fix retainLines for comments and block statements - fixes #1388

src/babel/generation/generators/base.js

@@ -13,7 +13,7 @@ export function BlockStatement(node, print) {
     this.push("{");
     this.newline();
     print.sequence(node.body, { indent: true });
-    this.removeLast("\n");
+    if (!this.format.retainLines) this.removeLast("\n");
     this.rightBrace();
   }
 }

src/babel/generation/index.js

@@ -376,6 +376,12 @@ class CodeGenerator {
         val = this.getIndent() + val;
       }
 
+      // force a newline for line comments when retainLines is set in case the next printed node
+      // doesn't catch up
+      if (this.format.retainLines && comment.type === "Line") {
+        val += "\n";
+      }
+
       //
       this._push(val);