feat(markdown): preserve break style (#3325)

src/doc-printer.js

@@ -398,7 +398,12 @@ function printDocToString(doc, options) {
                     out.pop();
                   }
 
-                  if (out.length) {
+                  if (
+                    out.length &&
+                    (options.parser !== "markdown" ||
+                      // preserve markdown's `break` node (two trailing spaces)
+                      !/\S {2}$/.test(out[out.length - 1]))
+                  ) {
                     out[out.length - 1] = out[out.length - 1].replace(
                       /[^\S\n]*$/,
                       ""

src/printer-markdown.js

@@ -315,7 +315,12 @@ function genericPrint(path, options, print) {
     case "tableCell":
       return printChildren(path, options, print);
     case "break":
-      return concat(["\\", hardline]);
+      return concat([
+        /\s/.test(options.originalText[node.position.start.offset])
+          ? "  "
+          : "\\",
+        hardline
+      ]);
     case "tableRow": // handled in "table"
     default:
       throw new Error(`Unknown markdown type ${JSON.stringify(node.type)}`);