add levenshtein suggestions to undeclared variable transformer

lib/6to5/helpers/levenshtein.js

@@ -0,0 +1,38 @@
+// not the fastest
+
+module.exports = function (a, b) {
+  if (a.length === 0) return b.length;
+  if (b.length === 0) return a.length;
+
+  var matrix = [];
+
+  // increment along the first column of each row
+  var i;
+  for(i = 0; i <= b.length; i++){
+    matrix[i] = [i];
+  }
+
+  // increment each column in the first row
+  var j;
+  for(j = 0; j <= a.length; j++){
+    matrix[0][j] = j;
+  }
+
+  // Fill in the rest of the matrix
+  for(i = 1; i <= b.length; i++){
+    for(j = 1; j <= a.length; j++){
+      if(b.charAt(i - 1) == a.charAt(j - 1)){
+        matrix[i][j] = matrix[i - 1][j - 1];
+      } else {
+        matrix[i][j] = Math.min(
+          matrix[i - 1][j - 1] + 1, // substitution
+          Math.min(
+            matrix[i][j - 1] + 1, // insertion
+            matrix[i - 1][j] + 1) // deletion
+          );
+      }
+    }
+  }
+
+  return matrix[b.length][a.length];
+}

lib/6to5/transformation/transformers/validation/undeclared-variable-check.js

@@ -1,9 +1,38 @@
 "use strict";
 
+var levenshtein = require("../../../helpers/levenshtein");
+var t           = require("../../../types");
+
 exports.optional = true;
 
 exports.Identifier = function (node, parent, scope, context, file) {
-  if (!scope.has(node.name, true)) {
-    throw file.errorWithNode(node, "Reference to undeclared variable", ReferenceError);
+  if (!t.isReferenced(node, parent)) return;
+  if (scope.has(node.name, true)) return;
+
+  var msg = "Reference to undeclared variable";
+
+  // get the closest declaration to offer as a suggestion
+  // the variable name may have just been mistyped
+
+  var declarations = scope.getAllDeclarations();
+
+  var closest;
+  var shortest = -1;
+
+  for (var name in declarations) {
+    var distance = levenshtein(node.name, name);
+    if (distance <= 0 || distance > 3) continue;
+    if (distance <= shortest) continue;
+
+    closest = name;
+    shortest = distance;
   }
+
+  if (closest) {
+    msg += " - Did you mean " + closest + "?";
+  }
+
+  //
+
+  throw file.errorWithNode(node, msg, ReferenceError);
 };

lib/6to5/traverse/scope.js

@@ -326,12 +326,31 @@ Scope.prototype.getFunctionParent = function () {
 };
 
 /**
- * Walks the scope tree and gathers all declarations of `kind`.
+ * Walks the scope tree and gathers **all** declarations.
  *
  * @returns {Object}
  */
 
-Scope.prototype.getAllOfKind = function (kind) {
+Scope.prototype.getAllDeclarations = function () {
+  var ids = object();
+
+  var scope = this;
+  do {
+    defaults(ids, scope.declarations);
+    scope = scope.parent;
+  } while (scope);
+
+  return ids;
+};
+
+/**
+ * Walks the scope tree and gathers all declarations of `kind`.
+ *
+ * @param {String} kind
+ * @returns {Object}
+ */
+
+Scope.prototype.getAllDeclarationsOfKind = function (kind) {
   var ids = object();
 
   var scope = this;