diesel-rs/diesel · critical

You've reached an impossible internal state. If you ever…

Error message

You've reached an impossible internal state. If you ever see this error message please open an issue at https://github.com/diesel-rs/diesel providing example code how to trigger this error.

What it means

An internal `unreachable!` in the SQLite statement iterator's duplicated-row handling (`handle_duplicated_row_case`). The pending row must be `PrivateSqliteRow::Direct`; any other variant means diesel's internal state machine was corrupted. A diesel bug, not user error.

Solutions

1. Upgrade diesel to the latest release and retest.
2. Do not run another query while a previous SQLite result iterator is only partially consumed.
3. Avoid sharing a single SqliteConnection across threads; pool connections instead.
4. Reproduce minimally and open an issue at https://github.com/diesel-rs/diesel.

let rows = users.load::<User>(&mut conn).expect("query failed"); // consume fully
let result = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| users.load::<User>(&mut conn))); // last-resort guard

When it happens

Trigger: Iterating SQLite query results when `handle_duplicated_row_case` encounters a non-`Direct` `PrivateSqliteRow` state — internal logic error around row buffering or duplicated-row (statement re-run) handling.

Common situations: Concurrent/partially-drained iterators on one `SqliteConnection`; diesel version regressions; misuse of low-level connection APIs that interleave statement execution.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• You've reached an impossible internal state. If you ever…
• Sqlite's documentation state that this case
• Error closing SQLite connection
• Error closing SQLite blob
• out of range integral type conversion attempted

AI-assisted analysis of diesel-rs/diesel@6fa6ed01b2 (2026-09-07). Data as JSON: /api/errors/74ea5f8930eab6bb. Report an issue: GitHub.

Appendix: source

Thrown at diesel/src/sqlite/connection/statement_iterator.rs:68

                // performed one step. For the first step we would have
                // used `PrivateStatementIterator::NotStarted` where we don't
                // have access to `PrivateSqliteRow` at all
                stmt.step(false)
            };
            *outer_last_row = Rc::new(RefCell::new(PrivateSqliteRow::Direct(stmt)));
            match res {
                Err(e) => Some(Err(e)),
                Ok(false) => None,
                Ok(true) => Some(Ok(SqliteRow {
                    inner: Rc::clone(outer_last_row),
                    field_count,
                })),
            }
        } else {
            // any other state than `PrivateSqliteRow::Direct` is invalid here
            // and should not happen. If this ever happens this is a logic error
            // in the code above
            unreachable!(
                "You've reached an impossible internal state. \
                             If you ever see this error message please open \
                             an issue at https://github.com/diesel-rs/diesel \
                             providing example code how to trigger this error."
            )
        }
    }
}

enum PrivateStatementIterator<'stmt, 'query> {
    NotStarted(Option<StatementUse<'stmt, 'query>>),
    Started(Rc<RefCell<PrivateSqliteRow<'stmt, 'query>>>),
}

impl<'stmt, 'query> StatementIterator<'stmt, 'query> {
    pub fn new(stmt: StatementUse<'stmt, 'query>) -> StatementIterator<'stmt, 'query> {
        Self {
            inner: PrivateStatementIterator::NotStarted(Some(stmt)),

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