Hojun-Cho/ww
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

check: reject an array-literal borrow into a union slice success variant (#13)

Browse Source 
A stack array literal returned into a tagged-union slice success variant (fn mk() ([]i32|e) = { return [10,20,30]; }) slipped past reject_arrlit_borrow — it bailed when the dst was not TY_SLICE, but a union dst is TY_TAGGED — so cgen built an all-zeros slice header: a silent both-stage miscompile (and the .ptr would dangle anyway, no outliving backing). Extend the reject to chase a TY_TAGGED dst to its slice success variant, then apply the existing reject; this is the #25/#31 treatment seen through the union, and matches Hare (rule-9). Reached by all acceptance sites (return/assign/call-arg) so the class closes by construction. Both stages converge on an identical accept/reject decision (an array literal assignable to a union is assignable to a slice or array variant; neither stage can accept it). Full support — promoting the literal to an outliving backing — is the separate #33 arc. Compile-error fixture + a positive over-reach guard (a real slice into the union still compiles). No asm emitted by a reject, so byte-id is unchanged (no floor ratchet).
This commit is contained in:
Hojun-Cho
2026-06-28 02:44:23 +09:00
parent 01649598f4
commit 6b36b050d7
4 changed files with 61 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
cmd/wcc/check.c
View File

@@ -1192,6 +1192,22 @@ reject_arrlit_borrow(Checker *c, Type *dst, Node *expr)
{
if (expr == NULL || expr->kind != N_ARRLIT) return 0;
Type *du = type_chase_named(dst);
/* #13: the borrow target may be a SLICE success variant of a tagged-
* union return — the same no-outliving-backing dangle as a bare slice,
* but it slips the TY_SLICE gate (c->ret chases to TY_TAGGED). Chase to
* the assignable slice variant so the reject sees through the union. An
* array-typed variant is the separate #5/#60 reject upstream; full
* non-let support (an outliving backing) is #33. */
if (du && du->kind == TY_TAGGED) {
for (Tparam *p = du->params; p; p = p->next) {
Type *pu = type_chase_named(p->type);
if (pu && pu->kind == TY_SLICE
&& type_assignable(p->type, expr->type)) {
du = pu;
break;
}
}
}
if (du == NULL || du->kind != TY_SLICE) return 0;
err(c, expr->pos, "array literal cannot borrow as a slice here; "
"bind it to a `let` first");