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wcc: tagged-union foundations (never, void, flatten, exhaust)

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- `never` bottom type: TY_NEVER, assignable to anything; size 0.
- Type-set normalization for N_TTAGGED in resolve_type:
  - flatten nested anonymous (A|B)|C → (A|B|C); named aliases stay
    nominal (not flattened through)
  - dedup duplicates (NAMED pointer-id; others structural)
  - drop `never` variants
  - collapse single-element set: (T|never) → T, (T|T) → T
- Match exhaustiveness: error when a variant is unhandled and no
  default arm covers it. Multi-pattern `case T1 | T2 =>` counts
  each alt.
- (T | void) optionals: bare `return;` from a tagged-union-returning
  fn emits the void variant's tag (payload undefined; void size 0).

selfhost mirrored: TY_NEVER constant + tynever in tctx + seedprim
entry; voidvariantindex helper; cgreturn bare-return handling.
This commit is contained in:
Hojun-Cho
2026-05-12 01:31:35 +09:00
parent 1ac1d985f6
commit fa070b6d07
11 changed files with 260 additions and 33 deletions
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4
cmd/wcc/type.c
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@@ -15,6 +15,7 @@ Type *ty_u8, *ty_u16, *ty_u32, *ty_u64;
Type *ty_int, *ty_uint, *ty_uintptr;
Type *ty_f32, *ty_f64, *ty_str;
Type *ty_err;
Type *ty_never;
Type *ty_untyped_int, *ty_untyped_float, *ty_untyped_str;
Type *ty_untyped_rune, *ty_untyped_bool, *ty_untyped_nil;
@@ -61,6 +62,7 @@ typesinit(Arena *a)
/* str is { *u8, len } — 16 bytes on amd64. ABI: pointer + u64. */
ty_str = prim(a, TY_STR, "str", 16, 8);
ty_err = prim(a, TY_ERR, "<err>", 0, 1);
ty_never = prim(a, TY_NEVER, "never", 0, 1);
ty_untyped_int = prim(a, TY_UNTYPED_INT, "untyped_int", 0, 1);
ty_untyped_float = prim(a, TY_UNTYPED_FLOAT, "untyped_float", 0, 1);
@@ -248,6 +250,7 @@ type_assignable(Type *dst, Type *src)
{
if (dst == NULL || src == NULL) return 0;
if (dst == ty_err || src == ty_err) return 1; /* swallow */
if (src == ty_never) return 1; /* bottom flows into anything */
if (type_eq(dst, src)) return 1;
/* Tagged-union variant inclusion: src is one of dst's variants.
@@ -327,6 +330,7 @@ type_name(Arena *a, Type *t)
case TY_F64: return "f64";
case TY_STR: return "str";
case TY_ERR: return "<err>";
case TY_NEVER: return "never";
case TY_UNTYPED_INT: return "untyped_int";
case TY_UNTYPED_FLOAT: return "untyped_float";
case TY_UNTYPED_STR: return "untyped_str";