1 files changed, 90 insertions, 0 deletions
diff --git a/tools/eslint/lib/rules/no-undef.js b/tools/eslint/lib/rules/no-undef.js
new file mode 100644
index 0000000000..5ee07f3124
--- /dev/null
+++ b/tools/eslint/lib/rules/no-undef.js
@@ -0,0 +1,90 @@
+/**
+ * @fileoverview Rule to flag references to undeclared variables.
+ * @author Mark Macdonald
+ * @copyright 2015 Nicholas C. Zakas. All rights reserved.
+ * @copyright 2013 Mark Macdonald. All rights reserved.
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+// none!
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+function isImplicitGlobal(variable) {
+    return variable.defs.every(function(def) {
+        return def.type === "ImplicitGlobalVariable";
+    });
+}
+
+/**
+ * Gets the declared variable, defined in `scope`, that `ref` refers to.
+ * @param {Scope} scope The scope in which to search.
+ * @param {Reference} ref The reference to find in the scope.
+ * @returns {Variable} The variable, or null if ref refers to an undeclared variable.
+ */
+function getDeclaredGlobalVariable(scope, ref) {
+    var declaredGlobal = null;
+    scope.variables.some(function(variable) {
+        if (variable.name === ref.identifier.name) {
+            // If it's an implicit global, it must have a `writeable` field (indicating it was declared)
+            if (!isImplicitGlobal(variable) || {}.hasOwnProperty.call(variable, "writeable")) {
+                declaredGlobal = variable;
+                return true;
+            }
+        }
+        return false;
+    });
+    return declaredGlobal;
+}
+
+/**
+ * Checks if the given node is the argument of a typeof operator.
+ * @param {ASTNode} node The AST node being checked.
+ * @returns {boolean} Whether or not the node is the argument of a typeof operator.
+ */
+function hasTypeOfOperator(node) {
+    var parent = node.parent;
+    return parent.type === "UnaryExpression" && parent.operator === "typeof";
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    var NOT_DEFINED_MESSAGE = "\"{{name}}\" is not defined.",
+        READ_ONLY_MESSAGE = "\"{{name}}\" is read only.";
+
+    return {
+
+        "Program:exit": function(/*node*/) {
+
+            var globalScope = context.getScope();
+
+            globalScope.through.forEach(function(ref) {
+                var variable = getDeclaredGlobalVariable(globalScope, ref),
+                    name = ref.identifier.name;
+
+                if (hasTypeOfOperator(ref.identifier)) {
+                    return;
+                }
+
+                if (!variable) {
+                    context.report(ref.identifier, NOT_DEFINED_MESSAGE, { name: name });
+                } else if (ref.isWrite() && variable.writeable === false) {
+                    context.report(ref.identifier, READ_ONLY_MESSAGE, { name: name });
+                }
+            });
+
+        }
+
+    };
+
+};