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fix: type verification panic for uncaptured recursive tagged alternations #280

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Merged
zharinov merged 1 commit into from
Jan 6, 2026
Merged

fix: type verification panic for uncaptured recursive tagged alternations #280

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30 changes: 24 additions & 6 deletions crates/plotnik-lib/src/analyze/type_check/infer.rs
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Expand Up @@ -135,22 +135,40 @@ impl<'a, 'd> InferenceVisitor<'a, 'd> {
let name = name_tok.text();
let name_sym = self.interner.intern(name);

// Recursive refs are opaque boundaries - they match but don't bubble captures.
// The Ref type is created when a recursive ref is captured (in infer_captured_expr).
let Some(body) = self.symbol_table.get(name) else {
return TermInfo::void();
};

// Recursive refs are opaque boundaries - they don't bubble captures.
// For tagged alternations, return Scalar(Ref) since they always produce Enum output.
// For other definitions, return Void to avoid type errors in untagged alternation contexts.
if let Some(def_id) = self.ctx.get_def_id_sym(name_sym)
&& self.ctx.is_recursive(def_id)
{
if self.body_produces_enum(body) {
let ref_type = self.ctx.intern_type(TypeShape::Ref(def_id));
return TermInfo::new(Arity::One, TypeFlow::Scalar(ref_type));
}
return TermInfo::new(Arity::One, TypeFlow::Void);
}

let Some(body) = self.symbol_table.get(name) else {
return TermInfo::void();
};

// Non-recursive refs are transparent
self.infer_expr(body)
}

/// Check if an expression body will produce an Enum type (Scalar flow).
///
/// This is a syntactic check for tagged alternations at the root of a definition.
/// Tagged alternations always produce Enum types, making them safe to reference
/// as Scalar(Ref) in uncaptured contexts.
fn body_produces_enum(&self, body: &Expr) -> bool {
if let Expr::AltExpr(alt) = body {
matches!(alt.kind(), AltKind::Tagged | AltKind::Mixed)
} else {
false
}
}

/// Sequence: Arity aggregation, strict field merging, and output propagation.
fn infer_seq_expr(&mut self, seq: &SeqExpr) -> TermInfo {
let children: Vec<_> = seq.children().collect();
Expand Down
36 changes: 36 additions & 0 deletions crates/plotnik-lib/src/analyze/type_check/tests.rs
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Expand Up @@ -734,6 +734,42 @@ fn recursive_type_in_quantified_context() {
");
}

#[test]
fn recursive_type_uncaptured_propagates() {
// Regression test: Q = (Rec) should inherit Rec's enum type, not infer as void.
// The recursive definition Rec is a tagged alternation, so its type propagates
// through the uncaptured reference.
let input = indoc! {r#"
Rec = [A: (program (expression_statement (Rec) @inner)) B: (identifier) @id]
Q = (Rec)
"#};

let res = Query::expect_valid_types(input);

// Q should have type Rec (aliased to the enum)
insta::assert_snapshot!(res, @r#"
export interface Node {
kind: string;
text: string;
span: [number, number];
}

export interface RecA {
$tag: "A";
$data: { inner: Rec };
}

export interface RecB {
$tag: "B";
$data: { id: Node };
}

export type Rec = RecA | RecB;

export type Q = Rec;
"#);
}

#[test]
fn scalar_propagates_through_named_node() {
let input = indoc! {r#"
Expand Down
33 changes: 25 additions & 8 deletions crates/plotnik-lib/src/compile/expressions.rs
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Expand Up @@ -85,8 +85,10 @@ impl Compiler<'_> {
.and_then(|i| i.as_expr())
.is_some_and(is_skippable_quantifier);

// With items: nav → items → Up → exit
// With items: nav → items → Up → [post_effects] → exit
// If first item is skippable: skip path → exit (bypass Up), match path → Up → exit
let final_exit = self.emit_post_effects_exit(exit, capture.post);

let up_label = self.fresh_label();
let skip_exit = first_is_skippable.then_some(exit);
let items_entry = self.compile_seq_items_inner(
Expand All @@ -106,18 +108,18 @@ impl Compiler<'_> {
pre_effects: vec![],
neg_fields: vec![],
post_effects: vec![],
successors: vec![exit],
successors: vec![final_exit],
}));

// Emit entry instruction into the node (capture effects go here at match time)
// Emit entry instruction into the node (only pre_effects here)
self.instructions.push(Instruction::Match(MatchIR {
label: entry,
nav,
node_type,
node_field: None,
pre_effects: capture.pre,
neg_fields,
post_effects: capture.post,
post_effects: vec![],
successors: vec![items_entry],
}));

Expand Down Expand Up @@ -151,7 +153,9 @@ impl Compiler<'_> {
up_nav: Nav,
capture: CaptureEffects,
) -> Label {
// up_check: Match(up_nav) → exit
let final_exit = self.emit_post_effects_exit(exit, capture.post);

// up_check: Match(up_nav) → final_exit
let up_check = self.fresh_label();
self.instructions.push(Instruction::Match(MatchIR {
label: up_check,
Expand All @@ -161,7 +165,7 @@ impl Compiler<'_> {
pre_effects: vec![],
neg_fields: vec![],
post_effects: vec![],
successors: vec![exit],
successors: vec![final_exit],
}));

// body: items with StayExact navigation → up_check
Expand Down Expand Up @@ -193,21 +197,34 @@ impl Compiler<'_> {
let down_wildcard = self.fresh_label();
self.emit_wildcard_nav(down_wildcard, Nav::Down, try_label);

// entry: match parent node → down_wildcard
// entry: match parent node → down_wildcard (only pre_effects here)
self.instructions.push(Instruction::Match(MatchIR {
label: entry,
nav,
node_type,
node_field: None,
pre_effects: capture.pre,
neg_fields,
post_effects: capture.post,
post_effects: vec![],
successors: vec![down_wildcard],
}));

entry
}

/// Emit post-effects on an epsilon step after the exit label.
///
/// Post-effects (like EndEnum) must execute AFTER children complete, not after
/// matching the parent node. This helper creates an epsilon step for the effects
/// when needed, or returns the original exit if no effects.
fn emit_post_effects_exit(&mut self, exit: Label, post: Vec<EffectIR>) -> Label {
if post.is_empty() {
exit
} else {
self.emit_effects_epsilon(exit, post, CaptureEffects::default())
}
}

/// Compile an anonymous node with capture effects.
pub(super) fn compile_anonymous_node_inner(
&mut self,
Expand Down
10 changes: 8 additions & 2 deletions crates/plotnik-lib/src/emit/mod.rs
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Expand Up @@ -458,7 +458,13 @@ impl TypeTableBuilder {
}

/// Resolve a query TypeId to bytecode QTypeId.
fn resolve_type(&self, type_id: TypeId, type_ctx: &TypeContext) -> Result<QTypeId, EmitError> {
///
/// Handles Ref types by following the reference chain to the actual type.
pub fn resolve_type(
&self,
type_id: TypeId,
type_ctx: &TypeContext,
) -> Result<QTypeId, EmitError> {
// Check if already mapped
if let Some(&bc_id) = self.mapping.get(&type_id) {
return Ok(bc_id);
Expand Down Expand Up @@ -804,7 +810,7 @@ fn emit_inner(
for (def_id, type_id) in type_ctx.iter_def_types() {
let name_sym = type_ctx.def_name_sym(def_id);
let name = strings.get_or_intern(name_sym, interner)?;
let result_type = types.get(type_id).expect("all def types should be mapped");
let result_type = types.resolve_type(type_id, type_ctx)?;

// Get actual target from compiled result
let target = compile_result
Expand Down
17 changes: 10 additions & 7 deletions ...tnik-lib/src/emit/snapshots/plotnik_lib__emit__codegen_tests__captures_deeply_nested.snap
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Expand Up @@ -48,11 +48,14 @@ _ObjWrap:

Test:
06 ε 07
07 ! (a) [Node Set(M0)] 09
09 ▽ (b) [Node Set(M1)] 11
11 ▽ (c) [Node Set(M2)] 13
13 ▽ (d) [Node Set(M3)] 15
07 ! (a) 08
08 ▽ (b) 09
09 ▽ (c) 10
10 ▽ (d) [Node Set(M3)] 12
12 △ 13
13 ε [Node Set(M2)] 15
15 △ 16
16 △ 17
17 △ 18
18 ▶
16 ε [Node Set(M1)] 18
18 △ 19
19 ε [Node Set(M0)] 21
21 ▶
12 changes: 7 additions & 5 deletions ...lotnik-lib/src/emit/snapshots/plotnik_lib__emit__codegen_tests__captures_nested_flat.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -42,9 +42,11 @@ _ObjWrap:

Test:
06 ε 07
07 ! (a) [Node Set(M0)] 09
09 ▽ (b) [Node Set(M1)] 11
11 ▽ (c) [Node Set(M2)] 13
13 △ 14
07 ! (a) 08
08 ▽ (b) 09
09 ▽ (c) [Node Set(M2)] 11
11 △ 12
12 ε [Node Set(M1)] 14
14 △ 15
15 ▶
15 ε [Node Set(M0)] 17
17 ▶
11 changes: 6 additions & 5 deletions ...es/plotnik-lib/src/emit/snapshots/plotnik_lib__emit__codegen_tests__recursion_simple.snap
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Expand Up @@ -56,11 +56,12 @@ _ObjWrap:

Expr:
06 ε 07
07 ε 13, 19
07 ε 13, 21
09 ε [Set(M2)] 11
11 △ 12
11 △ 16
12 ▶
13 ! [Enum(M3)] (number) [Text Set(M0) EndEnum] 12
16 ▷ arguments: (Expr) 06 : 09
17 ▽ function: (identifier) [Node Set(M1)] 16
19 ! [Enum(M4)] (call_expression) [EndEnum] 17
16 ε [EndEnum] 12
18 ▷ arguments: (Expr) 06 : 09
19 ▽ function: (identifier) [Node Set(M1)] 18
21 ! [Enum(M4)] (call_expression) 19
11 changes: 6 additions & 5 deletions ...rc/emit/snapshots/plotnik_lib__emit__codegen_tests__recursion_with_structured_result.snap
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Expand Up @@ -65,7 +65,7 @@ _ObjWrap:

Expr:
06 ε 07
07 ε 20, 26
07 ε 20, 28

Test:
09 ε 10
Expand All @@ -75,9 +75,10 @@ Test:
14 △ 15
15 ▶
16 ε [Set(M2)] 18
18 △ 19
18 △ 23
19 ▶
20 ! [Enum(M3)] (number) [Text Set(M0) EndEnum] 19
23 ▷ arguments: (Expr) 06 : 16
24 ▽ function: (identifier) [Node Set(M1)] 23
26 ! [Enum(M4)] (call_expression) [EndEnum] 24
23 ε [EndEnum] 19
25 ▷ arguments: (Expr) 06 : 16
26 ▽ function: (identifier) [Node Set(M1)] 25
28 ! [Enum(M4)] (call_expression) 26
24 changes: 12 additions & 12 deletions ...-lib/src/engine/snapshots/plotnik_lib__engine__engine_tests__quantifier_struct_array.snap
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Expand Up @@ -8,16 +8,16 @@ let a, b, c
{
"decls": [
{
"decl": {
"kind": "variable_declarator",
"name": {
"kind": "identifier",
"text": "a",
"span": [
4,
5
]
},
"name": {
"kind": "identifier",
"decl": {
"kind": "variable_declarator",
"text": "a",
"span": [
4,
Expand All @@ -26,16 +26,16 @@ let a, b, c
}
},
{
"decl": {
"kind": "variable_declarator",
"name": {
"kind": "identifier",
"text": "b",
"span": [
7,
8
]
},
"name": {
"kind": "identifier",
"decl": {
"kind": "variable_declarator",
"text": "b",
"span": [
7,
Expand All @@ -44,16 +44,16 @@ let a, b, c
}
},
{
"decl": {
"kind": "variable_declarator",
"name": {
"kind": "identifier",
"text": "c",
"span": [
10,
11
]
},
"name": {
"kind": "identifier",
"decl": {
"kind": "variable_declarator",
"text": "c",
"span": [
10,
Expand Down
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