Add NLOHMANN_JSON_SERIALIZE_ENUM_STRICT macro that throws type_error.302 on unknown JSON value (Fixes #3992) #4989

Ash-Jose · 2025-11-04T20:50:48Z

Summary

This PR fixes #3992 by introducing a new macro
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT, which throws a json.exception.type_error.302
when deserializing a JSON string that does not match any enumerator.

The existing NLOHMANN_JSON_SERIALIZE_ENUM macro remains unchanged to preserve backward compatibility.

Changes

Added new macro NLOHMANN_JSON_SERIALIZE_ENUM_STRICT in macro_scope.hpp that throws type_error.302 for unmapped enum strings.
Added new test file unit-serialize_enum_strict.cpp validating the strict throwing behavior.
Regenerated single-header files using make amalgamate.
Verified all tests using ctest --output-on-failure.

Expected test impact

All existing tests for NLOHMANN_JSON_SERIALIZE_ENUM continue to pass unchanged.
New tests for NLOHMANN_JSON_SERIALIZE_ENUM_STRICT confirm that unknown JSON values now trigger exceptions.

Other unrelated floating-point mismatches (e.g., test-regression1_cpp11) are not affected by this change.

Documentation

A new documentation entry will be added at
docs/api/macros/nlohmann_json_serialize_enum_strict.md describing the stricter deserialization behavior.

Checklist

Implementation complete
New strict macro added (NLOHMANN_JSON_SERIALIZE_ENUM_STRICT)
New test added and passing
Single-header regenerated (make amalgamate)
Backward compatibility preserved
DCO signed
Documentation pending maintainer confirmation

nlohmann

Please do not change the existing macros. This would break existing applications. Instead, add a macro NLOHMANN_JSON_SERIALIZE_ENUM_STRICT with the new behavior.

Ash-Jose · 2025-11-04T22:42:44Z

i have made changes accordingly pls review

github-actions · 2025-11-04T23:00:20Z

🔴 Amalgamation check failed! 🔴

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

coveralls · 2025-11-04T23:11:43Z

coverage: 99.192% (+0.001%) from 99.191%
when pulling 1231904 on Ash-Jose:fix/enum-deser-throw-on-unknown
into 49026f7 on nlohmann:develop.

nlohmann

Please add a new line at the end of unit-serialize_enum_strict.cpp.
Please run make amalgamation to properly indent the code.

include/nlohmann/detail/macro_scope.hpp

github-actions · 2025-11-05T09:25:48Z

🔴 Amalgamation check failed! 🔴

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

Ash-Jose · 2025-11-05T10:46:49Z

is this because of using concat
amalgamation check seems to have passed this time around

nlohmann · 2025-11-05T11:10:48Z

is this because of using concat amalgamation check seems to have passed this time around

You need to include #include <nlohmann/detail/string_concat.hpp>.

Ash-Jose · 2025-11-05T11:19:45Z

included the header

github-actions · 2025-11-05T11:46:09Z

🔴 Amalgamation check failed! 🔴

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

Ash-Jose · 2025-11-05T13:14:59Z

why are tests still failing??

nlohmann · 2025-11-05T14:11:40Z

Maybe some issue with the includes. Please try:

remove the string_concat.hpp include
revert the code to using std::string()... like you did before

Sorry for the confusion.

Ash-Jose · 2025-11-05T14:23:23Z

i have reverted it

Ash-Jose · 2025-11-05T15:20:18Z

should i redo in a different branch??
i dont understand why checks are failing

nlohmann · 2025-11-05T16:07:08Z

include/nlohmann/detail/macro_scope.hpp

+        });                                                                                     \
+        if (it == std::end(m))                                                                  \
+        {                                                                                       \
+            throw ::nlohmann::detail::type_error::create(                                       \


This should need the exceptions.hpp header which again includes macro_scope.hpp. I think this is the core of the issue.

ill try including the exceptions header

Also, this needs to use JSON_THROW.

This still needs to be changed, or this macro can't be used by people that disable exceptions.

Ash-Jose · 2025-11-05T17:48:31Z

i dont understand why they still fail

nlohmann · 2025-11-05T18:00:56Z

Because there is more to forward-declare. I'm sorry, but it seems to be a more complicated issue to use an exception in the macro header.

gregmarr · 2025-11-05T18:06:36Z

The forward declarations aren't required for the macro definition, they're required where the things are used.

~~I think the issue is that it's using the detail namespace. I don't think we do that for any of the other user space macros.~~
Nope, simple type issue.

gregmarr · 2025-11-05T18:19:40Z

include/nlohmann/detail/macro_scope.hpp

+            throw ::nlohmann::detail::type_error::create(                                       \
+                    302,                                                                        \
+                    std::string("invalid value for ") + #ENUM_TYPE + ": " + j.dump(),           \
+                    j);                                                                         \


This is your problem, it takes a pointer, it should be &j.

gregmarr · 2025-11-05T18:21:12Z

include/nlohmann/detail/macro_scope.hpp

+{
+class type_error;
+} // namespace detail
+} // namespace nlohmann


This is not needed.

Ash-Jose · 2025-11-05T18:48:45Z

i have made changes accordingly
this was the first version of my change
although back then i wasnt able to make amalgamate work

Ash-Jose · 2025-11-05T20:02:27Z

its still failing a few tests
is that concerning??

gregmarr · 2025-11-05T20:07:45Z

test.json

@@ -0,0 +1,7 @@
+{


This file should not be in the root of the repo. Is this just from local testing and got committed accidentally?

my bad ill take it out

Signed-off-by: Ash-Jose <[email protected]>

…_JSON_SERIALIZE_ENUM_STRICT - Added missing include for <nlohmann/detail/string_concat.hpp> - Replaced string concatenation with concat() call as suggested by maintainer - Re-ran `make amalgamate` to update single-header files Signed-off-by: Ash-Jose <[email protected]>

Signed-off-by: Ash-Jose <[email protected]>

…nown values Signed-off-by: Ash-Jose <[email protected]>

Signed-off-by: Ash-Jose <[email protected]>

included string header Signed-off-by: Ash-Jose <[email protected]>

Signed-off-by: Ash-Jose <[email protected]>

Signed-off-by: Ash Jose <[email protected]>

Signed-off-by: Ash-Jose <[email protected]>

Signed-off-by: Ashlin Jose <[email protected]>

Signed-off-by: Ash-Jose <[email protected]>

Signed-off-by: Ash-Jose <[email protected]> Signed-off-by: Ash-Jose <[email protected]>

Ash-Jose · 2025-11-18T14:36:10Z

are my changes sufficient this time around?
i will make the signoff change to avoid the DCO error
also this pr has become quite messy with all my unecessary commits
if you want i will submit another pr with only the necessary commits to keep things clean

gregmarr · 2025-11-18T15:08:59Z

@nlohmann Looks like the workflows here are awaiting approval. Not sure why since they ran before.

Ash-Jose requested a review from nlohmann as a code owner November 4, 2025 20:50

github-actions bot added L tests labels Nov 4, 2025

nlohmann requested changes Nov 4, 2025

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Ash-Jose force-pushed the fix/enum-deser-throw-on-unknown branch from 95a9a52 to 28866e1 Compare November 4, 2025 22:35

Ash-Jose changed the title ~~Throw type_error.302 on unknown JSON value in NLOHMANN_JSON_SERIALIZE_ENUM (Fixes #3992)~~ Add NLOHMANN_JSON_SERIALIZE_ENUM_STRICT macro that throws type_error.302 on unknown JSON value (Fixes #3992) Nov 4, 2025

nlohmann requested changes Nov 5, 2025

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include/nlohmann/detail/macro_scope.hpp Outdated Show resolved Hide resolved

Ash-Jose requested a review from nlohmann November 5, 2025 09:23

Ash-Jose force-pushed the fix/enum-deser-throw-on-unknown branch from 69b82a1 to a18ff7c Compare November 5, 2025 09:57

nlohmann reviewed Nov 5, 2025

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gregmarr reviewed Nov 5, 2025

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Ash-Jose and others added 16 commits November 14, 2025 01:58

style: apply concat() suggestion and rerun make amalgamate

576975f

Signed-off-by: Ash-Jose <[email protected]>

made few formatting changes in macro_scope.hpp

512f4b4

Signed-off-by: Ash-Jose <[email protected]>

ran make amalgamate again

f6bc704

Signed-off-by: Ash-Jose <[email protected]>

revert to std::string() concat in enum strict macro

d4f8289

Signed-off-by: Ash-Jose <[email protected]>

fix: include exceptions.hpp for type_error in enum strict macro

08f8570

Signed-off-by: Ash-Jose <[email protected]>

fix: add forward declaration for type_error to avoid circular include

089e0bf

Signed-off-by: Ash-Jose <[email protected]>

fix: make NLOHMANN_JSON_SERIALIZE_ENUM_STRICT throw type_error on unk…

4f4ac7f

…nown values Signed-off-by: Ash-Jose <[email protected]>

minor formatting changes

c69f8d3

Signed-off-by: Ash-Jose <[email protected]>

removed test,json which was left there by accident

c9b5137

included string header Signed-off-by: Ash-Jose <[email protected]>

changed formatting of unit-serialize_enum_strict.cpp and amalgamated

97ef95f

Signed-off-by: Ash-Jose <[email protected]>

aesthetic changes and included doctest_compatibility.h

638ec5f

Signed-off-by: Ash Jose <[email protected]>

changed position of string include in macro_scope.hpp

895d38e

Signed-off-by: Ash Jose <[email protected]>

amalgamated

ff46319

Signed-off-by: Ash Jose <[email protected]>

Merge branch 'nlohmann:develop' into fix/enum-deser-throw-on-unknown

988fdef

change github branch to match local

37018c1

Signed-off-by: Ash Jose <[email protected]>

Ash-Jose closed this Nov 13, 2025

Ash-Jose deleted the fix/enum-deser-throw-on-unknown branch November 13, 2025 21:21

Ash-Jose restored the fix/enum-deser-throw-on-unknown branch November 13, 2025 21:25

Ash-Jose deleted the fix/enum-deser-throw-on-unknown branch November 13, 2025 21:34

resolving merge conflict

94ef0ce

Signed-off-by: Ash-Jose <[email protected]>

Ash-Jose reopened this Nov 13, 2025

Ash-Jose and others added 3 commits November 14, 2025 03:26

removed merge conflicts again

d792400

Signed-off-by: Ashlin Jose <[email protected]>

added helper function

5944257

Signed-off-by: Ash-Jose <[email protected]>

formatting and correcting the helper

677f5d9

Signed-off-by: Ash-Jose <[email protected]>

Ash-Jose force-pushed the fix/enum-deser-throw-on-unknown branch from 9cadcca to d191b5d Compare November 13, 2025 22:46

migrated helper to include/nlohmann/detail/conversions/from_json.hpp

1231904

Signed-off-by: Ash-Jose <[email protected]> Signed-off-by: Ash-Jose <[email protected]>

Ash-Jose force-pushed the fix/enum-deser-throw-on-unknown branch from d191b5d to 1231904 Compare November 13, 2025 22:48

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Add NLOHMANN_JSON_SERIALIZE_ENUM_STRICT macro that throws type_error.302 on unknown JSON value (Fixes #3992) #4989

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Add NLOHMANN_JSON_SERIALIZE_ENUM_STRICT macro that throws type_error.302 on unknown JSON value (Fixes #3992) #4989

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