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fix: captured tagged alternation in field produces tagged union #269

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

fix: captured tagged alternation in field produces tagged union #269

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22 changes: 19 additions & 3 deletions crates/plotnik-lib/src/compile/capture.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -44,11 +44,16 @@ impl Compiler<'_> {
// Check if inner is a scope-creating expression (SeqExpr/AltExpr) that produces
// a structured type (Struct/Enum). Named nodes with bubble captures don't count -
// they still need Node because we're capturing the matched node, not the struct.
let creates_structured_scope = inner.is_some_and(|i| {
inner_creates_scope(i)
//
// For FieldExpr, look through to the value. The parser treats `field: expr @cap` as
// `(field: expr) @cap` so that quantifiers work on fields (e.g., `decorator: (x)*`
// for repeating fields). This means captures wrap the FieldExpr, but the value
// determines whether it produces a structured type. See `parse_expr_no_suffix`.
let creates_structured_scope = inner.and_then(unwrap_field_value).is_some_and(|ei| {
inner_creates_scope(&ei)
&& self
.type_ctx
.get_term_info(i)
.get_term_info(&ei)
.and_then(|info| info.flow.type_id())
.and_then(|id| self.type_ctx.get_type(id))
.is_some_and(|shape| matches!(shape, TypeShape::Struct(_) | TypeShape::Enum(_)))
Expand Down Expand Up @@ -148,6 +153,17 @@ impl Compiler<'_> {
}
}

/// Unwrap FieldExpr to get its value, pass through other expressions.
///
/// Used when checking properties of a captured expression - captures on fields
/// like `field: [A: B:] @cap` wrap the FieldExpr, but we need to inspect the value.
fn unwrap_field_value(expr: &Expr) -> Option<Expr> {
match expr {
Expr::FieldExpr(f) => f.value(),
other => Some(other.clone()),
}
}

/// Check if inner needs struct wrapper for array iterations.
///
/// Returns true when inner is a scope-creating expression (sequence/alternation)
Expand Down
20 changes: 20 additions & 0 deletions crates/plotnik-lib/src/compile/expressions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -453,6 +453,26 @@ impl Compiler<'_> {
};
}

// Handle scope-creating scalar expressions (tagged enums)
// Enum produces its own value via EndEnum - capture effects go AFTER, not inside
let inner_is_scope_creating_scalar = !inner_is_bubble
&& inner_creates_scope
&& inner_info
.as_ref()
.and_then(|info| info.flow.type_id())
.and_then(|id| self.type_ctx.get_type(id))
.is_some_and(|shape| matches!(shape, TypeShape::Enum(_)));

if inner_is_scope_creating_scalar {
let set_step = self.emit_effects_epsilon(exit, capture_effects, outer_capture);
return self.compile_expr_inner(
&inner,
set_step,
nav_override,
CaptureEffects::default(),
);
}

// Array: Arr → quantifier (with Push) → EndArr+capture → exit
// Check if inner is a * or + quantifier - these produce arrays regardless of arity
let inner_is_array = is_star_or_plus_quantifier(Some(&inner));
Expand Down
10 changes: 10 additions & 0 deletions crates/plotnik-lib/src/emit/codegen_tests.rs
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Expand Up @@ -358,6 +358,16 @@ fn alternations_no_internal_captures() {
"#});
}

#[test]
fn alternations_tagged_in_field_constraint() {
// Regression test: captured tagged alternation as field value should not emit Node effect.
// The capture `@kind` applies to the field expression, but the value determines
// whether it's a structured scope (enum in this case).
snap!(indoc! {r#"
Test = (foo field: [A: (x) @a B: (y)] @kind)
"#});
}

// ============================================================================
// 7. ANCHORS
// ============================================================================
Expand Down
15 changes: 8 additions & 7 deletions ...ib/src/emit/snapshots/plotnik_lib__emit__codegen_tests__alternations_captured_tagged.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -46,11 +46,12 @@ _ObjWrap:

Test:
06 ε 07
07 ε 14, 20
07 ε 16, 22
09 ▶
10 ε [EndEnum Set(M4)] 09
12 ! (identifier) [Node Set(M0)] 10
14 ε [Enum(M2)] 12
16 ε [EndEnum Set(M4)] 09
18 ! (number) [Node Set(M1)] 16
20 ε [Enum(M3)] 18
10 ε [Set(M4)] 09
12 ε [EndEnum] 10
14 ! (identifier) [Node Set(M0)] 12
16 ε [Enum(M2)] 14
18 ε [EndEnum] 10
20 ! (number) [Node Set(M1)] 18
22 ε [Enum(M3)] 20
37 changes: 19 additions & 18 deletions ...-lib/src/emit/snapshots/plotnik_lib__emit__codegen_tests__alternations_in_quantifier.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -53,26 +53,27 @@ Test:
06 ε 07
07 ! (object) 08
08 ε [Arr] 10
10 ε 43, 20
10 ε 45, 20
12 ε [EndArr Set(M5)] 14
14 △ 19
15 ε [EndObj Push] 17
17 ε 49, 12
17 ε 51, 12
19 ▶
20 ε [EndArr Set(M5)] 19
22 ε [EndEnum Set(M4)] 15
24 ! (pair) [Node Set(M0)] 22
26 ε [Enum(M2)] 24
28 ε [EndEnum Set(M4)] 15
30 ! (shorthand_property_identifier) [Node Set(M1)] 28
32 ε [Enum(M3)] 30
34 ε 26, 32
36 ε [Obj] 34
38 ▷ 41
39 ε 38, 20
41 ε 36, 39
43 ▽ 41
44 ▷ 47
45 ε 44, 12
47 ε 36, 45
49 ▷ 47
22 ε [Set(M4)] 15
24 ε [EndEnum] 22
26 ! (pair) [Node Set(M0)] 24
28 ε [Enum(M2)] 26
30 ε [EndEnum] 22
32 ! (shorthand_property_identifier) [Node Set(M1)] 30
34 ε [Enum(M3)] 32
36 ε 28, 34
38 ε [Obj] 36
40 ▷ 43
41 ε 40, 20
43 ε 38, 41
45 ▽ 43
46 ▷ 49
47 ε 46, 12
49 ε 38, 47
51 ▷ 49
59 changes: 59 additions & 0 deletions .../snapshots/plotnik_lib__emit__codegen_tests__alternations_tagged_in_field_constraint.snap
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@@ -0,0 +1,59 @@
---
source: crates/plotnik-lib/src/emit/codegen_tests.rs
---
Test = (foo field: [A: (x) @a B: (y)] @kind)
---
[flags]
linked = false

[strings]
S0 "Beauty will save the world"
S1 "a"
S2 "A"
S3 "B"
S4 "kind"
S5 "Test"
S6 "foo"
S7 "field"
S8 "x"
S9 "y"

[type_defs]
T0 = <Void>
T1 = <Node>
T2 = Struct M0:1 ; { a }
T3 = Enum M1:2 ; A | B
T4 = Struct M3:1 ; { kind }

[type_members]
M0: S1 → T1 ; a: <Node>
M1: S2 → T2 ; A: T2
M2: S3 → T0 ; B: <Void>
M3: S4 → T3 ; kind: T3

[type_names]
N0: S5 → T4 ; Test

[entrypoints]
Test = 06 :: T4

[transitions]
_ObjWrap:
00 ε [Obj] 02
02 Trampoline 03
03 ε [EndObj] 05
05 ▶

Test:
06 ε 07
07 ! (foo) 08
08 ▽ field: _ 09
09 ε 16, 21
11 ▶
12 ε [EndEnum Set(M3)] 23
14 ! (x) [Node Set(M0)] 12
16 ε [Enum(M1)] 14
18 ε [EndEnum Set(M3)] 23
20 ! (y) 18
21 ε [Enum(M2)] 20
23 △ 11
15 changes: 8 additions & 7 deletions .../snapshots/plotnik_lib__emit__codegen_tests__alternations_tagged_with_definition_ref.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -55,11 +55,12 @@ Inner:

Test:
10 ε 11
11 ε 17, 23
11 ε 19, 25
13 ▶
14 ε [EndEnum Set(M4)] 13
16 ! (Inner) 06 : 14
17 ε [Enum(M2)] 16
19 ε [EndEnum Set(M4)] 13
21 ! (number) [Node Set(M1)] 19
23 ε [Enum(M3)] 21
14 ε [Set(M4)] 13
16 ε [EndEnum] 14
18 ! (Inner) 06 : 16
19 ε [Enum(M2)] 18
21 ε [EndEnum] 14
23 ! (number) [Node Set(M1)] 21
25 ε [Enum(M3)] 23
15 changes: 8 additions & 7 deletions .../emit/snapshots/plotnik_lib__emit__codegen_tests__captures_enum_with_type_annotation.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -48,11 +48,12 @@ _ObjWrap:

Test:
06 ε 07
07 ε 14, 20
07 ε 16, 22
09 ▶
10 ε [EndEnum Set(M4)] 09
12 ! (identifier) [Node Set(M0)] 10
14 ε [Enum(M2)] 12
16 ε [EndEnum Set(M4)] 09
18 ! (number) [Node Set(M1)] 16
20 ε [Enum(M3)] 18
10 ε [Set(M4)] 09
12 ε [EndEnum] 10
14 ! (identifier) [Node Set(M0)] 12
16 ε [Enum(M2)] 14
18 ε [EndEnum] 10
20 ! (number) [Node Set(M1)] 18
22 ε [Enum(M3)] 20
9 changes: 8 additions & 1 deletion crates/plotnik-lib/src/parser/grammar/expressions.rs
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Expand Up @@ -35,7 +35,14 @@ impl Parser<'_, '_> {
}

/// Parse expression without applying quantifier/capture suffix.
/// Used for field values so that `field: (x)*` parses as `(field: (x))*`.
///
/// Used for field values so that suffixes apply to the whole field constraint:
/// - `field: (x)*` parses as `(field: (x))*` — repeat the field (e.g., decorators)
/// - `field: (x) @cap` parses as `(field: (x)) @cap` — capture the field expression
///
/// For captures on structured values (enums/structs), the compilation handles this
/// by looking through FieldExpr to determine the actual value type. See
/// `build_capture_effects` in compile/capture.rs.
pub(crate) fn parse_expr_no_suffix(&mut self) {
self.parse_expr_inner(false)
}
Expand Down
11 changes: 11 additions & 0 deletions docs/lang-reference.md
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Expand Up @@ -481,6 +481,17 @@ Output type:
{ target: string, value: Node }
```

### Quantifiers and Captures on Fields

Quantifiers and captures after a field value apply to the entire field constraint, not just the value:

```
decorator: (decorator)* @decorators ; repeats the whole field
value: [A: (x) B: (y)] @kind ; captures the field (containing the alternation)
```

This allows repeating fields (useful for things like decorators in JavaScript). The capture still correctly produces the value's type—for alternations, you get the tagged union, not a raw node.

### Negated Fields

Assert a field is absent with `-`:
Expand Down