add auxilary comment option to prepend to helpers - #777

lib/6to5/generation/whitespace.js

@@ -82,7 +82,7 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
     }
   }
 
-  if (endToken.type.type === "eof") {
+  if (endToken && endToken.type.type === "eof") {
     return 1;
   } else {
     var lines = this.getNewlinesBetween(startToken, endToken);
@@ -96,6 +96,8 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
 };
 
 Whitespace.prototype.getNewlinesBetween = function (startToken, endToken) {
+  if (!endToken || !endToken.loc) return 0;
+
   var start = startToken ? startToken.loc.end.line : 1;
   var end   = endToken.loc.start.line;
   var lines = 0;

lib/6to5/transformation/file.js

@@ -86,6 +86,7 @@ File.validOptions = [
   "experimental",
   "resolveModuleSource",
   "runtime",
+  "auxilaryComment",
 
   // these are used by plugins
   "ignore",
@@ -106,6 +107,7 @@ File.prototype.normalizeOptions = function (opts) {
   defaults(opts, {
     keepModuleIdExtensions: false,
     resolveModuleSource:    null,
+    auxilaryComment:        "",
     experimental:           false,
     reactCompat:            false,
     playground:             false,
@@ -298,6 +300,18 @@ File.prototype.isConsequenceExpressionStatement = function (node) {
   return t.isExpressionStatement(node) && this.lastStatements.indexOf(node) >= 0;
 };
 
+File.prototype.attachAuxilaryComment = function (node) {
+  var comment = this.opts.auxilaryComment;
+  if (comment) {
+    node.leadingComments = node.leadingComments || [];
+    node.leadingComments.push({
+      type: "Line",
+      value: " " + comment
+    });
+  }
+  return node;
+};
+
 File.prototype.addHelper = function (name) {
   if (!includes(File.helpers, name)) {
     throw new ReferenceError("Unknown helper " + name);

lib/6to5/transformation/transformers/internal/declarations.js

@@ -6,7 +6,7 @@ var t         = require("../../../types");
 exports.secondPass = true;
 
 exports.BlockStatement =
-exports.Program = function (node) {
+exports.Program = function (node, parent, scope, file) {
   if (!node._declarations) return;
 
   var kinds = {};
@@ -19,16 +19,16 @@ exports.Program = function (node) {
       kind = declar.kind || "var";
       var declarNode = t.variableDeclarator(declar.id, declar.init);
 
-      if (!declar.init) {
+      if (declar.init) {
+        node.body.unshift(file.attachAuxilaryComment(t.variableDeclaration(kind, [declarNode])));
+      } else {
         kinds[kind] = kinds[kind] || [];
         kinds[kind].push(declarNode);
-      } else {
-        node.body.unshift(t.variableDeclaration(kind, [declarNode]));
       }
     }
 
     for (kind in kinds) {
-      node.body.unshift(t.variableDeclaration(kind, kinds[kind]));
+      node.body.unshift(file.attachAuxilaryComment(t.variableDeclaration(kind, kinds[kind])));
     }
   });