src/language-markdown/printer-markdown.js/shouldNotPrePrintHardline
function shouldNotPrePrintHardline(node, data) {
  const isFirstNode = data.parts.length === 0;
  const isInlineNode = INLINE_NODE_TYPES.indexOf(node.type) !== -1;

  const isInlineHTML =
    node.type === "html" &&
    INLINE_NODE_WRAPPER_TYPES.indexOf(data.parentNode.type) !== -1;

  return isFirstNode || isInlineNode || isInlineHTML;
}