FP trait bound not satisfied

// check-pass

#![allow(dead_code)]

trait ParseError {
    type StreamError;
}

impl<T> ParseError for T {
    type StreamError = ();
}

trait Stream {
    type Item;
    type Error: ParseError;
}

trait Parser
where
    <Self as Parser>::PartialState: Default,
{
    type PartialState;
    fn parse_mode(_: &Self, _: Self::PartialState) {
        loop {}
    }
}

impl Stream for () {
    type Item = ();
    type Error = ();
}

impl Parser for () {
    type PartialState = ();
}

struct AndThen<A, B>(core::marker::PhantomData<(A, B)>);

impl<A, B> Parser for AndThen<A, B>
where
    A: Stream,
    B: Into<<A::Error as ParseError>::StreamError>,
{
    type PartialState = ();
}

fn expr<A>() -> impl Parser
where
    A: Stream<Error = <A as Stream>::Item>,
{
    AndThen::<A, ()>(core::marker::PhantomData)
}

fn parse_mode_impl<A>()
where
    <A as Stream>::Error: ParseError,
    A: Stream<Error = <A as Stream>::Item>,
{
    Parser::parse_mode(&expr::<A>(), Default::default())
}

fn main() {}

this compiles with rustc but fails with rust-analyzer diagnostics .

at crate f, file /tmp/f/src/main.rs: Error RustcHardError("E0277") from LineCol { line: 58, col: 4 } to LineCol { line: 58, col: 22 }: the trait bound `<impl Parser as Parser>::PartialState: Default` is not satisfied
at crate f, file /tmp/f/src/main.rs: Error RustcHardError("E0277") from LineCol { line: 58, col: 37 } to LineCol { line: 58, col: 53 }: the trait bound `<impl Parser as Parser>::PartialState: Default` is not satisfied

diagnostic scan complete

Error: diagnostic error detected

Stack backtrace:
   0: <anyhow::Error>::msg::<&str>
   1: 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>>
   2: <std::thread::lifecycle::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}
   3: <std::sys::thread::unix::Thread>::new::thread_start
   4: <unknown>
   5: <unknown>

Reproduce the report from the Rust source in /tmp/f/src/main.rs by comparing rustc with rust-analyzer diagnostics .. Trace the trait-bound diagnostic for the opaque impl Parser return and verify that rust-analyzer no longer reports the spurious E0277 errors while retaining valid diagnostics.