In this lesson, you will learn how to architect Rust documentation that remains cohesive across heterogeneous hardware targets without burying the reader in platform-specific noise.
When working with diverse runtimes—from bare-metal RISC-V controllers to cloud-based Wasm environments—the greatest risk to documentation is "conditional fragmentation." If your API behaves differently depending on the underlying hardware security integration or memory allocation policy, simple cfg attributes are often insufficient. They hide information from the compiler, but they make the documentation look incomplete or disjointed.
To build an elegant system, adopt a Tiered Documentation Strategy. Instead of using #[cfg(target_arch = ...)] to hide platform-specific functions entirely, use the doc_cfg feature. This allows you to include documentation that clearly flags which hardware features are required, providing a unified view of your library's capabilities.
/// Performs a secure memory wipe.
///
/// # Platform Availability
/// This operation is only available on hardware supporting the
/// Secure Enclave Interface (SEI).
#[cfg(feature = "secure-hardware")]
#[doc(cfg(feature = "secure-hardware"))]
pub fn secure_wipe(buffer: &mut [u8]) {
// Hardware-specific implementation
}
By using #[doc(cfg(...))], you generate documentation that explicitly labels the requirement within the rendered HTML. This prevents the "mystery function" problem where developers on non-supported platforms wonder why an API is missing.
For more complex hardware-agnostic HALs, avoid documenting the implementation details. Instead, use a "Contract-First" approach in your documentation. Define the behavior of the abstraction in the trait definition, then use a PLATFORMS.md manifest to link to specific driver implementations. This separates the high-level intent from the low-level register-manipulation documentation.
This approach treats documentation as a first-class citizen of your software architecture, just like your Cargo.toml features. By maintaining a single source of truth that acknowledges hardware constraints rather than masking them, you ensure that maintainers understand the intent of the code regardless of the target architecture.
Key Takeaway: Use #[doc(cfg(...))] to explicitly expose platform requirements in your documentation, turning hardware limitations into clearly communicated features rather than hidden implementation traps.