Issue #2540438 by znerol, timmillwood: Invalid format string when falling back to error_log in _drupal_log_error()

core/includes/errors.inc

@@ -159,7 +159,7 @@ function _drupal_log_error($error, $fatal = FALSE) {
     catch (\Exception $e) {
       // We can't log, for example because the database connection is not
       // available. At least try to log to PHP error log.
-      error_log(sprintf('Failed to log error: %type: !message in %function (line %line of %file).', $error['%type'], $error['%function'], $error['%line'], $error['%file']));
+      error_log(strtr('Failed to log error: %type: !message in %function (line %line of %file).', $error));
     }
   }
 

core/modules/system/src/Tests/System/UncaughtExceptionTest.php

@@ -185,6 +185,35 @@ class UncaughtExceptionTest extends WebTestBase {
     $this->assertRaw('PDOException');
   }
 
+  /**
+   * Tests fallback to PHP error log when an exception is thrown while logging.
+   */
+  public function testLoggerException() {
+    // Ensure the test error log is empty before these tests.
+    $this->assertNoErrorsLogged();
+
+    $this->expectedExceptionMessage = 'Deforestation';
+    \Drupal::state()->set('error_service_test.break_logger', TRUE);
+
+    $this->drupalGet('');
+    $this->assertResponse(500);
+    $this->assertText('The website encountered an unexpected error. Please try again later.');
+    $this->assertRaw($this->expectedExceptionMessage);
+
+    // Find fatal error logged to the simpletest error.log
+    $errors = file(\Drupal::root() . '/' . $this->siteDirectory . '/error.log');
+    $this->assertIdentical(count($errors), 1, 'Exactly one line logged to the PHP error log');
+
+    $expected_path = \Drupal::root() . '/core/modules/system/tests/modules/error_service_test/src/MonkeysInTheControlRoom.php';
+    $expected_line = 61;
+    $expected_entry = "Failed to log error: Exception: Deforestation in Drupal\\error_service_test\\MonkeysInTheControlRoom->handle() (line ${expected_line} of ${expected_path})";
+    $this->assert(strpos($errors[0], $expected_entry) !== FALSE, 'Original error logged to the PHP error log when an exception is thrown by a logger');
+
+    // The exception is expected. Do not interpret it as a test failure. Not
+    // using File API; a potential error must trigger a PHP warning.
+    unlink(\Drupal::root() . '/' . $this->siteDirectory . '/error.log');
+  }
+
   /**
    * {@inheritdoc}
    */

core/modules/system/tests/modules/error_service_test/error_service_test.services.yml

@@ -6,3 +6,8 @@ services:
   # Set up a service with a missing class dependency.
   broken_class_with_missing_dependency:
     class: Drupal\error_service_test\LonelyMonkeyClass
+  logger.broken:
+    class: Drupal\error_service_test\Logger\TestLog
+    tags:
+      - { name: logger }
+      - { name: backend_overridable }

core/modules/system/tests/modules/error_service_test/src/Logger/TestLog.php

@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\error_service_test\Logger\TestLog.
+ */
+
+namespace Drupal\error_service_test\Logger;
+
+use Drupal\Core\Logger\RfcLoggerTrait;
+use Psr\Log\LoggerInterface;
+
+/**
+ * Throws an exception while logging an exception.
+ *
+ * @see \Drupal\system\Tests\System\UncaughtExceptionTest::testLoggerException()
+ */
+class TestLog implements LoggerInterface {
+  use RfcLoggerTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function log($level, $message, array $context = array()) {
+    $trigger = [
+      '%type' => 'Exception',
+      '!message' => 'Deforestation',
+      '%function' => 'Drupal\error_service_test\MonkeysInTheControlRoom->handle()',
+      'severity_level' => 3,
+      'channel' => 'php',
+    ];
+    if (array_diff_assoc($trigger, $context) === []) {
+      throw new \Exception('Oh, oh, frustrated monkeys!');
+    }
+  }
+
+}

core/modules/system/tests/modules/error_service_test/src/MonkeysInTheControlRoom.php

@@ -57,6 +57,10 @@ class MonkeysInTheControlRoom implements HttpKernelInterface {
       throw new \Exception('Oh oh, bananas in the instruments.');
     }
 
+    if (\Drupal::state()->get('error_service_test.break_logger')) {
+      throw new \Exception('Deforestation');
+    }
+
     return $this->app->handle($request, $type, $catch);
   }