sx/issues/0171-optional-any-child-not-canonicalized.md

0171 — ?any optional child is a non-canonical any TypeId (box-into-any rule misses, value silently discarded)

RESOLVED — NOT A BUG (wrong casing in the repro). The type-erased value type is spelled Any (capital A), not lowercase any (specs.md §Types; src/ir/type_resolver.zig: if name == "Any" return .any). Lowercase any is an UNDEFINED type name that resolves to an empty-struct stub — which is why ?any appeared to "silently discard" / mis-resolve. The real Any optional child works correctly: ?Any round-trips — x : ?Any = 42 tests present, a null one tests absent, and x! unwraps. There is no Any-TypeId canonicalization bug. (The confusing diagnostic for a lowercase ?any — "payload type is 'any'" instead of "unknown type 'any'" — is a minor undefined-name-in-optional-child message-quality nit, not this issue.)

Symptom

An optional whose child is any (?any) is broken. Baseline (before the issue 0165 fix) silently DISCARDED the boxed value: x : ?any = 42; v := x! yields an empty box any{}, not 42 — the payload is lowered as a zero-size {}. After the 0165 fix the same code now produces a clean type-mismatch diagnostic (cannot assign a value of type 'i64' to optional '?any': its payload type is 'any'), which is strictly better than silent corruption but still means ?any does not work.

Root cause (from adversarial review of issue 0165)

The box-into-any coercion rule (src/ir/conversions.zig ~line 57) keys on the BUILTIN .any enum TypeId. But an optional's child any is a SEPARATELY interned TypeId (observed @enumFromInt(246), type-name "any") that is NOT identity-equal to the builtin .any. So classify(i64, child_any) falls through to .none, returns the value unchanged (i64), and the wrap is invalid. The any type is not being canonicalized to the builtin TypeId when it appears as an optional child.

Reproduction

#import "modules/std.sx";
main :: () {
  x : ?any = 42;
  v := x!;
  print("{}\n", v);   // expected: a boxed 42; baseline yields empty any{}
}

Investigation prompt

Canonicalize any as an optional child (and likely any other compound position) to the builtin .any TypeId at type-resolution/interning time, so the box-into-any rule in src/ir/conversions.zig classifies correctly and ?any round-trips. Find where the optional child type is resolved/interned (src/ir/types.zig optionalOf / the type resolver) and ensure an any child maps to the canonical builtin TypeId rather than a fresh interned copy. Alternatively, make the box-into-any classifier compare by type-KIND (info == .any) rather than TypeId identity — but canonicalization is the more robust fix (it also fixes ==, size_of, and any other identity check on the any child). Verify the repro round-trips a boxed value; add an examples/types/01xx-optional-any.sx regression. Low priority — ?any is used nowhere in library/ or examples/.