{"record":{"id":"f2af6349fec2869e","repo":"aaif-goose/goose","slug":"cannot-determine-the-role-of-an-empty-conversation","errorCode":null,"errorMessage":"cannot determine the role of an empty conversation","messagePattern":"cannot determine the role of an empty conversation","errorType":"exception","errorClass":"anyhow::Error","httpStatus":null,"severity":"error","filePath":"crates/goose-agent/src/operation.rs","lineNumber":41,"sourceCode":"        .iter()\n        .rposition(|message| {\n            message.role == rmcp::model::Role::User\n                && message.is_user_visible()\n                && !message.is_tool_response()\n        })\n        .ok_or_else(|| anyhow!(\"state machine conversation has no kickoff message\"))?;\n    Ok(&messages[start..])\n}\n\npub fn trailing_error(conversation: &Conversation) -> Option<MessageErrorKind> {\n    conversation.last().and_then(Message::error_kind)\n}\n\npub fn last_effective_role(messages: &[Message]) -> Result<EffectiveRole> {\n    messages\n        .last()\n        .map(effective_role)\n        .ok_or_else(|| anyhow!(\"cannot determine the role of an empty conversation\"))\n}\n\npub fn assistant_turn_count(messages: &[Message]) -> u32 {\n    let mut turns = 0;\n    let mut in_assistant_block = false;\n    for message in messages.iter().rev() {\n        if message.role == rmcp::model::Role::Assistant {\n            if !in_assistant_block {\n                turns += 1;\n                in_assistant_block = true;\n            }\n        } else {\n            in_assistant_block = false;\n        }\n    }\n    turns\n}\n","sourceCodeStart":23,"sourceCodeEnd":59,"githubUrl":"https://github.com/aaif-goose/goose/blob/3810898a7447ec3299be72e223d3570a7aabf0ab/crates/goose-agent/src/operation.rs#L23-L59","documentation":"anyhow error from last_effective_role (crates/goose-agent/src/operation.rs) when the messages slice it inspects is empty. The function decides the next actor by looking at the last message's effective role; with zero messages there is no basis for a decision.","triggerScenarios":"Calling last_effective_role on an empty slice — typically messages_since_kickoff-style slices that came back empty (e.g. right after cleanup, or a session whose messages were all filtered out), or a freshly built Conversation with nothing pushed yet.","commonSituations":"First iteration of a machine loop before any message is appended; tests passing empty vecs; context-management trimming everything; deserialization producing an empty message list.","solutions":["Guard the call site: skip or handle the empty case before computing the effective role","Ensure the conversation has at least one message (kickoff user message) before entering logic that calls last_effective_role","When trimming, never trim to zero — retain the kickoff message","In tests, seed the slice with a message or assert the error deliberately"],"exampleFix":"// before\nlet role = last_effective_role(&messages)?;\n\n// after\nlet role = match messages.last() {\n    Some(_) => last_effective_role(&messages)?,\n    None => EffectiveRole::User, // empty conversation: next speaker is the user side\n};","handlingStrategy":"type-guard","validationCode":"if messages.is_empty() { /* choose default role or skip */ }","typeGuard":"fn non_empty_messages(messages: &[Message]) -> bool {\n    !messages.is_empty()\n}","tryCatchPattern":"let role = if messages.is_empty() {\n    EffectiveRole::User // empty conversation defaults to user's turn\n} else {\n    last_effective_role(messages)?\n};","preventionTips":["Check emptiness before role-dependent logic","Never trim a conversation to zero messages","Seed new conversations with the kickoff message"],"tags":["rust","state-machine","conversation","empty-state"],"backgroundTag":null,"analyzedSha":"3810898a7447ec3299be72e223d3570a7aabf0ab","analyzedAt":"2026-08-16T10:14:26.282Z","schemaVersion":2},"datasetVersion":"2026-08-16T13:17:31.715Z"}