1 files changed, 113 insertions, 0 deletions
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/balanced-listeners.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/balanced-listeners.js
new file mode 100644
index 000000000..c658a6b44
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+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/balanced-listeners.js
@@ -0,0 +1,113 @@
+/**
+ * @fileoverview Check that there's a removeEventListener for each
+ * addEventListener and an off for each on.
+ * Note that for now, this rule is rather simple in that it only checks that
+ * for each event name there is both an add and remove listener. It doesn't
+ * check that these are called on the right objects or with the same callback.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+"use strict";
+
+// -----------------------------------------------------------------------------
+// Rule Definition
+// -----------------------------------------------------------------------------
+
+module.exports = function(context) {
+  // ---------------------------------------------------------------------------
+  // Helpers
+  // ---------------------------------------------------------------------------
+
+  var DICTIONARY = {
+    "addEventListener": "removeEventListener",
+    "on": "off"
+  };
+  // Invert this dictionary to make it easy later.
+  var INVERTED_DICTIONARY = {};
+  for (var i in DICTIONARY) {
+    INVERTED_DICTIONARY[DICTIONARY[i]] = i;
+  }
+
+  // Collect the add/remove listeners in these 2 arrays.
+  var addedListeners = [];
+  var removedListeners = [];
+
+  function addAddedListener(node) {
+    addedListeners.push({
+      functionName: node.callee.property.name,
+      type: node.arguments[0].value,
+      node: node.callee.property,
+      useCapture: node.arguments[2] ? node.arguments[2].value : null
+    });
+  }
+
+  function addRemovedListener(node) {
+    removedListeners.push({
+      functionName: node.callee.property.name,
+      type: node.arguments[0].value,
+      useCapture: node.arguments[2] ? node.arguments[2].value : null
+    });
+  }
+
+  function getUnbalancedListeners() {
+    var unbalanced = [];
+
+    for (var j = 0; j < addedListeners.length; j++) {
+      if (!hasRemovedListener(addedListeners[j])) {
+        unbalanced.push(addedListeners[j]);
+      }
+    }
+    addedListeners = removedListeners = [];
+
+    return unbalanced;
+  }
+
+  function hasRemovedListener(addedListener) {
+    for (var k = 0; k < removedListeners.length; k++) {
+      var listener = removedListeners[k];
+      if (DICTIONARY[addedListener.functionName] === listener.functionName &&
+          addedListener.type === listener.type &&
+          addedListener.useCapture === listener.useCapture) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+  // ---------------------------------------------------------------------------
+  // Public
+  // ---------------------------------------------------------------------------
+
+  return {
+    CallExpression: function(node) {
+      if (node.arguments.length === 0) {
+        return;
+      }
+
+      if (node.callee.type === "MemberExpression") {
+        var listenerMethodName = node.callee.property.name;
+
+        if (DICTIONARY.hasOwnProperty(listenerMethodName)) {
+          addAddedListener(node);
+        } else if (INVERTED_DICTIONARY.hasOwnProperty(listenerMethodName)) {
+          addRemovedListener(node);
+        }
+      }
+    },
+
+    "Program:exit": function() {
+      getUnbalancedListeners().forEach(function(listener) {
+        context.report(listener.node,
+          "No corresponding '{{functionName}}({{type}})' was found.",
+          {
+            functionName: DICTIONARY[listener.functionName],
+            type: listener.type
+          });
+      });
+    }
+  };
+};