m.render() ignores the key of the vnode returned by comnponents

[barneycarroll]

I keep running into this gotcha whereby I have a solitary dynamically-keyed node as the return value of a components view, and changing the vnode key doesn't cause the node to reinitialise. The reason this doesn't work is that AFAICT component instances are the only case in which a user-supplied vnode isn't normalised as a list item. Just as m(tag, ...vnodes) is equivalent to m(tag, [...vnodes]) & m.render(el, vnode) to m.render(el, [vnode]), I suggest we normalise component view output such that instances are always fragments - which as well as obviating this edge case would have the added benefit of making vnode tree traversal easier to reason about.

Reproduction here.

I'm happy to implement this myself.

[pygy]

I'd rather check for the presence of a key at diff-time, it will have the same ultimate result, and will be more efficient.

[barneycarroll]

I still think my suggestion is better because along the lines of #2669 it moves us towards monomorphic vnode structures which are more predictable. The counter proposal gets us into the same category of issues as #2669 where we introduce extra code paths for efficiency when IMO having a more consistent structure makes the codebase more maintainable and has the added benefit of making tools integrating with vnode easier to write.

[barneycarroll]

Closing this, keeping #1713