slint-ui/slint · error

repeated item_tree must have a parent

Error message

repeated item_tree must have a parent

What it means

After resolving the parent chain for a repeated item's model two-way binding, the final parent is required to exist so its `repeater_index` can be read. A missing parent means the repeated item_tree was compiled without a parent link it was expected to have.

Solutions

1. Check that the `for` loop with the two-way model binding lives inside a sub-component with a parent chain
2. Ensure the item_tree lowering preserves parent links for repeated roots
3. File a compiler bug with a minimal .slint repro if the code is valid

Example fix

// .slint — before
component Root { for x in model: Rect { property <int> i <=> model.data; } }
// after
wrap the repeated element in a sub-component so a parent chain exists for the binding

if ctx.current_scope_parent().is_none() { return Err("two-way model binding requires an enclosing sub-component"); }

When it happens

Trigger: A `for` loop body at the root level (or with an unpreserved parent chain) declares a two-way model binding that requires a parent sub-component context that does not exist.

Common situations: Using model two-way bindings inside top-level repeats without the enclosing sub-component structure the lowering expects; compiler regressions in item_tree parent tracking.

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

• parent_level should be valid
• repeated parent has a repeater_index
• a setter belongs to a field
• an identifier
• default value requested for unknown struct field

AI-assisted analysis of slint-ui/slint@3a7e700487 (2026-09-16). Data as JSON: /api/errors/4478b1b636d26b30. Report an issue: GitHub.

Appendix: source

Thrown at internal/compiler/llr/item_tree.rs:338

        ctx: &EvaluationContext<'a, T>,
    ) -> Option<ResolvedModelTwoWayBinding<'a>> {
        let index_prop = self.is_model?;
        let MemberReference::Relative { parent_level, local_reference } = &self.prop2 else {
            unreachable!("model two-way binding's prop2 is always a Relative reference")
        };
        debug_assert!(local_reference.sub_component_path.is_empty());
        let LocalMemberIndex::Property(data_prop) = local_reference.reference else {
            unreachable!("model two-way binding's prop2 always references a property")
        };
        let super::EvaluationScope::SubComponent(mut sc, mut par) = ctx.current_scope else {
            unreachable!("model two-way binding cannot be in a global")
        };
        for _ in 0..*parent_level {
            let x = par.expect("parent_level should be valid");
            par = x.parent;
            sc = x.sub_component;
        }
        let par = par.expect("repeated item_tree must have a parent");
        let data_prop_ty = &ctx.compilation_unit.sub_components[sc].properties[data_prop].ty;
        Some(ResolvedModelTwoWayBinding {
            parent_level: *parent_level,
            body_sub_component: sc,
            data_prop,
            data_prop_ty,
            index_prop,
            parent_sub_component: par.sub_component,
            repeater_index: par.repeater_index.expect("repeated parent has a repeater_index"),
        })
    }
}

#[derive(Debug, Default, Clone)]
pub struct Property {
    pub name: SmolStr,
    pub ty: Type,
    /// The amount of time this property is used of another property

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