ban backslashes

lib/config-utils.js

@@ -136,6 +136,13 @@ function validateAndSanitisePath(originalPath, propertyName, configFile) {
         core.warning(getConfigFilePropertyError(configFile, propertyName, '"' + originalPath + '" contains an unsupported character. ' +
             'The filter pattern characters ?, +, [, ], ! are not supported and will be matched literally.'));
     }
+    // Ban any uses of backslash for now.
+    // This may not play nicely with project layouts.
+    // This restriction can be lifted later if we determine they are ok.
+    if (path.indexOf('\\') !== -1) {
+        throw new Error(getConfigFilePropertyError(configFile, propertyName, '"' + originalPath + '" contains an "\\" character. These are not allowed in filters. ' +
+            'If running on windows we recommend using "/" instead for path filters.'));
+    }
     return path;
 }
 exports.validateAndSanitisePath = validateAndSanitisePath;