Fix `std::visit` for the zero variants case.
Summary:
The following code is broken:
```
std::visit([]{});
```
Reviewers: EricWF
Reviewed By: EricWF
Differential Revision: https://reviews.llvm.org/D33090
llvm-svn: 302773
diff --git a/libcxx/test/std/utilities/variant/variant.visit/visit.pass.cpp b/libcxx/test/std/utilities/variant/variant.visit/visit.pass.cpp
index 05b58c1..316f2d2 100644
--- a/libcxx/test/std/utilities/variant/variant.visit/visit.pass.cpp
+++ b/libcxx/test/std/utilities/variant/variant.visit/visit.pass.cpp
@@ -94,6 +94,16 @@
using Fn = ForwardingCallObject;
Fn obj{};
const Fn &cobj = obj;
+ { // test call operator forwarding - no variant
+ std::visit(obj);
+ assert(Fn::check_call<>(CT_NonConst | CT_LValue));
+ std::visit(cobj);
+ assert(Fn::check_call<>(CT_Const | CT_LValue));
+ std::visit(std::move(obj));
+ assert(Fn::check_call<>(CT_NonConst | CT_RValue));
+ std::visit(std::move(cobj));
+ assert(Fn::check_call<>(CT_Const | CT_RValue));
+ }
{ // test call operator forwarding - single variant, single arg
using V = std::variant<int>;
V v(42);