Respect attributions passed to TileJSON source

externs/olx.js

@@ -4980,7 +4980,8 @@ olx.source.ServerVectorOptions.prototype.projection;
 
 
 /**
- * @typedef {{crossOrigin: (null|string|undefined),
+ * @typedef {{attributions: (Array.<ol.Attribution>|undefined),
+ *     crossOrigin: (null|string|undefined),
  *     tileLoadFunction: (ol.TileLoadFunctionType|undefined),
  *     url: string,
  *     wrapX: (boolean|undefined)}}
@@ -4989,6 +4990,16 @@ olx.source.ServerVectorOptions.prototype.projection;
 olx.source.TileJSONOptions;
 
 
+/**
+ * Optional attributions for the source.  If provided, these will be used
+ * instead of any attribution data advertised by the server.  If not provided,
+ * any attributions advertised by the server will be used.
+ * @type {Array.<ol.Attribution>|undefined}
+ * @api stable
+ */
+olx.source.TileJSONOptions.prototype.attributions;
+
+
 /**
  * The `crossOrigin` attribute for loaded images.  Note that you must provide a
  * `crossOrigin` value if you are using the WebGL renderer or if you want to

src/ol/source/tilejsonsource.js

@@ -33,6 +33,7 @@ goog.require('ol.tilegrid.XYZ');
 ol.source.TileJSON = function(options) {
 
   goog.base(this, {
+    attributions: options.attributions,
     crossOrigin: options.crossOrigin,
     projection: ol.proj.get('EPSG:3857'),
     state: ol.source.State.LOADING,
@@ -87,7 +88,8 @@ ol.source.TileJSON.prototype.handleTileJSONResponse = function(tileJSON) {
       }),
       ol.TileUrlFunction.createFromTemplates(tileJSON.tiles));
 
-  if (goog.isDef(tileJSON.attribution)) {
+  if (goog.isDef(tileJSON.attribution) &&
+      goog.isNull(this.getAttributions())) {
     var attributionExtent = goog.isDef(extent) ?
         extent : epsg4326Projection.getExtent();
     /** @type {Object.<string, Array.<ol.TileRange>>} */