https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81167
--- Comment #5 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Note to self: I believe the "operator T() &&" here is a user-defined conversion
from an rvalue reference to T.
We have in joust at ../../src/gcc/cp/call.c:10071
10071 tree source = source_type (w->convs[0]);
(gdb) p source
$2 = <record_type 0x7ffff052ba80 Derived>
10072 if (! DECL_CONSTRUCTOR_P (w->fn))
10073 source = TREE_TYPE (source);
(gdb) p source
$4 = <tree 0x0>
Guarding that as follows:
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -10069,7 +10069,8 @@ joust (struct z_candidate *cand1, struct z_candidate
*cand2, bool warn,
else if (warn)
{
tree source = source_type (w->convs[0]);
- if (! DECL_CONSTRUCTOR_P (w->fn))
+ if (! DECL_CONSTRUCTOR_P (w->fn)
+ && TREE_TYPE (source))
source = TREE_TYPE (source);
if (warning (OPT_Wconversion, "choosing %qD over %qD", w->fn, l->fn)
&& warning (OPT_Wconversion, " for conversion from %qH to %qI",
fixes the problem (or papers over it?), giving:
../../src/pr81167.C: In function ‘void test()’:
../../src/pr81167.C:16:16: warning: choosing ‘bar::operator foo() &&’ over
‘foo::foo(const bar&)’ [-Wconversion]
foo f = bar ();
^
../../src/pr81167.C:16:16: warning: for conversion from ‘bar’ to ‘foo’
[-Wconversion]
../../src/pr81167.C:16:16: note: because conversion sequence for the argument
is better
