Captured optional scope `{...}? @cap` double-nullifies inner fields

[zharinov]

Problem

When you capture an optional scope {...}? @cap, the inner fields become nullable on top of the scope itself becoming nullable. The nullability gets applied twice.

cargo run -p plotnik -- infer -q 'Q = {(identifier) @foo}? @bar' -l typescript

interface QBar { foo: Node | null; }   // foo should not be nullable
interface Q    { bar: QBar | null; }

Without the ?, the scope is correct:

cargo run -p plotnik -- infer -q 'Q = {(identifier) @foo} @bar' -l typescript

interface QBar { foo: Node; }
interface Q    { bar: QBar; }

QBar should be the same type in both cases. Only the outer bar field should gain | null.

Why it's wrong

{(identifier) @foo}? @bar has two runtime outcomes:

• the group matched → bar is present, and @foo is unconditional inside it, so foo is present
• the group didn't match → bar is null

There is no state where bar is non-null but foo is null. The foo: Node | null type describes an unreachable value.

Expected:

interface QBar { foo: Node; }
interface Q    { bar: QBar | null; }

Cause

Two places each add optionality for the same ?:

• make_flow_optional (crates/plotnik-compiler/src/analyze/type_check/infer.rs:592) distributes make_optional() over every field of the scope struct, turning foo into Node | null.
• infer_captured_expr also marks the capture field itself optional via is_optional (infer.rs:383), turning bar into QBar | null.

When a ?-quantified scope is directly captured, the capture already absorbs the optionality at the scope boundary, so the field-distributing step is redundant.

Related

• Captured optional {...}? @cap at a navigating child drops its struct scope (VM panics / corrupts output) #470 — emission dropping the scope for the same pattern; it assumes { foo: Node | null } | null is the intended type. This issue argues that declared type is itself over-nullable, so the two should be reconciled together.
• Single source of truth for capture value semantics (inference vs emission) #420 — single source of truth for capture value semantics.