Inline const expression inside vec!/macros should suggest adding parentheses under edition <2024 #126459
Description
Code
fn main() {
// Works fine, no warning.
let _: [Vec<String>; 10] = [const { vec![] }; 10];
// Works fine, no warning.
let _: Vec<Vec<String>> = vec![(const { vec![] })];
// Works, but warns about unnecessary parentheses.
let _: Vec<Vec<String>> = vec![(const { vec![] }); 10];
// These fail on stable79/beta80/nightly81 with edition 2021.
// They work on nightly81 with edition 2024.
let _: Vec<Vec<String>> = vec![const { vec![] }];
let _: Vec<Vec<String>> = vec![const { vec![] }; 10];
}Current output
error: no rules expected the token `const`
--> src/main.rs:12:36
|
12 | let _: Vec<Vec<String>> = vec![const { vec![] }];
| ^^^^^ no rules expected this token in macro call
|
= note: while trying to match end of macro
error: no rules expected the token `const`
--> src/main.rs:13:36
|
13 | let _: Vec<Vec<String>> = vec![const { vec![] }; 10];
| ^^^^^ no rules expected this token in macro call
|
= note: while trying to match end of macroDesired output
help: consider surrounding the const expression with parentheses
|
12 - let _: Vec<Vec<String>> = vec![const { vec![] }];
12 + let _: Vec<Vec<String>> = vec![(const { vec![] })];
|Rationale and extra context
For compatibility reasons, macros under edition <2024 do not treat const as the start of an expr, so a layer of parentheses is needed to convince the macro to treat inline-const as an expression.
Other cases
No response
Rust Version
(Stable Rust 1.79.0 on playground.)