Fix return type of std::tuple_cat.

When the arguments to tuple cat were const, the const was incorrectly
propagated into the type of the resulting tuple. For example:

const std::tuple<int> t(42);
auto r = std::tuple_cat(t, t);
// Incorrect! should be std::tuple<int, int>.
static_assert(is_same_v<decltype(r), std::tuple<const int, const int>>);

llvm-svn: 359255

1 files changed, 15 insertions, 0 deletions

diff --git a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.creation/tuple_cat.pass.cpp b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.creation/tuple_cat.pass.cpp
index 40efbd1b801..5d5927d253a 100644
--- a/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.creation/tuple_cat.pass.cpp
+++ b/libcxx/test/std/utilities/tuple/tuple.tuple/tuple.creation/tuple_cat.pass.cpp
@@ -238,6 +238,21 @@ int main(int, char**)
         );
         assert(t2 == std::make_tuple(std::make_tuple(1), std::make_tuple(2)));
     }
+    {
+        int x = 101;
+        std::tuple<int, int&, const int&, int&&> t(42, x, x, std::move(x));
+        const auto& ct = t;
+        std::tuple<int, int&, const int&> t2(42, x, x);
+        const auto& ct2 = t2;
+
+        auto r = std::tuple_cat(std::move(t), std::move(ct), t2, ct2);
 
+        ASSERT_SAME_TYPE(decltype(r), std::tuple<
+            int, int&, const int&, int&&,
+            int, int&, const int&, int&&,
+            int, int&, const int&,
+            int, int&, const int&>);
+        ((void)r);
+    }
   return 0;
 }