1 Creating Documentation

Documenting Rust APIs is quite simple. To document a given item, we have "doc comments":

// the "link" crate attribute is currently required for rustdoc, but normally
// isn't needed.
#[crate_id = "universe"];
#[crate_type="lib"];

//! Tools for dealing with universes (this is a doc comment, and is shown on
//! the crate index page. The ! makes it apply to the parent of the comment,
//! rather than what follows).

/// Widgets are very common (this is a doc comment, and will show up on
/// Widget's documentation).
pub struct Widget {
    /// All widgets have a purpose (this is a doc comment, and will show up
    /// the field's documentation).
    purpose: ~str,
    /// Humans are not allowed to understand some widgets
    understandable: bool
}

pub fn recalibrate() {
    //! Recalibrate a pesky universe (this is also a doc comment, like above,
    //! the documentation will be applied to the *parent* item, so
    //! `recalibrate`).
    /* ... */
}

Doc comments are markdown, and are currently parsed with the sundown library. rustdoc does not yet do any fanciness such as referencing other items inline, like javadoc's @see. One exception to this is that the first paragrah will be used as the "summary" of an item in the generated documentation:

/// A whizbang. Does stuff. (this line is the summary)
///
/// Whizbangs are ...
struct Whizbang;

To generate the docs, run rustdoc universe.rs. By default, it generates a directory called doc, with the documentation for universe being in doc/universe/index.html. If you are using other crates with extern mod, rustdoc will even link to them when you use their types, as long as their documentation has already been generated by a previous run of rustdoc, or the crate advertises that its documentation is hosted at a given URL.

The generated output can be controlled with the doc crate attribute, which is how the above advertisement works. An example from the libstd documentation:

#[doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
      html_favicon_url = "http://www.rust-lang.org/favicon.ico",
      html_root_url = "http://static.rust-lang.org/doc/master")];

The html_root_url is the prefix that rustdoc will apply to any references to that crate's types etc.

rustdoc can also generate JSON, for consumption by other tools, with rustdoc --output-format json, and also consume already-generated JSON with rustdoc --input-format json.

2 Using the Documentation

The web pages generated by rustdoc present the same logical heirarchy that one writes a library with. Every kind of item (function, struct, etc) has its own color, and one can always click on a colored type to jump to its documentation. There is a search bar at the top, which is powered by some javascript and a statically-generated search index. No special web server is required for the search.

3 Testing the Documentation

rustdoc has support for testing code examples which appear in the documentation. This is helpful for keeping code examples up to date with the source code.

To test documentation, the --test argument is passed to rustdoc:

rustdoc --test crate.rs

```rust
// This is a testable code block
```

```
// This is not a testable code block
```

    // This is not a testable code block (4-space indent)

```rust,ignore
// This code block is ignored by rustdoc, but is passed through to the test
// harness
```

```rust,should_fail
// This code block is expected to generate a failure
```

```rust

do spawn { fib(200); }
```

// Only run tests containing 'foo' in their name
rustdoc --test lib.rs --test-args 'foo'

// See what's possible when running tests
rustdoc --test lib.rs --test-args '--help'

// Run all ignored tests
rustdoc --test lib.rs --test-args '--ignored'