Rust analyzer false positive error

[benluelo]

$ rust-analyzer --version
rust-analyzer 1.83.0-nightly (c52c23b6 2024-09-16)

$ rustc -V --verbose
rustc 1.83.0-nightly (c52c23b6f 2024-09-16)
binary: rustc
commit-hash: c52c23b6f44cd19718721a5e3b2eeb169e9c96ff
commit-date: 2024-09-16
host: aarch64-unknown-linux-gnu
release: 1.83.0-nightly
LLVM version: 19.1.0

pub enum Enum<T: Foo> {
    String(String),
    ImplsBar(T::UsedInEnum),
}

impl<T: Foo> Enum<T> {
    pub fn f(&self) {
        match *self {
            Enum::String(ref string) => dyn_bar(&string),
            Enum::ImplsBar(ref a1) => dyn_bar(&a1),
        };
    }
}

pub trait Foo {
    type UsedInEnum: Bar;
    type Unused1: Quux;
    type Unused2: Quux;
}

pub trait Quux {
    type Unused3: Bar;
}

pub trait Bar {}

impl Bar for String {}

impl<T: Bar> Bar for &'_ T {}

pub fn dyn_bar(_: &dyn Bar) {}

cargo check works fine, however rust-analyzer errors:

$ rust-analyzer diagnostics .
processing crate: playground, module: /redacted/src/main.rs
Error RustcHardError("E0308") from LineCol { line: 10, col: 48 } to LineCol { line: 10, col: 55 }: expected &dyn Bar, found &&String
Error RustcHardError("E0308") from LineCol { line: 11, col: 46 } to LineCol { line: 11, col: 49 }: expected &dyn Bar, found &&<T as Foo>::UsedInEnum

diagnostic scan complete

Error: diagnostic error detected

Stack backtrace:
   0: std::backtrace_rs::backtrace::libunwind::trace
             at /rustc/c52c23b6f44cd19718721a5e3b2eeb169e9c96ff/library/std/src/../../backtrace/src/backtrace/libunwind.rs:116:5
   1: std::backtrace_rs::backtrace::trace_unsynchronized
             at /rustc/c52c23b6f44cd19718721a5e3b2eeb169e9c96ff/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2: std::backtrace::Backtrace::create
             at /rustc/c52c23b6f44cd19718721a5e3b2eeb169e9c96ff/library/std/src/backtrace.rs:331:13
   3: <anyhow::Error>::msg::<&str>
   4: std::sys::backtrace::__rust_begin_short_backtrace::<<stdx::thread::Builder>::spawn<<rust_analyzer::cli::flags::Diagnostics>::run::{closure#0}, core::result::Result<(), anyhow::Error>>::{closure#0}, core::result::Result<(), anyhow::Error>>
   5: <<std::thread::Builder>::spawn_unchecked_<<stdx::thread::Builder>::spawn<<rust_analyzer::cli::flags::Diagnostics>::run::{closure#0}, core::result::Result<(), anyhow::Error>>::{closure#0}, core::result::Result<(), anyhow::Error>>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
   6: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
             at /rustc/c52c23b6f44cd19718721a5e3b2eeb169e9c96ff/library/alloc/src/boxed.rs:2453:9
   7: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
             at /rustc/c52c23b6f44cd19718721a5e3b2eeb169e9c96ff/library/alloc/src/boxed.rs:2453:9
   8: std::sys::pal::unix::thread::Thread::new::thread_start
             at /rustc/c52c23b6f44cd19718721a5e3b2eeb169e9c96ff/library/std/src/sys/pal/unix/thread.rs:105:17
   9: start_thread
  10: thread_start

Notably both String and T::UsedInEnum error. However! If any of the Unused* associated types are commented out, it compiles.

[ShoyuVanilla]

I've tried a bit but this seems to be a chalk issue 😢

[benluelo]

I've bisected this to:

rust-analyzer 1.82.0-nightly (0d634185 2024-08-29) -> works
rust-analyzer 1.82.0-nightly (a7399ba6 2024-08-31) -> doesn't work

[ShoyuVanilla]

I've bisected this to:

rust-analyzer 1.82.0-nightly (0d634185 2024-08-29) -> works rust-analyzer 1.82.0-nightly (a7399ba6 2024-08-31) -> doesn't work

Oh, that's cool. This might not be a chalk issue then. I'll look into this more. Thanks 😄

[ShoyuVanilla]

My bisection result is a bit different

rust-analyzer version: 0.4.2075-standalone (0765978 2024-08-16) -> Makes those false positives
rust-analyzer version: 0.4.2074-standalone (91aa3f4 2024-08-15) -> No false positives

[benluelo]

I use https://github.com/oxalica/rust-overlay - I'm unable to get those same commits as you seemingly:

rust-analyzer 1.82.0-nightly (2c93fabd 2024-08-15)
rust-analyzer 1.82.0-nightly (506052d4 2024-08-16)

(both of these work for me also)

[ShoyuVanilla]

Thanks!
I've found the most suspicious single commit.
Will work on this tommorrow but not sure if this could be fixed soon 😅

[ShoyuVanilla]

It seems that nix rust overlay prints versions from its own commit graphs btw

[ShoyuVanilla]

Bisected to 8a4261a

I guess that maybe the chalk is not so happy with the partialy implemented lifetimes in the above commit.

For instance, chalk solves this full explicit lifetime modification of the original code well and emits no false-positive diagnostics

pub enum Enum<T: Foo> {
    String(String),
    ImplsBar(T::UsedInEnum),
}

impl<T: Foo> Enum<T> {
    pub fn f<'a>(self: &'a Self) {
        match *self {
            Enum::String(ref string) => dyn_bar(&string),
            Enum::ImplsBar(ref a1) => dyn_bar(&a1),
        };
    }
}

pub trait Foo {
    type UsedInEnum: Bar;
    type Unused1: Quux;
    type Unused2: Quux;
}

pub trait Quux {
    type Unused3: Bar;
}

pub trait Bar {}

impl Bar for String {}

impl<'a, T: Bar> Bar for &'a T {}

pub fn dyn_bar<'a>(_: &'a dyn Bar) {}

Maybe I should implement lifetime elision inference, which r-a currently doesn't have.

[ShoyuVanilla]

As @dfireBird is working on lifetime elision, this seems to be resolved once his work is done. If this isn't fixed then, I'll look into this more.

[Veykril]

Likely the same issue as #18064