src/language-js/print/function-parameters.js/shouldGroupFunctionParameters
function shouldGroupFunctionParameters(functionNode, returnTypeDoc) {
  const returnTypeNode = getReturnTypeNode(functionNode);
  if (!returnTypeNode) {
    return false;
  }

  const typeParameters =
    functionNode.typeParameters && functionNode.typeParameters.params;
  if (typeParameters) {
    if (typeParameters.length > 1) {
      return false;
    }
    if (typeParameters.length === 1) {
      const typeParameter = typeParameters[0];
      if (typeParameter.constraint || typeParameter.default) {
        return false;
      }
    }
  }

  return (
    getFunctionParameters(functionNode).length === 1 &&
    (isObjectType(returnTypeNode) || willBreak(returnTypeDoc))
  );
}