add noexcept on assignment operators, and a test check those

Makefile

@@ -9,6 +9,9 @@ COMMON_FLAGS = -Wall -pedantic -Wextra -Wsign-compare -Wsign-conversion -Wshadow
 CXXFLAGS := $(CXXFLAGS)
 LDFLAGS := $(LDFLAGS)
 
+UNIT_TEST_SOURCES := $(wildcard test/t/*.cpp)
+UNIT_TEST_OBJECTS := $(patsubst test/t/%.cpp,out/%.o,$(UNIT_TEST_SOURCES))
+
 OS:=$(shell uname -s)
 ifeq ($(OS),Darwin)
 	CXXFLAGS += -stdlib=libc++
@@ -70,7 +73,7 @@ out/%.o: test/t/%.cpp Makefile optional.hpp recursive_wrapper.hpp variant.hpp va
 	mkdir -p ./out
 	$(CXX) -c -o $@ $< -I. -Itest/include $(DEBUG_FLAGS) $(COMMON_FLAGS) $(CXXFLAGS)
 
-out/unit: out/unit.o out/binary_visitor_1.o out/binary_visitor_2.o out/binary_visitor_3.o out/binary_visitor_4.o out/binary_visitor_5.o out/binary_visitor_6.o out/issue21.o out/mutating_visitor.o out/optional.o out/recursive_wrapper.o out/sizeof.o out/unary_visitor.o out/variant.o
+out/unit: out/unit.o $(UNIT_TEST_OBJECTS)
 	mkdir -p ./out
 	$(CXX) -o $@ $^ $(LDFLAGS)
 

recursive_wrapper.hpp

@@ -85,12 +85,14 @@ class recursive_wrapper
         : p_(new T(std::move(operand))) {}
 
     inline recursive_wrapper & operator=(recursive_wrapper const& rhs)
+        noexcept(std::is_nothrow_copy_assignable<T>::value)
     {
         assign(rhs.get());
         return *this;
     }
 
     inline recursive_wrapper & operator=(T const& rhs)
+        noexcept(std::is_nothrow_copy_assignable<T>::value)
     {
         assign(rhs);
         return *this;
@@ -110,6 +112,7 @@ class recursive_wrapper
     }
 
     recursive_wrapper & operator=(T && rhs)
+        noexcept(std::is_nothrow_move_assignable<T>::value)
     {
         get() = std::move(rhs);
         return *this;

test/t/noexcept.cpp

@@ -0,0 +1,284 @@
+#include "catch.hpp"
+#include "variant.hpp"
+
+#include <type_traits>
+
+// helper macros for concise checks, will be expanded in failure output
+#define nothrow_def_c(type, ...)        (std::is_nothrow_default_constructible<type<__VA_ARGS__>>::value)
+#define nothrow_copy_a(type, ...)       (std::is_nothrow_copy_assignable<type<__VA_ARGS__>>::value)
+#define nothrow_copy_c(type, ...)       (std::is_nothrow_copy_constructible<type<__VA_ARGS__>>::value)
+#define nothrow_move_a(type, ...)       (std::is_nothrow_move_assignable<type<__VA_ARGS__>>::value)
+#define nothrow_move_c(type, ...)       (std::is_nothrow_move_constructible<type<__VA_ARGS__>>::value)
+#define nothrow_destruct(type, ...)     (detail::is_nothrow_destructible<type<__VA_ARGS__>>::value)
+
+namespace detail {
+
+#if defined(__GNUC__) && (100 * __GNUC__ + __GNUC_MINOR__ < 408)
+    // GCC 4.7 doesn't have std::is_nothrow_destructible
+
+    template <typename T>
+    struct is_nothrow_destructible
+    {
+        static constexpr bool value = noexcept(std::declval<T&>().~T());
+    };
+
+#else
+
+    using std::is_nothrow_destructible;
+
+#endif
+
+} // namespace detail
+
+namespace { // internal
+
+struct throwing_default_ctor
+{
+    throwing_default_ctor() noexcept(false)
+    {
+        throw std::runtime_error("throwing_default_ctor");
+    }
+};
+
+struct throwing_copy
+{
+    throwing_copy() = default;
+    throwing_copy(throwing_copy && ) = default;
+    throwing_copy(throwing_copy const& ) noexcept(false)
+    {
+        throw std::runtime_error("throwing_copy:constructor");
+    }
+    throwing_copy & operator=(throwing_copy && ) = default;
+    throwing_copy & operator=(throwing_copy const& ) noexcept(false)
+    {
+        throw std::runtime_error("throwing_copy:assignment");
+        return *this;
+    }
+};
+
+struct throwing_move
+{
+    throwing_move() = default;
+    throwing_move(throwing_move const& ) = default;
+    throwing_move(throwing_move && ) noexcept(false)
+    {
+        throw std::runtime_error("throwing_move:constructor");
+    }
+    throwing_move & operator=(throwing_move const& ) = default;
+    throwing_move & operator=(throwing_move && ) noexcept(false)
+    {
+        throw std::runtime_error("throwing_move:assignment");
+        return *this;
+    }
+};
+
+struct throwing_dtor
+{
+    throwing_dtor() = default;
+    throwing_dtor(throwing_dtor const& ) = default;
+    throwing_dtor(throwing_dtor && ) = default;
+    throwing_dtor & operator=(throwing_dtor const& ) = default;
+    throwing_dtor & operator=(throwing_dtor && ) = default;
+    ~throwing_dtor() noexcept(false)
+    {
+        throw std::runtime_error("throwing_dtor");
+    }
+};
+
+} // namespace
+
+TEST_CASE("exception-specification : simple variant")
+{
+    // variant delegates noexcept to tuple in some cases; that's why we check
+    // tuple as well as variant here -- when a check on variant fails, seeing
+    // what the tuple's noexcept is can help us locate the culprit
+    using std::tuple;
+    using mapbox::util::variant;
+
+    SECTION("default constructor")
+    {
+        CHECK_NOFAIL(nothrow_def_c(tuple, int, float) == true);
+        CHECK_NOFAIL(nothrow_def_c(tuple, int, throwing_default_ctor) == false);
+        CHECK_NOFAIL(nothrow_def_c(tuple, throwing_default_ctor, int) == false);
+        CHECK_NOFAIL(nothrow_def_c(tuple, throwing_default_ctor) == false);
+        CHECK_NOFAIL(nothrow_def_c(tuple, throwing_copy, throwing_move) == true);
+        CHECK_NOFAIL(nothrow_def_c(tuple, throwing_default_ctor, throwing_copy, throwing_move) == false);
+
+        CHECK(nothrow_def_c(variant, int, float) == true);
+        CHECK(nothrow_def_c(variant, int, throwing_default_ctor) == true);
+        CHECK(nothrow_def_c(variant, throwing_default_ctor, int) == false);
+        CHECK(nothrow_def_c(variant, throwing_default_ctor) == false);
+        CHECK(nothrow_def_c(variant, throwing_copy, throwing_move) == true);
+        CHECK(nothrow_def_c(variant, throwing_default_ctor, throwing_copy, throwing_move) == false);
+    }
+
+    SECTION("copy constructor")
+    {
+        CHECK_NOFAIL(nothrow_copy_c(tuple, int, float) == true);
+        CHECK_NOFAIL(nothrow_copy_c(tuple, int, throwing_copy) == false);
+        CHECK_NOFAIL(nothrow_copy_c(tuple, throwing_copy) == false);
+        CHECK_NOFAIL(nothrow_copy_c(tuple, throwing_default_ctor, throwing_move) == true);
+        CHECK_NOFAIL(nothrow_copy_c(tuple, throwing_default_ctor, throwing_copy, throwing_move) == false);
+
+        CHECK(nothrow_copy_c(variant, int, float) == true);
+        CHECK(nothrow_copy_c(variant, int, throwing_copy) == false);
+        CHECK(nothrow_copy_c(variant, throwing_copy) == false);
+        CHECK(nothrow_copy_c(variant, throwing_default_ctor, throwing_move) == true);
+        CHECK(nothrow_copy_c(variant, throwing_default_ctor, throwing_copy, throwing_move) == false);
+    }
+
+    SECTION("move constructor")
+    {
+        CHECK_NOFAIL(nothrow_move_c(tuple, int, float) == true);
+        CHECK_NOFAIL(nothrow_move_c(tuple, int, throwing_move) == false);
+        CHECK_NOFAIL(nothrow_move_c(tuple, throwing_move) == false);
+        CHECK_NOFAIL(nothrow_move_c(tuple, throwing_default_ctor, throwing_copy) == true);
+        CHECK_NOFAIL(nothrow_move_c(tuple, throwing_default_ctor, throwing_copy, throwing_move) == false);
+
+        CHECK(nothrow_move_c(variant, int, float) == true);
+        CHECK(nothrow_move_c(variant, int, throwing_move) == false);
+        CHECK(nothrow_move_c(variant, throwing_move) == false);
+        CHECK(nothrow_move_c(variant, throwing_default_ctor, throwing_copy) == true);
+        CHECK(nothrow_move_c(variant, throwing_default_ctor, throwing_copy, throwing_move) == false);
+    }
+
+    SECTION("copy assignment")
+    {
+        CHECK_NOFAIL(nothrow_copy_a(tuple, int, float) == true);
+        CHECK_NOFAIL(nothrow_copy_a(tuple, int, throwing_copy) == false);
+        CHECK_NOFAIL(nothrow_copy_a(tuple, throwing_copy) == false);
+        CHECK_NOFAIL(nothrow_copy_a(tuple, throwing_default_ctor, throwing_move) == true);
+        CHECK_NOFAIL(nothrow_copy_a(tuple, throwing_default_ctor, throwing_copy, throwing_move) == false);
+
+        CHECK(nothrow_copy_a(variant, int, float) == true);
+        CHECK(nothrow_copy_a(variant, int, throwing_copy) == false);
+        CHECK(nothrow_copy_a(variant, throwing_copy) == false);
+        CHECK(nothrow_copy_a(variant, throwing_default_ctor, throwing_move) == true);
+        CHECK(nothrow_copy_a(variant, throwing_default_ctor, throwing_copy, throwing_move) == false);
+    }
+
+    SECTION("move assignment")
+    {
+        CHECK_NOFAIL(nothrow_move_a(tuple, int, float) == true);
+        CHECK_NOFAIL(nothrow_move_a(tuple, int, throwing_move) == false);
+        CHECK_NOFAIL(nothrow_move_a(tuple, throwing_move) == false);
+        CHECK_NOFAIL(nothrow_move_a(tuple, throwing_default_ctor, throwing_copy) == true);
+        CHECK_NOFAIL(nothrow_move_a(tuple, throwing_default_ctor, throwing_copy, throwing_move) == false);
+
+        CHECK(nothrow_move_a(variant, int, float) == true);
+        CHECK(nothrow_move_a(variant, int, throwing_move) == false);
+        CHECK(nothrow_move_a(variant, throwing_move) == false);
+        CHECK(nothrow_move_a(variant, throwing_default_ctor, throwing_copy) == true);
+        CHECK(nothrow_move_a(variant, throwing_default_ctor, throwing_copy, throwing_move) == false);
+    }
+
+    SECTION("destructor")
+    {
+        CHECK_NOFAIL(nothrow_destruct(tuple, int, float) == true);
+        CHECK_NOFAIL(nothrow_destruct(tuple, int, throwing_dtor) == false);
+        CHECK_NOFAIL(nothrow_destruct(tuple, throwing_dtor) == false);
+
+        // ~variant() is noexcept(true), regardless of exception-specification
+        // on stored alternatives' destructors
+        CHECK(nothrow_destruct(variant, int, float) == true);
+        CHECK(nothrow_destruct(variant, int, throwing_dtor) == true);
+        CHECK(nothrow_destruct(variant, throwing_dtor) == true);
+    }
+}
+
+namespace { // internal
+
+template <typename T> struct wrapped_alternative;
+template <typename T> using wrap_alternative = mapbox::util::recursive_wrapper<wrapped_alternative<T>>;
+template <typename T> using recursive_variant = mapbox::util::variant<wrap_alternative<T>>;
+
+template <typename T>
+struct wrapped_alternative : T
+{
+    recursive_variant<T> var;
+};
+
+} // namespace
+
+TEST_CASE("exception-specification : recursive variant")
+{
+    using mapbox::util::recursive_wrapper;
+
+    SECTION("default constructor")
+    {
+        // default-constructed wrapper allocates new T (default-constructed)
+        CHECK(nothrow_def_c(recursive_variant, throwing_default_ctor) == false);
+        CHECK(nothrow_def_c(recursive_variant, throwing_copy) == false);
+        CHECK(nothrow_def_c(recursive_variant, throwing_move) == false);
+        CHECK(nothrow_def_c(recursive_variant, throwing_dtor) == false);
+    }
+
+    SECTION("copy constructor")
+    {
+        // wrapper copy-constructor allocates new T (copy-constructed)
+        CHECK(nothrow_copy_c(recursive_variant, throwing_default_ctor) == false);
+        CHECK(nothrow_copy_c(recursive_variant, throwing_copy) == false);
+        CHECK(nothrow_copy_c(recursive_variant, throwing_move) == false);
+        CHECK(nothrow_copy_c(recursive_variant, throwing_dtor) == false);
+    }
+
+    SECTION("move constructor")
+    {
+        // wrapper move-constructor allocates new T (move-constructed)
+        CHECK(nothrow_move_c(recursive_variant, throwing_default_ctor) == false);
+        CHECK(nothrow_move_c(recursive_variant, throwing_copy) == false);
+        CHECK(nothrow_move_c(recursive_variant, throwing_move) == false);
+        CHECK(nothrow_move_c(recursive_variant, throwing_dtor) == false);
+    }
+
+    SECTION("copy assignment")
+    {
+        // wrapper copy-assignment copies wrapped value
+        CHECK(nothrow_copy_a(recursive_wrapper, throwing_default_ctor) == true);
+        CHECK(nothrow_copy_a(recursive_wrapper, throwing_copy) == false);
+        CHECK(nothrow_copy_a(recursive_wrapper, throwing_move) == true);
+        CHECK(nothrow_copy_a(recursive_wrapper, throwing_dtor) == true);
+
+        // variant copy-assignment destroys the original wrapper and then
+        // copy-constructs a new wrapper in its place, so we're actually
+        // testing recursive_wrapper's copy-constructor here
+        CHECK(nothrow_copy_a(recursive_variant, throwing_default_ctor) == false);
+        CHECK(nothrow_copy_a(recursive_variant, throwing_copy) == false);
+        CHECK(nothrow_copy_a(recursive_variant, throwing_move) == false);
+        CHECK(nothrow_copy_a(recursive_variant, throwing_dtor) == false);
+    }
+
+    SECTION("move assignment")
+    {
+        // wrapper move-assignment swaps internal pointers
+        CHECK(nothrow_move_a(recursive_wrapper, throwing_default_ctor) == true);
+        CHECK(nothrow_move_a(recursive_wrapper, throwing_copy) == true);
+        CHECK(nothrow_move_a(recursive_wrapper, throwing_move) == true);
+        CHECK(nothrow_move_a(recursive_wrapper, throwing_dtor) == true);
+
+        // variant move-assignment destroys the original wrapper and then
+        // move-constructs a new wrapper in its place, so we're actually
+        // testing recursive_wrapper's move-constructor here
+        CHECK(nothrow_move_a(recursive_variant, throwing_default_ctor) == false);
+        CHECK(nothrow_move_a(recursive_variant, throwing_copy) == false);
+        CHECK(nothrow_move_a(recursive_variant, throwing_move) == false);
+        CHECK(nothrow_move_a(recursive_variant, throwing_dtor) == false);
+    }
+
+    SECTION("conversion assignment")
+    {
+        CHECK((std::is_nothrow_assignable<recursive_wrapper<throwing_copy> & , throwing_copy const& >::value) == false);
+        CHECK((std::is_nothrow_assignable<recursive_wrapper<throwing_copy> & , throwing_copy && >::value) == true);
+        CHECK((std::is_nothrow_assignable<recursive_wrapper<throwing_move> & , throwing_move const& >::value) == true);
+        CHECK((std::is_nothrow_assignable<recursive_wrapper<throwing_move> & , throwing_move && >::value) == false);
+    }
+
+    SECTION("destructor")
+    {
+        // ~variant() is always noexcept(true)
+        CHECK(nothrow_destruct(recursive_variant, throwing_default_ctor) == true);
+        CHECK(nothrow_destruct(recursive_variant, throwing_copy) == true);
+        CHECK(nothrow_destruct(recursive_variant, throwing_move) == true);
+        CHECK(nothrow_destruct(recursive_variant, throwing_dtor) == true);
+    }
+}

variant.gyp

@@ -16,6 +16,7 @@
         "test/t/binary_visitor_6.cpp",
         "test/t/issue21.cpp",
         "test/t/mutating_visitor.cpp",
+        "test/t/noexcept.cpp",
         "test/t/optional.cpp",
         "test/t/recursive_wrapper.cpp",
         "test/t/sizeof.cpp",