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* Add `API-GUIDELINES.md` * Address review comments * Reference the API guidelines in contributing guide, README and PR template
55 lines
4.2 KiB
Markdown
55 lines
4.2 KiB
Markdown
# esp-rs API Guidelines
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## About
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This is a living document - make sure to check the latest version of this document.
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> [!NOTE]
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> Not all of the currently existing code follows this guideline, yet.
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In general, the [Rust API Guidelines](https://rust-lang.github.io/api-guidelines) apply to all projects in the ESP-RS GitHub organization where possible. (`C-RW-VALUE` and `C-SERDE` do not apply)
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Especially for public API but if possible also for internal APIs.
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The following paragraphs contain additional recommendations.
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## Construction and Destruction of Drivers
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- Drivers take peripherals and pins via the `PeripheralRef` pattern - they don't consume peripherals/pins
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- Consider adding a `Drop` implementation resetting the peripheral to idle state
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- Consider using a builder-like pattern for configuration which must be done during initialization
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## Interoperability
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- `cfg` gated `defmt` derives and impls are added to new structs and enums
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- see [this example](https://github.com/esp-rs/esp-hal/blob/df2b7bd8472cc1d18db0d9441156575570f59bb3/esp-hal/src/spi/mod.rs#L15)
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- e.g. `#[cfg_attr(feature = "defmt", derive(defmt::Format))]`
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- Don't use `log::XXX!` macros directly - use the wrappers in `fmt.rs` (e.g. just `info!` instead of `log::info!` or importing `log::*`)
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## API Surface
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- Add `#[deny(missing_docs)]` to new modules or when reworking a larger part of a module. In the end we will require this for whole crates.
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- API documentation shouldn't be an afterthought
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- Private details shouldn't leak into the public API, and should be made private where technically possible.
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- Implementation details that _need_ to be public should be marked with `#[doc(hidden)]` and a comment as to why it needs to be public.
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- Functions which technically need to be public but shouldn't be callable by the user need to be sealed.
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- see [this example in Rust's core library](https://github.com/rust-lang/rust/blob/044a28a4091f2e1a5883f7fa990223f8b200a2cd/library/core/src/error.rs#L89-L100)
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- Any public traits, that **must not** be implemented downstream need to be `Sealed`
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- Prefer compile-time checks over runtime checks where possible, prefer a fallible API over panics.
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- Follow naming conventions in order to be consistent across drivers - take inspiration from existing drivers
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- Design APIs in a way that they are easy to use.
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- Driver API decisions should be assessed individually, don't _not_ just follow embedded-hal or other ecosystem trait crates. Expose the capabilities of the hardware. (Ecosystem traits are implemented on top of the inherent API)
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- Avoid type states and extraneous generics whenever possible
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- These often lead to usability problems, and tend to just complicate things needlessly - sometimes it can be a good tradeoff to make a type not ZST
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- Common cases of useless type info is storing pin information - this is usually not required after configuring the pins and will bloat the complexity of the type massively. When following the `PeripheralRef` pattern it's not needed in order to keep users from re-using the pin while in use
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- Avoiding `&mut self` when `&self` is safe to use. `&self` is generally easier to use as an API. Typical applications of this are where the methods just do writes to registers which don't have side effects.
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- For example starting a timer is fine for `&self`, worst case a timer will be started twice if two parts of the program call it. You can see a real example of this [here](https://github.com/esp-rs/esp-hal/pull/1500#pullrequestreview-2015911974)
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## Maintainability
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- Avoid excessive use of macros unless there is no other option; modification of the PAC crates should be considered before resorting to macros.
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- Every line of code is a liability. Take some time to see if your implementation can be simplified before opening a PR.
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- If your are porting code from ESP-IDF (or anything else), please include a link WITH the commit hash in it, and please highlight the relevant line(s) of code
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- If necessary provide further context as comments (consider linking to code, PRs, TRM - make sure to use permanent links, e.g. include the hash when linking to a Git repository, include the revision, page number etc. when linking to TRMs)
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- Generally follow common "good practices" and idiomatic Rust style
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