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json/tests/src/unit-no_automatic_udls.cpp
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Niels Lohmann 330fbead59 Document clang-tidy exclusions, drop unneeded ones, and clean up doc examples (#5909)
* Document clang-tidy exclusions and drop unneeded ones

Re-enable every excluded check in a run of clang-tidy 22 over all tests
and remove the seven that never fire (cert-err58-cpp,
clang-analyzer-webkit.NoUncountedMemberChecker,
cppcoreguidelines-virtual-class-destructor, google-readability-function-size,
hicpp-function-size, hicpp-no-assembler, readability-function-size).

Document the reason for every remaining exclusion at the top of the file.

Exclude in advance the checks that only exist in clang-tidy 23 and are
noise here (bugprone-signed-bitwise, *-explicit-constructor,
readability-trailing-comma, modernize-use-string-view), plus
modernize-use-integer-sign-comparison, which needs C++20 std::cmp_less
and flags deliberate casts.

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

* Fix clang-tidy findings in documentation examples and replace redundant aliases

Apply clang-tidy fixes to the documentation examples:
- performance-avoid-endl: std::endl -> '\n'
- readability-qualified-auto: auto -> auto* / const auto*
- performance-for-range-copy: copy -> const reference
- google-readability-casting: C-style cast -> static_cast

Replace redundant aliases (readability-redundant-qualified-alias) such as
"using json = nlohmann::json;" with "using nlohmann::json;" in the
documentation, README, examples, tests, and benchmarks. Aliases at class
scope and aliases of other types (with_base_class_t etc.) are kept.

No changes to the library or its public API. All changed examples were
compiled and run; their output matches the stored .output files (except
max_size and meta, which depend on the platform and compiler).

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

* Format doc examples with the pinned astyle

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-25 12:07:51 +01:00

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// __ _____ _____ _____
// __| | __| | | | JSON for Modern C++ (supporting code)
// | | |__ | | | | | | version 3.12.0
// |_____|_____|_____|_|___| https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT
// This translation unit checks JSON_NO_AUTOMATIC_UDLS, which keeps
// <nlohmann/json.hpp> from including <nlohmann/json_literals.hpp> and thereby
// leaves out the user-defined string literals operator""_json and
// operator""_json_pointer (see #5294), and that including
// <nlohmann/json_literals.hpp> afterwards brings them back.
#define JSON_NO_AUTOMATIC_UDLS 1
#include "doctest_compatibility.h"
#include <cstddef>
#include <utility>
#include <nlohmann/json.hpp>
using nlohmann::json;
// An argument type whose associated namespace is the library namespace, so
// argument-dependent lookup of a literal operator called by its function name
// also searches the inline namespaces nlohmann::literals::json_literals.
NLOHMANN_JSON_NAMESPACE_BEGIN
struct no_automatic_udls_probe
{
operator const char* () const // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
{
return "";
}
};
NLOHMANN_JSON_NAMESPACE_END
namespace
{
// The calls below use a dependent argument, so a literal operator that is not
// declared at all is a substitution failure rather than a hard error: lookup is
// deferred to the point of instantiation, where it considers the declarations
// visible from here (the global using-declarations of JSON_USE_GLOBAL_UDLS) plus
// argument-dependent lookup (the literals in the library namespace).
#if !defined(__GNUC__) || defined(__clang__) || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
template<typename T>
using json_udl_t = decltype(operator""_json(std::declval<T>(), std::size_t()));
template<typename T>
using json_pointer_udl_t = decltype(operator""_json_pointer(std::declval<T>(), std::size_t()));
#else
// GCC 4.8 requires a space between "" and suffix
template<typename T>
using json_udl_t = decltype(operator"" _json(std::declval<T>(), std::size_t()));
template<typename T>
using json_pointer_udl_t = decltype(operator"" _json_pointer(std::declval<T>(), std::size_t()));
#endif
template<typename T>
using has_json_udl = nlohmann::detail::is_detected<json_udl_t, T>;
template<typename T>
using has_json_pointer_udl = nlohmann::detail::is_detected<json_pointer_udl_t, T>;
} // namespace
TEST_CASE("JSON_NO_AUTOMATIC_UDLS")
{
SECTION("literals are not declared")
{
// global namespace (JSON_USE_GLOBAL_UDLS defaults to 1)
CHECK_FALSE(has_json_udl<const char*>::value);
CHECK_FALSE(has_json_pointer_udl<const char*>::value);
// nlohmann::literals::json_literals
CHECK_FALSE(has_json_udl<nlohmann::no_automatic_udls_probe>::value);
CHECK_FALSE(has_json_pointer_udl<nlohmann::no_automatic_udls_probe>::value);
}
SECTION("the rest of the library keeps working")
{
const json j = json::parse(R"({"foo": {"bar": 42}})");
CHECK(j.dump() == R"({"foo":{"bar":42}})");
const json::json_pointer ptr("/foo/bar");
CHECK(j.at(ptr) == 42);
CHECK(j.contains(ptr));
}
}
// the literals can still be added where they are needed
#include <nlohmann/json_literals.hpp>
TEST_CASE("JSON_NO_AUTOMATIC_UDLS with <nlohmann/json_literals.hpp>")
{
#if !defined(JSON_USE_GLOBAL_UDLS) || JSON_USE_GLOBAL_UDLS
SECTION("global namespace")
{
CHECK("[1,2]"_json == json({1, 2}));
CHECK("/a/0"_json_pointer == json::json_pointer("/a/0"));
}
#endif
SECTION("nlohmann::literals::json_literals")
{
using namespace nlohmann::literals::json_literals; // NOLINT(google-build-using-namespace)
CHECK(R"({"a":[42]})"_json.at("/a/0"_json_pointer) == 42);
}
}