Add as_base_class to the docset search index

New public members get an entry in docs/docset/docSet.sql (as done for
to_bon8/from_bon8 in #2998). Without it, the Dash/Zeal docset built from
the documentation cannot find basic_json::as_base_class.

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

docs/docset/docSet.sql

@@ -16,6 +16,7 @@ INSERT INTO searchIndex(name, type, path) VALUES ('basic_json', 'Class', 'api/ba
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::accept', 'Function', 'api/basic_json/accept/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::array', 'Function', 'api/basic_json/array/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::array_t', 'Type', 'api/basic_json/array_t/index.html');
+INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::as_base_class', 'Method', 'api/basic_json/as_base_class/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::at', 'Method', 'api/basic_json/at/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::back', 'Method', 'api/basic_json/back/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::basic_json', 'Constructor', 'api/basic_json/basic_json/index.html');

docs/mkdocs/docs/api/basic_json/as_base_class.md

@@ -0,0 +1,53 @@
+# <small>nlohmann::basic_json::</small>as_base_class
+
+```cpp
+json_base_class_t& as_base_class() noexcept;
+const json_base_class_t& as_base_class() const noexcept;
+```
+
+Returns a reference to this object as its custom base class [`json_base_class_t`](json_base_class_t.md). No copy is
+made.
+
+Since `basic_json` derives from `json_base_class_t`, a member of `basic_json` hides any member of the custom base class
+with the same name. This function makes such hidden members accessible again.
+
+## Return value
+
+reference to this object as [`json_base_class_t`](json_base_class_t.md)
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Constant.
+
+## Notes
+
+The function is equivalent to `static_cast<json_base_class_t&>(j)` (or `static_cast<const json_base_class_t&>(j)`).
+
+## Examples
+
+??? example
+
+    The example shows how to use `as_base_class` to access members of the custom base class that are hidden by members
+    of `basic_json`.
+    
+    ```cpp
+    --8<-- "examples/as_base_class.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/as_base_class.output"
+    ```
+
+## See also
+
+- [json_base_class_t](json_base_class_t.md) - type of the custom base class
+
+## Version history
+
+- Added in version 3.13.0.

docs/mkdocs/docs/api/basic_json/index.md

@@ -200,6 +200,7 @@ Direct access to the stored value of a JSON value.
 - [**get_ref**](get_ref.md) - get a reference value
 - [**operator ValueType**](operator_ValueType.md) - get a value
 - [**get_binary**](get_binary.md) - get a binary value
+- [**as_base_class**](as_base_class.md) - access the custom base class
 
 ### Element access
 

docs/mkdocs/docs/api/basic_json/json_base_class_t.md

@@ -27,6 +27,18 @@ A `CustomBaseClass` with non-static data members forfeits `basic_json`'s
 [standard layout](https://en.cppreference.com/w/cpp/named_req/StandardLayoutType) guarantee. See
 [Template Parameter Requirements](../../features/types/template_parameters.md#custombaseclass).
 
+#### Name conflicts
+
+Since `basic_json` derives from `CustomBaseClass`, members of `basic_json` hide members of `CustomBaseClass` with the
+same name. Hidden members remain accessible via [`as_base_class`](as_base_class.md) or by casting the value to
+`json_base_class_t`.
+
+!!! warning "Avoid generic member names"
+
+    Future versions of the library may add members to `basic_json` that hide members of `CustomBaseClass` that are
+    accessible today. To reduce the risk of such conflicts, avoid generic names for the members of `CustomBaseClass`,
+    for instance by using a distinctive prefix.
+
 ## Examples
 
 ??? example
@@ -43,6 +55,11 @@ A `CustomBaseClass` with non-static data members forfeits `basic_json`'s
     --8<-- "examples/json_base_class_t.output"
     ```
 
+## See also
+
+- [as_base_class](as_base_class.md) - access the custom base class
+
 ## Version history
 
 - Added in version 3.12.0.
+- Made a public member type in version 3.13.0; it was private before, so it could not be named outside the class.

docs/mkdocs/docs/examples/as_base_class.cpp

@@ -0,0 +1,41 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+class base_class_with_hidden_members
+{
+  public:
+    const char* type_name() const noexcept
+    {
+        return "my_type_name";
+    }
+
+    std::size_t size() const noexcept
+    {
+        return 42;
+    }
+};
+
+using json = nlohmann::basic_json <
+             std::map,
+             std::vector,
+             std::string,
+             bool,
+             std::int64_t,
+             std::uint64_t,
+             double,
+             std::allocator,
+             nlohmann::adl_serializer,
+             std::vector<std::uint8_t>,
+             base_class_with_hidden_members
+             >;
+
+int main()
+{
+    json j = {1, 2, 3};
+
+    // the members of basic_json hide the members of the base class
+    std::cout << j.type_name() << ' ' << j.size() << '\n';
+
+    // access the hidden members of the base class
+    std::cout << j.as_base_class().type_name() << ' ' << j.as_base_class().size() << '\n';
+}

docs/mkdocs/docs/examples/as_base_class.output

@@ -0,0 +1,2 @@
+array 3
+my_type_name 42

docs/mkdocs/mkdocs.yml

@@ -114,6 +114,7 @@ nav:
           - 'accept': api/basic_json/accept.md
           - 'array': api/basic_json/array.md
           - 'array_t': api/basic_json/array_t.md
+          - 'as_base_class': api/basic_json/as_base_class.md
           - 'at': api/basic_json/at.md
           - 'back': api/basic_json/back.md
           - 'begin': api/basic_json/begin.md

include/nlohmann/json.hpp

@@ -153,7 +153,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// workaround type for MSVC
     using basic_json_t = NLOHMANN_BASIC_JSON_TPL;
-    using json_base_class_t = ::nlohmann::detail::json_base_class<CustomBaseClass>;
 
   JSON_PRIVATE_UNLESS_TESTED:
     // convenience aliases for types residing in namespace detail;
@@ -213,6 +212,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     using cbor_tag_handler_t = detail::cbor_tag_handler_t;
     /// how to encode BJData
     using bjdata_version_t = detail::bjdata_version_t;
+    /// base class used to inject custom functionality into each instance of basic_json
+    /// @sa https://json.nlohmann.me/api/basic_json/json_base_class_t/
+    using json_base_class_t = ::nlohmann::detail::json_base_class<CustomBaseClass>;
     /// helper type for initializer lists of basic_json values
     using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
 
@@ -2690,6 +2692,20 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return *get_ptr<const binary_t*>();
     }
 
+    /// @brief access the custom base class
+    /// @sa https://json.nlohmann.me/api/basic_json/as_base_class/
+    json_base_class_t& as_base_class() noexcept
+    {
+        return static_cast<json_base_class_t&>(*this);
+    }
+
+    /// @brief access the custom base class
+    /// @sa https://json.nlohmann.me/api/basic_json/as_base_class/
+    const json_base_class_t& as_base_class() const noexcept
+    {
+        return static_cast<const json_base_class_t&>(*this);
+    }
+
     /// @}
 
     ////////////////////

single_include/nlohmann/json.hpp

@@ -26036,7 +26036,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// workaround type for MSVC
     using basic_json_t = NLOHMANN_BASIC_JSON_TPL;
-    using json_base_class_t = ::nlohmann::detail::json_base_class<CustomBaseClass>;
 
   JSON_PRIVATE_UNLESS_TESTED:
     // convenience aliases for types residing in namespace detail;
@@ -26096,6 +26095,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     using cbor_tag_handler_t = detail::cbor_tag_handler_t;
     /// how to encode BJData
     using bjdata_version_t = detail::bjdata_version_t;
+    /// base class used to inject custom functionality into each instance of basic_json
+    /// @sa https://json.nlohmann.me/api/basic_json/json_base_class_t/
+    using json_base_class_t = ::nlohmann::detail::json_base_class<CustomBaseClass>;
     /// helper type for initializer lists of basic_json values
     using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
 
@@ -28573,6 +28575,20 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return *get_ptr<const binary_t*>();
     }
 
+    /// @brief access the custom base class
+    /// @sa https://json.nlohmann.me/api/basic_json/as_base_class/
+    json_base_class_t& as_base_class() noexcept
+    {
+        return static_cast<json_base_class_t&>(*this);
+    }
+
+    /// @brief access the custom base class
+    /// @sa https://json.nlohmann.me/api/basic_json/as_base_class/
+    const json_base_class_t& as_base_class() const noexcept
+    {
+        return static_cast<const json_base_class_t&>(*this);
+    }
+
     /// @}
 
     ////////////////////

tests/src/unit-custom-base-class.cpp

@@ -9,6 +9,8 @@
 #include <set>
 #include <sstream>
 #include <string>
+#include <type_traits>
+#include <utility>
 
 #include "doctest_compatibility.h"
 
@@ -333,3 +335,71 @@ TEST_CASE("JSON Visit Node")
         );
     CHECK(expected.empty());
 }
+
+// Test accessing members of a custom base class that are hidden by members of nlohmann::basic_json
+class base_class_with_hidden_members
+{
+  public:
+    const char* type_name() const noexcept
+    {
+        return "custom type_name";
+    }
+
+    std::size_t size() const noexcept
+    {
+        return m_size;
+    }
+
+    std::size_t m_size = 42;
+};
+
+using json_with_hidden_base_members =
+    nlohmann::basic_json <
+    std::map,
+    std::vector,
+    std::string,
+    bool,
+    std::int64_t,
+    std::uint64_t,
+    double,
+    std::allocator,
+    nlohmann::adl_serializer,
+    std::vector<std::uint8_t>,
+    base_class_with_hidden_members
+    >;
+
+TEST_CASE("JSON Node as_base_class")
+{
+    using json = json_with_hidden_base_members;
+
+    static_assert(std::is_same<decltype(std::declval<json&>().as_base_class()), json::json_base_class_t&>::value, "");
+    static_assert(std::is_same<decltype(std::declval<const json&>().as_base_class()), const json::json_base_class_t&>::value, "");
+    static_assert(noexcept(std::declval<json&>().as_base_class()), "");
+    static_assert(noexcept(std::declval<const json&>().as_base_class()), "");
+
+    SECTION("non-const")
+    {
+        json j = {1, 2, 3};
+
+        CHECK(std::string(j.type_name()) == "array");
+        CHECK(j.size() == 3);
+        CHECK(std::string(j.as_base_class().type_name()) == "custom type_name");
+        CHECK(j.as_base_class().size() == 42);
+        CHECK(&j.as_base_class() == &static_cast<json::json_base_class_t&>(j));
+
+        j.as_base_class().m_size = 7;
+        CHECK(j.as_base_class().size() == 7);
+        CHECK(j.size() == 3);
+    }
+
+    SECTION("const")
+    {
+        const json j = {1, 2, 3};
+
+        CHECK(std::string(j.type_name()) == "array");
+        CHECK(j.size() == 3);
+        CHECK(std::string(j.as_base_class().type_name()) == "custom type_name");
+        CHECK(j.as_base_class().size() == 42);
+        CHECK(&j.as_base_class() == &static_cast<const json::json_base_class_t&>(j));
+    }
+}

tests/src/unit-msgpack.cpp

@@ -2165,13 +2165,6 @@ TEST_CASE("MessagePack with std::byte")
 #endif
 
 // the fake sizes below do not fit into a 32-bit std::size_t
-// with clang and libstdc++ 10, the std::filesystem::path conversion that
-// C++17 builds consider for every string type is ambiguous for a class
-// derived from std::string, so the string case is not tested there
-#if !(defined(__clang__) && defined(_GLIBCXX_RELEASE) && _GLIBCXX_RELEASE < 11)
-    #define JSON_TEST_BEYOND_UINT32_STRING 1
-#endif
-
 #if SIZE_MAX > UINT32_MAX
 template<typename T, typename A = std::allocator<T>>
 struct huge_array : std::vector<T, A>
@@ -2269,12 +2262,11 @@ TEST_CASE("MessagePack Size above uint32 for object")
     object.fake_size = false;
 }
 
-#ifdef JSON_TEST_BEYOND_UINT32_STRING
 struct huge_string : std::string
 {
     using std::string::string;
 
-    std::size_t size() const noexcept // NOLINT(readability-convert-member-functions-to-static)
+    std::size_t size() const noexcept
     {
         return static_cast<std::size_t>(UINT32_MAX) + 1ULL;
     }
@@ -2295,20 +2287,20 @@ using huge_string_json = nlohmann::basic_json <
 
 TEST_CASE("MessagePack Size above uint32 for string")
 {
-    const huge_string_json j = "hello";
+
+    huge_string_json j = "hello";
 
     CHECK_THROWS_WITH_AS(
         huge_string_json::to_msgpack(j),
         "[json.exception.out_of_range.412] MessagePack length 4294967296 exceeds maximum of 4294967295",
         json::out_of_range&);
 }
-#endif
 
 struct huge_binary : std::vector<std::uint8_t>
 {
     using std::vector<std::uint8_t>::vector;
 
-    std::size_t size() const noexcept // NOLINT(readability-convert-member-functions-to-static)
+    std::size_t size() const noexcept
     {
         return static_cast<std::size_t>(UINT32_MAX) + 1ULL;
     }
@@ -2363,6 +2355,13 @@ class beyond_uint32_binary_t : public std::vector<std::uint8_t>
     }
 };
 
+// with clang and libstdc++ 10, the std::filesystem::path conversion that
+// C++17 builds consider for every string type is ambiguous for a class
+// derived from std::string, so the string case is not tested there
+#if !(defined(__clang__) && defined(_GLIBCXX_RELEASE) && _GLIBCXX_RELEASE < 11)
+    #define JSON_TEST_BEYOND_UINT32_STRING 1
+#endif
+
 #ifdef JSON_TEST_BEYOND_UINT32_STRING
 class beyond_uint32_string_t : public std::string
 {