[Blueprints] Prevent plugin activation error if plugin redirects during activation or produces an output

packages/playground/blueprints/src/lib/steps/activate-plugin.spec.ts

@@ -84,4 +84,45 @@ describe('Blueprint step activatePlugin()', () => {
 
 		expect(php.fileExists(createdFilePath)).toBe(true);
 	});
+
+	it('should succeed when the plugin redirects during activation', async () => {
+		const docroot = php.documentRoot;
+		php.writeFile(
+			`${docroot}/wp-content/plugins/test-plugin.php`,
+			`<?php
+			/**
+			 * Plugin Name: Test Plugin
+			 */
+			add_action( 'activated_plugin', function( $plugin ) {
+				if( $plugin == plugin_basename( __FILE__ ) ) {
+					wp_redirect( admin_url( 'edit.php' ) );
+					exit();
+				}
+			} );
+			`
+		);
+		await expect(async () => {
+			await activatePlugin(php, {
+				pluginPath: 'test-plugin.php',
+			});
+		}).not.toThrow();
+	});
+
+	it('should activate the plugin if it produces output during activation', async () => {
+		const docroot = php.documentRoot;
+		php.writeFile(
+			`${docroot}/wp-content/plugins/test-plugin.php`,
+			`<?php
+			/**
+			 * Plugin Name: Test Plugin
+			 */
+			echo 'Hello World';
+			`
+		);
+		await expect(async () => {
+			await activatePlugin(php, {
+				pluginPath: 'test-plugin.php',
+			});
+		}).not.toThrow();
+	});
 });

packages/playground/blueprints/src/lib/steps/activate-plugin.ts

@@ -1,7 +1,6 @@
 import { phpVar } from '@php-wasm/util';
 import { StepHandler } from '.';
 import { logger } from '@php-wasm/logger';
-
 /**
  * @inheritDoc activatePlugin
  * @example
@@ -39,7 +38,7 @@ export const activatePlugin: StepHandler<ActivatePluginStep> = async (
 	progress?.tracker.setCaption(`Activating ${pluginName || pluginPath}`);
 
 	const docroot = await playground.documentRoot;
-	const result = await playground.run({
+	const activatePluginResult = await playground.run({
 		code: `<?php
 			define( 'WP_ADMIN', true );
 			require_once( ${phpVar(docroot)}. "/wp-load.php" );
@@ -65,22 +64,61 @@ export const activatePlugin: StepHandler<ActivatePluginStep> = async (
 				}
 			}
 
-			if ( null === $response ) {
-				die('Plugin activated successfully');
-			} else if ( is_wp_error( $response ) ) {
-				throw new Exception( $response->get_error_message() );
+			if (is_wp_error($response)) {
+				die($response->get_error_message());
 			}
+		`,
+	});
+
+	/**
+	 * Instead of checking the plugin activation response,
+	 * check if the plugin is active by looking at the active plugins list.
+	 *
+	 * We have to split the activation and the check into two PHP runs
+	 * because some plugins might redirect during activation,
+	 * which would prevent any output that happens after activation from being returned.
+	 *
+	 * Relying on the plugin activation response is not reliable because if the plugin activation
+	 * produces any output, it will be threaded as an error.
+	 * See WordPress source code for more details:
+	 * https://github.com/WordPress/wordpress-develop/blob/6.7/src/wp-admin/includes/plugin.php#L733
+	 *
+	 * Because some plugins can create an output, we need to use output buffering
+	 * to ensure the 'true' response is not polluted by other outputs.
+	 * If the plugin activation fails, we will return the buffered output as it might
+	 * contain more information about the failure.
+	 */
+	const isActiveCheckResult = await playground.run({
+		code: `<?php
+			ob_start();
+			require_once( ${phpVar(docroot)}. "/wp-load.php" );
 
-			throw new Exception( 'Unable to activate plugin' );
+			$relative_plugin_path = str_replace( ${phpVar(
+				docroot
+			)}. "/wp-content/plugins/", '', ${phpVar(pluginPath)} );
+			$active_plugins = get_option( 'active_plugins' );
+			foreach ( $active_plugins as $plugin ) {
+				if ( strpos( $plugin, $relative_plugin_path ) === 0 ) {
+					ob_end_clean();
+					die('true');
+				}
+			}
+			die(ob_get_flush() ?? 'false');
 		`,
 	});
-	if (result.text !== 'Plugin activated successfully') {
-		logger.debug(result);
+
+	if (activatePluginResult.text) {
+		logger.warn(activatePluginResult.text);
+	}
+	if (isActiveCheckResult.text !== 'true') {
+		if (isActiveCheckResult.text !== 'false') {
+			logger.debug(isActiveCheckResult.text);
+		}
 		throw new Error(
 			`Plugin ${pluginPath} could not be activated – WordPress exited with no error. ` +
 				`Sometimes, when $_SERVER or site options are not configured correctly, ` +
 				`WordPress exits early with a 301 redirect. ` +
-				`Inspect the "debug" logs in the console for more details`
+				`Inspect the "debug" logs in the console for more details.`
 		);
 	}
 };