includes/StubObject.php

   1 <?php
   2 /**
   3  * Delayed loading of global objects.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  */
  22
  23 /**
  24  * Class to implement stub globals, which are globals that delay loading the
  25  * their associated module code by deferring initialisation until the first
  26  * method call.
  27  *
  28  * Note on reference parameters:
  29  *
  30  * If the called method takes any parameters by reference, the __call magic
  31  * here won't work correctly. The solution is to unstub the object before
  32  * calling the method.
  33  *
  34  * Note on unstub loops:
  35  *
  36  * Unstub loops (infinite recursion) sometimes occur when a constructor calls
  37  * another function, and the other function calls some method of the stub. The
  38  * best way to avoid this is to make constructors as lightweight as possible,
  39  * deferring any initialisation which depends on other modules. As a last
  40  * resort, you can use StubObject::isRealObject() to break the loop, but as a
  41  * general rule, the stub object mechanism should be transparent, and code
  42  * which refers to it should be kept to a minimum.
  43  */
  44 class StubObject {
  45         /** @var null|string */
  46         protected $global;
  47
  48         /** @var null|string */
  49         protected $class;
  50
  51         /** @var null|callable */
  52         protected $factory;
  53
  54         /** @var array */
  55         protected $params;
  56
  57         /**
  58          * Constructor.
  59          *
  60          * @param string $global Name of the global variable.
  61          * @param string|callable $class Name of the class of the real object
  62          *                               or a factory function to call
  63          * @param array $params Parameters to pass to constructor of the real object.
  64          */
  65         public function __construct( $global = null, $class = null, $params = [] ) {
  66                 $this->global = $global;
  67                 if ( is_callable( $class ) ) {
  68                         $this->factory = $class;
  69                 } else {
  70                         $this->class = $class;
  71                 }
  72                 $this->params = $params;
  73         }
  74
  75         /**
  76          * Returns a bool value whenever $obj is a stub object. Can be used to break
  77          * a infinite loop when unstubbing an object.
  78          *
  79          * @param object $obj Object to check.
  80          * @return bool True if $obj is not an instance of StubObject class.
  81          */
  82         public static function isRealObject( $obj ) {
  83                 return is_object( $obj ) && !$obj instanceof StubObject;
  84         }
  85
  86         /**
  87          * Unstubs an object, if it is a stub object. Can be used to break a
  88          * infinite loop when unstubbing an object or to avoid reference parameter
  89          * breakage.
  90          *
  91          * @param object $obj Object to check.
  92          * @return void
  93          */
  94         public static function unstub( &$obj ) {
  95                 if ( $obj instanceof StubObject ) {
  96                         $obj = $obj->_unstub( 'unstub', 3 );
  97                 }
  98         }
  99
 100         /**
 101          * Function called if any function exists with that name in this object.
 102          * It is used to unstub the object. Only used internally, PHP will call
 103          * self::__call() function and that function will call this function.
 104          * This function will also call the function with the same name in the real
 105          * object.
 106          *
 107          * @param string $name Name of the function called
 108          * @param array $args Arguments
 109          * @return mixed
 110          */
 111         public function _call( $name, $args ) {
 112                 $this->_unstub( $name, 5 );
 113                 return call_user_func_array( [ $GLOBALS[$this->global], $name ], $args );
 114         }
 115
 116         /**
 117          * Create a new object to replace this stub object.
 118          * @return object
 119          */
 120         public function _newObject() {
 121                 $params = $this->factory
 122                         ? [ 'factory' => $this->factory ]
 123                         : [ 'class' => $this->class ];
 124                 return ObjectFactory::getObjectFromSpec( $params + [
 125                         'args' => $this->params,
 126                         'closure_expansion' => false,
 127                 ] );
 128         }
 129
 130         /**
 131          * Function called by PHP if no function with that name exists in this
 132          * object.
 133          *
 134          * @param string $name Name of the function called
 135          * @param array $args Arguments
 136          * @return mixed
 137          */
 138         public function __call( $name, $args ) {
 139                 return $this->_call( $name, $args );
 140         }
 141
 142         /**
 143          * This function creates a new object of the real class and replace it in
 144          * the global variable.
 145          * This is public, for the convenience of external callers wishing to access
 146          * properties, e.g. eval.php
 147          *
 148          * @param string $name Name of the method called in this object.
 149          * @param int $level Level to go in the stack trace to get the function
 150          *   who called this function.
 151          * @return object The unstubbed version of itself
 152          * @throws MWException
 153          */
 154         public function _unstub( $name = '_unstub', $level = 2 ) {
 155                 static $recursionLevel = 0;
 156
 157                 if ( !$GLOBALS[$this->global] instanceof StubObject ) {
 158                         return $GLOBALS[$this->global]; // already unstubbed.
 159                 }
 160
 161                 if ( get_class( $GLOBALS[$this->global] ) != $this->class ) {
 162                         $caller = wfGetCaller( $level );
 163                         if ( ++$recursionLevel > 2 ) {
 164                                 throw new MWException( "Unstub loop detected on call of "
 165                                         . "\${$this->global}->$name from $caller\n" );
 166                         }
 167                         wfDebug( "Unstubbing \${$this->global} on call of "
 168                                 . "\${$this->global}::$name from $caller\n" );
 169                         $GLOBALS[$this->global] = $this->_newObject();
 170                         --$recursionLevel;
 171                         return $GLOBALS[$this->global];
 172                 }
 173         }
 174 }
 175
 176 /**
 177  * Stub object for the user language. Assigned to the $wgLang global.
 178  */
 179 class StubUserLang extends StubObject {
 180
 181         public function __construct() {
 182                 parent::__construct( 'wgLang' );
 183         }
 184
 185         /**
 186          * Call Language::findVariantLink after unstubbing $wgLang.
 187          *
 188          * This method is implemented with a full signature rather than relying on
 189          * __call so that the pass-by-reference signature of the proxied method is
 190          * honored.
 191          *
 192          * @param string &$link The name of the link
 193          * @param Title &$nt The title object of the link
 194          * @param bool $ignoreOtherCond To disable other conditions when
 195          *   we need to transclude a template or update a category's link
 196          */
 197         public function findVariantLink( &$link, &$nt, $ignoreOtherCond = false ) {
 198                 global $wgLang;
 199                 $this->_unstub( 'findVariantLink', 3 );
 200                 $wgLang->findVariantLink( $link, $nt, $ignoreOtherCond );
 201         }
 202
 203         /**
 204          * @return Language
 205          */
 206         public function _newObject() {
 207                 return RequestContext::getMain()->getLanguage();
 208         }
 209 }