Re: [PATCH v3 0/3] MR8507: widl: Drop an incorrect check on runtimeclass definitions.

[Rémi Bernon]

Rémi Bernon (@rbernon) commented about tools/widl/typetree.c:
> if (attr->type == ATTR_ACTIVATABLE || attr->type == ATTR_COMPOSABLE)
>          {
>              const expr_t *value = attr->u.pval;
> -            if (value->type == EXPR_MEMBER)
> +            if (value->type == EXPR_MEMBER && value->u.var->declspec.type->details.iface)

You should check that the type is TYPE_INTERFACE instead of checking details.iface, it is UB to access an union member that wasn't the one written to.

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/8507#note_108971