Separate out the sniffing for extract().

Currently only VIP checked for the usage of `extract()`, even though it is an explicit rule for core.

Ref: https://make.wordpress.org/core/handbook/best-practices/coding-standards/php/#dont-extract

Solved #90 for real ;-)

WordPress-Core/ruleset.xml

@@ -111,5 +111,6 @@
 	<rule ref="WordPress.WhiteSpace.CastStructureSpacing"/>
 	<rule ref="WordPress.PHP.YodaConditions"/>
 	<rule ref="WordPress.WP.I18n"/>
+	<rule ref="WordPress.Functions.DontExtract"/>
 
 </ruleset>

WordPress/Sniffs/Functions/DontExtractSniff.php

@@ -0,0 +1,48 @@
+<?php
+/**
+ * WordPress Coding Standard.
+ *
+ * @category PHP
+ * @package  PHP_CodeSniffer
+ * @link     https://make.wordpress.org/core/handbook/best-practices/coding-standards/
+ */
+
+/**
+ * Restricts the usage of extract().
+ *
+ * @link     https://make.wordpress.org/core/handbook/best-practices/coding-standards/php/#dont-extract
+ *
+ * @category PHP
+ * @package  PHP_CodeSniffer
+ * @author   Shady Sharaf <[email protected]>
+ */
+class WordPress_Sniffs_Functions_DontExtractSniff extends WordPress_AbstractFunctionRestrictionsSniff {
+
+	/**
+	 * Groups of functions to restrict.
+	 *
+	 * Example: groups => array(
+	 * 	'lambda' => array(
+	 * 		'type'      => 'error' | 'warning',
+	 * 		'message'   => 'Use anonymous functions instead please!',
+	 * 		'functions' => array( 'eval', 'create_function' ),
+	 * 	)
+	 * )
+	 *
+	 * @return array
+	 */
+	public function getGroups() {
+		return array(
+
+			'extract' => array(
+				'type'      => 'error',
+				'message'   => '%s() usage is highly discouraged, due to the complexity and unintended issues it might cause.',
+				'functions' => array(
+					'extract',
+				),
+			),
+
+		);
+	} // end getGroups()
+
+} // end class

WordPress/Sniffs/VIP/RestrictedFunctionsSniff.php

@@ -139,14 +139,6 @@ public function getGroups() {
 				),
 			),
 
-			'extract' => array(
-				'type'      => 'warning',
-				'message'   => '%s() usage is highly discouraged, due to the complexity and unintended issues it might cause.',
-				'functions' => array(
-					'extract',
-				),
-			),
-
 			'custom_role' => array(
 				'type'      => 'error',
 				'message'   => 'Use wpcom_vip_add_role() instead of add_role()',

WordPress/Tests/Functions/DontExtractUnitTest.inc

@@ -0,0 +1,9 @@
+<?php
+
+extract( array( 'a' => 1 ) ); // bad
+
+// Similarly named functions or methods however are fine.
+my_extract(); // Ok.
+My_Object::extract(); // Ok.
+$this->extract(); // Ok.
+$my_object->extract(); // Ok.

WordPress/Tests/Functions/DontExtractUnitTest.php

@@ -0,0 +1,53 @@
+<?php
+/**
+ * Unit test class for WordPress Coding Standard.
+ *
+ * @category PHP
+ * @package  PHP_CodeSniffer
+ * @link     https://make.wordpress.org/core/handbook/best-practices/coding-standards/
+ */
+
+/**
+ * A sniff unit test checks a .inc file for expected violations of a single
+ * coding standard. Expected errors and warnings are stored in this class.
+ *
+ * @category  PHP
+ * @package   PHP_CodeSniffer
+ * @author    Akeda Bagus <[email protected]>
+ * @author    Greg Sherwood <[email protected]>
+ * @author    Marc McIntyre <[email protected]>
+ * @license   https://github.com/squizlabs/PHP_CodeSniffer/blob/master/licence.txt BSD Licence
+ * @version   Release: @package_version@
+ * @link      http://pear.php.net/package/PHP_CodeSniffer
+ */
+class WordPress_Tests_Functions_DontExtractUnitTest extends AbstractSniffUnitTest {
+
+	/**
+	 * Returns the lines where errors should occur.
+	 *
+	 * The key of the array should represent the line number and the value
+	 * should represent the number of errors that should occur on that line.
+	 *
+	 * @return array(int => int)
+	 */
+	public function getErrorList() {
+		return array(
+			3  => 1,
+		);
+
+	} // end getErrorList()
+
+	/**
+	 * Returns the lines where warnings should occur.
+	 *
+	 * The key of the array should represent the line number and the value
+	 * should represent the number of warnings that should occur on that line.
+	 *
+	 * @return array(int => int)
+	 */
+	public function getWarningList() {
+		return array();
+
+	} // end getWarningList()
+
+} // end class

WordPress/Tests/VIP/RestrictedFunctionsUnitTest.inc

@@ -16,7 +16,7 @@ $ch = curl_init(); // bad
 
 curl_close( $ch ); // bad
 
-extract( array( 'a' => 1 ) ); // bad
+// Empty line - function moved to another sniff.
 
 add_role( 'test' ); // bad
 

WordPress/Tests/VIP/RestrictedFunctionsUnitTest.php

@@ -91,7 +91,6 @@ public function getWarningList() {
 			13 => 1,
 			15 => 1,
 			17 => 1,
-			19 => 1,
 			58 => 1,
 			59 => 1,
 			61 => 1,