called `Result::unwrap()` on an `Err` value: Error("EOF while parsing an object", line: 2, column: 0)

[ada4a]

I was debugging a Clippy lint, and added a big dbg! around the following section: https://github.com/rust-lang/rust-clippy/blob/e85b1dd6dae1429b384c63e46a61daa1c6aae134/clippy_lints/src/unnested_or_patterns.rs#L324-L334

resulting in:

&& dbg!(fps1.iter().enumerate().all(|(idx_1, fp1)| {
    if idx_1 == idx {
        // In the case of `k`, we merely require identical field names
        // so that we will transform into `ident_k: p1_k | p2_k`.
        let pos = fps2.iter().position(|fp2| eq_id(fp1.ident, fp2.ident));
        pos_in_2.set(pos);
        pos.is_some()
    } else {
        fps2.iter().any(|fp2| eq_field_pat(fp1, fp2))
    }
})))

Then I tried running the modified code on a test case. The case itself is not relevant to the bug I'm pretty sure, but here it is for completeness:

#![warn(clippy::unnested_or_patterns)]
#![allow(
    clippy::cognitive_complexity,
    clippy::match_ref_pats,
    clippy::upper_case_acronyms,
    clippy::needless_if,
    clippy::manual_range_patterns
)]
#![allow(unreachable_patterns, irrefutable_let_patterns, unused)]

fn issue15219() {
    struct Foo {
        bar: i8,
    }
    let u = Foo { bar: 8 };
    if let Foo { bar } | Foo { bar } = u {}
    //~^ unnested_or_patterns
}

When running the test, I got the following error:

thread '<unnamed>' panicked at ~/.cache/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ui_test-0.30.2/src/diagnostics/rustc.rs:108:88:
called `Result::unwrap()` on an `Err` value: Error("EOF while parsing an object", line: 2, column: 0)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

thread '<unnamed>' panicked at ~/.cache/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ui_test-0.30.2/src/status_emitter/text.rs:256:29:
0 (tests/ui/unnested3.rs: ) not finished

error: a bug in `ui_test` occurred
called `Result::unwrap()` on an `Err` value: Error("EOF while parsing an object", line: 2, column: 0)

Then I've tried to minimize the reproducer a little, and got the following results:

• this still gives the same panic:

  && dbg!(fps1.iter().enumerate().all(|(idx_1, fp1)| {
      if idx_1 == idx {
          true
      } else {
          fps2.iter().any(|fp2| eq_field_pat(fp1, fp2))
      }
  })))

• this results in a different panic:

  && dbg!(fps1.iter().enumerate().all(|(idx_1, _fp1)| {
      if idx_1 == idx {
          true
      } else {
          false
      }
  })))

  namely:

  thread '<unnamed>' panicked at ~/.cache/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ui_test-0.30.2/src/diagnostics/rustc.rs:108:88:
  called `Result::unwrap()` on an `Err` value: Error("key must be a string", line: 1, column: 3)
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
  
  thread '<unnamed>' panicked at ~/.cache/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ui_test-0.30.2/src/status_emitter/text.rs:256:29:
  0 (tests/ui/unnested3.rs: ) not finished
  
  error: a bug in `ui_test` occurred
  called `Result::unwrap()` on an `Err` value: Error("key must be a string", line: 1, column: 3)
  

• and this works just fine:

  && dbg!(fps1.iter().enumerate().all(|(_idx_1, _fp1)| {
          false
  })))

For even more context, the seemingly unbalanced closing paren is coming from the matches! invocation that this whole dbg! thing is contained in

[ada4a]

Since the error message mentions a failed attempt to parse a rustc diagnostic, I'd like to try to find which diagnostic it's referring to. Running cargo uitest -v --message-format=json didn't output any relevant JSON -- only some talking about the packages being rebuilt