A type prefixed with `!` is flagged as an error variant. When any
variant in a tagged union carries the flag, `?` propagation uses
those (and only those) as the error subset; the unflagged variant
is the success type. The legacy "first variant = success" rule still
applies when no `!`-flag is present, so existing code keeps working.
- TK_NOT in parsetype → N_TBANG wrapper (lhs = inner type expr).
Appended to Nkind tail for wwdump-diff byte stability.
- resolve_type N_TBANG: wraps primitives in a fresh Type copy so the
iserror bit doesn't taint shared globals like ty_str/ty_i32; flips
the bit in place on NAMED (already unique per alias decl).
- Type.iserror; type_named and typedecl inherit it from under.
- New check.c helpers: tagged_has_errflag, tagged_is_error_variant,
tagged_success_type. N_TRYPROP uses them to find the error subset
and verify each error variant is propagatable to the enclosing
return.
- cgen mirrors with cg_tagged_success_tag + cg_variant_is_error.
`?` compares AX against the success tag (no longer always 0) and
remaps each error variant's tag for the enclosing fn. `!` aborts
on any non-success tag.
strconv.invalid and strconv.overflow now use `!`-flagged shape
(`!i32` and `!void`) — visible signal in the API surface that they
are error types, matching Hare. The (i64 | invalid | overflow)
return shape and behavior are unchanged for callers; their match
arms still bind the same way.
Selfhost: lib/ww/parse/parse.ww recognises `!T` and emits N_TBANG.
The selfhost typechecker and cgen ignore the flag — none of the
selfhost sources use `!`, so byte-identity gates are unaffected.
The selfhost mirror catches up when there's a source using it.
`type invalid = i32` (payload: byte index of first bad rune; mirrors
Hare's strconv::invalid = !size) and `type overflow = void` (Hare's
overflow = !void). stoi64/stou64 now return these instead of the
str-error placeholder. atoi64 dropped — lib/CLAUDE.md says graduate
in one go, don't keep both shapes around.
To produce the void variant payload, `void` is now a real
expression literal (TK_VOID kw, N_VOIDLIT). It evaluates to ty_void;
codegen emits MOVQ $0, AX. Both kinds are appended at the tail of
their enums to keep prior numeric values byte-stable for the
wwdump-diff fixtures.
check_file reorder: USE declarations are now installed in pass 1
alongside the type-decl placeholders so dotted type references
(`strconv.invalid` from a typedecl body) resolve. DEF/FN/LET silently
overwrite a USE-occupied slot — matches the old behavior where USE
silently no-op'd when a same-name fn/def existed (the conflict
manifested in selfhost main.combined.ww at `use parse;` colliding
with `export fn parse(a)`).
selfhost mirror: lib/ww/lex/tok.ww kwtab+name; lib/ww/ast.ww
N_VOIDLIT def+print; lib/ww/parse/{expr,parse}.ww TK_VOID handling;
selfhost/cmd/wcc/cgenexpr.ww N_VOIDLIT codegen.
