Upgrade/Install: Select the main plugin file after installation

src/wp-admin/includes/class-plugin-upgrader.php

@@ -541,12 +541,25 @@ public function plugin_info() {
 			return false;
 		}
 
-		// Assume the requested plugin is the first in the list.
-		$plugin_files = array_keys( $plugin );
+		$plugin_files         = array_keys( $plugin );
+		$plugin_file          = $plugin_files[0];
+		$expected_plugin_file = $this->result['destination_name'] . '.php';
 
-		return $this->result['destination_name'] . '/' . $plugin_files[0];
-	}
+		// Prefer a root-level plugin file that matches the plugin directory name.
+		if ( in_array( $expected_plugin_file, $plugin_files, true ) ) {
+			$plugin_file = $expected_plugin_file;
+		} else {
+			// Otherwise, use the first root-level plugin file.
+			foreach ( $plugin_files as $candidate_plugin_file ) {
+				if ( ! str_contains( $candidate_plugin_file, '/' ) ) {
+					$plugin_file = $candidate_plugin_file;
+					break;
+				}
+			}
+		}
 
+		return $this->result['destination_name'] . '/' . $plugin_file;
+	}
 	/**
 	 * Deactivates a plugin before it is upgraded.
 	 *

tests/phpunit/tests/admin/pluginUpgrader.php

@@ -0,0 +1,105 @@
+<?php
+/**
+ * Tests the `Plugin_Upgrader` class.
+ *
+ * @group admin
+ * @group upgrade
+ */
+class Tests_Admin_PluginUpgrader extends WP_UnitTestCase {
+
+	/**
+	 * Test plugin directories and files.
+	 *
+	 * @var array[]
+	 */
+	private static $test_plugins = array(
+		'plugin-upgrader-nested-test' => array(
+			'main.php'              => 'Z Main Plugin',
+			'embedded/embedded.php' => 'A Embedded Plugin',
+		),
+		'plugin-upgrader-slug-test'   => array(
+			'another.php'                   => 'A Another Plugin',
+			'plugin-upgrader-slug-test.php' => 'Z Slug Plugin',
+		),
+	);
+
+	/**
+	 * Creates the test plugins before any tests run.
+	 */
+	public static function set_up_before_class() {
+		parent::set_up_before_class();
+
+		require_once ABSPATH . 'wp-admin/includes/class-wp-upgrader.php';
+		require_once ABSPATH . 'wp-admin/includes/class-plugin-upgrader.php';
+
+		foreach ( self::$test_plugins as $directory => $files ) {
+			foreach ( $files as $file => $name ) {
+				$path = WP_PLUGIN_DIR . "/$directory/$file";
+
+				wp_mkdir_p( dirname( $path ) );
+				file_put_contents( $path, "<?php\n/**\n * Plugin Name: $name\n */" );
+			}
+		}
+	}
+
+	/**
+	 * Removes the test plugins after all tests run.
+	 */
+	public static function tear_down_after_class() {
+		foreach ( self::$test_plugins as $directory => $files ) {
+			foreach ( $files as $file => $name ) {
+				unlink( WP_PLUGIN_DIR . "/$directory/$file" );
+			}
+
+			$subdirectories = glob( WP_PLUGIN_DIR . "/$directory/*", GLOB_ONLYDIR );
+			foreach ( $subdirectories as $subdirectory ) {
+				rmdir( $subdirectory );
+			}
+
+			rmdir( WP_PLUGIN_DIR . "/$directory" );
+		}
+
+		wp_clean_plugins_cache( false );
+
+		parent::tear_down_after_class();
+	}
+
+	/**
+	 * Tests that the main plugin file is selected for the activation link.
+	 *
+	 * @ticket 22287
+	 *
+	 * @covers Plugin_Upgrader::plugin_info
+	 *
+	 * @dataProvider data_plugin_info
+	 *
+	 * @param string $destination_name Plugin destination directory name.
+	 * @param string $expected         Expected main plugin file.
+	 */
+	public function test_plugin_info_should_select_main_plugin( $destination_name, $expected ) {
+		wp_clean_plugins_cache( false );
+
+		$upgrader         = new Plugin_Upgrader();
+		$upgrader->result = array( 'destination_name' => $destination_name );
+
+		$this->assertSame( $expected, $upgrader->plugin_info() );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array[]
+	 */
+	public function data_plugin_info() {
+		return array(
+			'nested plugin'      => array(
+				'destination_name' => 'plugin-upgrader-nested-test',
+				'expected'         => 'plugin-upgrader-nested-test/main.php',
+			),
+			'matching slug file' => array(
+				'destination_name' => 'plugin-upgrader-slug-test',
+				'expected'         => 'plugin-upgrader-slug-test/plugin-upgrader-slug-test.php',
+			),
+		);
+	}
+}