HTML Codegen

A safe and simple template engine with the ergonomics of JSX.

html-codegen itself is a combination of traits, structs and macros that eases and simplifies the experience of composing HTML tree-shaped data structures or string output. This works best with HTML and XML rendering.

Why is this different from...

handlebars?

Handlebars is an awesome spec that lets us devs define templates and work seemlessly between languages and frameworks.

Unfortunately, it does not guarantee any of Rust's type-safety. This forces you to write tests for validating types for your views, like you would in a dynamically typed language.

These tests weren't necessary in a type-safe language like Rust — but Handlebars is JSON-oriented, which doesn't comply Rust's type system.

html-codegen provides the same level of type-safety Rust provides, with no compromises of ergonomics or speed.

typed-html?

typed-html is a wonderful library. Unfortunately, it focused its power in strictness of the HTML spec itself, and doesn't allow arbitrary compositions of custom elements.

render takes a different approach. For now, HTML is not typed at all. It can get any key and get any string value. The main focus is custom components, so you can create a composable and declarative template with no runtime errors.

Usage

Simple HTML rendering

In order to render a simple HTML fragment into a String, use the rsx! macro to generate a component tree, and call render on it:

use html_codegen::{rsx, Render};

let tree = rsx! {
  <div>
    <h1>{"Hello!"}</h1>
    <p>{"Hello world!"}</p>
  </div>
};

assert_eq!(tree.render(), "<div><h1>Hello!</h1><p>Hello world!</p></div>");

Because this is so common, there's another macro called html! that calls rsx! to generate a component tree, and then calls render on it. Most of the time, you'll find yourself using the rsx! macro to compose arbitrary components, and only calling html! when you need a String output, when sending a response or generating a Markdown file.

In Render, attributes and plain strings are escaped using the html_codegen::html_escaping module. In order to use un-escaped values so you can dangerously insert raw HTML, use the raw! macro around your string:

use html_codegen::{html, raw};

let tree = html! {
  <div>
    <p>{"<Hello />"}</p>
    <p>{raw!("<Hello />")}</p>
  </div>
};

assert_eq!(tree, "<div><p>&lt;Hello /&gt;</p><p><Hello /></p></div>");

Custom components

Render's greatest ability is to provide type-safety along with custom renderable components. Introducing new components is as easy as defining a function that returns a Render value.

In order to build up components from other components or HTML nodes, you can use the rsx! macro, which generates a Render component tree:

use html_codegen::{component, rsx, html};

#[component]
fn Heading<'title>(title: &'title str) {
  rsx! { <h1 class={"title"}>{title}</h1> }
}

let rendered_html = html! {
  <Heading title={"Hello world!"} />
};

assert_eq!(rendered_html, r#"<h1 class="title">Hello world!</h1>"#);

If you pay close attention, you see that the function Heading is:

• declared with an uppercase. Underneath, it generates a struct with the same name, and implements the Render trait on it.
• does not have a return type. This is because everything is written to a writer, for performance reasons.

Visibility & Component Libraries

Often you're going to want to store your components somewhere else in your project tree other than the module you're working on (if not in a different module entirely!). In these cases, the visibility applied top the function that defines your component will flow down into all fields of that struct.

For example, if we add "pub" to the front of our Heading component above:

#[component]
pub fn Heading<'title>(title: &'title str) {
  rsx! { <h1 class={"title"}>{title}</h1> }
}

...the struct that is generated would look something like...

pub struct Heading {
  pub title: &'title str
}

This is important to understand from a safety point of view when structuring your libraries.

Full example

// A simple HTML 5 doctype declaration
use html_codegen::html::HTML5Doctype;
use html_codegen::{
    // A macro to create components
    component,
    // A macro to compose components in JSX fashion
    rsx,
    // A macro to render components in JSX fashion
    html,
    // A trait for custom components
    Render,
};

// This can be any layout we want
#[component]
fn Page<'a, Children: Render>(title: &'a str, children: Children) {
   rsx! {
     <>
       <HTML5Doctype />
       <html>
         <head><title>{title}</title></head>
         <body>
           {children}
         </body>
       </html>
     </>
   }
}

// This can be a route in Rocket, the web framework,
// for instance.
pub fn some_page(user_name: &str) -> String {
    html! {
      <Page title={"Home"}>
        {format!("Welcome, {user_name}")}
      </Page>
    }
}

License: MIT