Insert KaTeX autorender script into rustdoc

#[cfg_attr(doc, katexit::katexit)]
/// We can write $\LaTeX$ expressions
///
/// Display style
/// -------------
///
/// $$
/// c = \\pm\\sqrt{a^2   b^2}
/// $$
pub fn my_func() {}

See rendered result on docs.rs.

On nightly rustc, you can use #![katexit::katexit] for module level document:

#![cfg_attr(doc, feature(prelude_import, custom_inner_attributes))]
#![cfg_attr(doc, katexit::katexit)]
//! Module level document example with $\KaTeX$!

Be sure that cargo test will runs rustdoc for executing doc-test, and thus requires nightly compiler. See katexit-example-nightly for detail.

#[katexit] proc-macro inserts KaTeX autorender script as #[doc = "{script}"]. Since the markdown to HTML translator of rustdoc do not touch HTML partitions embedded in markdown, they will be passed as it is to the browser. The autorender script starts rendering the math expression enclosed by $ written in the document section when you open the page generated by rustdoc, i.e. this does not work offline.

• rustdoc-katex-demo and similar demo projects
  • They uses --html-in-header option in rustdoc to inserts KaTeX auto-render script. But it requires some complicated setting in Cargo.toml.
• aquamarine
  • The idea using proc-macro for cargo-doc is based on this crate.
• katex-rs
  • This is "Rust bindings to KaTeX". This crate aims to run KaTeX using QuickJS without external dependencies.