Fix the page URL when the parent is a top-level menu

page_url() passed parent_slug straight to admin_url(), which is only right
when the page hangs off one of core's menus and the slug is a filename --
options-general.php, edit.php. A plugin with its own top-level menu passes
that menu's slug instead, and admin_url( 'my-plugin' ) builds
/wp-admin/my-plugin?page=..., which is not an admin screen: WordPress serves
the front end from it.

Every tab link and every redirect after saving therefore left the admin
entirely, on any plugin registering its settings under its own menu.

register_menu() was already correct -- add_submenu_page() handles a non-file
parent by putting the page at admin.php?page=... -- so the fix is for
page_url() to resolve the same way.

The regression test reaches page_url() by reflection: both callers, the tab
links and the redirect, are private, and the bug is in the URL rather than in
either of them.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Tk8y5eZa3CHVVSM6nVxsJw

Author: arraypress

src/SettingFields.php

@@ -800,9 +800,22 @@ private function tab_links(): array {
 	 * @return string
 	 */
 	private function page_url( array $args = [] ): string {
+		$parent = (string) $this->config['parent_slug'];
+
+		// A parent slug is only a filename when the page hangs off one of
+		// core's menus -- options-general.php, edit.php. A plugin with its
+		// own top-level menu passes that menu's slug instead, and its
+		// children live at admin.php?page=..., exactly as add_submenu_page()
+		// registers them a few methods up. Passing the slug to admin_url()
+		// builds /wp-admin/my-plugin?page=..., which is not an admin screen
+		// at all -- WordPress serves the front end from it.
+		$base = ( '' !== $parent && str_ends_with( $parent, '.php' ) )
+			? $parent
+			: 'admin.php';
+
 		return add_query_arg(
 			array_merge( [ 'page' => (string) $this->config['menu_slug'] ], array_filter( $args ) ),
-			admin_url( '' !== (string) $this->config['parent_slug'] ? (string) $this->config['parent_slug'] : 'admin.php' )
+			admin_url( $base )
 		);
 	}
 

tests/PageUrlTest.php

@@ -0,0 +1,94 @@
+<?php
+/**
+ * The URL a settings screen links to itself with.
+ *
+ * @package ArrayPress\RegisterSettingFields
+ */
+
+declare( strict_types=1 );
+
+namespace ArrayPress\RegisterSettingFields\Tests;
+
+use ArrayPress\RegisterSettingFields\Registry;
+use ArrayPress\RegisterSettingFields\SettingFields;
+use PHPUnit\Framework\TestCase;
+use ReflectionMethod;
+
+/**
+ * A parent slug is only a filename when the page hangs off one of core's
+ * menus. A plugin with its own top-level menu passes that menu's slug, and
+ * passing that to admin_url() builds /wp-admin/my-plugin?page=... -- which is
+ * not an admin screen at all, so every tab link and every post-save redirect
+ * lands on the front end.
+ *
+ * Reached by reflection because both callers -- the tab links and the
+ * redirect after saving -- are private, and the bug is in the URL rather than
+ * in either of them.
+ */
+final class PageUrlTest extends TestCase {
+
+	protected function tearDown(): void {
+		foreach ( array_keys( Registry::instance()->all() ) as $id ) {
+			Registry::instance()->unregister( (string) $id );
+		}
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Build a page and read the URL it would link to.
+	 *
+	 * @param string $parent_slug What the page hangs off.
+	 * @param array  $args        Extra query arguments.
+	 *
+	 * @return string
+	 */
+	private function url( string $parent_slug, array $args = [] ): string {
+		$page = new SettingFields(
+			'sf_url_' . md5( $parent_slug ),
+			[
+				'option_name' => 'sf_url',
+				'menu_slug'   => 'my-plugin-settings',
+				'parent_slug' => $parent_slug,
+				'tabs'        => [ 'one' => 'One' ],
+				'fields'      => [ 'first' => [ 'type' => 'text', 'tab' => 'one' ] ],
+			]
+		);
+
+		// No setAccessible(): private methods have been reflectively
+		// callable without it since PHP 8.1, and the call is deprecated.
+		return (string) ( new ReflectionMethod( $page, 'page_url' ) )->invoke( $page, $args );
+	}
+
+	public function test_a_top_level_menu_parent_resolves_to_admin_php(): void {
+		$url = $this->url( 'my-plugin' );
+
+		$this->assertStringContainsString(
+			'admin.php',
+			$url,
+			'A parent that is not a file must resolve to admin.php, where add_submenu_page() puts it.'
+		);
+		$this->assertStringNotContainsString(
+			'/wp-admin/my-plugin',
+			$url,
+			'The parent slug was used as a path, which is a front end URL.'
+		);
+		$this->assertStringContainsString( 'page=my-plugin-settings', $url );
+	}
+
+	public function test_a_core_menu_parent_keeps_its_filename(): void {
+		$this->assertStringContainsString( 'options-general.php', $this->url( 'options-general.php' ) );
+		$this->assertStringContainsString( 'edit.php', $this->url( 'edit.php' ) );
+	}
+
+	public function test_no_parent_resolves_to_admin_php(): void {
+		$this->assertStringContainsString( 'admin.php', $this->url( '' ) );
+	}
+
+	public function test_extra_arguments_survive(): void {
+		$url = $this->url( 'my-plugin', [ 'tab' => 'payments' ] );
+
+		$this->assertStringContainsString( 'tab=payments', $url );
+		$this->assertStringContainsString( 'page=my-plugin-settings', $url );
+	}
+}