A plugin in the analysis server could support analysis results for file types that are neither Dart or HTML. For these files, DartCode wouldn't send analysis requests to the analysis server because the file ending is not matched by isAnalyzable:

Is there a reason not all files in the current workspace are marked analyzable? If there is, it would be amazing if we could make the analyzable file endings customizable. Then, plugins that support custom file endings could instruct users to mark the respective file ending as analyzable.