fix(ssr): extend component correctly if at root (vue2) (#1104)

* fix(ssr): extend component correctly if at root (vue2)

fixes #1054

Essentially the problem is that $vnode is usually available, but not when the this is a root Vue instance. In that case we are in the "Vue.component" case, which before now always was wrong (it takes two arguments, not one)

* not only

* Update src/util/__tests__/createServerRootMixin.test.js

Co-authored-by: Sarah Dayan <5370675+sarahdayan@users.noreply.github.com>

Co-authored-by: Sarah Dayan <5370675+sarahdayan@users.noreply.github.com>

src/util/__tests__/createServerRootMixin.test.js

@@ -719,6 +719,82 @@ Array [
     },
   },
 ]
+`);
+      });
+
+      it('works when component is at root (and therefore has no $vnode)', async () => {
+        const searchClient = createFakeClient();
+        let mainIndex;
+
+        const app = {
+          render: renderCompat(h =>
+            /**
+             * This code triggers this warning in Vue 3:
+             * > Non-function value encountered for default slot. Prefer function slots for better performance.
+             *
+             * To fix it, replace the third argument
+             * > [h(...), h(...)]
+             * with
+             * > { default: () => [h(...), h(...)] }
+             *
+             * but it's not important (and not compatible in vue2), we're leaving it as-is.
+             */
+            h(InstantSearchSsr, {}, [
+              h(Configure, {
+                attrs: {
+                  hitsPerPage: 100,
+                },
+              }),
+              h(SearchBox),
+            ])
+          ),
+        };
+
+        const wrapper = createSSRApp({
+          mixins: [
+            forceIsServerMixin,
+            createServerRootMixin({
+              searchClient,
+              indexName: 'hello',
+            }),
+          ],
+          serverPrefetch() {
+            return this.instantsearch.findResultsState({
+              component: this,
+              renderToString,
+            });
+          },
+          created() {
+            mainIndex = this.instantsearch.mainIndex;
+          },
+          render: renderCompat(h => h(app)),
+        });
+
+        await renderToString(wrapper);
+
+        expect(mainIndex.getWidgetState()).toMatchInlineSnapshot(`
+Object {
+  "hello": Object {
+    "configure": Object {
+      "hitsPerPage": 100,
+    },
+  },
+}
+`);
+
+        expect(searchClient.search).toHaveBeenCalledTimes(1);
+        expect(searchClient.search.mock.calls[0][0]).toMatchInlineSnapshot(`
+Array [
+  Object {
+    "indexName": "hello",
+    "params": Object {
+      "facets": Array [],
+      "hitsPerPage": 100,
+      "query": "",
+      "tagFilters": "",
+    },
+  },
+]
 `);
       });
     }

src/util/createServerRootMixin.js

@@ -56,7 +56,10 @@ function defaultCloneComponent(componentInstance, { mixins = [] } = {}) {
 
     const Extended = componentInstance.$vnode
       ? componentInstance.$vnode.componentOptions.Ctor.extend(options)
-      : Vue2.component(Object.assign({}, componentInstance.$options, options));
+      : Vue2.component(
+          options.name,
+          Object.assign({}, componentInstance.$options, options)
+        );
 
     app = new Extended({
       propsData: componentInstance.$options.propsData,