[PATCH] libstdc++: Make operator== for std::tuple convert to bool [PR119545]

[Jonathan Wakely]

The boolean-testable requirements don't require the type to be copyable,
so we need to convert to bool before it might need to be copied.

libstdc++-v3/ChangeLog:

        PR libstdc++/119545
        * include/std/tuple (operator==): Convert comparison results to
        bool.
        * testsuite/20_util/tuple/comparison_operators/119545.cc: New
        test.
---

Tested x86_64-linux.

For the recent r15-7897-ge6e7b477bbdbfb change to fix a similar problem
I used an explicit return type on the lambda, because that was what the
LWG issue said to do. In this case an explicit return type would also
work, but I used an explicit conversion to bool on each element of the
pack expansion instead. That matches what is done elsewhere in <tuple>
for the tuple-like equality comparison, so I preferred to be locally
consistent.

 libstdc++-v3/include/std/tuple                |  2 +-
 .../tuple/comparison_operators/119545.cc      | 24 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 
libstdc++-v3/testsuite/20_util/tuple/comparison_operators/119545.cc

diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index d3deb7bc124..2e69af13a98 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -2534,7 +2534,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
       return [&]<size_t... _Inds>(index_sequence<_Inds...>) {
        // Fold == over the tuples until non-equal elements are found.
-       return ((std::get<_Inds>(__t) == std::get<_Inds>(__u)) && ...);
+       return (bool(std::get<_Inds>(__t) == std::get<_Inds>(__u)) && ...);
       }(index_sequence_for<_Tps...>{});
     }
 
diff --git 
a/libstdc++-v3/testsuite/20_util/tuple/comparison_operators/119545.cc 
b/libstdc++-v3/testsuite/20_util/tuple/comparison_operators/119545.cc
new file mode 100644
index 00000000000..3a65ef53b01
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/tuple/comparison_operators/119545.cc
@@ -0,0 +1,24 @@
+// { dg-do compile { target c++11 } }
+// Bug libstdc++/119545
+// tuple::operator==()'s help lambda does not specify return type as bool
+
+#include <tuple>
+
+void
+test_pr119545()
+{
+  struct Bool {
+    Bool() = default;
+    Bool(const Bool&) = delete;
+    operator bool() const { return true; }
+  };
+
+  static Bool b;
+
+  struct Object {
+    const Bool& operator==(const Object&) const { return b; }
+  };
+
+  std::tuple<Object> t;
+  (void) (t == t);
+}
-- 
2.49.0