a-b-street/abstreet · error

doesn't touch

Error message

{} doesn't touch {}

What it means

other_endpt is called with an IntersectionID that is neither this road's src_i nor dst_i, so the road has no 'other' endpoint to return. The caller assumed the road touches the given intersection, but it doesn't — usually a mixup of road/intersection IDs or a caller that skipped checking road.endpoints().

Solutions

1. Check src_i == i || dst_i == i before the call, or obtain the intersection from road.src_i/dst_i directly.
2. Use the road's own endpoint fields instead of a separately tracked intersection ID.
3. Avoid persisting map-local IDs across reloads; look them up fresh.

Example fix

// before
let other = road.other_endpt(i);
// after
let other = if road.src_i == i { road.dst_i } else if road.dst_i == i { road.src_i } else { anyhow::bail!("{} not endpoint of {}", i, road.id) };

fn other_endpt_safe(road: &Road, i: IntersectionID) -> Option<IntersectionID> {
    if road.src_i == i { Some(road.dst_i) }
    else if road.dst_i == i { Some(road.src_i) }
    else { None }
}

When it happens

Trigger: Calling road.other_endpt(i) with an intersection not equal to src_i or dst_i — often from iterating intersections adjacent to a node and confusing road/intersection pairs, or stale IDs after regeneration.

Common situations: Graph traversal code building turns or shortest paths; manual construction of movement data; IDs carried across map reloads.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• doesn't contain
• doesn't point to
• doesn't have an endpoint at
• isn't an endpoint of
• must_get_sidewalk broken by

AI-assisted analysis of a-b-street/abstreet@0964f29315 (2026-09-13). Data as JSON: /api/errors/a9b0281cd39f0b3f. Report an issue: GitHub.

Appendix: source

Thrown at map_model/src/objects/road.rs:490

pub fn other_endpt(&self, i: IntersectionID) -> IntersectionID {
    if self.src_i == i {
        self.dst_i
    } else if self.dst_i == i {
        self.src_i
    } else {
        panic!("{} doesn't touch {}", self.id, i);
    }
}

View on GitHub (pinned to 0964f29315)