Code Modernization: Rename the `readonly()` function to `wp_readonly()`.

Since PHP 8.1, `readonly` is a reserved keyword and cannot be used as a function name.

In order to avoid PHP parser errors, the `readonly()` function was extracted to a separate file and is now only included conditionally on PHP < 8.1.

This commit also:
* Moves the tests for the `__checked_selected_helper()` function and all the related functions to their own file.
* Switches to named data providers. This makes the output when using the `--testdox` option more descriptive and is helpful when trying to debug which data set from a data provider failed the test.
* Improves the tests in question to make them feature-complete and expand test coverage.

Props jrf, ayeshrajans, haosun, knutsp, swissspidy, SergeyBiryukov.
Fixes #53858.
Built from https://develop.svn.wordpress.org/trunk@51586


git-svn-id: http://core.svn.wordpress.org/trunk@51197 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/general-template.php

@@ -4813,17 +4813,27 @@ function disabled( $disabled, $current = true, $echo = true ) {
  *
  * Compares the first two arguments and if identical marks as readonly
  *
- * @since 4.9.0
+ * @since 5.9.0
  *
  * @param mixed $readonly One of the values to compare
  * @param mixed $current  (true) The other value to compare if not just true
  * @param bool  $echo     Whether to echo or just return the string
  * @return string HTML attribute or empty string
  */
-function readonly( $readonly, $current = true, $echo = true ) {
+function wp_readonly( $readonly, $current = true, $echo = true ) {
 	return __checked_selected_helper( $readonly, $current, $echo, 'readonly' );
 }
 
+/*
+ * Include a compat `readonly()` function on PHP < 8.1. Since PHP 8.1,
+ * `readonly` is a reserved keyword and cannot be used as a function name.
+ * In order to avoid PHP parser errors, this function was extracted
+ * to a separate file and is only included conditionally on PHP < 8.1.
+ */
+if ( PHP_VERSION_ID < 80100 ) {
+	require_once __DIR__ . '/php-compat/readonly.php';
+}
+
 /**
  * Private helper function for checked, selected, disabled and readonly.
  *

wp-includes/php-compat/readonly.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * Conditionally declares a `readonly()` function, which was renamed
+ * to `wp_readonly()` in WordPress 5.9.0.
+ *
+ * In order to avoid PHP parser errors, this function was extracted
+ * to this separate file and is only included conditionally on PHP 8.1.
+ *
+ * Including this file on PHP >= 8.1 results in a fatal error.
+ *
+ * @package WordPress
+ * @since 5.9.0
+ */
+
+/**
+ * Outputs the HTML readonly attribute.
+ *
+ * Compares the first two arguments and if identical marks as readonly
+ *
+ * This function is deprecated, and cannot be used on PHP >= 8.1.
+ *
+ * @since 4.9.0
+ * @deprecated 5.9.0 Use `wp_readonly` introduced in 5.9.0.
+ *
+ * @see wp_readonly()
+ *
+ * @param mixed $readonly One of the values to compare
+ * @param mixed $current  (true) The other value to compare if not just true
+ * @param bool  $echo     Whether to echo or just return the string
+ * @return string HTML attribute or empty string
+ */
+function readonly( $readonly, $current = true, $echo = true ) {
+	_deprecated_function( __FUNCTION__, '5.9.0', 'wp_readonly()' );
+	return wp_readonly( $readonly, $current, $echo );
+}

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51585';
+$wp_version = '5.9-alpha-51586';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.