1 files changed, 67 insertions, 0 deletions
diff --git a/clang/test/SemaCXX/libstdcxx_libcxx_less_hack.cpp b/clang/test/SemaCXX/libstdcxx_libcxx_less_hack.cpp
new file mode 100644
index 00000000000..53b6a3b2c42
--- /dev/null
+++ b/clang/test/SemaCXX/libstdcxx_libcxx_less_hack.cpp
@@ -0,0 +1,67 @@
+// This is a test for a hack in Clang that works around a problem introduced by
+// DR583: it's no longer possible to compare a pointer against nullptr_t, but
+// we still want to permit those comparisons within less<> and friends.
+
+// RUN: %clang_cc1 -verify %s -std=c++14
+
+namespace std {
+  template<typename T = void> struct less {};
+  template<typename T = void> struct less_equal {};
+  template<typename T = void> struct greater {};
+  template<typename T = void> struct greater_equal {};
+
+  template<> struct less<> {
+    template <class T1, class T2>
+    auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t < u))
+        -> decltype(t < u) {
+      return t < u;
+    }
+  };
+
+  template<> struct less_equal<> {
+    template <class T1, class T2>
+    auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t <= u))
+        -> decltype(t <= u) {
+      return t <= u;
+    }
+  };
+
+  template<> struct greater<> {
+    template <class T1, class T2>
+    auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t > u))
+        -> decltype(t > u) {
+      return t > u;
+    }
+  };
+
+  template<> struct greater_equal<> {
+    template <class T1, class T2>
+    auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t >= u))
+        -> decltype(t >= u) {
+      return t >= u;
+    }
+  };
+
+  template<typename = void> struct unrelated;
+  template<> struct unrelated<> {
+    template <class T1, class T2>
+    auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t < u)) // expected-note {{substitution failure}}
+        -> decltype(t < u) {
+      return t < u;
+    }
+  };
+};
+
+void test(int *p) {
+  using namespace std;
+  less<>()(p, nullptr);
+  less<>()(nullptr, p);
+  less_equal<>()(p, nullptr);
+  less_equal<>()(nullptr, p);
+  greater<>()(p, nullptr);
+  greater<>()(nullptr, p);
+  greater_equal<>()(p, nullptr);
+  greater_equal<>()(nullptr, p);
+
+  unrelated<>()(p, nullptr); // expected-error {{no matching function}}
+}