https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101174
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2021-06-23
Status|UNCONFIRMED |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot
gnu.org
Ever confirmed|0 |1
--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
The particular problem here is that during dguide overload resolution for
multiset(42), we briefly consider the implicit deduction guide for the second
ctor:
template<class T = int, class U = S>
multiset(U) -> multiset<T, U>
which after substituting deduced template arguments becomes
multiset(int) -> multiset<int, int>
and after r12-926, its (substituted) DECL_CONTEXT is also multiset<int, int>
rather than empty.
Since DECL_CLASS_SCOPE_P is now true for implicit deduction guides, we try to
complete/instantiate its DECL_CONTEXT via the call to DERIVED_FROM_P in
joust():
/* F1 is a member of a class D, F2 is a member of a base class B of D, and
for all arguments the corresponding parameters of F1 and F2 have the same
type (CWG 2273/2277). */
if (DECL_P (cand1->fn) && DECL_CLASS_SCOPE_P (cand1->fn)
&& !DECL_CONV_FN_P (cand1->fn)
&& DECL_P (cand2->fn) && DECL_CLASS_SCOPE_P (cand2->fn)
&& !DECL_CONV_FN_P (cand2->fn))
{
tree base1 = DECL_CONTEXT (strip_inheriting_ctors (cand1->fn));
tree base2 = DECL_CONTEXT (strip_inheriting_ctors (cand2->fn));
bool used1 = false;
bool used2 = false;
if (base1 == base2)
/* No difference. */;
else if (DERIVED_FROM_P (base1, base2)) // XXX
used1 = true;
else if (DERIVED_FROM_P (base2, base1))
used2 = true;
which results in the hard error seen.
I'm testing setting DECL_BEFRIENDING_CLASSES instead of DECL_CONTEXT on an
implicit deduction guide, to avoid such accidental instantiations
