What causes "{:?} didn't map to exactly 1 crossing turn: {:?}" in a-b-street/abstreet?

Recreate the crosswalk edit on the current map so the movement maps to a single turn.

didn't map to exactly 1 crossing turn

Error message

{:?} didn't map to exactly 1 crossing turn: {:?}

What it means

When converting an edited crosswalk movement into a turn for a permanent edit, the library expects exactly one turn at the intersection matching the movement. Zero or multiple matching turns indicate the intersection's turn topology doesn't correspond to the edited crosswalk, so the mapping is ambiguous and the edit is rejected.

Solutions

Recreate the crosswalk edit on the current map so the movement maps to a single turn.
Check the intersection's current turns (map.get_i(i).turns) and confirm the edited movement still exists exactly once.
Remove the stale crosswalk from the edit if the intersection topology changed permanently.

Example fix

// before
bail!("{:?} didn't map to exactly 1 crossing turn: {:?}", movement, turn_ids);
// after: filter only crossing movements that exist
if turn_ids.len() == 1 {
    crosswalks.insert(turn_ids.pop().unwrap(), turn_type);
}

Defensive patterns

Strategy: validation

Validate before calling

let matching: Vec<_> = map.get_i(i).turns.iter()
    .filter(|t| t.id.to_movement(&map) == Some(movement))
    .collect();
if matching.len() != 1 { /* recreate the crosswalk edit */ }

Try / catch

match edits.to_permanent(&mut map) {
    Err(e) if e.to_string().contains("crossing turn") => recreate_crosswalk_edits(&map)?,
    other => other?,
}

Prevention

Apply crosswalk edits only to the map version they were created against
Re-verify crosswalks after any edit that changes intersection turns
Prefer recording crosswalk edits from the live UI rather than editing JSON by hand

When it happens

Trigger: with_permanent on an edit containing crosswalks (EditIntersectionControl) whose movement matches 0 or >1 turns in map.get_i(i).turns — e.g. after permanent edits changed the intersection's turns, or movements that aren't crossing movements.

Common situations: Applying crosswalk edits to a map where the intersection was rebuilt (turns changed); edits created from a different map version; complex intersections where a movement matches multiple turns after topology edits.

Understand the failure class

Background: "Not found" and "does not exist" errors: why "Task not found", "No such folder", and "Can't find" fire when a lookup comes back empty — this error's family across 14 libraries.

Related errors

AI-assisted analysis of a-b-street/abstreet@0964f29315 (2026-09-13). Data as JSON: /api/errors/713cd560fb61877c. Report an issue: GitHub.

Appendix: source

Thrown at map_model/src/edits/perma.rs:303

            }
            PermanentEditIntersectionControl::TrafficSignal(ts) => {
                EditIntersectionControl::TrafficSignal(ts)
            }
            PermanentEditIntersectionControl::Closed => EditIntersectionControl::Closed,
        };

        let mut crosswalks = BTreeMap::new();
        for (id, turn_type) in self.crosswalks {
            let movement = MovementID::from_permanent(id, map)?;
            // Find all TurnIDs that map to this MovementID
            let mut turn_ids = Vec::new();
            for turn in &map.get_i(i).turns {
                if turn.id.to_movement(map) == movement {
                    turn_ids.push(turn.id);
                }
            }
            if turn_ids.len() != 1 {
                bail!(
                    "{:?} didn't map to exactly 1 crossing turn: {:?}",
                    movement,
                    turn_ids
                );
            }
            crosswalks.insert(turn_ids.pop().unwrap(), turn_type);
        }

        Ok(EditIntersection {
            control,
            // TODO Express as GeoJSON
            modal_filter: self.modal_filter.clone(),
            crosswalks,
        })
    }
}

View on GitHub (pinned to 0964f29315)