Merge branch 'develop' into natvis-json-default-base

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/features/arbitrary_types.md

@@ -79,7 +79,6 @@ Some important things:
 * When using `get<your_type>()`, `your_type` **MUST** be [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible). (There is a way to bypass this requirement described later.)
 * In function `from_json`, use function [`at()`](../api/basic_json/at.md) to access the object values rather than `operator[]`. In case a key does not exist, `at` throws an exception that you can handle, whereas `operator[]` exhibits undefined behavior.
 * You do not need to add serializers or deserializers for STL types like `std::vector`: the library already implements these.
-* If you control the type, consider defining `to_json`/`from_json` as `friend` functions inside the class ("hidden friends"). Argument-dependent lookup then only finds them for your type, which also avoids a [GCC < 11 compilation error](../home/faq.md#incomplete-detector-type-with-gcc-11).
 
 
 ## Simplify your life with macros

docs/mkdocs/docs/home/faq.md

@@ -307,51 +307,6 @@ APP_CPPFLAGS += -frtti -fexceptions
 The code compiles successfully with [Android NDK](https://developer.android.com/ndk/index.html?hl=ml), Revision 9 - 11 (and possibly later) and [CrystaX's Android NDK](https://www.crystax.net/en/android/ndk) version 10.
 
 
-### Incomplete `detector` type with GCC < 11
-
-!!! question
-
-    Why does GCC 10 or older fail with `invalid use of incomplete type 'struct nlohmann::detail::detector<..., to_json_function, ...>'` for a type that holds an `optional` member?
-
-This happens with GCC 10 and older in C++11/C++14 mode when all of these hold:
-
-- a class `Holder` has an `optional<Dummy>` member (e.g., `boost::optional`),
-- `Dummy` has a constructor taking a `json` value, and
-- `to_json` for `Holder` is a free function in the namespace of `Dummy`.
-
-```cpp
-class Dummy {
-  public:
-    explicit Dummy(const nlohmann::json& j);
-};
-
-class Holder {
-    boost::optional<Dummy> d;
-};
-
-void to_json(nlohmann::json& j, const Holder& h);  // triggers the error
-```
-
-To decide whether `Dummy` is copyable, the compiler checks whether a `Dummy` can be converted to `json`. That check
-looks up `to_json` via argument-dependent lookup, finds the unrelated `to_json` for `Holder`, and eventually asks again
-whether `Dummy` is copyable. GCC before version 11 turns this cycle into a hard error; GCC 11 and later, Clang, and
-C++17 mode compile the code. The same error shows up without this library whenever a constrained converting constructor
-is involved, so the library can't avoid it.
-
-To work around this, define `to_json` (and `from_json`) as a *hidden friend* inside the class. That way,
-argument-dependent lookup only finds it for `Holder`:
-
-```cpp
-class Holder {
-    boost::optional<Dummy> d;
-
-    friend void to_json(nlohmann::json& j, const Holder& h) { /* ... */ }
-};
-```
-
-The [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](../api/macros/nlohmann_define_type_intrusive.md) macros define hidden friends as
-well. See [#3669](https://github.com/nlohmann/json/issues/3669) for details.
-
 ### Missing STL function
 
 !!! question "Questions"

tests/src/unit-regression2.cpp

@@ -241,52 +241,6 @@ class my_allocator : public std::allocator<T>
     };
 };
 
-/////////////////////////////////////////////////////////////////////
-// for #3669
-/////////////////////////////////////////////////////////////////////
-
-// mimics boost::optional's converting constructor, whose SFINAE check asks
-// whether T is constructible from const U&
-template<class T, class Arg>
-struct issue3669_is_constructible
-{
-    template<class T2, class A2, class = decltype(T2(std::declval<A2>()))>
-    static char test(int);
-    template<class, class>
-    static long test(...);
-    static constexpr bool value = sizeof(test<T, Arg>(0)) == 1;
-};
-
-template<class T>
-class issue3669_optional
-{
-  public:
-    issue3669_optional() = default;
-    template<class U>
-    issue3669_optional(const issue3669_optional<U>& /*unused*/, // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
-                       typename std::enable_if<issue3669_is_constructible<T, const U&>::value, bool>::type /*unused*/ = true) {}
-};
-
-class Issue3669Dummy
-{
-  public:
-    explicit Issue3669Dummy(const json& /*unused*/) {}
-};
-
-class Issue3669Holder
-{
-    issue3669_optional<Issue3669Dummy> d{};
-
-    // GCC < 11 (C++11/14) rejects a free to_json(json&, const Issue3669Holder&)
-    // here, because ADL for Issue3669Dummy finds it and closes an instantiation
-    // cycle; a hidden friend is only visible to ADL for Issue3669Holder
-    friend void to_json(json& j, const Issue3669Holder& h)
-    {
-        static_cast<void>(h.d); // silence -Wunused-private-field
-        j = "holder";
-    }
-};
-
 TEST_CASE("regression tests 2")
 {
     SECTION("issue #1001 - Fix memory leak during parser callback")
@@ -812,14 +766,6 @@ TEST_CASE("regression tests 2")
         CHECK(j == k);
     }
 
-    SECTION("issue #3669 - invalid use of incomplete type with optional member and to_json")
-    {
-        const Issue3669Holder h{};
-        const Issue3669Holder h2(h); // NOLINT(performance-unnecessary-copy-initialization)
-        const json j = h2;
-        CHECK(j == "holder");
-    }
-
 }
 
 TEST_CASE("regression test - parser callback must not lose a duplicate key's prior value")

tools/generate_natvis/nlohmann_json.natvis.j2

@@ -36,5 +36,31 @@
         </Expand>
     </Type>
 
+    <!-- Fallback for when the basic_json entry above does not match: json_default_base is the (empty) default
+         base class of basic_json, and base class visualizers are inherited by derived types and evaluated
+         against the derived object, so m_data is accessible here. The class lives in {{ ns }} after
+         3.12.0 (#5238) and in {{ ns }}::detail up to 3.12.0, so both names are listed. -->
+{% for default_base in ['json_default_base', 'detail::json_default_base'] %}
+    <Type Name="{{ ns }}::{{ default_base }}">
+        <DisplayString Condition="m_data.m_type == {{ ns }}::detail::value_t::null">null</DisplayString>
+        <DisplayString Condition="m_data.m_type == {{ ns }}::detail::value_t::object">{*(m_data.m_value.object)}</DisplayString>
+        <DisplayString Condition="m_data.m_type == {{ ns }}::detail::value_t::array">{*(m_data.m_value.array)}</DisplayString>
+        <DisplayString Condition="m_data.m_type == {{ ns }}::detail::value_t::string">{*(m_data.m_value.string)}</DisplayString>
+        <DisplayString Condition="m_data.m_type == {{ ns }}::detail::value_t::boolean">{m_data.m_value.boolean}</DisplayString>
+        <DisplayString Condition="m_data.m_type == {{ ns }}::detail::value_t::number_integer">{m_data.m_value.number_integer}</DisplayString>
+        <DisplayString Condition="m_data.m_type == {{ ns }}::detail::value_t::number_unsigned">{m_data.m_value.number_unsigned}</DisplayString>
+        <DisplayString Condition="m_data.m_type == {{ ns }}::detail::value_t::number_float">{m_data.m_value.number_float}</DisplayString>
+        <DisplayString Condition="m_data.m_type == {{ ns }}::detail::value_t::discarded">discarded</DisplayString>
+        <Expand>
+            <ExpandedItem Condition="m_data.m_type == {{ ns }}::detail::value_t::object">
+                *(m_data.m_value.object),view(simple)
+            </ExpandedItem>
+            <ExpandedItem Condition="m_data.m_type == {{ ns }}::detail::value_t::array">
+                *(m_data.m_value.array),view(simple)
+            </ExpandedItem>
+        </Expand>
+    </Type>
+
+{% endfor %}
 {% endfor %}
 </AutoVisualizer>