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Move templated_json_throw into nlohmann::detail

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templated_json_throw() was defined in macro_scope.hpp, which is included
outside NLOHMANN_JSON_NAMESPACE_BEGIN, so the helper leaked into the
global namespace as ::templated_json_throw with no ABI tag. Unqualified
lookup in NLOHMANN_JSON_SERIALIZE_ENUM_STRICT could then bind to a
same-named function declared in the user's own namespace instead, which
fails to compile with Clang ("does not name a template").

Move the helper next to the exception classes in exceptions.hpp, inside
nlohmann::detail, and call it qualified as
::nlohmann::detail::templated_json_throw<...>(...) from both macro
expansion sites. Rewrite the doc comment to give the real reason for the
helper (JSON_THROW may expand to code that discards its argument, e.g.
when exceptions are disabled) and fix the "supress" typo.

templated_json_throw was never released (added by #5151 after v3.12.0),
so it can be moved freely.

Adds a regression test that expands NLOHMANN_JSON_SERIALIZE_ENUM_STRICT
inside a namespace declaring its own templated_json_throw.

Public API: no change (::templated_json_throw was an unreleased,
unintentional global-namespace leak with no callers relying on its
location).

Overlaps #5698, which rewrites the same two macro call lines; the
overlapping hunks are small and should be trivial to reconcile on
rebase.

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

#5708 item 2
This commit is contained in:
Niels Lohmann
2026-09-30 18:08:45 +02:00
parent 23aa069e63
commit d254f62764
4 changed files with 74 additions and 34 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/nlohmann/detail/exceptions.hpp
+21
View File
@@ -286,6 +286,27 @@ class other_error : public exception
other_error(int id_, const char* what_arg) : exception(id_, what_arg) {}
};
/*!
@brief helper function to call JSON_THROW from a template
@note JSON_THROW is a macro that, depending on the JSON_THROW_USER /
JSON_TRY_USER / JSON_NOEXCEPTION configuration, may expand to code
that does not reference its argument (e.g. `std::abort()`), which
would trigger a compilation error if the argument's type depends on
a template parameter that is otherwise unused. Wrapping the call in
a templated function avoids this and gives the compiler a single
place to see the (possibly unused) parameter.
*/
template<typename ExceptionType>
void templated_json_throw(ExceptionType exception)
{
JSON_THROW(exception);
// JSON_THROW may expand to code that discards its argument (e.g. when
// exceptions are disabled) - the cast below avoids an unused-parameter
// warning with -Werror in that case
(void)exception;
}
} // namespace detail
NLOHMANN_JSON_NAMESPACE_END
include/nlohmann/detail/macro_scope.hpp
+2 -17
View File
@@ -287,21 +287,6 @@
/*!
@brief function to wrap JSON_THROW_MACRO - there can be compilation errors about
there being no arguments to JSON_THROW that depend on template arguments
if this is not used to call JSON_THROW
*/
template<typename ExceptionType>
void templated_json_throw(ExceptionType exception)
{
JSON_THROW(exception);
/* JSON_THROW(exception) discards exception and aborts - void cast needed to supress
compilation error if compiled with -Werror and Wunused-parameter */
(void)exception;
}
/*!
@brief macro to briefly define a mapping between an enum and JSON with exception
on invalid input
@@ -322,7 +307,7 @@ void templated_json_throw(ExceptionType exception)
return ej_pair.first == e; \
}); \
if (it != std::end(m)) j = it->second; \
else templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE, nullptr)); \
else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE, nullptr)); \
} \
template<typename BasicJsonType> \
inline void from_json(const BasicJsonType& j, ENUM_TYPE& e) \
@@ -337,7 +322,7 @@ void templated_json_throw(ExceptionType exception)
return ej_pair.second == j; \
}); \
if (it != std::end(m)) e = it->first; \
else templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE ": " + j.dump(), &j)); \
else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE ": " + j.dump(), &j)); \
}
// Ugly macros to avoid uglier copy-paste when specializing basic_json. They
single_include/nlohmann/json.hpp
+23 -17
View File
@@ -2601,21 +2601,6 @@ JSON_HEDLEY_DIAGNOSTIC_POP
/*!
@brief function to wrap JSON_THROW_MACRO - there can be compilation errors about
there being no arguments to JSON_THROW that depend on template arguments
if this is not used to call JSON_THROW
*/
template<typename ExceptionType>
void templated_json_throw(ExceptionType exception)
{
JSON_THROW(exception);
/* JSON_THROW(exception) discards exception and aborts - void cast needed to supress
compilation error if compiled with -Werror and Wunused-parameter */
(void)exception;
}
/*!
@brief macro to briefly define a mapping between an enum and JSON with exception
on invalid input
@@ -2636,7 +2621,7 @@ void templated_json_throw(ExceptionType exception)
return ej_pair.first == e; \
}); \
if (it != std::end(m)) j = it->second; \
else templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE, nullptr)); \
else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE, nullptr)); \
} \
template<typename BasicJsonType> \
inline void from_json(const BasicJsonType& j, ENUM_TYPE& e) \
@@ -2651,7 +2636,7 @@ void templated_json_throw(ExceptionType exception)
return ej_pair.second == j; \
}); \
if (it != std::end(m)) e = it->first; \
else templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE ": " + j.dump(), &j)); \
else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE ": " + j.dump(), &j)); \
}
// Ugly macros to avoid uglier copy-paste when specializing basic_json. They
@@ -5360,6 +5345,27 @@ class other_error : public exception
other_error(int id_, const char* what_arg) : exception(id_, what_arg) {}
};
/*!
@brief helper function to call JSON_THROW from a template
@note JSON_THROW is a macro that, depending on the JSON_THROW_USER /
JSON_TRY_USER / JSON_NOEXCEPTION configuration, may expand to code
that does not reference its argument (e.g. `std::abort()`), which
would trigger a compilation error if the argument's type depends on
a template parameter that is otherwise unused. Wrapping the call in
a templated function avoids this and gives the compiler a single
place to see the (possibly unused) parameter.
*/
template<typename ExceptionType>
void templated_json_throw(ExceptionType exception)
{
JSON_THROW(exception);
// JSON_THROW may expand to code that discards its argument (e.g. when
// exceptions are disabled) - the cast below avoids an unused-parameter
// warning with -Werror in that case
(void)exception;
}
} // namespace detail
NLOHMANN_JSON_NAMESPACE_END
tests/src/unit-conversions.cpp
+28
View File
@@ -1749,6 +1749,34 @@ NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(StrictTaskState,
{STRICT_TS_COMPLETED, "completed"},
})
// regression test for #5708 item 2: NLOHMANN_JSON_SERIALIZE_ENUM_STRICT must not rely on
// unqualified lookup of a helper name that a user's own namespace may also declare
namespace ns_with_colliding_name
{
// NOLINTNEXTLINE(misc-use-internal-linkage) - used to shadow the library's internal helper name
inline void templated_json_throw(int /*unused*/) {}
enum class colliding_enum { a, b };
// NOLINTNEXTLINE(misc-use-internal-linkage,misc-const-correctness,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(colliding_enum,
{
{colliding_enum::a, "a"},
{colliding_enum::b, "b"}
})
} // namespace ns_with_colliding_name
TEST_CASE("NLOHMANN_JSON_SERIALIZE_ENUM_STRICT in a namespace with a colliding name")
{
using ns_with_colliding_name::colliding_enum;
CHECK(json(colliding_enum::a) == "a");
CHECK(colliding_enum::b == json("b"));
json _;
CHECK_THROWS_WITH_AS(_ = json("nope").get<colliding_enum>(), "[json.exception.out_of_range.410] enum value out of range for colliding_enum: \"nope\"", json::out_of_range&);
}
TEST_CASE("Strict JSON to enum mapping")
{
SECTION("enum class")