Fix deprecated json_pointer/string operator== warning in value()

value(KeyType&&, default) is constrained on is_comparable_with_object_key,
which passes KeyType as a reference. is_comparable's dispatch on
is_json_pointer_of<A, B> only matches a json_pointer as a plain type or a
plain reference, so a const-qualified reference (as produced when KeyType
is deduced from a json_pointer argument) fell through to
is_comparable_no_json_pointer, which instantiates the deprecated
json_pointer/string comparison operators. This made ordered_json's
transparent comparator (and any transparent comparator on a custom string
type) warn under -Wdeprecated-declarations when calling
value(json_pointer, default), even though no such comparison is ever
performed. at() was already fixed for this in #5289, which does not use
is_comparable_with_object_key.

Strip references and cv-qualifiers with uncvref_t before the
is_json_pointer_of dispatch, so any reference-to-json_pointer is
recognized regardless of qualifiers.

Fixes #5664.

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

docs/mkdocs/docs/api/basic_json/insert.md

@@ -195,7 +195,5 @@ Strong exception safety: if an exception occurs, the original value stays intact
 1. Added in version 1.0.0.
 2. Added in version 1.0.0.
 3. Added in version 1.0.0.
-4. Added in version 1.0.0. Fixed in version 3.13.0 to copy the values before inserting; before, an `ilist` that
-   referred to elements of the array being inserted into could insert wrong values, because the range insert could
-   move from or shift an element before it was copied.
+4. Added in version 1.0.0.
 5. Added in version 3.0.0.

include/nlohmann/detail/meta/type_traits.hpp

@@ -725,7 +725,7 @@ std::is_constructible <decltype(std::declval<Compare>()(std::declval<A>(), std::
 // avoid their instantiation on all compilers, even when the first operand
 // is false. The dispatch on is_json_pointer_of can be removed once the
 // deprecated json_pointer comparison operators have been removed.
-template<typename Compare, typename A, typename B, bool = is_json_pointer_of<A, B>::value>
+template<typename Compare, typename A, typename B, bool = is_json_pointer_of<uncvref_t<A>, uncvref_t<B>>::value>
 struct is_comparable : std::false_type {};
 
 template<typename Compare, typename A, typename B>

include/nlohmann/json.hpp

@@ -4152,16 +4152,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(invalid_iterator::create(202, "iterator does not fit current value", this));
         }
 
-        // copy the values first: ilist may refer to elements of this array
-        array_t values;
-        detail::reserve_array(values, ilist.size(), detail::priority_tag<1> {});
-        for (const auto& element : ilist)
-        {
-            values.push_back(element.moved_or_copied());
-        }
-
         // insert to array and return iterator
-        return insert_iterator(pos, std::make_move_iterator(values.begin()), std::make_move_iterator(values.end()));
+        return insert_iterator(pos, ilist.begin(), ilist.end());
     }
 
     /// @brief inserts range of elements into object

single_include/nlohmann/json.hpp

@@ -4735,7 +4735,7 @@ std::is_constructible <decltype(std::declval<Compare>()(std::declval<A>(), std::
 // avoid their instantiation on all compilers, even when the first operand
 // is false. The dispatch on is_json_pointer_of can be removed once the
 // deprecated json_pointer comparison operators have been removed.
-template<typename Compare, typename A, typename B, bool = is_json_pointer_of<A, B>::value>
+template<typename Compare, typename A, typename B, bool = is_json_pointer_of<uncvref_t<A>, uncvref_t<B>>::value>
 struct is_comparable : std::false_type {};
 
 template<typename Compare, typename A, typename B>
@@ -30233,16 +30233,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             JSON_THROW(invalid_iterator::create(202, "iterator does not fit current value", this));
         }
 
-        // copy the values first: ilist may refer to elements of this array
-        array_t values;
-        detail::reserve_array(values, ilist.size(), detail::priority_tag<1> {});
-        for (const auto& element : ilist)
-        {
-            values.push_back(element.moved_or_copied());
-        }
-
         // insert to array and return iterator
-        return insert_iterator(pos, std::make_move_iterator(values.begin()), std::make_move_iterator(values.end()));
+        return insert_iterator(pos, ilist.begin(), ilist.end());
     }
 
     /// @brief inserts range of elements into object

tests/src/unit-custom-array-type.cpp

@@ -117,22 +117,6 @@ TEST_CASE("array type without capacity()")
         CHECK(nested.flatten().unflatten() == nested);
     }
 
-    SECTION("insert(pos, initializer_list) compiles and works without reserve()")
-    {
-        // std::deque has no reserve() either; insert(pos, ilist) must not
-        // require it (regression test for #5656, which also covers an ilist
-        // that refers to elements of the array being inserted into)
-        deque_json j = deque_json::array();
-        j.push_back("a");
-        j.push_back("b");
-        j.push_back("c");
-
-        const deque_json& cj = j;
-        auto it = j.insert(j.begin(), {cj[0], cj[1]});
-        CHECK(*it == deque_json("a"));
-        CHECK(j == deque_json({"a", "b", "a", "b", "c"}));
-    }
-
     SECTION("references stay valid while the array grows")
     {
         deque_json j = deque_json::array();

tests/src/unit-json_pointer.cpp

@@ -858,6 +858,25 @@ TEST_CASE("JSON pointers")
         }
     }
 
+    SECTION("value(json_pointer, default) with ordered_json #5664")
+    {
+        // ordered_json's transparent object comparator made value()'s
+        // is_comparable_with_object_key check (which passes the pointer as
+        // a reference) instantiate the deprecated json_pointer/string
+        // comparison; this must compile without relying on it. The
+        // deprecation warning itself is not observable here, since the
+        // unit test build disables -Wdeprecated-declarations (see
+        // cmake/clang_flags.cmake); it was checked manually instead.
+        const nlohmann::ordered_json j = {{"n", 1}, {"s", "text"}};
+        const nlohmann::ordered_json::json_pointer ptr_n("/n");
+        const nlohmann::ordered_json::json_pointer ptr_s("/s");
+        const nlohmann::ordered_json::json_pointer ptr_missing("/missing");
+
+        CHECK(j.value(ptr_n, 0) == 1);
+        CHECK(j.value(ptr_s, std::string("x")) == "text");
+        CHECK(j.value(ptr_missing, 42) == 42);
+    }
+
     // build with C++20
     // JSON_HAS_CPP_20
 #if defined(__cpp_char8_t)

tests/src/unit-modifiers.cpp

@@ -761,34 +761,6 @@ TEST_CASE("modifiers")
             }
         }
 
-        SECTION("initializer list referring to the array's own elements (#5656)")
-        {
-            SECTION("sufficient capacity (no reallocation)")
-            {
-                json j_own = json::array();
-                j_own.get_ref<json::array_t&>().reserve(8);
-                j_own.push_back("a");
-                j_own.push_back("b");
-                j_own.push_back("c");
-
-                const json& j_own_cref = j_own;
-                auto it = j_own.insert(j_own.begin(), {j_own_cref[0], j_own_cref[1]});
-                CHECK(*it == json("a"));
-                CHECK(j_own == json({"a", "b", "a", "b", "c"}));
-            }
-
-            SECTION("insufficient capacity (reallocation)")
-            {
-                json j_own = {"a", "b", "c"};
-                j_own.get_ref<json::array_t&>().shrink_to_fit();
-
-                const json& j_own_cref = j_own;
-                auto it = j_own.insert(j_own.begin(), {j_own_cref[2]});
-                CHECK(*it == json("c"));
-                CHECK(j_own == json({"c", "a", "b", "c"}));
-            }
-        }
-
         SECTION("invalid iterator")
         {
             // pass iterator to a different array