rustdoc-twoslash

A fork of rust-lang/rust's rustdoc with twoslash-style type hover annotations on code blocks.

Hover over any identifier in a ```rust doc example to see its inferred type — the same information your IDE shows on hover, rendered directly in the documentation.

How it works

Doc comment ````rust code blocks
        │
        ▼
   pulldown-cmark (markdown.rs)
        │
        ▼
   CodeBlocks iterator extracts code text
        │
        ▼
   twoslash.rs ──► twoslash-rust ──► rust-analyzer
        │              │                  │
        │              │    scaffolds a temp Cargo project,
        │              │    runs rust-analyzer, returns
        │              │    type info per identifier
        │              ◄──────────────────┘
        ▼
   highlight.rs merges annotations into DecorationInfo
        │
        ▼
   push_token() emits <span data-type="..."> attributes
        │
        ▼
   rustdoc.css renders hover popovers via CSS + JS

Changed files

This repo contains only the modified src/librustdoc/ files from the rust-lang/rust fork. Apply the included twoslash.patch to a fresh checkout of rust-lang/rust to reproduce:

File	Change
src/librustdoc/Cargo.toml	Added twoslash_rust and once_cell dependencies
src/librustdoc/html/twoslash.rs	New — integration module: process_code_block(), is_enabled(), needs_main_wrapper() with offset adjustment
src/librustdoc/html/highlight.rs	Extended DecorationInfo with type_annotations, fuzzy token matching, data-type attribute emission
src/librustdoc/html/highlight/tests.rs	Updated tests for new DecorationInfo field
src/librustdoc/html/markdown.rs	Modified CodeBlocks::next() to call twoslash when RUSTDOC_TWOSLASH=1
src/librustdoc/html/mod.rs	Added mod twoslash
src/librustdoc/html/render/mod.rs	Minor update for annotation plumbing
src/librustdoc/html/static/css/rustdoc.css	Hover popover styles for [data-type] elements
src/librustdoc/html/static/js/main.js	Interactive popover positioning

Usage

# 1. Clone rust-lang/rust and apply the patch
git clone --depth 1 https://github.com/rust-lang/rust.git rustdoc-twoslash
cd rustdoc-twoslash
git apply /path/to/twoslash.patch

# 2. Build rustdoc
./x.py build library/std src/librustdoc

# 3. Run on your crate with twoslash enabled
cd /path/to/your-crate
RUSTDOC_TWOSLASH=1 \
  RUSTDOC=.../build/host/stage1/bin/rustdoc \
  RUSTC=.../build/host/stage1/bin/rustc \
  cargo doc --no-deps

Dependencies

• twoslash-rust — extracts type information from Rust code via rust-analyzer
• rust-lang/rust — the base rustdoc being modified

Demo

See tmm/twoslash-demo for a sample crate with generated docs.