## Skerry: Super Kool ERRors Yoh
Example:
```rust
use skerry::*;
// Define your error boundary, there can be only one #[sherry_mod] in your project
#[skerry_mod]
pub mod errors {
pub struct DatabaseErr;
pub struct AuthErr;
pub struct ValidationErr;
pub struct InvalidParse;
pub struct LibErr(ErrorFromLib);
impl From<ErrorFromLib> for LibErr {
fn from(val: ErrorFromLib) -> Self {
Self(val)
}
}
}
// Generates a CheckAuthError enum automatically
#[skerry_fn]
fn check_auth() -> Result<(), e![AuthErr]> {
Err(CheckAuthError::AuthErr(AuthErr))
}
struct Controller;
#[skerry_impl(prefix(Controller))] // This allows #[skerry_fn] to run on impl blocks
impl Controller {
// Use '*' to expand and bubble up sub-errors seamlessly.
#[skerry_fn]
pub fn run() -> Result<(), e![ValidationErr, LibErr, *CheckAuthError]> {
// AuthErr is pulled in from check_auth via '*CheckAuthError'.
check_auth()?;
// Automatically bubble up library errors as long as an error
// from `#[skerry_mod]` implements `From` for it.
lib_fn_that_returns_error()?;
Ok(())
}
}
#[skerry_trait]
trait ToJson {
#[skerry_fn]
fn to_json(&self) -> Result<(), e![InvalidParse]>;
}
#[skerry_impl]
impl ToJson for Controller {
// Whenever you do not want to generate a new error just don't use e![]
// this will instead reuse an existing error
#[skerry_fn]
fn to_json(&self) -> Result<(), ToJsonError> {
Ok(())
}
}
```
### Core Workflow
- Define all possible error structs in a `#[skerry_mod]`.
- Mark functions with `#[skerry_fn]`.
- Use the `*` operator to bubble up errors from sub-functions without manually mapping variants.
---
### The Error Module
Every project needs one module (usually `errors.rs`) that acts as the source of truth.
```rust
pub use skerry::*; // Recommended to be pub for easier macro expansions
#[skerry_mod]
mod errors {
pub struct ErrA;
pub struct ErrB;
pub struct ErrC;
pub struct DatabaseErr;
}
```
*Note: When using errors in any other file, import them via `crate::errors::*;` instead
of individual imports to ensure the macros can resolve the paths correctly.*
---
### Function-Specific Enums
By using `#[skerry_fn]`, you define a return type using a tuple of error structs.
Skerry transforms this into a unique enum named `{FunctionName}Error`.
```rust
#[skerry_fn]
pub fn low_level() -> Result<(), e![ErrA, ErrB]> {
// Generates LowLevelError { ErrA(ErrA), ErrB(ErrB) }
Err(LowLevelError::ErrA(ErrA)) // You can also type Err(ErrA.into())
}
```
---
### The Asterisk (`*`) Expansion
When you put `*OtherFnError` in your return array it pulls all
variants from `OtherFnError` into your current function's list.
* **Deduplication**: Variants are deduplicated automatically. If `ErrA` is added manually
and also exists inside a `*` expansion, only one variant is generated.
```rust
#[skerry_fn]
pub fn high_level() -> Result<(), e![ErrC, *LowLevelError]> {
// 1. Sees ErrC -> Adds variant
// 2. Sees *LowLevelError -> Inspects LowLevelError, finds (ErrA, ErrB)
// 3. Final HighLevelError contains variants: ErrA, ErrB, ErrC
low_level()?; // Bubbles up automatically
Ok(())
}
```
The syntax below has the exact same effects, `*LowLevelError` is nothing more than syntatic sugar
```rust
#[skerry_fn]
pub fn high_level() -> Result<(), e![ErrA, ErrB, ErrC]> {
// ...
# Ok(())
}
```
In the cases above the generated enum looks like this
```rust
pub enum HighLevelError {
ErrA(ErrA),
ErrB(ErrB),
ErrC(ErrC),
}
```
### Using Skerry inside Impl Blocks
Skerry provides the `#[skerry_impl]` attribute to handle methods within `impl` blocks.
This attribute coordinates with `#[skerry_fn]` to split the generated code
so error enums are generated outside the `impl` block.
#### Example
```rust
use skerry::*;
#
pub struct Database;
#[skerry_impl(prefix(Database))] // Optional prefix for functions inside impl block
impl Database {
#[skerry_fn]
pub fn connect(&self) -> Result<(), e![*RemoteCallError]> {
remote_call()?;
Ok(())
}
}
fn main() {
let db = Database;
let result: Result<(), DatabaseConnectError> = db.connect();
assert!(result.is_ok());
}
```
### Using Skerry inside Trait Blocks
Skerry provides the `#[skerry_trait]` attribute to handle methods within `trait` blocks.
This attribute coordinates with `#[skerry_fn]` to split the generated code
so error enums are generated outside the `trait` block.
#### Example
```rust
use skerry::*;
#
#[skerry_impl(prefix(ToJson))] // Optional prefix for functions inside trait block
trait ToJson {
#[skerry_fn]
pub fn parse(&self) -> Result<(), e![*ParseFailed]>;
}
```
---
### Compile-Time Safety
Skerry uses a custom trait system (`MissingConvert`) to verify error bounds at
compile-time. If you try to use `?` on a function whose errors are not represented
in your current return tuple, the compiler will refuse to build.
License: MIT