Merge branch 'develop' into claude/issue-5066-24ba30

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Add regression test for converting json to std::variant<json> (#5066 )
2026-09-28 10:40:30 +00:00 · 2026-09-27 20:57:55 +02:00 · 2026-09-27 16:49:33 +02:00
3 changed files with 14 additions and 5702 deletions
@@ -766,6 +766,20 @@ TEST_CASE("regression tests 2")
        CHECK(j == k);
    }

+#ifdef JSON_HAS_CPP_17
+    SECTION("issue #5066 - MSVC converts json to std::variant<json> via the conversion operator")
+    {
+        // std::variant<json> must not be retrievable via get<>(), because otherwise the
+        // implicit conversion operator becomes a candidate that MSVC picks over the variant's
+        // converting constructor, routing a number through the string from_json overload
+        static_assert(!nlohmann::detail::is_detected<nlohmann::detail::get_template_function, const json&, std::variant<json>>::value,
+                      "std::variant<json> must not be retrievable via get<>()");
+
+        std::vector<std::variant<json>> v;
+        v.push_back(json(1));
+        CHECK(std::get<0>(v[0]) == 1);
+    }
+#endif
 }

 TEST_CASE("regression test - parser callback must not lose a duplicate key's prior value")
@@ -36,31 +36,5 @@
        </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>