Allow LRU cache to gracefully handle cases where the same key is adde…

…d twice

fixes #2201

debug/site.js

@@ -5,7 +5,7 @@ var map = new mapboxgl.Map({
     container: 'map',
     zoom: 12.5,
     center: [-77.01866, 38.888],
-    style: 'mapbox://styles/mapbox/streets-v8',
+    style: 'mapbox://styles/mapbox/satellite-hybrid-v8',
     hash: true
 });
 

js/util/lru_cache.js

@@ -44,12 +44,20 @@ LRUCache.prototype.reset = function() {
  * @private
  */
 LRUCache.prototype.add = function(key, data) {
-    this.data[key] = data;
-    this.order.push(key);
 
-    if (this.order.length > this.max) {
-        var removedData = this.get(this.order[0]);
-        if (removedData) this.onRemove(removedData);
+    if (this.has(key)) {
+        this.order.splice(this.order.indexOf(key), 1);
+        this.data[key] = data;
+        this.order.push(key);
+
+    } else {
+        this.data[key] = data;
+        this.order.push(key);
+
+        if (this.order.length > this.max) {
+            var removedData = this.get(this.order[0]);
+            if (removedData) this.onRemove(removedData);
+        }
     }
 
     return this;

test/js/util/lru_cache.test.js

@@ -18,13 +18,27 @@ test('LRUCache', function(t) {
     t.end();
 });
 
+test('LRUCache - duplicate add', function(t) {
+    var cache = new LRUCache(10, function() {
+        t.fail();
+    });
+
+    cache.add('a', 'b');
+    cache.add('a', 'c');
+
+    t.deepEqual(cache.keys(), ['a']);
+    t.ok(cache.has('a'));
+    t.equal(cache.get('a'), 'c');
+    t.end();
+});
+
 test('LRUCache - overflow', function(t) {
     var cache = new LRUCache(1, function(removed) {
-        t.equal(removed, 'c');
+        t.equal(removed, 'b');
         t.end();
     });
     cache.add('a', 'b');
-    cache.add('a', 'c');
+    cache.add('c', 'd');
 });
 
 test('LRUCache#reset', function(t) {