Add ROADMAP.md

[kellytk]

Description

I'm submitting a ...

• feature request

A roadmap is a document summarizing the high-level direction of a project and enumerating its milestones. Roadmaps are useful to current users and prospective users alike.

As Yew matures, and a 1.0 release begins to come slowly into view, I think it would be a good addition.

[hgzimmerman]

Yew 1.0

Ergonomics/Usability:

• Some CSS in Rust functionality: Styling Brainstorming #533
  • I have a prototype here - https://github.com/hgzimmerman/yew_css
  • I don't think it needs to be a part of the framework, but having it ready before 1.0 would be highly desirable.
• I'm in favor of waiting until expression proc macros stabilize so we can move away from proc-macro-hack to lift the limit on number of nested html! invocations. That may take some time though.
• VDom access: Add support for setting refs on elements for DOM reference #665
• I want to see pure components make their way into the ecosystem in some form.
• I'm finding that having the returned Html<_> require a type parameter relating to the component it's callbacks have messages for gets in the way of writing concise generic components that can contain arbitrary content, especially nested components. Sadly, I don't have any real suggestions on how to remove this type parameter and allow simplification of the message/callback system.

Performance:

• Keyed VList items seem like a huge performance win for large lists (especially the benchmark mentioned below): Issue with unkeyed VDOM list items #479
• Update/Rerun benchmarks - It would be nice to know how things have changed over the year+ since they were last ran, it would be nice to be able to mention speed as a benefit of the framework Performance details #5
• Feature gating is easy to do and can offer small load-time benefits for already small apps Feature-gate sections of Yew #648
• Why not just do this before 1.0, its an easy enough change: Clippy: large size difference between variants #571

Documentation:

• Getting started guide.
• Internal implementation details, opinionated guidance to achieve best performance in apps.
• Best practices for readability.
• Global State management strategies.
• Other misc patterns

Punting for Yew 2.0+

These would be breaking changes to a 1.0 release, and I am of the opinion that they could wait until 2.0.

• callbacks vs futures: Consider handling async service effects through futures #364
  • Edit: I looked a little closer at that PR, and it seems like significant progress is being made there. I don't think this feature is required for 1.0, but if it gets finished before then, then I'm all for it.
  • Edit again: Delaying support for futures would be done on the basis that a callback model is good enough. I've done a 180 on this topic and now think that callbacks aren't good enough. Having to involve a component or agent's update loop makes code reuse rather hard, while there are many places where futures that can be composed together would be significantly more ergonomic, performant and readable.
• I don't think we should abandon the virtual dom as it is right now. I don't know how hard it will be to adapt Yew to use an alternative VDom implementation. Use of Dodrio virtual DOM #482
  • There might be performance benefits to doing this that make it worthwhile for a 2.0 breakage.

Orthogonal to 1.0

• I really want code splitting, but its a hard problem and might be able to be implemented via a separate library: WASM file size optimization #599

Toss up

• I would really rather not wait until 2.0 for a transition to web_sys from stdweb (if that's a thing that is going to happen). But it seems like a huge thing to change and would consume a bunch of resources to implement it. https://rustwasm.github.io/wasm-bindgen/api/web_sys/
  • I'm just scared that a breakage this large could break most existing libraries reliant on yew, so ripping the band-aid off sooner rather than later would be a be a good choice if this is going to happen.

[jstarry]

Thanks @hgzimmerman we've made a lot of progress on the things you've listed here! I've written up a roadmap doc here: https://yew.rs/docs/roadmap let's work together to flush that out 👍