I18N: Initialize WP_Locale array properties.

Initializing the `WP_Locale` array properties to an empty array at the class definition point. Why?

* Ensure the properties initialize to an `array` data type at instantiation (rather than `null`).

This initialization is needed to ensure the properties are not `null` if another class inherits from `WP_Locale` but does not run `WP_Locale::init()` from the constructor. In this case, the initialization prevents

{{{
Warning: array_values() expects parameter 1 to be array, null given
}}}

when Core uses any of the properties.

* Good design practice.

The code and documentation are clearly expecting these properties to be an `array` data type. Setting each to a default `array()` state further helps to clearly communicate the code design.

Follow-up to [37889], [36292], [31078], [3676], [6589].

Props tyxla, SergeyBiryukov, azaozz, hellofromTonya, mukesh27.
See #57427.

git-svn-id: https://develop.svn.wordpress.org/trunk@55047 602fd350-edb4-49c9-b593-d223f7449a82

Author: hellofromtonya

src/wp-includes/class-wp-locale.php

@@ -19,9 +19,10 @@ class WP_Locale {
 	 * Stores the translated strings for the full weekday names.
 	 *
 	 * @since 2.1.0
+	 * @since 6.2.0 Initialized to an empty array.
 	 * @var string[]
 	 */
-	public $weekday;
+	public $weekday = array();
 
 	/**
 	 * Stores the translated strings for the one character weekday names.
@@ -32,51 +33,57 @@ class WP_Locale {
 	 * @see WP_Locale::init() for how to handle the hack.
 	 *
 	 * @since 2.1.0
+	 * @since 6.2.0 Initialized to an empty array.
 	 * @var string[]
 	 */
-	public $weekday_initial;
+	public $weekday_initial = array();
 
 	/**
 	 * Stores the translated strings for the abbreviated weekday names.
 	 *
 	 * @since 2.1.0
+	 * @since 6.2.0 Initialized to an empty array.
 	 * @var string[]
 	 */
-	public $weekday_abbrev;
+	public $weekday_abbrev = array();
 
 	/**
 	 * Stores the translated strings for the full month names.
 	 *
 	 * @since 2.1.0
+	 * @since 6.2.0 Initialized to an empty array.
 	 * @var string[]
 	 */
-	public $month;
+	public $month = array();
 
 	/**
 	 * Stores the translated strings for the month names in genitive case, if the locale specifies.
 	 *
 	 * @since 4.4.0
+	 * @since 6.2.0 Initialized to an empty array.
 	 * @var string[]
 	 */
-	public $month_genitive;
+	public $month_genitive = array();
 
 	/**
 	 * Stores the translated strings for the abbreviated month names.
 	 *
 	 * @since 2.1.0
+	 * @since 6.2.0 Initialized to an empty array.
 	 * @var string[]
 	 */
-	public $month_abbrev;
+	public $month_abbrev = array();
 
 	/**
 	 * Stores the translated strings for 'am' and 'pm'.
 	 *
 	 * Also the capitalized versions.
 	 *
 	 * @since 2.1.0
+	 * @since 6.2.0 Initialized to an empty array.
 	 * @var string[]
 	 */
-	public $meridiem;
+	public $meridiem = array();
 
 	/**
 	 * The text direction of the locale language.
@@ -92,9 +99,10 @@ class WP_Locale {
 	 * The thousands separator and decimal point values used for localizing numbers.
 	 *
 	 * @since 2.3.0
+	 * @since 6.2.0 Initialized to an empty array.
 	 * @var array
 	 */
-	public $number_format;
+	public $number_format = array();
 
 	/**
 	 * The separator string used for localizing list item separator.

tests/phpunit/tests/locale.php

@@ -15,6 +15,39 @@ public function set_up() {
 		$this->locale = new WP_Locale();
 	}
 
+	/**
+	 * @ticket 57427
+	 *
+	 * @dataProvider data_property_initializes_to_array
+	 *
+	 * @param string $name Property name to test.
+	 */
+	public function test_property_initializes_to_array( $name ) {
+		$this->assertIsArray( $this->locale->$name, "WP_Locale::{$name} property should be an array" );
+
+		// Test a custom implementation when `init()` is not invoked in the constructor.
+		$wp_locale = new Custom_WP_Locale();
+		$this->assertIsArray( $wp_locale->$name, "Custom_WP_Locale::{$name} property should be an array" );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array
+	 */
+	public function data_property_initializes_to_array() {
+		return array(
+			'weekday'         => array( 'weekday' ),
+			'weekday_initial' => array( 'weekday_initial' ),
+			'weekday_abbrev'  => array( 'weekday_abbrev' ),
+			'month'           => array( 'month' ),
+			'month_genitive'  => array( 'month_genitive' ),
+			'month_abbrev'    => array( 'month_abbrev' ),
+			'meridiem'        => array( 'meridiem' ),
+			'number_format'   => array( 'number_format' ),
+		);
+	}
+
 	/**
 	 * @covers WP_Locale::get_weekday
 	 */
@@ -141,3 +174,11 @@ public function test_is_rtl() {
 		$this->assertFalse( $this->locale->is_rtl() );
 	}
 }
+
+class Custom_WP_Locale extends WP_Locale {
+	public function __construct() {
+		// Do not initialize to test property initialization.
+		// $this->init();
+		$this->register_globals();
+	}
+}