{"record":{"id":"fb0cfad8ac659079","repo":"diesel-rs/diesel","slug":"you-ve-reached-an-impossible-internal-state-if-yo","errorCode":null,"errorMessage":"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.","messagePattern":"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\\.","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"critical","filePath":"diesel/src/mysql_like/connection/stmt/iterator.rs","lineNumber":70,"sourceCode":"    }\n}\n\nimpl<DB: MysqlLikeBackend> Iterator for StatementIterator<'_, DB> {\n    type Item = QueryResult<MysqlRow<DB>>;\n\n    fn next(&mut self) -> Option<Self::Item> {\n        // check if we own the only instance of the bind buffer\n        // if that's the case we can reuse the underlying allocations\n        // if that's not the case, we need to copy the output bind buffers\n        // to somewhere else\n        let res = if let Some(binds) = Rc::get_mut(&mut self.last_row) {\n            if let PrivateMysqlRow::Direct(binds) = RefCell::get_mut(binds) {\n                self.stmt.populate_row_buffers(binds)\n            } else {\n                // any other state than `PrivateMysqlRow::Direct` is invalid here\n                // and should not happen. If this ever happens this is a logic error\n                // in the code above\n                unreachable!(\n                    \"You've reached an impossible internal state. \\\n                     If you ever see this error message please open \\\n                     an issue at https://github.com/diesel-rs/diesel \\\n                     providing example code how to trigger this error.\"\n                )\n            }\n        } else {\n            // The shared bind buffer is in use by someone else,\n            // this means we copy out the values and replace the used reference\n            // by the copied values. After this we can advance the statement\n            // another step\n            let mut last_row = {\n                let mut last_row = match self.last_row.try_borrow_mut() {\n                    Ok(o) => o,\n                    Err(_e) => {\n                        return Some(Err(DeserializationError(\n                            \"Failed to reborrow row. Try to release any `MysqlField` or `MysqlValue` \\\n                             that exists at this point\"","sourceCodeStart":52,"sourceCodeEnd":88,"githubUrl":"https://github.com/diesel-rs/diesel/blob/6fa6ed01b24b24248ab2a611698d0a7c6a2e9120/diesel/src/mysql_like/connection/stmt/iterator.rs#L52-L88","documentation":"An internal `unreachable!` in the MySQL/MariaDB statement iterator (`Iterator::next`). While fetching rows, the iterator's pending binds are expected to be in the `PrivateMysqlRow::Direct` state; any other state means diesel's internal state machine got corrupted. This is a diesel bug, not a user error — the message asks for a bug report.","triggerScenarios":"Calling `next()` on a `MysqlConnection` query iterator while internal row buffers were left in a non-`Direct` state — caused by internal logic bugs around `populate_row_buffers`, interleaved statement use, or concurrent use of the same connection mid-fetch.","commonSituations":"Sharing a `MysqlConnection` across threads without pooling; using the connection for another query while a previous result set was only partially consumed; diesel version regressions on MariaDB/mysqlclient; unsafe misuse via `with_raw_connection`-style APIs.","solutions":["Ensure the previous query's rows are fully consumed or the iterator is dropped before reusing the connection.","Do not share one connection across threads; use a pool (r2d2/deadpool-diesel) or `Pool`-managed connections.","Upgrade diesel to the latest patch release — this is an internal invariant the maintainers may have fixed.","Reproduce with a minimal example and open an issue at https://github.com/diesel-rs/diesel as the message requests."],"exampleFix":null,"handlingStrategy":"try-catch","validationCode":null,"typeGuard":null,"tryCatchPattern":"// panics are not catchable normally; guard by never sharing a connection mid-fetch\nlet rows = users.load::<User>(&mut conn).expect(\"query failed\"); // fully consume before reusing conn\n// if catching panics is essential:\nlet result = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| users.load::<User>(&mut conn)));","preventionTips":["Never share one MysqlConnection across threads; use a pool.","Fully consume or drop result iterators before the next query.","Keep diesel updated and read changelogs for iterator fixes."],"tags":["mysql","internal-bug","iterator","unreachable"],"backgroundTag":"internal-invariant-violation","analyzedSha":"6fa6ed01b24b24248ab2a611698d0a7c6a2e9120","analyzedAt":"2026-09-07T01:50:13.074Z","contentChangedAt":"2026-09-07T01:50:13.074Z","schemaVersion":2},"datasetVersion":"2026-09-16T09:17:16.951Z"}