Display an admin notice if dependencies are missing. See #76

docs/installation.md

@@ -6,7 +6,7 @@ Requires PHP 7.0 or later.
 
 ## Zip
 
-1. Download the [latest release](https://github.com/cedaro/satispress/releases/latest) from GitHub.
+1. Download the [latest release](https://github.com/cedaro/satispress/releases/latest) from GitHub (use the asset named `satispress-{version}.zip`).
 2. Go to the _Plugins → Add New_ screen in your WordPress admin panel and click the __Upload Plugin__ button at the top.
 3. Upload the zipped archive.
 4. Click the __Activate Plugin__ link after installation completes.
@@ -17,6 +17,6 @@ SatisPress is available on [Packagist](https://packagist.org/packages/cedaro/sat
 
 ```bash
 composer require cedaro/satispress
-``` 
+```
 
 [Back to Index](index.md)

satispress.php

@@ -44,6 +44,13 @@
 	require __DIR__ . '/vendor/autoload.php';
 }
 
+// Display a notice and bail if dependencies are missing.
+if ( ! function_exists( __NAMESPACE__ . '\autoloader_classmap' ) ) {
+	require_once __DIR__ . '/src/functions.php';
+	add_action( 'admin_notices', __NAMESPACE__ . '\display_missing_dependencies_notice' );
+	return;
+}
+
 // Autoload mapped classes.
 spl_autoload_register( __NAMESPACE__ . '\autoloader_classmap' );
 

src/functions.php

@@ -143,3 +143,30 @@ function get_edited_user_id(): int {
 function is_plugin_file( $plugin_file ) {
 	return '.php' === substr( $plugin_file, -4 );
 }
+
+/**
+ * Display a notice about missing dependencies.
+ *
+ * @since 0.3.1
+ */
+function display_missing_dependencies_notice() {
+	$message = sprintf(
+		/* translators: %s: documentation URL */
+		__( 'SatisPress is missing required dependencies. <a href="%s" target="_blank" rel="noopener noreferer">Learn more.</a>', 'satispress' ),
+		'https://github.com/cedaro/satispress/blob/master/docs/installation.md'
+	);
+
+	printf(
+		'<div class="satispress-compatibility-notice notice notice-error"><p>%s</p></div>',
+		wp_kses(
+			$message,
+			[
+				'a' => [
+					'href'   => true,
+					'rel'    => true,
+					'target' => true,
+				],
+			]
+		)
+	);
+}