ace_it/lib.rs
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//! # Auto Convert Enums
//! This crate provides a proc macro that generates [From] impls for unnamed enum fields that have a type.
//!
//! Ever get tired of writing the same From impls to enable using `?` on some [Result] types? This crate is for you!
//!
//! This is useful for enums that are used as a wrapper for a collecting multiple errors into one big enum.
//!
//! ## Example
//! ```
//! #[macro_use] extern crate ace_it;
//!
//! #[derive(Debug)]
//! #[ace_it]
//! enum Error {
//! Io(std::io::Error),
//! ParseInt(std::num::ParseIntError),
//! ParseFloat(std::num::ParseFloatError),
//! }
//! ```
//! After this, Error has three [From] impls:
//! * [From]<[std::io::Error]> for Error
//! * [From]<[std::num::ParseIntError]> for Error
//! * [From]<[std::num::ParseFloatError]> for Error
//!
//! Now you can use `?` on any of these types and get an Error back.
//! ```
//! # #[macro_use] extern crate ace_it;
//! #
//! # #[derive(Debug)]
//! # #[ace_it]
//! # enum Error {
//! # Io(std::io::Error),
//! # ParseInt(std::num::ParseIntError),
//! # ParseFloat(std::num::ParseFloatError),
//! # }
//!
//! use std::io::Read;
//!
//! fn read_int<R: Read>(reader: &mut R) -> Result<i32, Error> {
//! let mut buf = String::new();
//! reader.read_to_string(&mut buf)?;
//! Ok(buf.parse()?)
//! }
use std::collections::HashSet;
use proc_macro2::{Ident, Span, TokenStream};
use quote::{quote, ToTokens};
use syn::{spanned::Spanned, Fields, Variant};
/// Generates [From] impls for the given enum.
/// ## Usage
/// ### Applying the macro
/// This will generate the From impls for each type and turns it into an accompanying variant.
/// ```
/// # #[macro_use] extern crate ace_it;
/// #[ace_it]
/// enum Error {
/// Io(std::io::Error),
/// ParseInt(std::num::ParseIntError),
/// ParseFloat(std::num::ParseFloatError),
/// }
/// ```
/// ### Compile errors
/// This will error because there are two variants with the same type.
/// There is no way to know which one to use.
/// ```compile_fail
/// # #[macro_use] extern crate ace_it;
/// #[ace_it]
/// enum SomeEnum {
/// A(i32),
/// B(i32) // Duplicate i32, shouldn't compile
/// }
/// ```
#[proc_macro_attribute]
pub fn ace_it(
_: proc_macro::TokenStream,
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let parsed = syn::parse(input);
let parsed = match parsed {
Ok(parsed) => parsed,
Err(e) => return e.to_compile_error().into(),
};
ace_it_impl(parsed).into()
}
/// Generates From impls for the given enum.
fn process_variants<'a>(
variants: impl Iterator<Item = &'a Variant>,
enum_name: &Ident,
) -> Vec<TokenStream> {
let mut from_impls = Vec::new();
for variant in variants {
let variant_name = &variant.ident;
if let Fields::Unnamed(fields) = &variant.fields {
let types = &fields.unnamed;
let imp = quote! {
impl From<#types> for #enum_name {
fn from(value: #types) -> Self {
Self::#variant_name(value)
}
}
};
from_impls.push(imp);
}
}
from_impls
}
fn find_duplicate_variant_type<'a>(variants: impl Iterator<Item = &'a Variant>) -> Option<Span> {
let mut types_map = HashSet::new();
for variant in variants {
if let Fields::Unnamed(fields) = &variant.fields {
let types = fields.unnamed.to_token_stream().to_string();
if !types_map.insert(types) {
return Some(variant.span());
}
}
}
None
}
fn ace_it_impl(parsed: syn::ItemEnum) -> TokenStream {
let mut enum_def = parsed.to_token_stream();
if let Some(var) = find_duplicate_variant_type(parsed.variants.iter()) {
return syn::Error::new(
var,
"Duplicate variant type, can't auto-generate From impls",
)
.to_compile_error();
}
let for_impls = process_variants(parsed.variants.iter(), &parsed.ident);
for impls in for_impls {
impls.to_tokens(&mut enum_def);
}
enum_def
}
#[cfg(test)]
mod tests {
use super::*;
use quote::quote;
use syn::parse2;
#[test]
fn ace_it() {
let input = quote! {
enum Test {
A,
B(u32),
C { a: u32, b: u32 },
}
};
let expected = quote! {
enum Test {
A,
B(u32),
C { a: u32, b: u32 },
}
impl From<u32> for Test {
fn from(value: u32) -> Self {
Self::B(value)
}
}
};
let parsed: syn::ItemEnum = parse2(input).unwrap();
let result = ace_it_impl(parsed);
assert_eq!(result.to_string(), expected.to_string());
}
#[test]
fn repeating_types_error() {
let input = quote! {
enum Test {
A,
B(u32),
C(u32),
}
};
let parsed: syn::ItemEnum = parse2(input).unwrap();
let result = ace_it_impl(parsed);
assert!(result.to_string().contains("Duplicate variant type"));
}
}