Fix toVNode() for comment nodes, lacking some fields

Comment nodes when converted to VNode were lacking vnode.data and
vnode.elm, which in turn would break use cases with modules such as the
style module (Which assumed vnode.data to be defined). Since toVNode is
used as an initial step (e.g. for server-side rendered content), there
is no reason to not provide vnode.elm since that vnode may be used as
the "prevVNode" during patch. Also, because comment vnodes have the '!'
sel, most logic in snabbdom that detects a truthy sel will also assume a
truthy data field. It is easier to build the comment vnode with those
fields than to modify all the logic elsewhere in snabbdom.

src/tovnode.ts

@@ -30,7 +30,7 @@ export function toVNode(node: Node, domApi?: DOMAPI): VNode {
     return vnode(undefined, undefined, undefined, text, node);
   } else if (api.isComment(node)) {
     text = api.getTextContent(node) as string;
-    return vnode('!', undefined, undefined, text, undefined);
+    return vnode('!', {}, [], text, node as any);
   } else {
     return vnode('', {}, [], undefined, undefined);
   }

test/style.js

@@ -7,6 +7,7 @@ var patch = snabbdom.init([
   require('../modules/style').default,
 ]);
 var h = require('../h').default;
+var toVNode = require('../tovnode').default;
 
 describe('style', function() {
   var elm, vnode0;
@@ -115,6 +116,20 @@ describe('style', function() {
     fakeRaf.step();
     assert.equal(elm.style.fontSize, '20px');
   });
+  describe('using toVNode()', function () {
+    it('handles (ignoring) comment nodes', function() {
+      var comment = document.createComment('yolo');
+      var prevElm = document.createElement('div');
+      prevElm.appendChild(comment);
+      var nextVNode = h('div', [h('span', 'Hi')]);
+      elm = patch(toVNode(prevElm), nextVNode).elm;
+      assert.strictEqual(elm, prevElm);
+      assert.equal(elm.tagName, 'DIV');
+      assert.strictEqual(elm.childNodes.length, 1);
+      assert.strictEqual(elm.childNodes[0].tagName, 'SPAN');
+      assert.strictEqual(elm.childNodes[0].textContent, 'Hi');
+    });
+  });
 });
 
 fakeRaf.restore();