Issue follow-up #927138 by manarth, handrus, David_Rothstein: Fail image...

Issue follow-up #927138 by manarth, handrus, David_Rothstein: Fail image generation with 404 instead of 500, when source file is missing.

core/modules/image/image.module

@@ -562,7 +562,7 @@ function image_style_deliver($style, $scheme) {
 
   // Don't try to generate file if source is missing.
   if (!file_exists($image_uri)) {
-    watchdog('image', 'Unable to generate the derived image from image at %path.', array('%path' => $derivative_uri));
+    watchdog('image', 'Source image at %source_image_path not found while trying to generate derivative image at %derivative_path.',  array('%source_image_path' => $image_uri, '%derivative_path' => $derivative_uri));
     return new Response(t('Error generating image, missing source file.'), 404);
   }
 

core/modules/image/lib/Drupal/image/Tests/ImageStylesPathAndUrlTest.php

@@ -90,6 +90,16 @@ function testImageStyleUrlExtraSlash() {
     $this->_testImageStyleUrlAndPath('public', TRUE, TRUE);
   }
 
+  /**
+   * Tests that an invalid source image returns a 404.
+   */
+  function testImageStyleUrlForMissingSourceImage() {
+    $non_existent_uri = 'public://foo.png';
+    $generated_url = image_style_url($this->style_name, $non_existent_uri);
+    $this->drupalGet($generated_url);
+    $this->assertResponse(404, 'Accessing an image style URL with a source image that does not exist provides a 404 error response.');
+  }
+
   /**
    * Tests image_style_url().
    */