Code Modernisation: Document when the Hash polyfills can be removed.

The Hash extension cannot be disabled as of PHP 7.4. So, while we can't remove these polyfills yet, we can document when we'll be able to.

Props jrf.
Fixes #47698.


Built from https://develop.svn.wordpress.org/trunk@45638


git-svn-id: http://core.svn.wordpress.org/trunk@45449 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/compat.php

@@ -221,6 +221,13 @@ if ( ! function_exists( 'hash_hmac' ) ) :
 	/**
 	 * Compat function to mimic hash_hmac().
 	 *
+	 * The Hash extension is bundled with PHP by default since PHP 5.1.2.
+	 * However, the extension may be explicitly disabled on select servers.
+	 * As of PHP 7.4.0, the Hash extension is a core PHP extension and can no
+	 * longer be disabled.
+	 * I.e. when PHP 7.4.0 becomes the minimum requirement, this polyfill
+	 * and the associated `_hash_hmac()` function can be safely removed.
+	 *
 	 * @ignore
 	 * @since 3.2.0
 	 *
@@ -335,10 +342,15 @@ if ( ! function_exists( 'hash_equals' ) ) :
 	 *
 	 * Compares two strings using the same time whether they're equal or not.
 	 *
-	 * This function was added in PHP 5.6.
-	 *
 	 * Note: It can leak the length of a string when arguments of differing length are supplied.
 	 *
+	 * This function was added in PHP 5.6.
+	 * However, the Hash extension may be explicitly disabled on select servers.
+	 * As of PHP 7.4.0, the Hash extension is a core PHP extension and can no
+	 * longer be disabled.
+	 * I.e. when PHP 7.4.0 becomes the minimum requirement, this polyfill
+	 * can be safely removed.
+	 *
 	 * @since 3.9.2
 	 *
 	 * @param string $a Expected string.

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45637';
+$wp_version = '5.3-alpha-45638';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.