1 files changed, 85 insertions, 0 deletions
diff --git a/tools/eslint/lib/rules/no-param-reassign.js b/tools/eslint/lib/rules/no-param-reassign.js
new file mode 100644
index 0000000000..c38f0ef6f4
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+++ b/tools/eslint/lib/rules/no-param-reassign.js
@@ -0,0 +1,85 @@
+/**
+ * @fileoverview Disallow reassignment of function parameters.
+ * @author Nat Burns
+ * @copyright 2014 Nat Burns. All rights reserved.
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    //--------------------------------------------------------------------------
+    // Helpers
+    //--------------------------------------------------------------------------
+
+    /**
+     * Finds the declaration for a given variable by name, searching up the scope tree.
+     * @param {Scope} scope The scope in which to search.
+     * @param {String} name The name of the variable.
+     * @returns {Variable} The declaration information for the given variable, or null if no declaration was found.
+     */
+    function findDeclaration(scope, name) {
+        var variables = scope.variables;
+
+        for (var i = 0; i < variables.length; i++) {
+            if (variables[i].name === name) {
+                return variables[i];
+            }
+        }
+
+        if (scope.upper) {
+            return findDeclaration(scope.upper, name);
+        } else {
+            return null;
+        }
+    }
+
+    /**
+     * Determines if a given variable is declared as a function parameter.
+     * @param {Variable} variable The variable declaration.
+     * @returns {boolean} True if the variable is a function parameter, false otherwise.
+     */
+    function isParameter(variable) {
+        var defs = variable.defs;
+
+        for (var i = 0; i < defs.length; i++) {
+            if (defs[i].type === "Parameter") {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * Checks whether a given node is an assignment to a function parameter.
+     * If so, a linting error will be reported.
+     * @param {ASTNode} node The node to check.
+     * @param {String} name The name of the variable being assigned to.
+     * @returns {void}
+     */
+    function checkParameter(node, name) {
+        var declaration = findDeclaration(context.getScope(), name);
+
+        if (declaration && isParameter(declaration)) {
+            context.report(node, "Assignment to function parameter '{{name}}'.", { name: name });
+        }
+    }
+
+    //--------------------------------------------------------------------------
+    // Public
+    //--------------------------------------------------------------------------
+
+    return {
+        "AssignmentExpression": function(node) {
+            checkParameter(node, node.left.name);
+        },
+
+        "UpdateExpression": function(node) {
+            checkParameter(node, node.argument.name);
+        }
+    };
+};