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fix: nested untagged alternation containing tagged alternation #271

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Merged
zharinov merged 1 commit into from
Jan 5, 2026
Merged

fix: nested untagged alternation containing tagged alternation #271

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9 changes: 8 additions & 1 deletion crates/plotnik-lib/src/compile/sequences.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -195,7 +195,14 @@ impl Compiler<'_> {
.get_term_info(&alt_expr)
.and_then(|info| info.flow.type_id());
let alt_type_shape = alt_type_id.and_then(|id| self.type_ctx.get_type(id));
let is_enum = alt_type_shape.is_some_and(|shape| matches!(shape, TypeShape::Enum(_)));

// Check if THIS alternation is syntactically tagged (all branches have labels).
// This is distinct from whether the type is an Enum - a nested untagged alternation
// like `[[A: (x)]]` can inherit an enum type from its inner branch while the outer
// branches have no labels.
let is_tagged_alt = branches.iter().all(|b| b.label().is_some());
let is_enum = is_tagged_alt
&& alt_type_shape.is_some_and(|shape| matches!(shape, TypeShape::Enum(_)));

// For tagged alternations: build map from label Symbol to (member index, payload TypeId)
// This ensures we use the correct BTreeMap order indices, not AST iteration order
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