1. Rename sniff.

2. Adjust the logic per #52769 (comment).

test/php/gutenberg-coding-standards/Gutenberg/Sniffs/NamingConventions/ValidBlockLibraryFunctionName.php

@@ -0,0 +1,128 @@
+<?php
+/**
+ * Gutenberg Coding Standards.
+ *
+ * @package gutenberg/gutenberg-coding-standards
+ * @link    https://github.com/WordPress/gutenberg
+ * @license https://opensource.org/licenses/MIT MIT
+ */
+
+namespace GutenbergCS\Gutenberg\Sniffs\NamingConventions;
+
+use PHP_CodeSniffer\Files\File;
+use PHP_CodeSniffer\Sniffs\Sniff;
+
+/**
+ * The sniff implements the Gutenberg coding standard to verify whether functions and classes
+ * are enclosed with function_exists() and !class_exists(). This check ensures that the functions
+ * and classes are not already defined, and recommends the use of function_exists() and class_exists()
+ * to prevent fatal errors during the integration of the feature to the Core.
+ *
+ * @link https://github.com/WordPress/gutenberg/blob/trunk/lib/README.md#wrap-functions-and-classes-with--function_exists-and--class_exists
+ *
+ * @package gutenberg/gutenberg-coding-standards
+ *
+ * @since   1.0.0
+ */
+final class ValidBlockLibraryFunctionNameSniff implements Sniff {
+	/**
+	 * Target prefixes.
+	 *
+	 * @var array
+	 */
+	public $prefixes = array();
+
+	/**
+	 * Registers the tokens that this sniff wants to listen for.
+	 *
+	 * @since 3.0.0
+	 *
+	 * @return array
+	 */
+	public function register() {
+		$this->onRegisterEvent();
+
+		return array( T_FUNCTION );
+	}
+
+	/**
+	 * Processes function and class tokens.
+	 *
+	 * @param File $phpcsFile The file being scanned.
+	 * @param int  $stackPtr  The position of the current token
+	 *                        in the stack passed in $tokens.
+	 *
+	 * @return void
+	 */
+	public function process( File $phpcsFile, $stackPtr ) {
+		$tokens = $phpcsFile->getTokens();
+		$token  = $tokens[ $stackPtr ];
+
+		if ( 'T_FUNCTION' !== $token['type'] ) {
+			return;
+		}
+
+		$this->processFunctionToken( $phpcsFile, $stackPtr );
+	}
+
+	/**
+	 * Functions should be wrapped with !function_exists() to avoid fatal errors.
+	 * E.g.:
+	 * if ( ! function_exists( 'wp_get_navigation' ) ) {
+	 *     function wp_get_navigation( $slug ) { ... }
+	 * }
+	 *
+	 * @param File $phpcsFile    The file being scanned.
+	 * @param int  $stackPointer The position of the current token
+	 *                           in the stack passed in $tokens.
+	 *
+	 * @return void
+	 */
+	private function processFunctionToken( File $phpcsFile, $stackPointer ) {
+		$tokens        = $phpcsFile->getTokens();
+		$functionToken = $phpcsFile->findNext( T_STRING, $stackPointer );
+
+		$wrappingTokensToCheck = array(
+			T_CLASS,
+			T_INTERFACE,
+			T_TRAIT,
+		);
+
+		foreach ( $wrappingTokensToCheck as $wrappingTokenToCheck ) {
+			if ( false !== $phpcsFile->getCondition( $functionToken, $wrappingTokenToCheck, false ) ) {
+				// This sniff only processes functions, not class methods.
+				return;
+			}
+		}
+
+		$functionName = $tokens[ $functionToken ]['content'];
+
+		foreach ( $this->whitelistedFunctions as $functionRegExp ) {
+			if ( preg_match( $functionRegExp, $functionName ) ) {
+				// Ignore whitelisted function names.
+				return;
+			}
+		}
+	}
+
+	/**
+	 * The purpose of this method is to sanitize the input data
+	 * after the properties have been set.
+	 */
+	private function onRegisterEvent() {
+		$this->prefixes = self::sanitize( $this->prefixes );
+	}
+
+	/**
+	 * Input data needs to be sanitized.
+	 *
+	 * @param array $values The values being sanitized.
+	 *
+	 * @return array
+	 */
+	private static function sanitize( $values ) {
+		$values = array_map( 'trim', $values );
+
+		return array_filter( $values );
+	}
+}