Use procedural macro for parsing jsx-like syntax

[jstarry]

Using a procedural macro makes it possible to generate nice compile time error messages when the jsx-like syntax is malformed or misused. No more panics at run-time!

This change utilizes https://github.com/dtolnay/proc-macro-hack to allow using the html! macro for expressions. The proc-macro-hack crate requires splitting code into two crates and so we have an yew-macro crate as well as an yew-macro-impl crate.

The goal is to start with backwards compatibility with the old declarative macro and then move forward with more user-friendly syntax that is more similar to what you would use with actual JSX. This new proc macro can be enabled using the proc_macro feature.

Feature Checklist:

• lists <></>
• blocks { self.subview() }
• iterables { for children.into_iter() }
• full tag support
  • basic tags <div><img /></div>
  • tag attributes (no commas!) <span class={"header"}></span>
  • backwards compatible <span class={"header"}, ></span>
  • tag input events <button onclick=|_| Msg::Update>{ "Update" }</button>
• full component support
  • basic components <SubComponent />
  • backwards compatible <SubComponent: />
  • comp properties <SubComponent prop={value} />
• empty invocation html! {}
• nested invocation { for (0..3).map(|num| { html! { <span>{num}</span> }}) }

[jstarry]

bors try

[bors]

try

Build succeeded

• continuous-integration/travis-ci/push

[jstarry]

bors try

[bors]

try

Build succeeded

• continuous-integration/travis-ci/push

[therustmonk]

This PR changes everything in the framework and we can have some new issues later, but it's important changes and we will merge it to start improving templates usability.

Thanks @jstarry !

[therustmonk]

bors r+

[bors]

Build succeeded

• continuous-integration/travis-ci/push

[LifeIsStrange]

Hi, how to actually use the new proc macro ?
I updated yew to master and was not able to declare html tags without useless commas.
Is there something special to do to enable it ?

[jstarry]

@LifeIsStrange soon it will be enabled by default. For now, enable it by adding features = ["proc_macro"] to the yew dependency in your Cargo.toml file

yew = { git = "https://github.com/DenisKolodin/yew", features = ["proc_macro"] }