BoundaryML/baml · critical · anyhow::Error

This should never happen - Please report this error to our…

Error message

This should never happen - Please report this error to our team with BAML_LOG=info enabled so we can improve this error message

What it means

result_with_constraints_content reaches its final branch when the LLMResponse is Success — meaning a parsed result exists yet the code path expected a failure. This is unreachable by construction and signals a BAML runtime invariant violation; the message asks users to report it with BAML_LOG=info.

Solutions

1. Update the BAML runtime and generated clients to matching, current versions.
2. Re-run with BAML_LOG=info and file a bug report with the trace, as instructed by the message.
3. Catch the error at the boundary and retry, since the state is transient to that chain instance.

match chain.content() {
    Ok(v) => Ok(v),
    Err(e) if e.to_string().contains("This should never happen") => {
        report_bug_with_baml_log(&e);
        retry_or_default()
    }
    Err(e) => Err(e),
}

When it happens

Trigger: result_with_constraints() returned None (no parsed result slot) while llm_response() is LLMResponse::Success — an internally inconsistent ResponseChain state.

Common situations: BAML runtime bugs where the success result was not stored into the chain; partially-constructed or deserialized response chains; version mismatch between runtime and bindings.

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

• ======================================== BAML Internal…
• Internal error
• internal error
• internal error: cannot convert value
• internal error: cannot convert value

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/6cae5cf2afabd572. Report an issue: GitHub.

Appendix: source

Thrown at engine/baml-runtime/src/types/response.rs:161

                                    detailed_message: err.message.clone(),
                                    raw_response: err.raw_response.clone(),
                                }
                            )),
                        }
                    }
                    LLMResponse::UserFailure(message) => {
                        Err(anyhow::anyhow!("User Failure: {message}.\nPlease report this error to our team with BAML_LOG=info enabled so we can catch this error earlier and improve your development experience."))
                    }
                    LLMResponse::InternalFailure(message) => {
                        Err(anyhow::anyhow!("Internal Failure: {message}.\nThis should not happen - please report this error to our team with BAML_LOG=info enabled so we can catch this error earlier and improve your development experience."))
                    }
                    LLMResponse::Cancelled(message) => {
                        Err(anyhow::anyhow!(crate::errors::ExposedError::AbortError {
                            detailed_message: message.clone(),
                        }))
                    }
                    LLMResponse::Success(_) => {
                        Err(anyhow::anyhow!("This should never happen - Please report this error to our team with BAML_LOG=info enabled so we can improve this error message"))
                    }
                };
        };

        result
    }

    fn format_last_error_with_details(&self, last_error: &anyhow::Error) -> ExposedError {
        let detailed_message = self.create_detailed_message();

        if let Some(exposed_error) = last_error.downcast_ref::<ExposedError>() {
            return self.add_detailed_message_to_exposed(exposed_error.clone(), detailed_message);
        }

        self.add_detailed_message_to_exposed(self.format_single_error(last_error), detailed_message)
    }

    fn format_single_error(&self, err: &anyhow::Error) -> ExposedError {

View on GitHub (pinned to bd85ce9dee)