astral-sh/ruff · error

extra use-def data should have been retained

Error message

extra use-def data should have been retained

What it means

UseDefMap stores rarely used tables (bindings-by-use, member place states, enclosing snapshots, loop headers) in an optional extra box that is only allocated when at least one of those collections is non-empty when the map finishes building (use_def.rs:2925-2937). extra() panics when an accessor that reads those tables (loop_header, member end-of-scope queries, bindings-by-use lookups) is called on a map built with extra == None.

Solutions

1. Re-derive LoopHeaderId/ScopedPlaceId/use IDs from the current semantic model instead of caching them across revisions, so IDs and the map they index come from the same snapshot
2. Guard the query: only call extra-backed accessors for constructs that exist in this file's current semantic index (e.g., only for loops actually present)
3. If the ID provably came from the same map, capture the backtrace and file a ty issue: the map handed out an ID whose backing table it did not retain

// Re-derive IDs from the current snapshot instead of caching them:
let index = semantic_index(db, file); // current revision
let loop_id = index.loop_header(loop_node); // matches this UseDefMap
let header = use_def_map.loop_header(loop_id);

When it happens

Trigger: Calling UseDefMap::loop_header(LoopHeaderId), end_of_scope_declarations on a member place, or a bindings-by-use lookup on a map whose four extra collections were all empty at finish time. In practice this means the ID being looked up came from a different or stale use-def map revision, or a builder path recorded IDs but dropped their table.

Common situations: Editor/LSP flows where a cached LoopHeaderId or ScopedPlaceId outlives the Salsa revision that produced it after an edit; new query code that assumes a table always exists without checking that the module contains loops, member places, or multi-bindings.

Related errors

• binding definition should have retained declarations
• Expected live-declarations length to fit into a u32
• accumulator should not be empty
• anchor should not be NodeIndex::NONE
• argument index should be valid

AI-assisted analysis of astral-sh/ruff@5bb508f594 (2026-08-20). Data as JSON: /api/errors/d6bc26410d8ea977. Report an issue: GitHub.

Appendix: source

Thrown at crates/ty_python_core/src/use_def.rs:903

    }

    fn intern_table<T: Eq + std::hash::Hash>(
        values: &mut FxHashSet<Arc<T>>,
        value: Arc<T>,
    ) -> Arc<T> {
        if let Some(existing) = values.get(value.as_ref()) {
            Arc::clone(existing)
        } else {
            values.insert(Arc::clone(&value));
            value
        }
    }
}

/// Information about a given range of source code.
#[derive(Debug, Copy, Clone, PartialEq, Eq, get_size2::GetSize)]
struct RangeInfo {
    reachability: ScopedReachabilityConstraintId,
    in_type_checking_block: bool,
}

impl Default for RangeInfo {
    fn default() -> Self {
        Self {
            reachability: ScopedReachabilityConstraintId::ALWAYS_TRUE,
            in_type_checking_block: false,
        }
    }
}

#[derive(Debug, PartialEq, Eq, get_size2::GetSize)]
struct MultiBindingsByUse(ThinVec<(ScopedUseId, Box<[Bindings]>)>);

impl MultiBindingsByUse {
    fn from_map(map: FxHashMap<ScopedUseId, Vec<Bindings>>) -> Self {
        let mut entries = ThinVec::with_capacity(map.len());

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