"error[E0596]: cannot borrow data in a `&` reference as mutable" error doesn't say what's wrong or where it's actually wrong; same code diagnoses OK when the deductions are simpler

Code

/*
[package]
name = "b"
version = "0.1.0"
edition = "2024"

[dependencies]
rusqlite = "0.38"
*/
use rusqlite::{Statement, Connection};
struct Statements<'conn> {
    known: Option<Statement<'conn>>,
}
impl Statements<'_> {
    fn prepare<'s, 'conn>(_: &'s mut Option<Statement<'conn>>, _: &'conn Connection, _: &str)
                          -> Result<&'s Statement<'conn>, String> {
        unimplemented!();
    }
}
fn main() -> Result<(), String> {
    let sqlite = Connection::open_in_memory().unwrap();
    let sqlite = &sqlite;
    let path_sql = "";
    let mut statements = Statements{known:None};

    if Statements::prepare(&mut statements.known, sqlite, "SELECT EXISTS(SELECT 1 FROM history WHERE file=?1);")?
        .query_row(&[&path_sql], |row| row.get(0))
        .map_err(|e| format!("known: {}", e))? {
        return Ok(());
    }

    Ok(())
}

Current output

Compiling b v0.1.0 (/home/nabijaczleweli/uwu/b)
error[E0596]: cannot borrow data in a `&` reference as mutable
  --> lib.rs:17:8
   |
17 |     if Statements::prepare(&mut statements.known, sqlite, "SELECT EXISTS(SELECT 1 FROM history WHERE file=?1);")?
   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable

For more information about this error, try `rustc --explain E0596`.
error: could not compile `b` (lib) due to 1 previous error

Desired output

error[E0599]: no method named `query_row` found for reference `&Statement<'_>` in the current scope
  --> a.rs:24:10
   |
23 |        if Statements::prepare(&mut statements.known, sqlite, "SELECT EXISTS(SELECT 1 FROM history WHERE file=?1);")?
   |   ________-
   |  |________|
24 | ||         .query_row(&[&path_sql], |row| row.get(0))
   | ||_________-^^^^^^^^^_______________________________- help: use associated function syntax instead: `Statement::<'_>::query_row(&[&path_sql], |row| row.get(0))`
   | |          ||
   | |__________|this is an associated function, not a method
   |
   |
   = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
note: the candidate is defined in an impl for the type `Statement<'conn>`
  --> a.rs:4:5
   |
 4 |     fn query_row(_: &[&()], _: fn(&[()]) -> Option<&()>) -> Result<bool, String> {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Rationale and extra context

I obtained the output above by mocking up an equivalent scenario without any deductive complications:

type Connection = ();
struct Statement<'conn>(&'conn ());
impl<'conn> Statement<'conn> {
    fn query_row(_: &[&()], _: fn(&[()]) -> Option<&()>) -> Result<bool, String> {
        unimplemented!();
    }
}
struct Statements<'conn> {
    known: Option<Statement<'conn>>,
}
impl Statements<'_> {
    fn prepare<'s, 'conn>(_: &'s mut Option<Statement<'conn>>, _: &'conn Connection, _: &str)
                          -> Result<&'s Statement<'conn>, String> {
        unimplemented!();
    }
}
fn main() -> Result<(), String> {
    let sqlite = ();
    let sqlite = &sqlite;
    let path_sql = ();
    let mut statements = Statements{known:None};

    if Statements::prepare(&mut statements.known, sqlite, "SELECT EXISTS(SELECT 1 FROM history WHERE file=?1);")?
        .query_row(&[&path_sql], |row| row.get(0))
        .map_err(|e| format!("known: {}", e))? {
        return Ok(());
    }

    Ok(())
}

Other cases

Rust Version

rustc 1.92.0 (ded5c06cf 2025-12-08)
binary: rustc
commit-hash: ded5c06cf21d2b93bffd5d884aa6e96934ee4234
commit-date: 2025-12-08
host: x86_64-unknown-linux-gnu
release: 1.92.0
LLVM version: 21.1.3

Anything else?

No response

Reproduce the reported diagnostics from the Rust example in lib.rs, then compare them with the simplified equivalent in a.rs. Trace why the compiler selects E0596 instead of the more specific E0599 diagnostic and identify the relevant diagnostic behavior. The work is done when the original example produces the expected method-resolution explanation without regressing the simpler case.