Closed
Description
I tried this code:
pub trait Foo<'a> {
fn apply(_: &mut ()) -> Result<Self, impl Bar>
where
Self: Sized;
}
trait Bar {
fn apply(&self, _: &mut ());
}
impl Bar for () {
fn apply(&self, _: &mut ()) {
todo!()
}
}
struct F<'a>(&'a ());
impl<'a> F<'a> {
fn apply(arg: &mut ()) -> Result<F<'a>, impl Bar> {
Err(())
}
}
impl<'a> Foo<'a> for F<'a> {
fn apply(arg: &mut ()) -> Result<F<'a>, impl Bar> {
Err(())
}
}
fn check(arg: &mut ()) {
if let Err(e) = F::apply(arg) {
e.apply(arg);
} else {
todo!()
}
if let Err(e) = <F as Foo>::apply(arg) {
e.apply(arg);
} else {
todo!()
}
}I expected to see this happen: lifetime checking passed
Instead, this happened:
error[E0499]: cannot borrow `*arg` as mutable more than once at a time
--> src/main.rs:39:17
|
38 | if let Err(e) = <F as Foo>::apply(arg) {
| ----------------------
| | |
| | first mutable borrow occurs here
| a temporary with access to the first borrow is created here ...
39 | e.apply(arg);
| ^^^ second mutable borrow occurs here
...
43 | }
| - ... and the first borrow might be used here, when that temporary is dropped and runs the destructor for type `std::result::Result<F<'_>, impl Bar>`
Meta
rustc --version --verbose:
rustc 1.77.0-nightly (e51e98dde 2023-12-31)
binary: rustc
commit-hash: e51e98dde6a60637b6a71b8105245b629ac3fe77
commit-date: 2023-12-31
host: x86_64-unknown-linux-gnu
release: 1.77.0-nightly
LLVM version: 17.0.6