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
2026-09-29 19:20:30 +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
4 changed files with 43 additions and 28 deletions
@@ -19,17 +19,11 @@ namespace detail
 /*!
@brief the number of nesting levels an operation recurses into

-Operations that walk a value (copying, comparing, serializing, hashing, merging,
-...) recurse once
+Operations that walk a value (serializing, hashing, merging, ...) recurse once
 per nesting level, which is fastest, but a value nested deeply enough would
 exhaust the call stack. So they recurse only this many levels deep and finish
 whatever lies below with an explicit stack. All of them share this limit.

-Most of them pass the depth down as an argument. The copy constructor and the
-comparison operators cannot, as their signatures are fixed, so they count it
-in basic_json::nesting_depth() instead, a byte per thread; the limit must
-therefore stay below 255.
-
@sa https://github.com/nlohmann/json/issues/5387
 */
 constexpr std::size_t recursion_depth_limit() noexcept
@@ -898,8 +898,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    }

 #ifndef JSON_NO_THREAD_LOCAL
-    // nesting_depth() is a byte and may exceed the limit by one level
-    static_assert(detail::recursion_depth_limit() < 255, "the nesting depth count must fit in a byte");
+    /// the number of levels an operation descends into before it finishes the
+    /// value below it without the call stack
+    static constexpr std::uint8_t nesting_depth_limit()
+    {
+        return 128;
+    }

    /*!
    @brief how many levels the operation going on in this thread has descended into
@@ -941,7 +945,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
        static_cast<void>(may_descend);
        return true;
 #else
-        return !may_descend || nesting_depth() >= detail::recursion_depth_limit();
+        return !may_descend || nesting_depth() >= nesting_depth_limit();
 #endif
    }

@@ -965,7 +969,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 #ifdef JSON_NO_THREAD_LOCAL
            : m_okay(false)
 #else
-            : m_okay(nesting_depth() < detail::recursion_depth_limit())
+            : m_okay(nesting_depth() < nesting_depth_limit())
 #endif
        {
 #ifndef JSON_NO_THREAD_LOCAL
@@ -1169,7 +1173,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec

    The values whose copy has not been created yet are kept on an explicit
    worklist rather than on the call stack. This is only reached for values
-    nested deeper than @ref detail::recursion_depth_limit levels, which is why it copies
+    nested deeper than @ref nesting_depth_limit levels, which is why it copies
    every container by hand instead of letting the container do it: the fast
    ways of doing so would descend into the elements and defeat the purpose.
    */
@@ -1235,7 +1239,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec

    Copying a container copies its elements, so a value nested deeply enough
    used to exhaust the call stack. The descent is bounded here: the first
-    @ref detail::recursion_depth_limit levels are copied by the containers themselves, just
+    @ref nesting_depth_limit levels are copied by the containers themselves, just
    as they always were, and anything below that is copied without the call
    stack by @ref copy_iteratively. Copying a value can therefore no longer
    exhaust the stack, however deeply it is nested, just like destroying one
@@ -1373,7 +1377,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /*!
    @brief compare @a lhs and @a rhs without descending into them

-    Reached once a comparison has descended @ref detail::recursion_depth_limit levels, so
+    Reached once a comparison has descended @ref nesting_depth_limit levels, so
    that comparing values cannot exhaust the call stack however deeply they are
    nested. The two values are walked in lockstep on an explicit stack and
    compared lexicographically, element by element in the order the containers
@@ -7281,17 +7281,11 @@ namespace detail
 /*!
@brief the number of nesting levels an operation recurses into

-Operations that walk a value (copying, comparing, serializing, hashing, merging,
-...) recurse once
+Operations that walk a value (serializing, hashing, merging, ...) recurse once
 per nesting level, which is fastest, but a value nested deeply enough would
 exhaust the call stack. So they recurse only this many levels deep and finish
 whatever lies below with an explicit stack. All of them share this limit.

-Most of them pass the depth down as an argument. The copy constructor and the
-comparison operators cannot, as their signatures are fixed, so they count it
-in basic_json::nesting_depth() instead, a byte per thread; the limit must
-therefore stay below 255.
-
@sa https://github.com/nlohmann/json/issues/5387
 */
 constexpr std::size_t recursion_depth_limit() noexcept
@@ -26985,8 +26979,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    }

 #ifndef JSON_NO_THREAD_LOCAL
-    // nesting_depth() is a byte and may exceed the limit by one level
-    static_assert(detail::recursion_depth_limit() < 255, "the nesting depth count must fit in a byte");
+    /// the number of levels an operation descends into before it finishes the
+    /// value below it without the call stack
+    static constexpr std::uint8_t nesting_depth_limit()
+    {
+        return 128;
+    }

    /*!
    @brief how many levels the operation going on in this thread has descended into
@@ -27028,7 +27026,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
        static_cast<void>(may_descend);
        return true;
 #else
-        return !may_descend || nesting_depth() >= detail::recursion_depth_limit();
+        return !may_descend || nesting_depth() >= nesting_depth_limit();
 #endif
    }

@@ -27052,7 +27050,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 #ifdef JSON_NO_THREAD_LOCAL
            : m_okay(false)
 #else
-            : m_okay(nesting_depth() < detail::recursion_depth_limit())
+            : m_okay(nesting_depth() < nesting_depth_limit())
 #endif
        {
 #ifndef JSON_NO_THREAD_LOCAL
@@ -27256,7 +27254,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec

    The values whose copy has not been created yet are kept on an explicit
    worklist rather than on the call stack. This is only reached for values
-    nested deeper than @ref detail::recursion_depth_limit levels, which is why it copies
+    nested deeper than @ref nesting_depth_limit levels, which is why it copies
    every container by hand instead of letting the container do it: the fast
    ways of doing so would descend into the elements and defeat the purpose.
    */
@@ -27322,7 +27320,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec

    Copying a container copies its elements, so a value nested deeply enough
    used to exhaust the call stack. The descent is bounded here: the first
-    @ref detail::recursion_depth_limit levels are copied by the containers themselves, just
+    @ref nesting_depth_limit levels are copied by the containers themselves, just
    as they always were, and anything below that is copied without the call
    stack by @ref copy_iteratively. Copying a value can therefore no longer
    exhaust the stack, however deeply it is nested, just like destroying one
@@ -27460,7 +27458,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
    /*!
    @brief compare @a lhs and @a rhs without descending into them

-    Reached once a comparison has descended @ref detail::recursion_depth_limit levels, so
+    Reached once a comparison has descended @ref nesting_depth_limit levels, so
    that comparing values cannot exhaust the call stack however deeply they are
    nested. The two values are walked in lockstep on an explicit stack and
    compared lexicographically, element by element in the order the containers
@@ -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