fix(lifecycle): save configuration done in widget.init

Before this commit, every configuration done in widget.init would not
be remembered when going back in the browser history.

Scenario: You built a custom widget using helper.setQueryParameter in
widget.init. Then you load "/", widget.init() sets some helper params,
you go to page 2, you click on <= back. Before this commit we would
forget what was done in widget.init(). Now it works.

This was needed to fix the "rootPath" option of the hierarchicalMenu.
The rootPath option triggers a state change from inside the helper
(which may have been a bad idea after all) => it was not remembered
when going back to empty url.

Thanks to @maxiloc for the bug report and big help solving this!

dev/app.js

@@ -305,6 +305,7 @@ search.addWidget(
       link: 'facet-value',
       count: 'facet-count pull-right'
     },
+    rootPath: 'Cameras & Camcorders > Digital Camera Accessories',
     templates: {
       header: 'Hierarchical categories'
     }

dev/index.html

@@ -67,11 +67,11 @@ <h1><a href="./">Instant search demo</a> <small>using instantsearch.js</small></
               </div>
             </div>
           </div>
+          <div id="pagination" class="text-center"></div>
           <h3>Results overview</h3>
           <div id="hits-table"></div>
           <h3>Results</h3>
           <div id="hits"></div>
-          <div id="pagination" class="text-center"></div>
         </div>
       </div>
     </div>

src/lib/InstantSearch.js

@@ -102,14 +102,15 @@ Usage: instantsearch({
   start() {
     if (!this.widgets) throw new Error('No widgets were added to instantsearch.js');
 
+    let syncWidget;
+
     if (this.urlSync) {
-      let syncWidget = urlSyncWidget(this.urlSync);
+      syncWidget = urlSyncWidget(this.urlSync);
       this._createURL = syncWidget.createURL.bind(syncWidget);
       this._onHistoryChange = syncWidget.onHistoryChange.bind(syncWidget);
-      this.widgets.push(syncWidget);
     } else {
       this._createURL = defaultCreateURL;
-      this._onHistoryChange = function() {};
+      this._onHistoryChange = () => {};
     }
 
     this.searchParameters = this.widgets.reduce(enhanceConfiguration, this.searchParameters);
@@ -128,6 +129,12 @@ Usage: instantsearch({
     this.helper = helper;
 
     this._init(helper.state, helper);
+
+    if (this.urlSync) {
+      helper.setState(enhanceConfiguration(helper.state, syncWidget));
+      syncWidget.init({helper});
+    }
+
     helper.on('result', this._render.bind(this, helper));
     helper.search();
   }

src/lib/__tests__/InstantSearch-test.js

@@ -23,6 +23,7 @@ describe('InstantSearch lifecycle', () => {
   let searchParameters;
   let search;
   let helperSearchSpy;
+  let urlSync;
 
   beforeEach(() => {
     client = {algolia: 'client', addAlgoliaAgent: () => {}};
@@ -33,10 +34,18 @@ describe('InstantSearch lifecycle', () => {
     helperSearchSpy = sinon.spy();
     helper.search = helperSearchSpy;
     helper.getState = sinon.stub().returns({});
+    helper.setState = sinon.spy();
     helper.state = {
       setQueryParameters: function(params) { return new SearchParameters(params); }
     };
 
+    urlSync = {
+      createURL: sinon.spy(),
+      onHistoryChange: () => {},
+      getConfiguration: sinon.spy(),
+      init: () => {}
+    };
+
     algoliasearch = sinon.stub().returns(client);
     algoliasearchHelper = sinon.stub().returns(helper);
 
@@ -51,6 +60,7 @@ describe('InstantSearch lifecycle', () => {
       another: {config: 'parameter'}
     };
 
+    InstantSearch.__Rewire__('urlSyncWidget', () => urlSync);
     InstantSearch.__Rewire__('algoliasearch', algoliasearch);
     InstantSearch.__Rewire__('algoliasearchHelper', algoliasearchHelper);
 
@@ -64,6 +74,7 @@ describe('InstantSearch lifecycle', () => {
   });
 
   afterEach(() => {
+    InstantSearch.__ResetDependency__('urlSyncWidget');
     InstantSearch.__ResetDependency__('algoliasearch');
     InstantSearch.__ResetDependency__('algoliasearchHelper');
   });
@@ -111,7 +122,9 @@ describe('InstantSearch lifecycle', () => {
     beforeEach(() => {
       widget = {
         getConfiguration: sinon.stub().returns({some: 'modified', another: {different: 'parameter'}}),
-        init: sinon.spy(),
+        init: sinon.spy(() => {
+          helper.state.sendMeToUrlSync = true;
+        }),
         render: sinon.spy()
       };
       search.addWidget(widget);
@@ -160,6 +173,14 @@ describe('InstantSearch lifecycle', () => {
         expect(args.onHistoryChange).toBe(search._onHistoryChange);
       });
 
+      it('calls urlSync.getConfiguration after every widget', () => {
+        expect(urlSync.getConfiguration.calledOnce).toBe(true, 'urlSync.getConfiguration called once');
+        expect(widget.init.calledAfter(widget.getConfiguration))
+          .toBe(true, 'urlSync.getConfiguration was called after widget.init');
+        expect(urlSync.getConfiguration.getCall(0).args[0].sendMeToUrlSync)
+          .toBe(true, 'state modifications done in widget.init should be sent to urlSync.getConfiguration');
+      });
+
       it('does not call widget.render', () => {
         expect(widget.render.notCalled).toBe(true);
       });
@@ -235,8 +256,10 @@ describe('InstantSearch lifecycle', () => {
       search.start();
     });
 
-    it('creates a URL', () => {
-      expect(search.createURL({hitsPerPage: 42})).toEqual('?q=&hPP=42&idx=&p=0');
+    it('has a createURL method', () => {
+      search.createURL({hitsPerPage: 542});
+      expect(urlSync.createURL.calledOnce).toBe(true);
+      expect(urlSync.createURL.getCall(0).args[0].hitsPerPage).toBe(542);
     });
 
     it('emits render when all render are done (using on)', () => {