Show a preview image in builtin attachment select autocomplete.

src/Services/Attachments/AttachmentPathResolver.php

@@ -101,6 +101,7 @@ class AttachmentPathResolver
     /**
      * Converts a path passed by parameter from services.yaml (which can be an absolute path or relative to project dir)
      * to an absolute path. When a relative path is passed, the directory must exist or null is returned.
+     * Returns an absolute path with "/" no matter, what system is used.
      *
      * @internal
      *
@@ -132,8 +133,8 @@ class AttachmentPathResolver
             return null;
         }
 
-        //Otherwise return resolved path
-        return $tmp;
+        //Normalize file path (use / instead of \)
+        return str_replace('\\', '/', $tmp);
     }
 
     /**

src/Services/Attachments/AttachmentURLGenerator.php

@@ -91,6 +91,8 @@ class AttachmentURLGenerator
             $public_path = $this->public_path;
         }
 
+
+
         //Our absolute path must begin with public path or we can not use it for asset pathes.
         if (0 !== strpos($absolute_path, $public_path)) {
             return null;
@@ -100,6 +102,19 @@ class AttachmentURLGenerator
         return substr($absolute_path, strlen($public_path) + 1);
     }
 
+    /**
+     * Converts a placeholder path to a path to a image path.
+     *
+     * @param string      $placeholder_path the placeholder path that should be converted
+     *
+     * @return string|null
+     */
+    public function placeholderPathToAssetPath(string $placeholder_path): ?string
+    {
+        $absolute_path = $this->pathResolver->placeholderToRealPath($placeholder_path);
+        return $this->absolutePathToAssetPath($absolute_path);
+    }
+
     /**
      * Returns a URL under which the attachment file can be viewed.
      */