Manual:Coding conventions/PHP

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This page describes the coding conventions used within files of the MediaWiki codebase written in PHP. See also the general conventions that apply to all program languages, including PHP. If you would like a short checklist to help you review your commits, try using the pre-commit checklist.

To help developers fix code with an inadequately spacey style, a tool called stylize.php has been created, which uses PHP's tokenizer extension to add spaces at the relevant places; the tool is also available with a web interface. It's recommended to run this over files committed to Git.

Rules for PHP_CodeSniffer are also available. For more information, see Continuous integration/PHP CodeSniffer. The git repository https://github.com/wikimedia/mediawiki-tools-codesniffer.git contains the PHP CodeSniffer settings for MediaWiki code.

Code structure[edit]

Spaces[edit]

MediaWiki favors a heavily-spaced style for optimum readability.

Put spaces on either side of binary operators, for example:

// No:
$a=$b+$c;

// Yes:
$a = $b + $c;

Put spaces next to parentheses on the inside, except where the parentheses are empty. Do not put a space following a function name.

$a = getFoo( $b );
$c = getBar();

Put spaces in brackets when declaring an array, except where the array is empty. Do not put spaces in brackets when accessing array elements.

// Yes
$a = [ 'foo', 'bar' ];
$c = $a[0];
$x = [];

//No
$a = ['foo', 'bar'];
$c = a[ 0 ];
$x = [ ];

Control structures such as if, while, for, foreach, and switch, as well as the catch keyword, should be followed by a space:

// Yes
if ( isFoo() ) {
	$a = 'foo';
}

// No
if( isFoo() ) {
	$a = 'foo';
}

When type casting, do not use a space within or after the cast operator:

// Yes
(int)$foo;

// No
(int) $bar;
( int )$bar;
( int ) $bar;

In comments there should be one space between the # or // character and the comment.

// Yes: Proper inline comment
//No: Missing space
/***** Do not comment like this ***/

To help developers fix code with an inadequately spacey style, a tool called stylize.php has been created, which uses PHP's tokenizer extension to enforce most whitespace conventions automatically.

Ternary operator[edit]

The ternary operator can be used profitably if the expressions are very short and obvious:

$wiki = isset( $this->mParams['wiki'] ) ? $this->mParams['wiki'] : false;

But if you're considering a multi-line expression with a ternary operator, please consider using an if () block instead. Remember, disk space is cheap, code readability is everything, "if" is English and ?: is not.

Since MediaWiki requires PHP 5.5.9 or later, use of the shorthand ternary operator (?:) also known as the elvis operator, introduced in PHP 5.3, is allowed.

String literals[edit]

For simple string literals, single quotes are slightly faster for PHP to parse than double quotes. Also for people using US/UK qwerty keyboards, they are easier to type, since it avoids the need to press shift. For these reasons, single quotes are preferred in cases where they are equivalent to double quotes.

However, do not be afraid of using PHP's double-quoted string interpolation feature: $elementId = "myextension-$index"; This has slightly better performance characteristics than the equivalent using the concatenation (dot) operator, and it looks nicer too.

Heredoc-style strings are sometimes useful:

$s = <<<EOT
<div class="mw-some-class">
$boxContents
</div>
EOT;

Some authors like to use END as the ending token, which is also the name of a PHP function. This leads to IRC conversations like the following:

<Simetrical>      vim also has ridiculously good syntax highlighting.
<TimStarling>     it breaks when you write <<<END in PHP
<Simetrical>      TimStarling, but if you write <<<HTML it syntax-highlights as HTML!
<TimStarling>     I have to keep changing it to ENDS so it looks like a string again
<brion-codereview>        fix the bug in vim then!
<TimStarling>     brion-codereview: have you ever edited a vim syntax script file?
<brion-codereview>        hehehe
<TimStarling>     http://tstarling.com/stuff/php.vim
<TimStarling>     that's half of it...
<TimStarling>     here's the other half: http://tstarling.com/stuff/php-syntax.vim
<TimStarling>     1300 lines of sparsely-commented code in a vim-specific language
<TimStarling>     which turns out to depend for its operation on all kinds of subtle inter-pass effects
<werdnum> TimStarling: it looks like some franken-basic language.

Functions and parameters[edit]

Avoid passing huge numbers of parameters to functions or constructors:

// Constructor for Block.php from 1.17 to 1.26. *DON'T* do this!
function __construct( $address = '', $user = 0, $by = 0, $reason = '',
	$timestamp = 0, $auto = 0, $expiry = '', $anonOnly = 0, $createAccount = 0, $enableAutoblock = 0,
	$hideName = 0, $blockEmail = 0, $allowUsertalk = 0
) {
	...
}

It quickly becomes impossible to remember the order of parameters, and you will inevitably end up having to hardcode all the defaults in callers just to customise a parameter at the end of the list. If you are tempted to code a function like this, consider passing an associative array of named parameters instead.

In general, using boolean parameters is discouraged in functions. In $object->getSomething( $input, true, true, false ), without looking up the documentation for MyClass::getSomething(), it is impossible to know what those parameters are meant to indicate. Much better is to either use class constants, and make a generic flag parameter:

$myResult = MyClass::getSomething( $input, MyClass::FROM_DB | MyClass::PUBLIC_ONLY );

Or to make your function accept an array of named parameters:

$myResult = MyClass::getSomething( $input, [ 'fromDB', 'publicOnly' ] );

Try not to repurpose variables over the course of a function, and avoid modifying the parameters passed to a function (unless they're passed by reference and that's the whole point of the function, obviously).

Assignment expressions[edit]

Using assignment as an expression is surprising to the reader and looks like an error. Do not write code like this:

if ( $a = foo() ) {
    bar();
}

Space is cheap, and you're a fast typist, so instead use:

$a = foo();
if ( $a ) {
    bar();
}

Using assignment in a while() clause used to be legitimate, for iteration:

$res = $dbr->query( 'SELECT * FROM some_table' );
while ( $row = $dbr->fetchObject( $res ) ) {
    showRow( $row );
}

This is unnecessary in new code; instead use:

$res = $dbr->query( 'SELECT * FROM some_table' );
foreach ( $res as $row ) {
    showRow( $row );
}

C borrowings[edit]

The PHP language was designed by people who love C and wanted to bring souvenirs from that language into PHP. But PHP has some important differences from C.

In C, constants are implemented as preprocessor macros and are fast. In PHP, they are implemented by doing a runtime hashtable lookup for the constant name, and are slower than just using a string literal. In most places where you would use an enum or enum-like set of macros in C, you can use string literals in PHP.

PHP has three special literals for which upper-/lower-/mixed-case is insignificant in the language (since PHP 5.1.3), but for which our convention is always lowercase : true, false and null.

Use elseif not else if. They have subtly different meanings:

// This:
if ( $foo == 'bar' ) {
	echo 'Hello world';
} else if ( $foo == 'Bar' ) {
	echo 'Hello world';
} else if ( $baz == $foo ) {
	echo 'Hello baz';
} else {
	echo 'Eh?';
}

// Is actually equivalent to:
if ( $foo == 'bar' ) {
	echo 'Hello world';
} else {
	if ( $foo == 'Bar' ) {
		echo 'Hello world';
	} else {
		if ( $baz == $foo ) {
			echo 'Hello baz';
		} else {
			echo 'Eh?';
		}
	}
}

And the latter has poorer performance.

Alternative syntax for control structures[edit]

PHP offers an alternative syntax for control structures using colons and keywords such as "endif", "endwhile", etc.:

if ( $foo == $bar ):
    echo "<div>Hello world</div>";
endif;

This syntax should be avoided, as it prevents many text editors from automatically matching and folding braces. Standard syntax should be used instead:

if ( $foo == $bar ) {
    echo "<div>Hello world</div>";
}

Brace placement[edit]

See Manual:Coding conventions#Indenting and alignment.

Type declarations in function parameters[edit]

Use type declarations (type hinting) when applicable.

Naming[edit]

Use lowerCamelCase when naming functions or variables. For example:

private function doSomething( $userPrefs, $editSummary )

Use UpperCamelCase when naming classes: class ImportantClass. Use uppercase with underscores for global and class constants: DB_MASTER, Revision::REV_DELETED_TEXT. Other variables are usually lowercase or lowerCamelCase; avoid using underscores in variable names.

There are also some prefixes used in different places:

Functions[edit]

  • wf (wiki functions) – top-level functions, e.g.
    function wfFuncname() { ... }
    
  • ef (extension functions) = global functions in extensions, although "in most cases modern style puts hook functions as static methods on a class, leaving few or no raw top-level functions to be so named." (-- brion in Manual_talk:Coding_conventions#ef_prefix_9510)

Verb phrases are preferred: use getReturnText() instead of returnText().

Variables[edit]

  • $wg – global variables, e.g. $wgVersion, $wgTitle. Always use this for new globals, so that it's easy to spot missing "global $wgFoo" declarations. In extensions, the extension name should be used as a namespace delimiter. For example, $wgAbuseFilterConditionLimit, not $wgConditionLimit.
  • Global declarations should be at the beginning of a function so dependencies can be determined without having to read the whole function.

It is common to work with an instance of the Database class; we have a naming convention for these which helps keep track of the nature of the server to which we are connected. This is of particular importance in replicated environments, such as Wikimedia and other large wikis; in development environments there is usually no difference between the two types, which can conceal subtle errors.

  • $dbw – a Database object for writing (a master connection)
  • $dbr – a Database object for non-concurrency-sensitive reading (this may be a read-only slave, slightly behind master state, so don't ever try to write to the database with it, or get an "authoritative" answer to important queries like permissions and block status)

The following may be seen in old code but are discouraged in new code:

  • $ws – Session variables, e.g. $_SESSION['wsSessionName']
  • $wc – Cookie variables, e.g. $_COOKIE['wcCookieName']
  • $wp – Post variables (submitted via form fields), e.g. $wgRequest->getText( 'wpLoginName' )
  • $m – object member variables: $this->mPage. This is discouraged in new code, but try to stay consistent within a class.

Pitfalls[edit]

empty()[edit]

The empty() function should only be used when you want to suppress errors. Otherwise just use ! (boolean conversion).

  • empty( $var ) essentially does !isset( $var ) || !$var.
    Common use case: Optional boolean configuration options that default to false. $this->enableFoo = !empty( $options['foo'] );
  • Beware of boolean conversion pitfalls.
  • It suppresses errors about undefined properties and variables. If only intending to test for undefined, use !isset(). If only intending to test for "empty" values (e.g. false, zero, empty array, etc.), use !.

isset()[edit]

Do not use isset() to test for null. Using isset() in this situation could introduce errors by hiding misspelled variable names. Instead, use $var === null.

Boolean conversion[edit]

if ( !$var ) {
 ...
}
  • Study the rules for conversion to boolean. Be careful when converting strings to boolean.
  • Do not use it to test if a string is empty, because PHP considers '0' and similar expressions to be falsy. Use === '' instead.

Other[edit]

  • Array plus does not renumber the keys of numerically-indexed arrays, so [ 'a' ] + [ 'b' ] === [ 'a' ]. If you want keys to be renumbered, use array_merge(): array_merge( [ 'a' ], [ 'b' ] ) == [ 'a', 'b' ]
  • Make sure you have error_reporting() set to E_ALL for PHP 5. This will notify you of undefined variables and other subtle gotchas that stock PHP will ignore. See also Manual:How to debug.
  • When working in a pure PHP environment, remove any trailing ?> tags. These tags often cause issues with trailing white-space and "headers already sent" error messages (cf. bugzilla:17642 and http://news.php.net/php.general/280796).
  • Do not use the 'goto' syntax introduced in 5.3. PHP may have introduced the feature, but that does not mean we should use it.
  • Do not pass by reference when traversing an array unless you have to. Even then, be aware of the consequences. (See http://www.king-foo.be/2010/10/php-quirks-passing-an-array-by-reference/)
  • PHP lets you declare static variables even within a non-static method of a class. This has led to subtle bugs in some cases, as the variables are shared between instances. Where you would not use a private static property, do not use a static variable either.

Equality operators[edit]

Be careful with double-equals comparison operators. Triple-equals (===) is generally more intuitive and should be preferred unless you have a reason to use double-equals (==).

  • 'foo' == 0 is true (!)
  • '000' == '0' is true (!)
  • '000' === '0' is false
  • To check if two scalars that are supposed to be numeric are equal, use ==, e.g. 5 == "5" is true.
  • To check if two variables are both of type 'string' and are the same sequence of characters, use ===, e.g. "1.e6" === "1.0e6" is false.
  • To check if two scalars that should be treated as strings are equal as strings, use strcmp(), e.g. strcmp(13,"13") is 0.

Comments and documentation[edit]

It is essential that your code be well documented so that other developers and bug fixers can easily navigate the logic of your code. New classes, methods, and member variables should include comments providing brief descriptions of their functionality (unless it is obvious), even if private. In addition, all new methods should document their parameters and return values.

We use the Doxygen documentation style (it is very similar to PHPDoc for the subset that we use) to produce auto-generated documentation from code comments (see Manual:mwdocgen.php). Begin a block of Doxygen comments with /**, instead of the Qt-style formatting /*!. Doxygen structural commands start with @tagname. (Use @ rather than \ as the escape character – both styles work in Doxygen, but for backwards and future compatibility MediaWiki has chosen the @param style.) They organize the generated documentation (using @ingroup) and identify authors (using @author tags).

They describe a function or method, the parameters it takes (using @param), and what the function returns (using @return). The format for parameters is:

@param type $paramName Description of parameter

If a parameter can be of multiple types, separate them with the pipe '|' character, for example:

@param string|Language|bool $lang Language for the toc title, defaults to user language

Continue sentences belonging to an annotation on the next line, indented with one additional space.

For every public interface (method, class, variable, whatever) you add or change, provide a @since VERSION tag, so people extending the code via this interface know they are breaking compatibility with older versions of the code.

class Foo {

	/**
	 * @var array $bar: Description here
	 * @example [ 'foo' => Bar, 'quux' => Bar, .. ]
	 */
	protected $bar;

	/**
	 * Description here, following by documentation of the parameters.
	 *
	 * Some example:
	 * @code
	 * ...
	 * @endcode
	 *
	 * @since 1.24
	 * @param FooContext $context context for decoding Foos
	 * @param array|string $options Optionally pass extra options. Either a string
	 *  or an array of strings.
	 * @return Foo|null New instance of Foo or null of quuxification failed.
	 */
	public function makeQuuxificatedFoo( FooContext $context = null, $options = [] ) {
		/* .. */
	}

}

FIXME usually means something is bad or broken. TODO means that improvements are needed; it does not necessarily mean that the person adding the comment is going to do it. HACK means that a quick but inelegant, awkward or otherwise suboptimal solution to an immediate problem was made, and that eventually a more thorough rewrite of the code should be done.

@var: documenting class members[edit]

There is a 'bug' in Doxygen[1] which affects MediaWiki's documentation: using @var to specify the class members' type only works if the variable name is appended:

	/**
	 * Some explanation about the variable
	 *
	 * @var string $msg
	 */
	protected $msg;


If you don't append the variable name Doxygen will ignore the entire comment block and it will not be included in the docs.

Source file headers[edit]

In order to be compliant with most licenses you should have something similar to the following (specific to GPLv2 applications) at the top of every source file.

<?php
/**
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 * 
 * @file
 */

Doxygen tags[edit]

We use the following annotations which Doxygen recognizes. Use them in this order, for consistency:

File level:

  • @file
  • @ingroup
  • @author

Class, class member, or global member:

  • @todo
  • @var
  • @deprecated
  • @class
  • @since
  • @param
  • @return
  • @throws
  • @private
  • @see

Test annotations[edit]

In tests, we use the following annotations among others. These aren't merely documentation, they mean something to PHPUnit and affect test execution.

  • @depends
  • @group
  • @covers
  • @dataProvider
  • @expectedException
  • @expectedExceptionMessage

Integration[edit]

There are a few pieces of code in the MediaWiki codebase which are intended to be standalone and easily portable to other applications. While some of these now exist as separate libraries, others remain within the MediaWiki source tree (e.g. the files in /includes/libs). Apart from these, code should be integrated into the rest of the MediaWiki environment, and should allow other areas of the codebase to integrate with it in return.

Visibility[edit]

Make methods public/protected/private (think what makes sense). Don't just make everything public!

Global objects[edit]

Do not access the PHP superglobals $_GET, $_POST, etc, directly; use $request->get*( 'param' ) instead; there are various functions depending on what type of value you want. You can get a WebRequest from the nearest RequestContext, or if absolutely necessary $wgRequest. Equally, do not access $_SERVER directly; use $request->getIP() if you want to get the IP address of the current user.

Static methods and properties[edit]

Static methods and properties are useful for programmers because they act like globals without polluting the global namespace. However, they make subclassing and reuse more difficult for other developers. Generally, you should avoid introducing static functions and properties when you can, especially if the sole purpose is to just save typing.

For example, lots of developers would prefer to write something like:

Foo::bar();

This is because it is shorter and takes less keystrokes. However, by doing this you've made the Foo class much harder to subclass and reuse. Instead of introducing a static method, you could just type:

$f = new Foo();
$f->bar();

Remember, shorter does not always mean better, and you should take the time to design your classes in a way that makes them easy to reuse.

Late static binding[edit]

In PHP 5.3, a new feature called "Late Static Binding" (LSB) (e.g. static::bar()) was added to help work around this perceived lack of functionality in static functions. However, the usefulness of LSB is debated among MediaWiki developers: it should be avoided for the time being.

Classes[edit]

Encapsulate your code in an object-oriented class, or add functionality to existing classes; do not add new global functions or variables. Try to be mindful of the distinction between 'backend' classes, which represent entities in the database (eg User, Block, Revision, etc), and 'frontend' classes, which represent pages or interfaces visible to the user (SpecialPage, Article, ChangesList, etc. Even if your code is not obviously object-oriented, you can put it in a static class (eg IP or Html).

As a holdover from PHP 4's lack of private class members and methods, older code will be marked with comments such as /** @private */ to indicate the intention; respect this as if it were enforced by the interpreter.

Mark new code with proper visibility modifiers, including public if appropriate, but do not add visibility to existing code without first checking, testing and refactoring as required. It's generally a good idea to avoid visibility changes unless you're making changes to the function which would break old uses of it anyway.

Error handling[edit]

Don't suppress errors with PHP's @ operator, for any reason ever. It's broken when E_STRICT is enabled and it causes an unlogged, unexplained error if there is a fatal, which is hard to support.

The proper method of handling errors is to actually handle the errors. For example, if you are thinking of using an error suppression operator to suppress an invalid array index warning, you should instead perform an isset() check on the array index before trying to access it. When possible, always prevent PHP errors rather than catching and handling them afterward. It makes the code more understandable and avoids dealing with slow error suppression methods.

If and only if there is a situation where you are expecting an unavoidable PHP warning, you may use MediaWiki\suppressWarnings() and MediaWiki\restoreWarnings() from the at-ease library instead of the @ operator. This is for cases where:

  1. It is impossible to anticipate the error that is about to occur; and
  2. You are planning on handling the error in an appropriate manner after it occurs.

An example of this is opening a file with fopen(). You can anticipate the error by calling file_exists() and is_readable(), but it is possible the file will have been deleted in between the check and the actual fopen() call. In this case, your code should be ready to handle the case that the file will fail to open, and you can use MediaWiki\suppressWarnings() to prevent PHP from being noisy. Note that using MediaWiki\suppressWarnings() and MediaWiki\restoreWarnings() are slow. They are much slower than using the @ operator, since it involves at least four function calls and reference counting, rather than just an opcode.

When your code encounters a sudden error, you should throw an exception rather than using PHP's trigger_error. The exception handler will display this as nicely as possible to the end user and wiki administrator, and also provides a stack trace to developers. Don't throw an instance of Exception itself, but instead a subclass of it. Exceptions that indicate programming errors should be one of the exceptions that ship with PHP or a more specific subclass, while exceptions that indicate errors that are relevant to the end user should be an ErrorPageError or one of its subclasses.

References[edit]

See also[edit]

External links[edit]

Coding conventionsManual:Coding conventions
General All languagesManual:Coding conventions#Code structure · Development policyDevelopment policy · Security for developersSecurity for developers · Pre-commit checklistManual:Pre-commit checklist · Performance guidelinesPerformance guidelines(draft) · Style guideDesign/Living style guide · Accessibility guide for developersAccessibility guide for developers(draft)
PHP Code conventionsManual:Coding conventions/PHP · PHPUnit test conventionsManual:PHP unit testing/Writing unit tests#Test_conventions · Security checklist for developersSecurity checklist for developers
JavaScript Code conventionsManual:Coding conventions/JavaScript · Learning JavaScriptLearning JavaScript
CSS Code conventionsManual:Coding conventions/CSS
Database Code conventionsManual:Coding conventions/Database · Database policyDevelopment policy#Database policy
Python Code conventionsManual:Coding conventions/Python
Ruby Code conventionsManual:Coding conventions/Ruby
Selenium/Cucumber Code conventionsManual:Coding conventions/Selenium
Java Code conventionsManual:Coding conventions/Java
API client code Standards for API client librariesAPI:Client code/Gold standard