Re-template json_pointer on string type (#3415)

* Make exception context optional

Change exception context parameter to pointer and replace context with
nullptr where appropriate.

* Support escaping other string types

* Add string concatenation function

Add variadic concat() function for concatenating char *, char, and
string types.

* Replace string concatenations using + with concat()

* Template json_pointer on string type

Change json_pointer from being templated on basic_json to being
templated on string type.

* Add unit test for #3388

Closes #3388.

* Fix regression test for #2958

* Add backwards compatibility with json_pointer<basic_json>

* Update json_pointer docs

* Allow comparing different json_pointers

* Update version numbers

test/src/unit-alt-string.cpp

@@ -49,6 +49,8 @@ class alt_string
   public:
     using value_type = std::string::value_type;
 
+    static constexpr auto npos = static_cast<std::size_t>(-1);
+
     alt_string(const char* str): str_impl(str) {}
     alt_string(const char* str, std::size_t count): str_impl(str, count) {}
     alt_string(size_t count, char chr): str_impl(count, chr) {}
@@ -144,11 +146,38 @@ class alt_string
         str_impl.clear();
     }
 
-    const value_type* data()
+    const value_type* data() const
     {
         return str_impl.data();
     }
 
+    bool empty() const
+    {
+        return str_impl.empty();
+    }
+
+    std::size_t find(const alt_string& str, std::size_t pos = 0) const
+    {
+        return str_impl.find(str.str_impl, pos);
+    }
+
+    std::size_t find_first_of(char c, std::size_t pos = 0) const
+    {
+        return str_impl.find_first_of(c, pos);
+    }
+
+    alt_string substr(std::size_t pos = 0, std::size_t count = npos) const
+    {
+        std::string s = str_impl.substr(pos, count);
+        return {s.data(), s.size()};
+    }
+
+    alt_string& replace(std::size_t pos, std::size_t count, const alt_string& str)
+    {
+        str_impl.replace(pos, count, str.str_impl);
+        return *this;
+    }
+
   private:
     std::string str_impl {};
 
@@ -296,4 +325,20 @@ TEST_CASE("alternative string type")
             CHECK_FALSE(const_doc["Who are you?"] == "I'm Bruce Wayne");
         }
     }
+
+    SECTION("JSON pointer")
+    {
+        // conversion from json to alt_json fails to compile (see #3425);
+        // attempted fix(*) produces: [[['b','a','r'],['b','a','z']]] (with each char being an integer)
+        // (*) disable implicit conversion for json_refs of any basic_json type
+        // alt_json j = R"(
+        // {
+        //     "foo": ["bar", "baz"]
+        // }
+        // )"_json;
+        auto j = alt_json::parse(R"({"foo": ["bar", "baz"]})");
+
+        CHECK(j.at(alt_json::json_pointer("/foo/0")) == j["foo"][0]);
+        CHECK(j.at(alt_json::json_pointer("/foo/1")) == j["foo"][1]);
+    }
 }

test/src/unit-convenience.cpp

@@ -37,6 +37,84 @@ using nlohmann::json;
 
 namespace
 {
+struct alt_string_iter
+{
+    alt_string_iter() = default;
+    alt_string_iter(const char* cstr)
+        : impl(cstr)
+    {}
+
+    void reserve(std::size_t s)
+    {
+        impl.reserve(s);
+    }
+
+    template<typename Iter>
+    void append(Iter first, Iter last)
+    {
+        impl.append(first, last);
+    }
+
+    std::string::const_iterator begin() const
+    {
+        return impl.begin();
+    }
+
+    std::string::const_iterator end() const
+    {
+        return impl.end();
+    }
+
+    std::size_t size() const
+    {
+        return impl.size();
+    }
+
+    alt_string_iter& operator+=(const char c)
+    {
+        impl += c;
+        return *this;
+    }
+
+    std::string impl{};
+};
+
+struct alt_string_data
+{
+    alt_string_data() = default;
+    alt_string_data(const char* cstr)
+        : impl(cstr)
+    {}
+
+    void reserve(std::size_t s)
+    {
+        impl.reserve(s);
+    }
+
+    void append(const char* p, std::size_t s)
+    {
+        impl.append(p, s);
+    }
+
+    const char* data() const
+    {
+        return impl.data();
+    }
+
+    std::size_t size() const
+    {
+        return impl.size();
+    }
+
+    alt_string_data& operator+=(const char c)
+    {
+        impl += c;
+        return *this;
+    }
+
+    std::string impl{};
+};
+
 void check_escaped(const char* original, const char* escaped = "", bool ensure_ascii = false);
 void check_escaped(const char* original, const char* escaped, const bool ensure_ascii)
 {
@@ -110,4 +188,39 @@ TEST_CASE("convenience functions")
 
         CHECK_THROWS_WITH_AS(check_escaped("\xC2"), "[json.exception.type_error.316] incomplete UTF-8 string; last byte: 0xC2", json::type_error&);
     }
+
+    SECTION("string concat")
+    {
+        using nlohmann::detail::concat;
+
+        const char* expected = "Hello, world!";
+        alt_string_iter hello_iter{"Hello, "};
+        alt_string_data hello_data{"Hello, "};
+        std::string world = "world";
+
+        SECTION("std::string")
+        {
+            std::string str1 = concat(hello_iter, world, '!');
+            std::string str2 = concat(hello_data, world, '!');
+            std::string str3 = concat("Hello, ", world, '!');
+
+            CHECK(str1 == expected);
+            CHECK(str2 == expected);
+            CHECK(str3 == expected);
+        }
+
+        SECTION("alt_string_iter")
+        {
+            alt_string_iter str = concat<alt_string_iter>(hello_iter, world, '!');
+
+            CHECK(str.impl == expected);
+        }
+
+        SECTION("alt_string_data")
+        {
+            alt_string_data str = concat<alt_string_data>(hello_data, world, '!');
+
+            CHECK(str.impl == expected);
+        }
+    }
 }

test/src/unit-json_pointer.cpp

@@ -660,4 +660,54 @@ TEST_CASE("JSON pointers")
         CHECK(j[ptr] == j["object"]["/"]);
         CHECK(ptr.to_string() == "/object/~1");
     }
+
+    SECTION("equality comparison")
+    {
+        auto ptr1 = json::json_pointer("/foo/bar");
+        auto ptr2 = json::json_pointer("/foo/bar");
+
+        CHECK(ptr1 == ptr2);
+        CHECK_FALSE(ptr1 != ptr2);
+    }
+
+    SECTION("backwards compatibility and mixing")
+    {
+        json j = R"(
+        {
+            "foo": ["bar", "baz"]
+        }
+        )"_json;
+
+        using nlohmann::ordered_json;
+        using json_ptr_str = nlohmann::json_pointer<std::string>;
+        using json_ptr_j = nlohmann::json_pointer<json>;
+        using json_ptr_oj = nlohmann::json_pointer<ordered_json>;
+
+        CHECK(std::is_same<json_ptr_str::string_t, json::json_pointer::string_t>::value);
+        CHECK(std::is_same<json_ptr_str::string_t, ordered_json::json_pointer::string_t>::value);
+        CHECK(std::is_same<json_ptr_str::string_t, json_ptr_j::string_t>::value);
+        CHECK(std::is_same<json_ptr_str::string_t, json_ptr_oj::string_t>::value);
+
+        json_ptr_str ptr{"/foo/0"};
+        json_ptr_j ptr_j{"/foo/0"};
+        json_ptr_oj ptr_oj{"/foo/0"};
+
+        CHECK(j.contains(ptr));
+        CHECK(j.contains(ptr_j));
+        CHECK(j.contains(ptr_oj));
+
+        CHECK(j.at(ptr) == j.at(ptr_j));
+        CHECK(j.at(ptr) == j.at(ptr_oj));
+
+        CHECK(j[ptr] == j[ptr_j]);
+        CHECK(j[ptr] == j[ptr_oj]);
+
+        CHECK(j.value(ptr, "x") == j.value(ptr_j, "x"));
+        CHECK(j.value(ptr, "x") == j.value(ptr_oj, "x"));
+
+        CHECK(ptr == ptr_j);
+        CHECK(ptr == ptr_oj);
+        CHECK_FALSE(ptr != ptr_j);
+        CHECK_FALSE(ptr != ptr_oj);
+    }
 }

test/src/unit-regression2.cpp

@@ -760,7 +760,6 @@ TEST_CASE("regression tests 2")
     {
         std::string p = "/root";
 
-        // matching types
         json test1;
         test1[json::json_pointer(p)] = json::object();
         CHECK(test1.dump() == "{\"root\":{}}");
@@ -769,10 +768,11 @@ TEST_CASE("regression tests 2")
         test2[ordered_json::json_pointer(p)] = json::object();
         CHECK(test2.dump() == "{\"root\":{}}");
 
-        // mixed type - the JSON Pointer is implicitly converted into a string "/root"
+        // json::json_pointer and ordered_json::json_pointer are the same type; behave as above
         ordered_json test3;
         test3[json::json_pointer(p)] = json::object();
-        CHECK(test3.dump() == "{\"/root\":{}}");
+        CHECK(std::is_same<json::json_pointer::string_t, ordered_json::json_pointer::string_t>::value);
+        CHECK(test3.dump() == "{\"root\":{}}");
     }
 
     SECTION("issue #2982 - to_{binary format} does not provide a mechanism for specifying a custom allocator for the returned type")