1 files changed, 72 insertions, 0 deletions
diff --git a/tools/eslint/lib/rules/no-shadow.js b/tools/eslint/lib/rules/no-shadow.js
new file mode 100644
index 0000000000..4906fa58f2
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+++ b/tools/eslint/lib/rules/no-shadow.js
@@ -0,0 +1,72 @@
+/**
+ * @fileoverview Rule to flag on declaring variables already declared in the outer scope
+ * @author Ilya Volodin
+ * @copyright 2013 Ilya Volodin. All rights reserved.
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    /**
+     * Checks if a variable is contained in the list of given scope variables.
+     * @param {Object} variable The variable to check.
+     * @param {Array} scopeVars The scope variables to look for.
+     * @returns {boolean} Whether or not the variable is contains in the list of scope variables.
+     */
+    function isContainedInScopeVars(variable, scopeVars) {
+        return scopeVars.some(function (scopeVar) {
+            if (scopeVar.identifiers.length > 0) {
+                return variable.name === scopeVar.name;
+            }
+            return false;
+        });
+    }
+
+    /**
+     * Checks if the given variables are shadowed in the given scope.
+     * @param {Array} variables The variables to look for
+     * @param {Object} scope The scope to be checked.
+     * @returns {void}
+     */
+    function checkShadowsInScope(variables, scope) {
+        variables.forEach(function (variable) {
+            if (isContainedInScopeVars(variable, scope.variables) &&
+                    // "arguments" is a special case that has no identifiers (#1759)
+                    variable.identifiers.length > 0 &&
+
+                    // function names are exempt
+                    variable.defs.length && variable.defs[0].type !== "FunctionName"
+            ) {
+                context.report(variable.identifiers[0], "{{a}} is already declared in the upper scope.", {a: variable.name});
+            }
+        });
+    }
+
+    /**
+     * Checks the current context for shadowed variables.
+     * @returns {void}
+     */
+    function checkForShadows() {
+        var scope = context.getScope(),
+            variables = scope.variables;
+
+        // iterate through the array of variables and find duplicates with the upper scope
+        var upper = scope.upper;
+        while (upper) {
+            checkShadowsInScope(variables, upper);
+            upper = upper.upper;
+        }
+    }
+
+    return {
+        "FunctionDeclaration": checkForShadows,
+        "FunctionExpression": checkForShadows,
+        "ArrowFunctionExpression": checkForShadows
+    };
+
+};