iced-rs/iced · error

Node configuration and count do not match

Error message

Node configuration and count do not match

What it means

`Node::compute_regions` walks a pane_grid `Node` tree alongside a parallel `Count` tree and reaches a shape pair (node kind, count kind) that cannot correspond — e.g. a `Node::Split` paired with `Count::Pane`, or a `Node::Pane` paired with `Count::Split`. This indicates the count structure was computed from a different tree than the node tree, so the library calls `unreachable!`.

Source

Thrown at widget/src/pane_grid/node.rs:292

                    Axis::Vertical => (count_a.vertical(), count_b.vertical()),
                };

                let (region_a, region_b, _ratio) = axis.split(
                    current,
                    *ratio,
                    spacing,
                    min_size * (a_factor + 1) as f32 + spacing * a_factor as f32,
                    min_size * (b_factor + 1) as f32 + spacing * b_factor as f32,
                );

                a.compute_regions(spacing, min_size, &region_a, count_a, regions);
                b.compute_regions(spacing, min_size, &region_b, count_b, regions);
            }
            (Node::Pane(pane), Count::Pane) => {
                let _ = regions.insert(*pane, *current);
            }
            _ => {
                unreachable!("Node configuration and count do not match")
            }
        }
    }

    fn compute_splits(
        &self,
        spacing: f32,
        min_size: f32,
        current: &Rectangle,
        count: &Count,
        splits: &mut BTreeMap<Split, (Axis, Rectangle, f32)>,
    ) {
        match (self, count) {
            (
                Node::Split {
                    axis,
                    ratio,
                    a,

View on GitHub (pinned to d146509d89)

Solutions

1. Regenerate the `Count` tree from the same `PaneGridState`/node snapshot used for region computation so both structures match.
2. If layout is persisted, save node and count together atomically and validate on load (recompute counts by walking the node tree).
3. Check that split/close operations update the cached count structure in the same update cycle as the node mutation.
4. Report if triggered by ordinary `PaneGrid` usage — it indicates an internal desync bug.

Example fix

// before
counts = old_snapshot.counts(); // stale
regions = node.compute_regions(..., counts, ...);
// after
counts = state.counts(); // derived from the same PaneGridState as `node`
regions = node.compute_regions(..., counts, ...);

// Re-derive counts from the same node snapshot before layout
fn counts_match(node: &Node, count: &Count) -> bool {
    match (node, count) {
        (Node::Split { a, b }, Count::Split { a: ca, b: cb }) => {
            counts_match(a, ca) && counts_match(b, cb)
        }
        (Node::Pane(_), Count::Pane) => true,
        _ => false,
    }
}

fn is_consistent(node: &Node, count: &Count) -> bool {
    matches!(
        (node, count),
        (Node::Split { .. }, Count::Split { .. }) | (Node::Pane(_), Count::Pane)
    )
}

// unreachable! panics; validate before calling pane_regions
if !is_consistent(&node, &count) { return Err("node/count desync"); }
let regions = node.compute_regions(...);

When it happens

Trigger: Calling `pane_regions`/`PaneGrid::layout` where the `Count` snapshot and the `Node` tree were produced at different times — e.g. a pane was split/removed after the count was derived, or application code deserialized/constructed a mismatched node/count pair.

Common situations: Custom pane_grid state restoration (saving/loading layouts) where counts and nodes drift out of sync; racing state updates that split a pane while regions are computed; hand-built `Node` values in tests or custom widgets.

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

• Node configuration and split count do not match
• Caches must not be empty
• Downcast widget state
• Downcast on stateless state
• {error:?}

AI-assisted analysis of iced-rs/iced@d146509d89 (2026-09-11). Data as JSON: /api/errors/dcf6c578e7a813e9. Report an issue: GitHub.