1 files changed, 84 insertions, 0 deletions
diff --git a/tools/eslint/lib/rules/no-extra-strict.js b/tools/eslint/lib/rules/no-extra-strict.js
new file mode 100644
index 0000000000..4c6ac16a42
--- /dev/null
+++ b/tools/eslint/lib/rules/no-extra-strict.js
@@ -0,0 +1,84 @@
+/**
+ * @fileoverview Rule to flag unnecessary strict directives.
+ * @author Ian Christian Myers
+ * @copyright 2014 Ian Christian Myers. All rights reserved.
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    function directives(block) {
+        var ds = [], body = block.body, e, i, l;
+
+        if (body) {
+            for (i = 0, l = body.length; i < l; ++i) {
+                e = body[i];
+
+                if (
+                    e.type === "ExpressionStatement" &&
+                    e.expression.type === "Literal" &&
+                    typeof e.expression.value === "string"
+                ) {
+                    ds.push(e.expression);
+                } else {
+                    break;
+                }
+            }
+        }
+
+        return ds;
+    }
+
+    function isStrict(directive) {
+        return directive.value === "use strict";
+    }
+
+    function checkForUnnecessaryUseStrict(node) {
+        var useStrictDirectives = directives(node).filter(isStrict),
+            scope,
+            upper;
+
+        switch (useStrictDirectives.length) {
+            case 0:
+                break;
+
+            case 1:
+                scope = context.getScope();
+                upper = scope.upper;
+
+                if (upper && upper.functionExpressionScope) {
+                    upper = upper.upper;
+                }
+
+                if (upper && upper.isStrict) {
+                    context.report(useStrictDirectives[0], "Unnecessary 'use strict'.");
+                }
+                break;
+
+            default:
+                context.report(useStrictDirectives[1], "Multiple 'use strict' directives.");
+        }
+    }
+
+    return {
+
+        "Program": checkForUnnecessaryUseStrict,
+
+        "ArrowFunctionExpression": function(node) {
+            checkForUnnecessaryUseStrict(node.body);
+        },
+
+        "FunctionExpression": function(node) {
+            checkForUnnecessaryUseStrict(node.body);
+        },
+
+        "FunctionDeclaration": function(node) {
+            checkForUnnecessaryUseStrict(node.body);
+        }
+    };
+
+};