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E0434 suggests changing the fn item of a trait impl to a closure #153363
Description
Code
trait T {
fn t() -> impl FnOnce() -> ();
}
fn f(x: String) {
struct S;
impl T for S {
fn t() -> impl FnOnce() -> () {
move || {let _ = x;}
}
}
}Current output
error[E0434]: can't capture dynamic environment in a fn item
--> src/lib.rs:9:30
|
9 | move || {let _ = x;}
| ^
|
= help: use the `|| { ... }` closure form insteadDesired output
error[E0434]: can't capture dynamic environment in a fn item
--> src/lib.rs:9:30
|
9 | move || {let _ = x;}
| ^
|Rationale and extra context
I don't think it's possible to implement a trait without using a fn item. A more detailed hint that refers to the exect fn keyword would also be nice (see #112845).
The suggestion is wrong in this case.
Other cases
Rust Version
rustc 1.93.1 (01f6ddf75 2026-02-11)
binary: rustc
commit-hash: 01f6ddf7588f42ae2d7eb0a2f21d44e8e96674cf
commit-date: 2026-02-11
host: x86_64-unknown-linux-gnu
release: 1.93.1
LLVM version: 21.1.8Anything else?
No response
Activity
[-]E0434 suggests changing the fn of a trait impl to a closure[/-][+]E0434 suggests changing the fn item of a trait impl to a closure[/+]mvanhorn commentedon Mar 9, 2026
mvanhorn commentedon Mar 9, 2026
Rollup merge of rust-lang#162821 - kulinsky:fix-153363-closure-sugges…
Unrolled build for #162821 in rollup 163111
Rollup merge of #162821 - kulinsky:fix-153363-closure-suggestion, r=m…
Rollup merge of #162821 - kulinsky:fix-153363-closure-suggestion, r=m…