add retainLines code generator option

src/babel/generation/buffer.js

@@ -70,7 +70,7 @@ export default class Buffer {
   }
 
   newline(i, removeLast) {
-    if (this.format.compact) return;
+    if (this.format.compact || this.format.retainLines) return;
 
     if (this.format.concise) {
       this.space();
@@ -99,7 +99,7 @@ export default class Buffer {
     this._newline(removeLast);
   }
 
-  _newline(removeLast) {
+  _newline(removeLast, force) {
     // never allow more than two lines
     if (this.endsWith("\n\n")) return;
 

src/babel/generation/index.js

@@ -34,6 +34,7 @@ class CodeGenerator {
     }
 
     var format = {
+      retainLines: opts.retainLines,
       comments: opts.comments == null || opts.comments,
       compact: opts.compact,
       quotes: CodeGenerator.findCommonStringDelimeter(code, tokens),
@@ -149,6 +150,13 @@ class CodeGenerator {
   print(node, parent, opts = {}) {
     if (!node) return;
 
+    // catch up to this nodes newline if we're behind
+    if (node.loc && this.format.retainLines) {
+      while (this.position.line < node.loc.start.line) {
+        this._push("\n");
+      }
+    }
+
     if (parent && parent._compact) {
       node._compact = true;
     }

src/babel/transformation/file/options.json

@@ -25,6 +25,13 @@
     "type": "string"
   },
 
+  "retainLines": {
+    "hidden": true,
+    "type": "boolean",
+    "default": false,
+    "description": "retain line numbers - will result in really ugly code"
+  },
+
   "nonStandard": {
     "type": "boolean",
     "default": true,