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

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Fix clang-tidy and clang 6 in the #5066 regression test
2026-09-30 03:30:31 +00:00 · 2026-09-28 22:22:36 +02:00 · 2026-09-28 18:22:16 +02:00 · 2026-09-27 20:57:55 +02:00 · 2026-09-27 16:49:33 +02:00
5 changed files with 28 additions and 24 deletions
@@ -7,15 +7,15 @@ void clear() noexcept;
 Clears the content of a JSON value and resets it to the default value as if [`basic_json(value_t)`](basic_json.md) would
 have been called with the current value type from [`type()`](type.md):

-| Value type | initial value                          |
-|------------|-----------------------------------------|
-| null       | `null`                                  |
-| boolean    | `false`                                 |
-| string     | `""`                                    |
-| number     | `0`                                     |
-| binary     | An empty byte vector with no subtype    |
-| object     | `{}`                                    |
-| array      | `[]`                                    |
+| Value type | initial value        |
+|------------|----------------------|
+| null       | `null`               |
+| boolean    | `false`              |
+| string     | `""`                 |
+| number     | `0`                  |
+| binary     | An empty byte vector |
+| object     | `{}`                 |
+| array      | `[]`                 |

 Has the same effect as calling

@@ -56,4 +56,3 @@ All iterators, pointers, and references related to this container are invalidate

 - Added in version 1.0.0.
 - Added support for binary types in version 3.8.0.
- Fixed in version 3.13.0 to also clear the subtype of a binary value; before, the subtype was left unchanged.
@@ -3833,7 +3833,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
            case value_t::binary:
            {
                m_data.m_value.binary->clear();
-                m_data.m_value.binary->clear_subtype();
                break;
            }

@@ -29914,7 +29914,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
            case value_t::binary:
            {
                m_data.m_value.binary->clear();
-                m_data.m_value.binary->clear_subtype();
                break;
            }

@@ -155,18 +155,6 @@ TEST_CASE("modifiers")
                CHECK(j == json(json::value_t::binary));
                CHECK(j == json(k.type()));
            }
-
-            SECTION("filled binary with subtype")
-            {
-                json j = json::binary({1, 2, 3, 4, 5}, 42);
-                json const k = j;
-
-                j.clear();
-                CHECK(!j.empty());
-                CHECK(!j.get_binary().has_subtype());
-                CHECK(j == json(json::value_t::binary));
-                CHECK(j == json(k.type()));
-            }
        }

        SECTION("number (integer)")
@@ -766,6 +766,25 @@ 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<>()");
+
+        // clang before 7 cannot instantiate libstdc++'s std::variant<json>
+#if !(defined(__clang__) && __clang_major__ < 7)
+        // push_back, not emplace_back: #5066 needs the implicit conversion
+        // from json to the vector's value type
+        std::vector<std::variant<json>> v;
+        v.push_back(json(1)); // NOLINT(hicpp-use-emplace,modernize-use-emplace)
+        CHECK(std::get<0>(v[0]) == 1);
+#endif
+    }
+#endif
 }

 TEST_CASE("regression test - parser callback must not lose a duplicate key's prior value")
Author	SHA1	Message	Date
Niels Lohmann	14558ba011	Merge branch 'develop' into claude/issue-5066-24ba30 Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-28 22:22:36 +02:00
Niels Lohmann	ccb419ca64	Fix clang-tidy and clang 6 in the #5066 regression test ci_clang_tidy asked for emplace_back instead of push_back. The push_back is the point of the test: #5066 is about the implicit conversion from json to the vector's value type, which emplace_back would bypass. Silence the check on that line. clang 5 and 6 cannot instantiate std::variant<json> from libstdc++ 10's <variant> ("cannot cast private base class"), which broke ci_test_compilers_clang (6). Tested with the CI images: clang 7 to 11 compile and pass, including clang 11 with libstdc++ 10. Skip the runtime check for clang before 7; the static_assert still runs. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-28 18:22:16 +02:00
Niels Lohmann	4494890be6	Merge branch 'develop' into claude/issue-5066-24ba30 Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-27 20:57:55 +02:00
Niels Lohmann	c4469c9f82	Add regression test for converting json to std::variant<json> (#5066 ) With 3.10.5, get<std::variant<json>>() was well-formed through the string from_json overload, so the implicit conversion operator was a candidate when converting json to std::variant<json>, and MSVC picked it over the variant's converting constructor. The tightened constraints from #3427 and #3604 (3.11.0) removed that path; this test guards against regressions. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-27 16:49:33 +02:00