST NOT
be a space after the opening parenthesis, and there MUST NOT be a space
before the closing parenthesis. In the argument list, there MUST NOT be
a space before each comma, and there MUST be one space after each comma.

.. code-block:: php

    <?php
    bar();
    $foo->bar($arg1);
    Foo::bar($arg2, $arg3);

Argument lists MAY be split across multiple lines, where each subsequent
line is indented once. When doing so, the first item in the list MUST be
on the next line, and there MUST be only one argument per line.

.. code-block:: php

    <?php
    $foo->bar(
        $longArgument,
        $longerArgument,
        $muchLongerArgument
    );

---------------------
5. Control Structures
---------------------

The general style rules for control structures are as follows:

-  There MUST be one space after the control structure keyword
-  There MUST NOT be a space after the opening parenthesis
-  There MUST NOT be a space before the closing parenthesis
-  There MUST be one space between the closing parenthesis and the
   opening brace
-  The structure body MUST be indented once
-  The closing brace MUST be on the next line after the body

The body of each structure MUST be enclosed by braces. This standardizes
how the structures look, and reduces the likelihood of introducing
errors as new lines get added to the body.

5.1. ``if``, ``elseif``, ``else``
---------------------------------

An ``if`` structure looks like the following. Note the placement of
parentheses, spaces, and braces; and that ``else`` and ``elseif`` are on
the same line as the closing brace from the earlier body.

.. code-block:: php

    <?php
    if ($expr1) {
        // if body
    } elseif ($expr2) {
        // elseif body
    } else {
        // else body;
    }

The keyword ``elseif`` SHOULD be used instead of ``else if`` so that all
control keywords look like single words.

5.2. ``switch``, ``case``
-------------------------

A ``switch`` structure looks like the following. Note the placement of
parentheses, spaces, and braces. The ``case`` statement MUST be indented
once from ``switch``, and the ``break`` keyword (or other terminating
keyword) MUST be indented at the same level as the ``case`` body. There
MUST be a comment such as ``// no break`` when fall-through is
intentional in a non-empty ``case`` body.

.. code-block:: php

    <?php
    switch ($expr) {
        case 0:
            echo 'First case, with a break';
            break;
        case 1:
            echo 'Second case, which falls through';
            // no break
        case 2:
        case 3:
        case 4:
            echo 'Third case, return instead of break';
            return;
        default:
            echo 'Default case';
            break;
    }

5.3. ``while``, ``do while``
----------------------------

A ``while`` statement looks like the following. Note the placement of
parentheses, spaces, and braces.

.. code-block:: php

    <?php
    while ($expr) {
        // structure body
    }

Similarly, a ``do while`` statement looks like the following. Note the
placement of parentheses, spaces, and braces.

.. code-block:: php

    <?php
    do {
        // structure body;
    } while ($expr);

5.4. ``for``
------------

A ``for`` statement looks like the following. Note the placement of
parentheses, spaces, and braces.

.. code-block:: php

    <?php
    for ($i = 0; $i < 10; $i++) {
        // for body
    }

5.5. ``foreach``
----------------

A ``foreach`` statement looks like the following. Note the placement of
parentheses, spaces, and braces.

.. code-block:: php

    <?php
    foreach ($iterable as $key => $value) {
        // foreach body
    }

5.6. ``try``, ``catch``
-----------------------

A ``try catch`` block looks like the following. Note the placement of
parentheses, spaces, and braces.

.. code-block:: php

    <?php
    try {
        // try body
    } catch (FirstExceptionType $e) {
        // catch body
    } catch (OtherExceptionType $e) {
        // catch body
    }

-----------
6. Closures
-----------

Closures MUST be declared with a space after the ``function`` keyword,
and a space before and after the ``use`` keyword.

The opening brace MUST go on the same line, and the closing brace MUST
go on the next line following the body.

There MUST NOT be a space after the opening parenthesis of the argument
list or variable list, and there MUST NOT be a space before the closing
parenthesis of the argument list or variable list.

In the argument list and variable list, there MUST NOT be a space before
each comma, and there MUST be one space after each comma.

Closure arguments with default values MUST go at the end of the argument
list.

A closure declaration looks like the following. Note the placement of
parentheses, commas, spaces, and braces:

.. code-block:: php

    <?php
    $closureWithArgs = function ($arg1, $arg2) {
        // body
    };

    $closureWithArgsAndVars = function ($arg1, $arg2) use ($var1, $var2) {
        // body
    };


Argument lists and variable lists MAY be split across multiple lines,
where each subsequent line is indented once. When doing so, the first
item in the list MUST be on the next line, and there MUST be only one
argument or variable per line.

When the ending list (whether or arguments or variables) is split across
multiple lines, the closing parenthesis and opening brace MUST be placed
together on their own line with one space between them.

The following are examples of closures with and without argument lists
and variable lists split across multiple lines.

.. code-block:: php

    <?php
    $longArgs_noVars = function (
        $longArgument,
        $longerArgument,
        $muchLongerArgument
    ) {
       // body
    };

    $noArgs_longVars = function () use (
        $longVar1,
        $longerVar2,
        $muchLongerVar3
    ) {
       // body
    };

    $longArgs_longVars = function (
        $longArgument,
        $longerArgument,
        $muchLongerArgument
    ) use (
        $longVar1,
        $longerVar2,
        $muchLongerVar3
    ) {
       // body
    };

    $longArgs_shortVars = function (
        $longArgument,
        $longerArgument,
        $muchLongerArgument
    ) use ($var1) {
       // body
    };

    $shortArgs_longVars = function ($arg) use (
        $longVar1,
        $longerVar2,
        $muchLongerVar3
    ) {
       // body
    };

Note that the formatting rules also apply when the closure is used
directly in a function or method call as an argument.

.. code-block:: php

    <?php
    $foo->bar(
        $arg1,
        function ($arg2) use ($var1) {
            // body
        },
        $arg3
    );

-------------
7. Conclusion
-------------

There are many elements of style and practice intentionally omitted by
this guide. These include but are not limited to:

-  Declaration of global variables and global constants

-  Declaration of functions

-  Operators and assignment

-  Inter-line alignment

-  Comments and documentation blocks

-  Class name prefixes and suffixes

-  Best practices

Future recommendations MAY revise and extend this guide to address those or other
elements of style and practice.