Issue #3224414 by alexpott, varshith, dagmar, daffie: Installing the syslog module uses its configuration before it is written

(cherry picked from commit 58a4457b91)

core/modules/syslog/src/Logger/SysLog.php

@@ -63,6 +63,14 @@ class SysLog implements LoggerInterface {
   public function log($level, $message, array $context = []) {
     global $base_url;
 
+    $format = $this->config->get('format');
+    // If no format is configured then a message will not be written to syslog
+    // so return early. This occurs during installation of the syslog module
+    // before configuration has been written.
+    if (empty($format)) {
+      return;
+    }
+
     // Ensure we have a connection available.
     $this->openConnection();
 
@@ -70,7 +78,7 @@ class SysLog implements LoggerInterface {
     $message_placeholders = $this->parser->parseMessagePlaceholders($message, $context);
     $message = empty($message_placeholders) ? $message : strtr($message, $message_placeholders);
 
-    $entry = strtr($this->config->get('format'), [
+    $entry = strtr($format, [
       '!base_url' => $base_url,
       '!timestamp' => $context['timestamp'],
       '!type' => $context['channel'],

core/modules/syslog/syslog.module

@@ -55,6 +55,7 @@ function syslog_form_system_logging_settings_alter(&$form, FormStateInterface $f
     '#type'          => 'textarea',
     '#title'         => t('Syslog format'),
     '#default_value' => $config->get('format'),
+    '#required'      => TRUE,
     '#description'   => t('Specify the format of the syslog entry. Available variables are: <dl><dt><code>!base_url</code></dt><dd>Base URL of the site.</dd><dt><code>!timestamp</code></dt><dd>Unix timestamp of the log entry.</dd><dt><code>!type</code></dt><dd>The category to which this message belongs.</dd><dt><code>!ip</code></dt><dd>IP address of the user triggering the message.</dd><dt><code>!request_uri</code></dt><dd>The requested URI.</dd><dt><code>!referer</code></dt><dd>HTTP Referer if available.</dd><dt><code>!severity</code></dt><dd>The severity level of the event; ranges from 0 (Emergency) to 7 (Debug).</dd><dt><code>!uid</code></dt><dd>User ID.</dd><dt><code>!link</code></dt><dd>A link to associate with the message.</dd><dt><code>!message</code></dt><dd>The message to store in the log.</dd></dl>'),
   ];
 

core/modules/syslog/tests/src/Kernel/SyslogTest.php

@@ -51,6 +51,15 @@ class SyslogTest extends KernelTestBase {
     $this->assertEquals('42', $log[6]);
     $this->assertEquals('/my-link', $log[7]);
     $this->assertEquals('My warning message.', $log[8]);
+
+    // Test that an empty format prevents writing to the syslog.
+    /** @var \Drupal\Core\Config\Config $config */
+    $config = $this->container->get('config.factory')->getEditable('syslog.settings');
+    $config->set('format', '');
+    $config->save();
+    unlink($log_filename);
+    \Drupal::logger('my_module')->warning('My warning message.', ['link' => '/my-link']);
+    $this->assertFileDoesNotExist($log_filename);
   }
 
   /**