Closed
Description
I tried this code (reduced testcase from code in cap-std):
use std::path::Path;
use std::ffi::OsStr;
use std::ops::Deref;
fn frob(path: &str) -> impl Deref<Target = Path> + '_ {
OsStr::new(path).as_ref()
}
fn open_parent<'path>(_path: &'path Path) {
todo!()
}
fn main() {
let old_path = frob("hello");
open_parent(&old_path);
}When compiled with stable Rust, it compiles with no errors.
When compiled with nightly Rust, it gets the following error:
error[E0308]: mismatched types
--> src/main.rs:16:17
|
5 | fn frob(path: &str) -> impl Deref<Target = Path> + '_ {
| ------------------------------ the found opaque type
...
16 | open_parent(&old_path);
| ^^^^^^^^^ expected struct `Path`, found opaque type
|
= note: expected struct `Path`
found opaque type `impl Deref<Target = Path>`
For more information about this error, try `rustc --explain E0308`.
error: could not compile `abc` due to previous error
The error can be avoided by changing &old_path to &*old_path, which works on both stable and nightly. I've already fixed the upstream code do to this; I'm filing this bug as it may affect other users as well.
Meta
Stable rustc --version --verbose:
rustc 1.58.1 (db9d1b20b 2022-01-20)
binary: rustc
commit-hash: db9d1b20bba1968c1ec1fc49616d4742c1725b4b
commit-date: 2022-01-20
host: x86_64-unknown-linux-gnu
release: 1.58.1
LLVM version: 13.0.0
Nightly rustc --version --verbose:
rustc 1.60.0-nightly (0c292c966 2022-02-08)
binary: rustc
commit-hash: 0c292c9667f1b202a9150d58bdd2e89e3e803996
commit-date: 2022-02-08
host: x86_64-unknown-linux-gnu
release: 1.60.0-nightly
LLVM version: 13.0.0
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