public void ensureStartRuleExists(VirtualFile grammarFile) {
PreviewState previewState =
ANTLRv4PluginController.getInstance(project).getPreviewState(grammarFile);
// if start rule no longer exists, reset display/state.
if (previewState.g != ParsingUtils.BAD_PARSER_GRAMMAR && previewState.startRuleName != null) {
Rule rule = previewState.g.getRule(previewState.startRuleName);
if (rule == null) {
previewState.startRuleName = null;
inputPanel.resetStartRuleLabel();
}
}
}
