Fix msvc unreachable code warnings

include/range/v3/detail/config.hpp

@@ -99,6 +99,21 @@ namespace ranges
 #define RANGES_ENSURE(...) RANGES_ENSURE_MSG((__VA_ARGS__), #__VA_ARGS__)
 #endif
 
+#ifndef RANGES_EXPECT_UNREACHABLE_RETURN
+#if defined(NDEBUG) && defined(_MSC_VER)
+// In release builds, RANGES_EXPECT(false) for msvc invokes an intrinsic that indicates
+// subsequent operations are unreachable. Do not invoke a return after its evaluation,
+// lest the compiler warn that the return is unreachable.
+#define RANGES_EXPECT_UNREACHABLE_RETURN(RETURN_VALUE) RANGES_EXPECT(false)
+#else
+#define RANGES_EXPECT_UNREACHABLE_RETURN(RETURN_VALUE) \
+    do                                                 \
+    {                                                  \
+        return (RANGES_EXPECT(false), RETURN_VALUE);   \
+    } while(false)
+#endif
+#endif // RANGES_EXPECT_UNREACHABLE_RETURN
+
 #define RANGES_DECLTYPE_AUTO_RETURN(...) \
     ->decltype(__VA_ARGS__)              \
     {                                    \

include/range/v3/detail/variant.hpp

@@ -339,7 +339,7 @@ namespace ranges
         template<typename Fun, typename Proj = indexed_element_fn>
         constexpr int variant_visit_(std::size_t, variant_nil, Fun, Proj = {})
         {
-            return (RANGES_EXPECT(false), 0);
+            RANGES_EXPECT_UNREACHABLE_RETURN(0);
         }
         template<typename Data, typename Fun, typename Proj = indexed_element_fn>
         constexpr int variant_visit_(std::size_t n, Data & self, Fun fun, Proj proj = {})

test/CMakeLists.txt

@@ -21,4 +21,6 @@ rv3_add_test(test.bug1322 bug1322 bug1322.cpp)
 rv3_add_test(test.bug1335 bug1335 bug1335.cpp)
 rv3_add_test(test.bug1633 bug1633 bug1633.cpp)
 rv3_add_test(test.bug1729 bug1729 bug1729.cpp)
+rv3_add_test(test.bug1762 bug1762 bug1762.cpp)
+rv3_add_test(test.bug1814 bug1814 bug1814.cpp)
 rv3_add_test(test.bug-guard bug-guard bug-guard.cpp)

test/bug1762.cpp

@@ -0,0 +1,17 @@
+#if defined(_MSC_VER)
+// Enable level 4 "unreachable code" warning
+#pragma warning(error : 4702)
+#elif defined(__clang__)
+#pragma clang diagnostic error "-Wunreachable-code-aggressive"
+#elif defined(__GNUC__)
+// Unsupported and ignored in gcc >= 5
+#pragma GCC diagnostic error "-Wunreachable-code"
+#endif
+
+#include <range/v3/range/conversion.hpp>
+#include <range/v3/view/generate_n.hpp>
+
+int main()
+{
+    ranges::views::generate_n(rand, 5) | ranges::to<std::vector>();
+}

test/bug1814.cpp

@@ -0,0 +1,22 @@
+#if defined(_MSC_VER)
+// Enable level 4 "unreachable code" warning
+#pragma warning(error : 4702)
+#elif defined(__clang__)
+#pragma clang diagnostic error "-Wunreachable-code-aggressive"
+#elif defined(__GNUC__)
+// Unsupported and ignored in gcc >= 5
+#pragma GCC diagnostic error "-Wunreachable-code"
+#endif
+
+#include <vector>
+
+#include <range/v3/range/conversion.hpp>
+#include <range/v3/view/join.hpp>
+#include <range/v3/view/transform.hpp>
+
+int main()
+{
+    const std::vector<std::vector<int>> v{{{1, 2, 3}}, {{4, 5, 6}}};
+    v | ranges::views::transform([](const auto & sub_v) { return sub_v; }) |
+        ranges::views::join | ranges::to_vector;
+}