Error handling for diff() using Result

[qknight]

motivation

this PR adds Result<...> to diff() and was added to give users some feedback what went wrong when trying to create a diff on a vdom with concepts which are not supported. i.e. "

" two roots as in this example.

it works great if this two roots example is nested inside a div itself:

<div>
<div></div><div></div>
</div>

therefore the diff can now return InvalidRootNodeCount

details

Please have a look at:

• SkipDiffError which is returned instead of vec![], not sure if this is wanted
• also check the new InvalidRootNodeCount error, maybe this should actually be supported but is just broken in the recursive diff iteration

+        return Ok(vec![]);
+    }
+
+    // multiple root nodes are not supported. this would be two root nodes "<div></div><div></div>"
+    // the diff will work but the result is wrong, so instead we bail out here
+    match new_node {
+        Node::Leaf(leaf) => match leaf {
+            Leaf::NodeList(list) => {
+                if list.len() > 1 {
+                    log::error!("invalid root node cound: input needs exactly one root node and childs, not several root nodes");
+                    return Err(DiffError::InvalidRootNodeCount(list.len()));
+                }
+            }
+            _ => {}
+        },
+        Node::Element(_) => {}

motivation: a diff can't be computed for:

<div></div><div></div>

I don't know why but I made sure that the user who tries this gets a error message: InvalidRootNodeCount until it is implemented.

tests status

just test runs all tests successfully

prototype code remark

i've been playing with websocket auto-reconnect and article updates based on html generated from pandoc. so it works great and it is fast! thanks for this wonderful tool!