Rust Documentation Practices

Comprehensive guidance on documenting Rust code in the HASH repository following rustdoc conventions.

Core Principles

Follow high-quality standards like time, jiff, and serde:

✅ DO:

• Begin every doc comment with single-line summary
• Use intra-doc links for all type references
• Document all error conditions with # Errors
• Include practical examples for public APIs
• Link standard library types: [Vec], [HashMap], etc.
• Use inline parameter descriptions for simple functions (0-2 params)
• Describe return values in main text, not separate sections

❌ DON'T:

• Document standard trait implementations (Debug, Display, From)
• Add separate # Returns sections (inline instead)
• Mention variable types already in signatures
• Use comments on same line as code
• Skip error documentation for fallible functions

Quick Reference

Basic Doc Comment

/// Retrieves an entity by its UUID.
///
/// Loads the entity from the store and verifies access permissions.
/// Returns the [`Entity`] if found and accessible.
///
/// # Errors
///
/// - [`NotFound`] if the entity doesn't exist
/// - [`AuthorizationError`] if access is denied
///
/// [`NotFound`]: EntityError::NotFound
/// [`AuthorizationError`]: EntityError::Authorization
pub fn get_entity(&self, id: EntityId) -> Result<Entity, Report<EntityError>> {

Intra-Doc Links

/// Updates the [`User`] using [`UserUpdateStrategy`].
///
/// See [`validation::user`] for validation rules.
///
/// [`validation::user`]: crate::validation::user

Documentation Patterns

Simple Functions (0-2 params)

Describe parameters inline:

/// Processes the `input` elements and returns filtered results.
///
/// Takes a collection of `input` elements, applies the `filter_fn`,
/// and returns a [`Vec`] containing only matching elements.

Complex Functions (3+ params)

Use explicit # Arguments section:

/// Merges multiple data sources with transformation rules.
///
/// # Arguments
///
/// * `sources` - Collection of data sources to merge
/// * `rules` - Transformation rules to apply
/// * `options` - Configuration controlling merge behavior
/// * `callback` - Optional function for each merged item

Error Documentation

/// # Errors
///
/// - [`WebAlreadyExists`] if web ID is taken
/// - [`AuthorizationError`] if permission denied
///
/// [`WebAlreadyExists`]: WebError::WebAlreadyExists
/// [`AuthorizationError`]: WebError::Authorization

Module Documentation

//! Entity management functionality.
//!
//! Main types:
//! - [`Entity`] - Core entity type
//! - [`EntityStore`] - Storage trait
//!
//! # Examples
//!
//! ```
//! use hash_graph::entity::Entity;
//! ```

Examples with Error Handling

/// # Examples
///
/// ```rust
/// let entities = get_entities_by_type(type_id)?;
/// assert_eq!(entities.len(), 2);
/// # Ok::<(), Box<dyn core::error::Error>>(())
/// ```

Verification

cargo doc --no-deps --all-features

Exploring Crates

Generate and use Rust documentation to understand crate APIs, structure, and code organization.

Generating Documentation

# For a specific package
cargo doc --no-deps --all-features --package <package-name>

# For the entire workspace
cargo doc --no-deps --all-features --workspace

# Include private items for internal implementation details
cargo doc --no-deps --all-features --document-private-items

Key Flags

What Generated Docs Provide

1. Crate organization - Module hierarchy and component relationships
2. Public API surface - All public functions, types, traits, and constants
3. Usage examples - Code examples from doctest blocks
4. Error documentation - Documented error conditions and handling
5. Type relationships - Trait implementations, type aliases, associated types

Viewing Documentation

Docs are generated at:

target/doc/<crate_name>/index.html

Tips:

• Generate docs before diving into unfamiliar Rust code
• Cross-reference # Errors sections for error handling patterns
• Look for # Examples sections for idiomatic usage patterns

References

• references/function-documentation.md: Functions and methods documentation patterns
• references/type-documentation.md: Types, structs, enums, and traits documentation
• references/error-documentation.md: Error conditions and panics documentation
• references/examples-and-links.md: Examples and intra-doc links usage