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Move the user-defined string literals to <nlohmann/json_literals.hpp>

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Following the review in #5294, the literals now live in their own header
instead of being removed entirely: <nlohmann/json.hpp> includes it at the
end unless JSON_NO_AUTOMATIC_UDLS (renamed from JSON_NO_UDLS) is defined,
so a project can opt out globally and include the header only where the
literals are used.

The header only uses public and standard macros, because the library's
internal macros are undefined at the end of json.hpp and the amalgamation
inlines macro_scope.hpp only once. For the same reason, the library no
longer defines and undefines JSON_USE_GLOBAL_UDLS, so a user's definition
is still visible to the header. The single-header copy is identical to
the multi-header one, as it only includes <nlohmann/json.hpp>. The module
always exports the literals.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-28 21:49:37 +02:00
parent e0ee07fe73
commit 1419aeff60
23 changed files with 418 additions and 233 deletions
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tests/src/unit-no_udls.cpp → tests/src/unit-no_automatic_udls.cpp
+28 -8
View File
@@ -6,10 +6,12 @@
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT
// This translation unit checks JSON_NO_UDLS, which leaves out the user-defined
// string literals operator""_json and operator""_json_pointer entirely (see
// #5294), while the rest of the library keeps working.
#define JSON_NO_UDLS 1
// 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"
@@ -23,7 +25,7 @@ using json = nlohmann::json;
// 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_udls_probe
struct no_automatic_udls_probe
{
operator const char* () const // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
{
@@ -52,7 +54,7 @@ template<typename T>
using has_json_pointer_udl = nlohmann::detail::is_detected<json_pointer_udl_t, T>;
} // namespace
TEST_CASE("JSON_NO_UDLS")
TEST_CASE("JSON_NO_AUTOMATIC_UDLS")
{
SECTION("literals are not declared")
{
@@ -61,8 +63,8 @@ TEST_CASE("JSON_NO_UDLS")
CHECK_FALSE(has_json_pointer_udl<const char*>::value);
// nlohmann::literals::json_literals
CHECK_FALSE(has_json_udl<nlohmann::no_udls_probe>::value);
CHECK_FALSE(has_json_pointer_udl<nlohmann::no_udls_probe>::value);
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")
@@ -75,3 +77,21 @@ TEST_CASE("JSON_NO_UDLS")
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>")
{
SECTION("global namespace")
{
CHECK("[1,2]"_json == json({1, 2}));
CHECK("/a/0"_json_pointer == json::json_pointer("/a/0"));
}
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);
}
}