Hojun-Cho
68bd8197d5
The selfhost checker did name resolution only — anything tagged- union-shaped sailed through silently. The C check.c implements three structural checks; this commit mirrors them at the AST level in selfhost/cmd/wcc/check.ww: 1. Match exhaustiveness: every variant of the scrutinee's tagged union must be covered by a case arm (incl. multi-pattern alts) or a default arm. Operates on the scrutinee's declared type (N_TTAGGED via N_IDENT's sym.decl.lhs). 2. ? subset propagation: each error variant of the operand's type must be a variant of the enclosing fn's return type. Enclosing return must itself be a tagged union when the operand has any errors. 3. !-flag semantics: in flag-aware mode (any variant marked `!T`), error subset = flagged variants. Legacy mode (no flags) = everything-but-first. is_error_variant unifies both rules. No tinfo / type-inference work: the checks read declared AST type nodes directly. `resolvealias` chases N_TNAME → typedecl body to handle aliased tagged unions. `type_eq_ast` does structural comparison on the subset of type-expression shapes the checks encounter (TNAME by string, TPTR/TSLICE/TCHAN recursive). Folded into resolvewalk rather than a separate second pass, so the checks see the same per-statement scope state as resolve. fnret is threaded through resolvefnbody so ? can find the enclosing return. New test/wcc/950_selfcheck.c — five rows exercising each error path (missing variant, non-tagged enclosing, missing error subset member, the flag-aware happy path, the flag-aware missing-error case). Test suite now reports 21 ok.