add shouldPrintComment option and output comments when compact option is set to true - fixes #1810

packages/babel/src/generation/index.js

@@ -47,6 +47,7 @@ class CodeGenerator {
     }
 
     var format = {
+      shouldPrintComment: opts.shouldPrintComment,
       retainLines: opts.retainLines,
       comments: opts.comments == null || opts.comments,
       compact: opts.compact,
@@ -377,16 +378,32 @@ class CodeGenerator {
     return (node && node[key]) || [];
   }
 
+  /**
+   * [Please add a description.]
+   */
+
+  shouldPrintComment(comment) {
+    if (this.format.shouldPrintComment) {
+      return this.format.shouldPrintComment(comment.value);
+    } else {
+      if (comment.value.indexOf("@license") >= 0 || comment.value.indexOf("@preserve") >= 0) {
+        return true;
+      } else {
+        return this.format.comments;
+      }
+    }
+  }
+
   /**
    * [Please add a description.]
    */
 
   _printComments(comments) {
-    if (this.format.compact) return;
-    if (!this.format.comments) return;
     if (!comments || !comments.length) return;
 
     for (var comment of (comments: Array)) {
+      if (!this.shouldPrintComment(comment)) continue;
+
       var skip = false;
 
       if (this.ast.comments) {

packages/babel/src/transformation/file/options/config.json

@@ -163,6 +163,11 @@
     "description": "strip/output comments in generated output (on by default)"
   },
 
+  "shouldPrintComment": {
+    "hidden": true,
+    "description": "optional callback to control whether a comment should be inserted, when this is used the comments option is ignored"
+  },
+
   "compact": {
     "type": "booleanString",
     "default": "auto",