add strict enum de/serialization macro #4612

hnampally · 2025-01-20T04:53:58Z

#3992

The changes are described in detail, both the what and why.
If applicable, an #3992 is referenced.
The Code coverage remained at 100%. A test case for every new line of code.
If applicable, the documentation is updated.
The source code is amalgamated by running make amalgamate.

Read the Contribution Guidelines for detailed information.

Signed-off-by: Harinath Nampally <[email protected]>

github-actions · 2025-01-20T04:56:45Z

🔴 Amalgamation check failed! 🔴

The source code has not been amalgamated. @hnampally
Please read and follow the Contribution Guidelines.

coveralls · 2025-01-20T05:25:14Z

coverage: 99.186%. remained the same
when pulling 6747555 on hnampally:issue-3992
into 606b634 on nlohmann:develop.

Signed-off-by: Harinath Nampally <[email protected]>

docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md

docs/mkdocs/docs/examples/nlohmann_json_deserialize_enum_strict.cpp

Signed-off-by: Harinath Nampally <[email protected]>

include/nlohmann/detail/macro_scope.hpp

github-actions · 2025-01-26T22:03:23Z

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The source code has not been amalgamated. @hnampally
Please read and follow the Contribution Guidelines.

Signed-off-by: Harinath Nampally <[email protected]>

docs/mkdocs/docs/examples/nlohmann_json_serialize_enum_strict.cpp

docs/mkdocs/docs/features/enum_conversion.md

include/nlohmann/detail/macro_scope.hpp

Signed-off-by: Harinath Nampally <[email protected]>

nlohmann · 2025-01-27T06:45:30Z

include/nlohmann/detail/macro_scope.hpp

+template<typename T>
+[[noreturn]] inline void json_throw_from_serialize_macro(T&& exception)
+{
+#if defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND) || defined(EXCEPTIONS)


When defining JSON_THROW in the same file, we use the following code to detect exceptions. Please use the same here to avoid issues.

#if (defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)) && !defined(JSON_NOEXCEPTION)

oh okay, thanks!

nlohmann · 2025-01-27T06:49:56Z

include/nlohmann/detail/macro_scope.hpp

+        });                                                                                     \
+        if (it == std::end(m)) { \
+            auto value = static_cast<typename std::underlying_type<ENUM_TYPE>::type>(e); \
+            nlohmann::detail::json_throw_from_serialize_macro(nlohmann::detail::type_error::create(302, nlohmann::detail::concat("can't serialize - enum value ", std::to_string(value), " out of range"), &j)); \


I don't like the exception message. What about

serialization failed: enum value ... is out of range

Yes that sounds better, thanks!

nlohmann · 2025-01-27T06:52:01Z

include/nlohmann/detail/macro_scope.hpp

+            return ej_pair.second == j;                                                         \
+        });                                                                                     \
+        if (it == std::end(m))            \
+            nlohmann::detail::json_throw_from_serialize_macro(nlohmann::detail::type_error::create(302, nlohmann::detail::concat("can't deserialize - invalid json value : ", j.dump()), &j)); \


Same as above:

deserialization failed: invalid JSON value '...'

Signed-off-by: Harinath Nampally <[email protected]>

gregmarr · 2025-01-28T03:08:08Z

docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md

+#define NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(type, conversion...)
+```
+
+The `NLOHMANN_JSON_SERIALIZE_ENUM_STRICT` allows to define a user-defined serialization for every enumerator.


This is missing some words.

The ... macro allows defining a ...
or
The ... macro allows one to define a ...

I can see this is basically the same text as in the original, it should probably be updated there too.

gregmarr · 2025-01-28T03:15:56Z

docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md

+:   name of the enum to serialize/deserialize
+
+`conversion` (in)
+:   a pair of an enumerator and a JSON serialization; arbitrary pairs can be given as a comma-separated list


I would say "pairs" rather than "a pair", and "a JSON serialization" is odd, maybe "the string to be used in the JSON serialization. The "arbitrary pairs can be given as a comma-separated list" sounds weird to me.
Maybe

A list of parameters alternating between an enumerator value and a string to use in the JSON serialization.

gregmarr · 2025-01-28T03:17:35Z

docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md

+!!! important "Important notes"
+
+    - If an enum value appears more than once in the mapping, only the first occurrence will be used for serialization, 
+        subsequent mappings for the same enum value will be ignored.


Would it be worth putting in something here like "will currently be ignored but may result in an error in the future"?

gregmarr · 2025-01-28T03:28:58Z

docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md

+
+    - If an enum value appears more than once in the mapping, only the first occurrence will be used for serialization, 
+        subsequent mappings for the same enum value will be ignored.
+    - If a JSON value appears more than once in the mapping, only the first occurrence will be used for deserialization, 


"If a string value" since it's not an arbitrary json value but a string....

Oh, OH, it doesn't require that it be a string, does it?

😮

There's nothing in the code that requires that this be a string.

NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(Color, { { Red, "red" }, { Green, nlohmann::json(1) }, { Blue, nlohmann::json({{{"purple", "people eater"}}})} }) int main() { nlohmann::json j; j = { Red, Green, Blue }; std::cout << j.dump() << "\n"; auto j2 = nlohmann::json::parse(j.dump()); std::vector<Color> vec = j2; std::cout << vec[0] << vec[1] << vec[2]; }

["red",1,[{"purple":"people eater"}]] 012

@hnampally Is this intended behavior, or did this just accidentally fall out of the second parameter being BasicJsonType instead of std::string?

If this is intended behavior, it should definitely be documented before someone trips upon it accidentally, or someone relies on it and then someone else "fixes" it.

If it's not intended behavior, then it should be fixed.

@gregmarr thanks for bringing this up but I am not really sure about the requirements for this feature but I am open for either, @nlohmann please weigh in!

Signed-off-by: Harinath Nampally <[email protected]>

nlohmann · 2025-01-31T15:51:40Z

docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md

+    Expected output:
+
+    ```
+    [json.exception.type_error.302] serialization failed: enum value 3 is out of range


Also use an include here:

--8<-- "examples/nlohmann_json_serialize_enum_strict.output"

nlohmann · 2025-01-31T15:52:15Z

docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md

+    Expected output:
+
+    ```
+    [json.exception.type_error.302] deserialization failed: invalid JSON value "yellow"


Also use an include here:

--8<-- "examples/nlohmann_json_deserialize_enum_strict.output"

nlohmann · 2025-01-31T15:53:34Z

docs/mkdocs/docs/examples/nlohmann_json_deserialize_enum_strict.cpp

+
+int main()
+{
+


Remove the empty line.

Also: move line

json j_yellow = "yellow";

above the comment

// deserialization

gregmarr · 2025-01-31T17:59:48Z

It looks like you have a space in your filename here:
docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum _strict.md

Also, the discussion about strings vs arbitrary json for the value has been marked outdated because there was a change in the file. @nlohmann did you see that discussion?

Signed-off-by: Harinath Nampally <[email protected]>

hnampally requested a review from nlohmann as a code owner January 20, 2025 04:53

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add strict enum de/serialization macro

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add strict enum de/serialization macro #4612

add strict enum de/serialization macro #4612

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add strict enum de/serialization macro #4612

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add strict enum de/serialization macro #4612

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