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E0726 makes invalid mid-keyword suggestion with proc-macro derived on struct #108256
Description
I tried this code:
extern crate sort_by_derive;
use sort_by_derive::SortBy;
use std::borrow::Cow;
pub trait Ctx: Clone {}
#[derive(Clone, SortBy)]
pub struct ContextWrapper<'a, T>
where T: Ctx,
{
ctx: Cow<'a, T>,
#[sort_by]
elapsed: i32,
}
impl<'a, T: Ctx> ContextWrapper<'a, T> {
pub fn new(ctx: T) -> ContextWrapper<'a, T> {
ContextWrapper {
ctx: Cow::Owned(ctx),
elapsed: 0,
}
}
}and in Cargo.toml:
[dependencies]
sort_by_derive = "0.1.10"I expected either:
- the code compiles with
cargo check - any errors point out what needs to be changed
Instead, this error appeared:
error[E0726]: implicit elided lifetime not allowed here
--> src/lib.rs:12:1
|
12 | pub struct ContextWrapper<'a, T>
| ^^^^^^^^^^^^^^^^^^^^^^^^^ expected lifetime parameter
|
= note: assuming a `'static` lifetime...
help: indicate the anonymous lifetime
|
12 | p'_, ub struct ContextWrapper<'a, T>
| +++
For more information about this error, try `rustc --explain E0726`.I'm guessing the error being pointed to is in the procedural macro generated code, but that's not immediately clear as it points to my struct definition. This code compiles when I remove SortBy and its attribute.
Meta
rustc --version --verbose:
rustc 1.67.1 (d5a82bbd2 2023-02-07) (Fedora 1.67.1-1.fc37)
binary: rustc
commit-hash: d5a82bbd26e1ad8b7401f6a718a9c57c96905483
commit-date: 2023-02-07
host: x86_64-unknown-linux-gnu
release: 1.67.1
LLVM version: 15.0.7
(Issue template requested a backtrace but RUST_BACKTRACE=1 cargo build did not produce additional output.)
Activity
[-]E0726 makes invalid mid-keyword suggestion with proc-macro-derived on struct[/-][+]E0726 makes invalid mid-keyword suggestion with proc-macro derived on struct[/+]estebank commentedon Mar 14, 2023
sort_by_derive Is effectively using the wrong span on their expanded code. If they were doing nothing then #109082 would eliminate the issue, but the best bet we have here is to modify sort_by_derive itself, instead of adding more heuristics to rustc to detect that the macros of the Token Stream coming out of a proc-macro might be misleading (at least in the short term).
Zannick commentedon Mar 14, 2023
valsteen commentedon Jun 17, 2023
hi, crate author here 👋
Indeed the problem is on my side and lifetimes were missing from the expanded code, so I fixed that and released the fix. I should probably check if I can highlight the derive macro itself when it generated something invalid, but it's going to be of limited value to the users, except indeed signaling that it's not their fault.