`#![feature(arbitrary_self_types)]` - "type of `self` must not be a method generic parameter type"

[johamster]

Up to version 1.83 the following code compiled successfully:

Code

#![feature(arbitrary_self_types)]                                                                                                                                                                                                                                 

struct Foo;
impl Foo {
    fn foo(self: &impl std::ops::Deref<Target = Self>) {}
}

With version 1.84 we get the following error:

error[E0801]: invalid generic `self` parameter type: `&impl std::ops::Deref<Target = Self>`
...
note: "type of `self` must not be a method generic parameter type"

Version it worked on

It most recently worked on: 1.83

Version with regression

rustc --version --verbose:

rustc 1.84.0 (9fc6b4312 2025-01-07)
binary: rustc
commit-hash: 9fc6b43126469e3858e2fe86cafb4f0fd5068869
commit-date: 2025-01-07
host: aarch64-apple-darwin
release: 1.84.0
LLVM version: 19.1.5

[Noratrieb]

I assume this is expected and not a bug, but it would be good to confirm that, I recommend using cargo-bisect-rustc to figure out which PR made this info an error.

[schreter]

I assume this is expected and not a bug, but it would be good to confirm that, I recommend using cargo-bisect-rustc to figure out which PR made this info an error.

What do you mean with "info"? Previously, it didn't generate any message, no warnings or so. It was correctly compiled and worked as expected. So I'd personally see this as a regression/error.

[Noratrieb]

I meant "into" that was a typo. This is an unstable feature, so it is expected to change. I know there were some recent changes to it which have probably causes this. That's why I asked for a bisection, so we can find the PR that regressed this, which will probably tell us whether it was an accidental regression (and therefore a bug) or an expected change (not a bug).

[ranger-ross]

bisects to #130098 in nightly-2024-10-31

[ranger-ross]

@rustbot label +S-has-bisection -E-needs-bisection