zed-industries/zed · error

shared scroll anchor references a non native display map, bu

Error message

shared scroll anchor references a non native display map, but snapshot has no companion

What it means

A state-mismatch guard in SharedScrollAnchor::scroll_position: in the split diff view both sides share one anchor plus the display-map id it was written from. Resolving the scroll position for a non-native snapshot requires translating through that snapshot's companion map; the expect fires when the anchor references a non-native display map but the provided snapshot has no companion — i.e. the anchor's display_map_id and the snapshot's map identity disagree, so there is no valid translation path.

Source

Thrown at crates/editor/src/scroll.rs:82

/// In the split diff view, the two sides share a ScrollAnchor using this struct.
/// Either side can set a ScrollAnchor that points to its own multibuffer, and we store the ID of the display map
/// that the last-written anchor came from so that we know how to resolve it to a DisplayPoint.
///
/// For normal editors, this just acts as a wrapper around a ScrollAnchor.
#[derive(Clone, Copy, Debug)]
pub struct SharedScrollAnchor {
    pub scroll_anchor: ScrollAnchor,
    pub display_map_id: Option<EntityId>,
}

impl SharedScrollAnchor {
    pub fn scroll_position(&self, snapshot: &DisplaySnapshot) -> gpui::Point<ScrollOffset> {
        let snapshot = if let Some(display_map_id) = self.display_map_id
            && display_map_id != snapshot.display_map_id
        {
            let companion_snapshot = snapshot
                .companion_snapshot()
                .expect("shared scroll anchor references a non native display map, but snapshot has no companion");
            assert_eq!(
                companion_snapshot.display_map_id, display_map_id,
                "shared scroll anchor display map should match the snapshot's split companion"
            );
            companion_snapshot
        } else {
            snapshot
        };

        self.scroll_anchor.scroll_position(snapshot)
    }

    pub fn scroll_top_display_point(&self, snapshot: &DisplaySnapshot) -> DisplayPoint {
        let snapshot = if let Some(display_map_id) = self.display_map_id
            && display_map_id != snapshot.display_map_id
        {
            let companion_snapshot = snapshot
                .companion_snapshot()

View on GitHub (pinned to f4178619ac)

Solutions

1. Fall back to treating the anchor as native (or returning the snapshot's own scroll position) when no companion exists instead of panicking
2. Clear or re-baseline the shared anchor when either diff side is rebuilt or its map id changes
3. Add a debug assertion comparing display_map_id to snapshot ids before translation to catch divergence early

When it happens

Trigger: Thrown at crates/editor/src/scroll.rs:82 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of zed-industries/zed@f4178619ac (2026-08-20). Data as JSON: /api/errors/af635bd6c6e74f14. Report an issue: GitHub.