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/to_bson.md

@@ -43,9 +43,6 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [`out_of_range.412`](../../home/exceptions.md#jsonexceptionout_of_range412) if the length of a document, array,
   string, or binary value exceeds the range of the 32-bit BSON length field; example:
   `"BSON length 2147483661 exceeds maximum of 2147483647"`
-- Throws [`out_of_range.415`](../../home/exceptions.md#jsonexceptionout_of_range415) if the subtype of a binary value
-  exceeds 255, the maximum of the BSON binary subtype; example:
-  `"subtype 70000 is too large for the BSON binary subtype (max 255)"`
 
 ## Complexity
 
@@ -81,4 +78,3 @@ pass before anything is written.
 
 - Added in version 3.4.0.
 - Linear in the size of `j`, and no longer limited by the call stack for deeply nested values, since version 3.13.0.
-- `out_of_range.415` is now detected before anything is written, like the other exceptions above, since version 3.13.0.

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/detail/output/binary_writer.hpp

@@ -1055,26 +1055,15 @@ class binary_writer
     }
 
     /*!
-    @return The size of the BSON-encoded binary array in @a j
-    @throw out_of_range.415 if the subtype of @a j does not fit into a byte,
-           before anything is written
+    @return The size of the BSON-encoded binary array @a value
     */
-    static std::size_t calc_bson_binary_size(const BasicJsonType& j)
+    static std::size_t calc_bson_binary_size(const typename BasicJsonType::binary_t& value)
     {
-        const auto& value = *j.m_data.m_value.binary;
-
-        if (value.has_subtype() && JSON_HEDLEY_UNLIKELY(value.subtype() > (std::numeric_limits<std::uint8_t>::max)()))
-        {
-            JSON_THROW(out_of_range::create(415, concat("subtype ", std::to_string(value.subtype()), " is too large for the BSON binary subtype (max 255)"), &j));
-        }
-
         return sizeof(std::int32_t) + value.size() + 1ul;
     }
 
     /*!
     @brief Writes a BSON element with key @a name and binary value @a value
-    @pre    @a value's subtype, if any, fits into a byte; @ref calc_bson_sizes
-            checks this for every binary value in the document beforehand.
     */
     void write_bson_binary(const string_t& name,
                            const binary_t& value)
@@ -1083,6 +1072,11 @@ class binary_writer
 
         write_number<std::int32_t>(to_bson_length(value.size()), true);
 
+        if (value.has_subtype() && JSON_HEDLEY_UNLIKELY(value.subtype() > (std::numeric_limits<std::uint8_t>::max)()))
+        {
+            JSON_THROW(out_of_range::create(415, concat("subtype ", std::to_string(value.subtype()), " is too large for the BSON binary subtype (max 255)"), nullptr));
+        }
+
         write_number(value.has_subtype() ? static_cast<std::uint8_t>(value.subtype()) : static_cast<std::uint8_t>(0x00));
 
         oa.write_characters(reinterpret_cast<const CharType*>(value.data()), value.size());
@@ -1091,15 +1085,13 @@ class binary_writer
     /*!
     @return The size of the value of the BSON document entry for @a j, which
             is neither an object nor an array
-    @throw out_of_range.415 if @a j is binary with a subtype that does not fit
-           into a byte, before anything is written
     */
     static std::size_t calc_bson_value_size(const BasicJsonType& j)
     {
         switch (j.type())
         {
             case value_t::binary:
-                return calc_bson_binary_size(j);
+                return calc_bson_binary_size(*j.m_data.m_value.binary);
 
             case value_t::boolean:
                 return 1ul;
@@ -1225,8 +1217,6 @@ class binary_writer
     @return the size of @a document
     @throw out_of_range.409 if a key contains U+0000, before anything is
            written
-    @throw out_of_range.415 if a binary value's subtype does not fit into a
-           byte, before anything is written
     */
     static std::size_t calc_bson_sizes(const BasicJsonType& document, std::vector<std::size_t>& nested_sizes)
     {

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>
@@ -21385,26 +21385,15 @@ class binary_writer
     }
 
     /*!
-    @return The size of the BSON-encoded binary array in @a j
-    @throw out_of_range.415 if the subtype of @a j does not fit into a byte,
-           before anything is written
+    @return The size of the BSON-encoded binary array @a value
     */
-    static std::size_t calc_bson_binary_size(const BasicJsonType& j)
+    static std::size_t calc_bson_binary_size(const typename BasicJsonType::binary_t& value)
     {
-        const auto& value = *j.m_data.m_value.binary;
-
-        if (value.has_subtype() && JSON_HEDLEY_UNLIKELY(value.subtype() > (std::numeric_limits<std::uint8_t>::max)()))
-        {
-            JSON_THROW(out_of_range::create(415, concat("subtype ", std::to_string(value.subtype()), " is too large for the BSON binary subtype (max 255)"), &j));
-        }
-
         return sizeof(std::int32_t) + value.size() + 1ul;
     }
 
     /*!
     @brief Writes a BSON element with key @a name and binary value @a value
-    @pre    @a value's subtype, if any, fits into a byte; @ref calc_bson_sizes
-            checks this for every binary value in the document beforehand.
     */
     void write_bson_binary(const string_t& name,
                            const binary_t& value)
@@ -21413,6 +21402,11 @@ class binary_writer
 
         write_number<std::int32_t>(to_bson_length(value.size()), true);
 
+        if (value.has_subtype() && JSON_HEDLEY_UNLIKELY(value.subtype() > (std::numeric_limits<std::uint8_t>::max)()))
+        {
+            JSON_THROW(out_of_range::create(415, concat("subtype ", std::to_string(value.subtype()), " is too large for the BSON binary subtype (max 255)"), nullptr));
+        }
+
         write_number(value.has_subtype() ? static_cast<std::uint8_t>(value.subtype()) : static_cast<std::uint8_t>(0x00));
 
         oa.write_characters(reinterpret_cast<const CharType*>(value.data()), value.size());
@@ -21421,15 +21415,13 @@ class binary_writer
     /*!
     @return The size of the value of the BSON document entry for @a j, which
             is neither an object nor an array
-    @throw out_of_range.415 if @a j is binary with a subtype that does not fit
-           into a byte, before anything is written
     */
     static std::size_t calc_bson_value_size(const BasicJsonType& j)
     {
         switch (j.type())
         {
             case value_t::binary:
-                return calc_bson_binary_size(j);
+                return calc_bson_binary_size(*j.m_data.m_value.binary);
 
             case value_t::boolean:
                 return 1ul;
@@ -21555,8 +21547,6 @@ class binary_writer
     @return the size of @a document
     @throw out_of_range.409 if a key contains U+0000, before anything is
            written
-    @throw out_of_range.415 if a binary value's subtype does not fit into a
-           byte, before anything is written
     */
     static std::size_t calc_bson_sizes(const BasicJsonType& document, std::vector<std::size_t>& nested_sizes)
     {

tests/src/unit-bson.cpp

@@ -797,11 +797,7 @@ TEST_CASE("regression test - BSON binary subtype rejects a value that doesn't fi
     CHECK(json::from_bson(json::to_bson(doc255))["b"].get_binary().subtype() == 255);
 
     CHECK_THROWS_AS(json::to_bson(json{{"b", json::binary({1, 2}, 256)}}), json::out_of_range);
-#if JSON_DIAGNOSTICS
-    CHECK_THROWS_WITH_AS(json::to_bson(json {{"b", json::binary({1, 2}, 300)}}), "[json.exception.out_of_range.415] (/b) subtype 300 is too large for the BSON binary subtype (max 255)", json::out_of_range);
-#else
-    CHECK_THROWS_WITH_AS(json::to_bson(json {{"b", json::binary({1, 2}, 300)}}), "[json.exception.out_of_range.415] subtype 300 is too large for the BSON binary subtype (max 255)", json::out_of_range);
-#endif
+    CHECK_THROWS_WITH_AS(json::to_bson(json{{"b", json::binary({1, 2}, 300)}}), "[json.exception.out_of_range.415] subtype 300 is too large for the BSON binary subtype (max 255)", json::out_of_range);
 }
 
 TEST_CASE("BSON input/output_adapters")
@@ -1809,21 +1805,6 @@ value = depth % 2 == 0 ? json{{"a", std::move(value)}, {"b", {1, "x"}}} :
         CHECK(output.empty());
     }
 
-    SECTION("a binary subtype that doesn't fit a byte is rejected before anything is written (#5675)")
-    {
-        // the offending value is nested, so this also covers that the check
-        // is not limited to a directly written value's own document
-        json const j = {{"a", {{"b", json::binary({1, 2}, 300)}}}};
-
-        std::vector<std::uint8_t> vector_output;
-        CHECK_THROWS_AS(json::to_bson(j, vector_output), json::out_of_range&);
-        CHECK(vector_output.empty());
-
-        std::string string_output;
-        CHECK_THROWS_AS(json::to_bson(j, string_output), json::out_of_range&);
-        CHECK(string_output.empty());
-    }
-
     SECTION("values nested too deeply for the call stack (#5392)")
     {
         // serializing recursed once per nesting level, and computed every

tests/src/unit-diagnostics.cpp

@@ -101,12 +101,6 @@ TEST_CASE("Regression tests for extended diagnostics")
         CHECK_THROWS_WITH_AS(j.unflatten(), "[json.exception.type_error.315] (/~1foo) values in object must be primitive", json::type_error);
     }
 
-    SECTION("Regression test for issue #5675 - to_bson: out_of_range.415 has no diagnostics context")
-    {
-        json const j = {{"a", {{"b", json::binary({1, 2}, 300)}}}};
-        CHECK_THROWS_WITH_AS(json::to_bson(j), "[json.exception.out_of_range.415] (/a/b) subtype 300 is too large for the BSON binary subtype (max 255)", json::out_of_range);
-    }
-
     SECTION("Regression test for issue #2838 - Assertion failure when inserting into arrays with JSON_DIAGNOSTICS set")
     {
         // void push_back(basic_json&& val)

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)