1 unstable release
0.1.0 | Jun 15, 2021 |
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#1800 in Procedural macros
8KB
error_spanned
This crate is meant to be used inside a proc macro lib.
This crate provides a trait ErrorSpanned
and a derive macro error_spanned_derive::ErrorSpanned
.
The trait enforces that the error type supports conversion to syn::Error
and proc_macro2::TokenStream
.
This trait is implemented for a wrapper struct generated by the
#[derive(ErrorSpanned)]
. The struct generated by it stores line, file and span info.
Example
For a file named error_spanned.rs
:
use std::fmt::Display;
use error_spanned::{ErrorSpanned as _, ErrorSpanned};
use proc_macro2::Span;
// Deriving ErrorSpanned generates a struct named `CustomErrorSpanned`
// and a function-like macro named custom_error!().
#[derive(Debug, ErrorSpanned)]
enum CustomError {
Error1,
Error2(String),
Error3 {
x: i32,
y: i32,
},
}
impl Display for CustomError {
fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
match self {
CustomError::Error1 => write!(f, "Error1"),
CustomError::Error2(string) => write!(f, "Error2({})", string),
CustomError::Error3 {x, y} => write!(f, "Error3 {{ x = {}, y = {} }}",x, y),
}
}
}
impl std::error::Error for CustomError {}
fn main() -> Result<(), Box<dyn std::error::Error>> {
// Printing the following errors will also print line and file
println!("{}", custom_error!(Error1, Span::call_site()));
println!("{}", custom_error!(Error2("Hello world".into()), Span::call_site()));
println!("{}", custom_error!(Error3{x: 1, y: 2}, Span::call_site()));
Ok(())
}
Output is as follows:
Line: 31, File: /Users/mihir/rust_crates/error_spanned/tests/error_spanned.rs:
Error1
Line: 32, File: /Users/mihir/rust_crates/error_spanned/tests/error_spanned.rs:
Error2(Hello world)
Line: 33, File: /Users/mihir/rust_crates/error_spanned/tests/error_spanned.rs:
Error3 { x = 1, y = 2 }
As shown in the above example, errors should be propagated by the generated macro
(like custom_error!()
). The generated macro is the snake cased version of the error enum.
The generated macro accepts the error variant (not complete path) as the first arg and span as the second arg.
The type returned by the macro is <enum_named>Spanned
. This type can be converted to
proc_macro2::TokenStream
or syn::Error
as it implements ErrorSpanned
.
On conversion to proc_macro2::TokenStream
or syn::Error
it preseves span information.
Dependencies
~1.5MB
~36K SLoC