Refactor in the WC_Settings_Page class for PHP 8 compatibility

- Turn get_settings into a parameterless method, but accept one
  parameter via func_get_arg; and mark the method as deprecated.
- Rename the existing get_settings to get_settings_for_section;
  and mark the method as final.
- Rename the existing get_settings_for_section to get_settings_for_section_core.

See the comment added to get_settings for the rationale for the change.

includes/admin/settings/class-wc-settings-page.php

@@ -77,12 +77,25 @@ if ( ! class_exists( 'WC_Settings_Page', false ) ) :
 		/**
 		 * Get settings array for the default section.
 		 *
+		 * External settings classes (registered via 'woocommerce_get_settings_pages' filter)
+		 * might have redefined this method as "get_settings($section_id='')", thus we need
+		 * to use this method internally instead of 'get_settings_for_section' to register settings
+		 * and render settings pages.
+		 *
+		 * *But* we can't just redefine the method as "get_settings($section_id='')" here, since this
+		 * will break on PHP 8 if any external setting class have it as 'get_settings()'.
+		 *
+		 * Thus we leave the method signature as is and use 'func_get_arg' to get the setting id
+		 * if it's supplied, and we use this method internally; but it's deprecated and should
+		 * otherwise never be used.
+		 *
 		 * @deprecated 5.4.0 Use 'get_settings_for_section' (passing an empty string for default section)
 		 *
 		 * @return array Settings array, each item being an associative array representing a setting.
 		 */
 		public function get_settings() {
-			return $this->get_settings_for_section( '' );
+			$section_id = 0 === func_num_args() ? '' : func_get_arg( 0 );
+			return $this->get_settings_for_section( $section_id );
 		}
 
 		/**

includes/class-wc-install.php

@@ -603,8 +603,13 @@ class WC_Install {
 			}
 			$subsections = array_unique( array_merge( array( '' ), array_keys( $section->get_sections() ) ) );
 
+			/**
+			 * We are using 'WC_Settings_Page::get_settings' on purpose even thought it's deprecated.
+			 * See the method documentation for an explanation.
+			 */
+
 			foreach ( $subsections as $subsection ) {
-				foreach ( $section->get_settings_for_section( $subsection ) as $value ) {
+				foreach ( $section->get_settings( $subsection ) as $value ) {
 					if ( isset( $value['default'] ) && isset( $value['id'] ) ) {
 						$autoload = isset( $value['autoload'] ) ? (bool) $value['autoload'] : true;
 						add_option( $value['id'], $value['default'], '', ( $autoload ? 'yes' : 'no' ) );

includes/class-wc-register-wp-admin-settings.php

@@ -114,11 +114,16 @@ class WC_Register_WP_Admin_Settings {
 		$sections = $this->object->get_sections();
 		if ( empty( $sections ) ) {
 			// Default section is just an empty string, per admin page classes.
-			$sections = array( '' );
+			$sections = array( ''  => '' );
 		}
 
+		/**
+		 * We are using 'WC_Settings_Page::get_settings' on purpose even thought it's deprecated.
+		 * See the method documentation for an explanation.
+		 */
+
 		foreach ( $sections as $section => $section_label ) {
-			$settings_from_section = $this->object->get_settings_for_section( $section );
+			$settings_from_section = $this->object->get_settings( $section );
 			foreach ( $settings_from_section as $setting ) {
 				if ( ! isset( $setting['id'] ) ) {
 					continue;

tests/legacy/unit-tests/settings/register-wp-admin-settings.php

@@ -186,7 +186,7 @@ class WC_Tests_Register_WP_Admin_Settings extends WC_Unit_Test_Case {
 	 * @since 3.0.0
 	 * @covers WC_Register_WP_Admin_Settings::register_page_settings
 	 */
-	public function test_register_settings_one_section() {
+	public function test_register_settings_default_section_no_settings() {
 		$this->page
 			->expects( $this->any() )
 			->method( 'get_sections' )
@@ -194,8 +194,8 @@ class WC_Tests_Register_WP_Admin_Settings extends WC_Unit_Test_Case {
 
 		$this->page
 			->expects( $this->once() )
-			->method( 'get_settings_for_section' )
-			->with( $this->equalTo( 0 ) )
+			->method( 'get_settings' )
+			->with( $this->equalTo( '' ) )
 			->will( $this->returnValue( array() ) );
 
 		$settings = new WC_Register_WP_Admin_Settings( $this->page, 'page' );
@@ -210,7 +210,7 @@ class WC_Tests_Register_WP_Admin_Settings extends WC_Unit_Test_Case {
 	 * @since 3.0.0
 	 * @covers WC_Register_WP_Admin_Settings::register_page_settings
 	 */
-	public function test_register_settings() {
+	public function test_register_settings_default_section_with_settings() {
 		$this->page
 			->expects( $this->any() )
 			->method( 'get_sections' )
@@ -235,7 +235,7 @@ class WC_Tests_Register_WP_Admin_Settings extends WC_Unit_Test_Case {
 
 		$this->page
 			->expects( $this->any() )
-			->method( 'get_settings_for_section' )
+			->method( 'get_settings' )
 			->will( $this->returnValue( $settings ) );
 
 		$settings = new WC_Register_WP_Admin_Settings( $this->page, 'page' );

tests/php/includes/settings/class-wc-settings-page-test.php

@@ -59,12 +59,36 @@ class WC_Settings_Page_Test extends WC_Unit_Test_Case {
 		$this->assertEquals( $expected, $actual );
 	}
 
+	/**
+	 * Test for get_settings_for_section (default section).
+	 */
+	public function test_get_settings_for_section__default_section() {
+		$sut = new WC_Settings_Example();
+
+		$actual = $sut->get_settings_for_section( '' );
+
+		$expected = array( 'key' => 'value' );
+		$this->assertEquals( $expected, $actual );
+	}
+
 	/**
 	 * Test for get_settings (named section with its own get_settings_for_X_section method).
 	 */
 	public function test_get_settings__named_section_with_own_method() {
 		$sut = new WC_Settings_Example();
 
+		$actual = $sut->get_settings( 'foobar' );
+
+		$expected = array( 'foo' => 'bar' );
+		$this->assertEquals( $expected, $actual );
+	}
+
+	/**
+	 * Test for get_settings_for_section (named section with its own get_settings_for_X_section method).
+	 */
+	public function test_get_settings_for_section__named_section_with_own_method() {
+		$sut = new WC_Settings_Example();
+
 		$actual = $sut->get_settings_for_section( 'foobar' );
 
 		$expected = array( 'foo' => 'bar' );