Move UDLs out of the global namespace (#3605)

* Move UDLs into nlohmann::literals::json_literals namespace

* Add 'using namespace' to unit tests

* Add 'using namespace' to examples

* Add 'using namespace' to README

* Move UDL mkdocs pages out of basic_json/

* Update documentation

* Update docset index

* Add JSON_GlobalUDLs CMake option

* Add unit test

* Build examples without global UDLs

* Add CI target

tests/src/unit-class_parser.cpp

@@ -11,6 +11,7 @@
 #define JSON_TESTS_PRIVATE
 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 #include <valarray>
 

tests/src/unit-deserialization.cpp

@@ -11,6 +11,7 @@
 
 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 #include <iostream>
 #include <iterator>

tests/src/unit-element_access2.cpp

@@ -10,6 +10,7 @@
 #include "doctest_compatibility.h"
 
 #include <nlohmann/json.hpp>
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 TEST_CASE_TEMPLATE("element access 2", Json, nlohmann::json, nlohmann::ordered_json)
 {

tests/src/unit-json_patch.cpp

@@ -10,6 +10,7 @@
 
 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 #include <fstream>
 #include "make_test_data_available.hpp"

tests/src/unit-json_pointer.cpp

@@ -11,6 +11,7 @@
 #define JSON_TESTS_PRIVATE
 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 #include <sstream>
 

tests/src/unit-merge_patch.cpp

@@ -10,6 +10,7 @@
 
 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 TEST_CASE("JSON Merge Patch")
 {

tests/src/unit-msgpack.cpp

@@ -10,6 +10,7 @@
 
 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 #include <fstream>
 #include <sstream>

tests/src/unit-readme.cpp

@@ -10,6 +10,7 @@
 
 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 #include <deque>
 #include <forward_list>

tests/src/unit-regression1.cpp

@@ -14,6 +14,7 @@
 #define JSON_TESTS_PRIVATE
 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 #include <fstream>
 #include <sstream>

tests/src/unit-regression2.cpp

@@ -22,6 +22,7 @@
 #include <nlohmann/json.hpp>
 using json = nlohmann::json;
 using ordered_json = nlohmann::ordered_json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 #include <cstdio>
 #include <list>

tests/src/unit-udl.cpp

@@ -0,0 +1,51 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.10.5
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2022 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#undef JSON_USE_GLOBAL_UDLS
+#define JSON_USE_GLOBAL_UDLS 0
+#include <nlohmann/json.hpp>
+
+TEST_CASE("user-defined string literals")
+{
+    auto j_expected = nlohmann::json::parse(R"({"foo": "bar", "baz": 42})");
+    auto ptr_expected = nlohmann::json::json_pointer("/foo/bar");
+
+    SECTION("using namespace nlohmann::literals::json_literals")
+    {
+        using namespace nlohmann::literals::json_literals; // NOLINT(google-build-using-namespace)
+
+        CHECK(R"({"foo": "bar", "baz": 42})"_json == j_expected);
+        CHECK("/foo/bar"_json_pointer == ptr_expected);
+    }
+
+    SECTION("using namespace nlohmann::json_literals")
+    {
+        using namespace nlohmann::json_literals; // NOLINT(google-build-using-namespace)
+
+        CHECK(R"({"foo": "bar", "baz": 42})"_json == j_expected);
+        CHECK("/foo/bar"_json_pointer == ptr_expected);
+    }
+
+    SECTION("using namespace nlohmann::literals")
+    {
+        using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
+
+        CHECK(R"({"foo": "bar", "baz": 42})"_json == j_expected);
+        CHECK("/foo/bar"_json_pointer == ptr_expected);
+    }
+
+    SECTION("using namespace nlohmann")
+    {
+        using namespace nlohmann; // NOLINT(google-build-using-namespace)
+
+        CHECK(R"({"foo": "bar", "baz": 42})"_json == j_expected);
+        CHECK("/foo/bar"_json_pointer == ptr_expected);
+    }
+}

tests/src/unit-udt.cpp

@@ -14,6 +14,7 @@ DOCTEST_GCC_SUPPRESS_WARNING("-Wnoexcept")
 
 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 
 #include <map>
 #include <memory>