Keep external headers as #include when amalgamating

A header that builds on json.hpp (such as the planned json_view.hpp) must
not inline json.hpp: its single-header version would contain a second copy
of the library, and that copy would change with every library change.

The optional config key "external" lists include paths that are kept as
#include directives. Only the first directive per path is kept; repeated
ones are commented out, as the tool already does for inlined headers.
config_json_view.json uses it for json_view.hpp; the existing configs do
not set it, and json.hpp and json_fwd.hpp regenerate byte-identically.

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

docs/mkdocs/docs/api/ordered_map.md

@@ -28,11 +28,6 @@ A minimal map-like container that preserves insertion order for use within [`nlo
 The type uses a `std::vector` to store object elements. Therefore, adding elements can yield a reallocation in which
 case all iterators (including the `end()` iterator) and all references to the elements are invalidated.
 
-When the storage grows, the keys are copied and the mapped values are moved to the new storage. A plain `std::vector`
-would copy the whole elements instead, because their `#!cpp const` keys make them not nothrow move constructible; for
-[`ordered_json`](ordered_json.md), this would be a deep copy of every nested value. The values are only copied if
-`T` is not default constructible or not nothrow move assignable.
-
 ## Member types
 
 - **key_type** - key type (`Key`)
@@ -61,11 +56,6 @@ std::equal_to<>     // since C++14
 - **find**
 - **insert**
 
-## Exception safety
-
-**emplace**, **operator\[\]**, and **insert(value)** have the strong exception guarantee: if an exception is thrown (for
-instance, because copying a key or allocating memory fails), the contents of the container are unchanged.
-
 ## Complexity
 
 Because the elements are stored in a `std::vector` in insertion order, there is no index to look a key up by. Every
@@ -132,4 +122,3 @@ This differs from `#!cpp std::map`, where the same operations are O(log n).
 
 - Added in version 3.9.0 to implement [`nlohmann::ordered_json`](ordered_json.md).
 - Added **key_compare** member in version 3.11.0.
-- Changed in version 3.13.0: growing the storage moves the mapped values instead of copying them.

include/nlohmann/ordered_map.hpp

@@ -8,15 +8,13 @@
 
 #pragma once
 
-#include <algorithm> // max, min
 #include <functional> // equal_to, less
 #include <initializer_list> // initializer_list
 #include <iterator> // input_iterator_tag, iterator_traits
 #include <memory> // allocator
 #include <stdexcept> // for out_of_range
-#include <tuple> // forward_as_tuple
-#include <type_traits> // enable_if, integral_constant, is_convertible, is_nothrow_move_constructible
-#include <utility> // forward, move, pair, piecewise_construct
+#include <type_traits> // enable_if, is_convertible
+#include <utility> // pair
 #include <vector> // vector
 
 #include <nlohmann/detail/macro_scope.hpp>
@@ -81,7 +79,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(key, std::forward<T>(t));
+        Container::emplace_back(key, std::forward<T>(t));
         return {std::prev(this->end()), true};
     }
 
@@ -96,7 +94,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(std::forward<KeyType>(key), std::forward<T>(t));
+        Container::emplace_back(std::forward<KeyType>(key), std::forward<T>(t));
         return {std::prev(this->end()), true};
     }
 
@@ -370,7 +368,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(value);
+        Container::push_back(value);
         return {--this->end(), true};
     }
 
@@ -388,64 +386,6 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
     }
 
 private:
-    /*!
-    @brief add an element whose key is not yet contained at the end
-
-    A std::vector copies all elements when it grows, because their const keys
-    make them not nothrow move constructible. For ordered_json, this is a deep
-    copy of every value. Where the strong exception guarantee can be kept, grow
-    the storage here instead, copying only the keys and moving the values.
-    */
-    template<typename... Args>
-    void append(Args&& ... args)
-    {
-        // evaluated here rather than at class scope, because T is still
-        // incomplete when basic_json instantiates its object_t
-        using move_values = std::integral_constant<bool, detail::conjunction<
-                detail::negation<std::is_nothrow_move_constructible<value_type>>,
-                std::is_copy_constructible<key_type>,
-                detail::is_default_constructible<mapped_type>,
-                std::is_nothrow_move_assignable<mapped_type>>::value>;
-        append_impl(move_values{}, std::forward<Args>(args)...);
-    }
-
-    template<typename... Args>
-    void append_impl(std::true_type /*unused*/, Args&& ... args)
-    {
-        if (this->size() < this->capacity())
-        {
-            Container::emplace_back(std::forward<Args>(args)...);
-            return;
-        }
-
-        // 1. May throw, but only changes tmp: copy the keys, value-initialize
-        //    the values, and add the new element. The arguments may refer to
-        //    elements of this container, so they are used before any value is
-        //    moved out of it.
-        Container tmp(this->get_allocator()); // equal allocators, so swap() is valid
-        tmp.reserve((std::min)(this->max_size(), (std::max)(size_type{1}, 2 * this->size())));
-        for (const auto& element : *this)
-        {
-            tmp.emplace_back(std::piecewise_construct, std::forward_as_tuple(element.first), std::forward_as_tuple());
-        }
-        tmp.emplace_back(std::forward<Args>(args)...);
-
-        // 2. Cannot throw: move the values over and adopt the new storage.
-        auto it = tmp.begin();
-        for (auto& element : *this)
-        {
-            it->second = std::move(element.second);
-            ++it;
-        }
-        Container::swap(tmp);
-    }
-
-    template<typename... Args>
-    void append_impl(std::false_type /*unused*/, Args&& ... args)
-    {
-        Container::emplace_back(std::forward<Args>(args)...);
-    }
-
     JSON_NO_UNIQUE_ADDRESS key_compare m_compare = key_compare();
 };
 

single_include/nlohmann/json.hpp

@@ -25768,15 +25768,13 @@ NLOHMANN_JSON_NAMESPACE_END
 
 
 
-#include <algorithm> // max, min
 #include <functional> // equal_to, less
 #include <initializer_list> // initializer_list
 #include <iterator> // input_iterator_tag, iterator_traits
 #include <memory> // allocator
 #include <stdexcept> // for out_of_range
-#include <tuple> // forward_as_tuple
-#include <type_traits> // enable_if, integral_constant, is_convertible, is_nothrow_move_constructible
-#include <utility> // forward, move, pair, piecewise_construct
+#include <type_traits> // enable_if, is_convertible
+#include <utility> // pair
 #include <vector> // vector
 
 // #include <nlohmann/detail/macro_scope.hpp>
@@ -25843,7 +25841,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(key, std::forward<T>(t));
+        Container::emplace_back(key, std::forward<T>(t));
         return {std::prev(this->end()), true};
     }
 
@@ -25858,7 +25856,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(std::forward<KeyType>(key), std::forward<T>(t));
+        Container::emplace_back(std::forward<KeyType>(key), std::forward<T>(t));
         return {std::prev(this->end()), true};
     }
 
@@ -26132,7 +26130,7 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
                 return {it, false};
             }
         }
-        append(value);
+        Container::push_back(value);
         return {--this->end(), true};
     }
 
@@ -26150,64 +26148,6 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
     }
 
 private:
-    /*!
-    @brief add an element whose key is not yet contained at the end
-
-    A std::vector copies all elements when it grows, because their const keys
-    make them not nothrow move constructible. For ordered_json, this is a deep
-    copy of every value. Where the strong exception guarantee can be kept, grow
-    the storage here instead, copying only the keys and moving the values.
-    */
-    template<typename... Args>
-    void append(Args&& ... args)
-    {
-        // evaluated here rather than at class scope, because T is still
-        // incomplete when basic_json instantiates its object_t
-        using move_values = std::integral_constant<bool, detail::conjunction<
-                detail::negation<std::is_nothrow_move_constructible<value_type>>,
-                std::is_copy_constructible<key_type>,
-                detail::is_default_constructible<mapped_type>,
-                std::is_nothrow_move_assignable<mapped_type>>::value>;
-        append_impl(move_values{}, std::forward<Args>(args)...);
-    }
-
-    template<typename... Args>
-    void append_impl(std::true_type /*unused*/, Args&& ... args)
-    {
-        if (this->size() < this->capacity())
-        {
-            Container::emplace_back(std::forward<Args>(args)...);
-            return;
-        }
-
-        // 1. May throw, but only changes tmp: copy the keys, value-initialize
-        //    the values, and add the new element. The arguments may refer to
-        //    elements of this container, so they are used before any value is
-        //    moved out of it.
-        Container tmp(this->get_allocator()); // equal allocators, so swap() is valid
-        tmp.reserve((std::min)(this->max_size(), (std::max)(size_type{1}, 2 * this->size())));
-        for (const auto& element : *this)
-        {
-            tmp.emplace_back(std::piecewise_construct, std::forward_as_tuple(element.first), std::forward_as_tuple());
-        }
-        tmp.emplace_back(std::forward<Args>(args)...);
-
-        // 2. Cannot throw: move the values over and adopt the new storage.
-        auto it = tmp.begin();
-        for (auto& element : *this)
-        {
-            it->second = std::move(element.second);
-            ++it;
-        }
-        Container::swap(tmp);
-    }
-
-    template<typename... Args>
-    void append_impl(std::false_type /*unused*/, Args&& ... args)
-    {
-        Container::emplace_back(std::forward<Args>(args)...);
-    }
-
     JSON_NO_UNIQUE_ADDRESS key_compare m_compare = key_compare();
 };
 

tests/benchmarks/src/benchmarks.cpp

@@ -119,39 +119,6 @@ BENCHMARK_CAPTURE(ParseIndented, canada / 4,       TEST_DATA_DIRECTORY "/nativej
 BENCHMARK_CAPTURE(ParseIndented, citm_catalog / 4, TEST_DATA_DIRECTORY "/nativejson-benchmark/citm_catalog.json", 4);
 BENCHMARK_CAPTURE(ParseIndented, twitter / 4,      TEST_DATA_DIRECTORY "/nativejson-benchmark/twitter.json",      4);
 
-//////////////////////////////////////////////////////////////////////////////
-// parse JSON from string into an ordered_json
-//
-// Same as ParseString above, but with nlohmann::ordered_json, whose objects
-// keep their members in a vector: the pair of rows shows what preserving the
-// insertion order costs.
-//////////////////////////////////////////////////////////////////////////////
-
-static void ParseStringOrdered(benchmark::State& state, const char* filename)
-{
-    std::ifstream f(filename);
-    std::string str((std::istreambuf_iterator<char>(f)), std::istreambuf_iterator<char>());
-
-    while (state.KeepRunning())
-    {
-        state.PauseTiming();
-        auto* j = new nlohmann::ordered_json();
-        state.ResumeTiming();
-
-        *j = nlohmann::ordered_json::parse(str);
-
-        state.PauseTiming();
-        delete j;
-        state.ResumeTiming();
-    }
-
-    state.SetBytesProcessed(state.iterations() * str.size());
-}
-BENCHMARK_CAPTURE(ParseStringOrdered, jeopardy,     TEST_DATA_DIRECTORY "/jeopardy/jeopardy.json");
-BENCHMARK_CAPTURE(ParseStringOrdered, canada,       TEST_DATA_DIRECTORY "/nativejson-benchmark/canada.json");
-BENCHMARK_CAPTURE(ParseStringOrdered, citm_catalog, TEST_DATA_DIRECTORY "/nativejson-benchmark/citm_catalog.json");
-BENCHMARK_CAPTURE(ParseStringOrdered, twitter,      TEST_DATA_DIRECTORY "/nativejson-benchmark/twitter.json");
-
 //////////////////////////////////////////////////////////////////////////////
 // serialize JSON
 //////////////////////////////////////////////////////////////////////////////

tests/src/unit-disabled_exceptions.cpp

@@ -46,24 +46,6 @@ TEST_CASE("Tests with disabled exceptions")
         CHECK(*sax_no_exception::error_string == "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: 'x'");
         delete sax_no_exception::error_string; // NOLINT(cppcoreguidelines-owning-memory)
     }
-
-    SECTION("growing an ordered_json object")
-    {
-        auto j = nlohmann::ordered_json::object();
-        for (int i = 0; i < 100; ++i)
-        {
-            j[std::to_string(i)] = {{"nested", i}};
-        }
-
-        CHECK(j.size() == 100);
-        int i = 0;
-        for (const auto& element : j.items())
-        {
-            CHECK(element.key() == std::to_string(i));
-            CHECK(element.value()["nested"] == i);
-            ++i;
-        }
-    }
 }
 
 DOCTEST_GCC_SUPPRESS_WARNING_POP

tests/src/unit-ordered_map.cpp

@@ -11,97 +11,6 @@
 #include <nlohmann/json.hpp>
 using nlohmann::ordered_map;
 
-#include <stdexcept>
-#include <string>
-#include <type_traits>
-#include <utility>
-#include <vector>
-
-// The EDG front end (Intel icpc, NVIDIA nvc++) considers the defaulted move
-// constructor of std::pair<const Key, T> noexcept even if copying Key can
-// throw. std::vector then moves such elements itself when it grows (and calls
-// std::terminate if a key copy throws), so ordered_map leaves growing to it.
-#if defined(__EDG__)
-    #define JSON_TEST_PAIR_MOVE_IS_NOEXCEPT
-#endif
-
-namespace
-{
-// number of copies made of counted values
-int value_copies = 0;
-
-// a mapped type that counts its copies; moving from it leaves -1 behind
-struct counted // NOLINT(cppcoreguidelines-special-member-functions,hicpp-special-member-functions)
-{
-    int payload = 0;
-
-    counted() = default;
-    explicit counted(int p) noexcept : payload(p) {}
-    counted(const counted& other) : payload(other.payload)
-    {
-        ++value_copies;
-    }
-    counted(counted&& other) noexcept : payload(other.payload)
-    {
-        other.payload = -1;
-    }
-    counted& operator=(const counted&) = delete;
-    counted& operator=(counted&& other) noexcept
-    {
-        payload = other.payload;
-        other.payload = -1;
-        return *this;
-    }
-};
-
-#if !defined(JSON_NOEXCEPTION) && !defined(JSON_TEST_PAIR_MOVE_IS_NOEXCEPT)
-// number of throwing_key copies that still succeed; the next one throws
-// (a negative value means that copies never throw)
-int key_copies_until_throw = -1;
-
-// a key type whose copy constructor can be made to throw
-struct throwing_key // NOLINT(cppcoreguidelines-special-member-functions,hicpp-special-member-functions)
-{
-    int id = 0;
-
-    explicit throwing_key(int i) noexcept : id(i) {}
-    throwing_key(const throwing_key& other) : id(other.id)
-    {
-        if (key_copies_until_throw == 0)
-        {
-            throw std::runtime_error("key copy failed");
-        }
-        if (key_copies_until_throw > 0)
-        {
-            --key_copies_until_throw;
-        }
-    }
-    throwing_key& operator=(const throwing_key&) = delete;
-
-    friend bool operator==(const throwing_key& lhs, const throwing_key& rhs) noexcept
-    {
-        return lhs.id == rhs.id;
-    }
-};
-#endif
-
-// a mapped type that cannot be default-constructed
-struct no_default
-{
-    explicit no_default(int v) noexcept : value(v) {}
-    int value;
-};
-
-// ordered_json must keep moving its values when an object grows
-using ordered_object_t = nlohmann::ordered_json::object_t;
-#if !defined(JSON_TEST_PAIR_MOVE_IS_NOEXCEPT)
-    static_assert(!std::is_nothrow_move_constructible<ordered_object_t::value_type>::value, "std::vector would move the elements itself");
-#endif
-static_assert(std::is_copy_constructible<ordered_object_t::key_type>::value, "keys must be copyable");
-static_assert(std::is_default_constructible<ordered_object_t::mapped_type>::value, "values must be default-constructible");
-static_assert(std::is_nothrow_move_assignable<ordered_object_t::mapped_type>::value, "values must be nothrow move-assignable");
-} // namespace
-
 TEST_CASE("ordered_map")
 {
     SECTION("constructor")
@@ -404,270 +313,3 @@ TEST_CASE("ordered_map")
         }
     }
 }
-
-TEST_CASE("ordered_map growth")
-{
-    SECTION("values are moved, not copied, when the storage grows")
-    {
-        ordered_map<std::string, counted> om;
-        std::size_t growths = 0;
-        value_copies = 0;
-
-        // inserts 100 elements with the given function and counts the growths
-        const auto fill = [&om, &growths](void (*insert)(ordered_map<std::string, counted>&, int))
-        {
-            for (int i = 0; i < 100; ++i)
-            {
-                const auto old_capacity = om.capacity();
-                insert(om, i);
-                if (om.capacity() > old_capacity)
-                {
-                    ++growths;
-                }
-            }
-        };
-
-        // checks that the elements are in insertion order with their values
-        const auto check_contents = [&om]
-        {
-            CHECK(om.size() == 100);
-            int i = 0;
-            for (const auto& element : om)
-            {
-                CHECK(element.first == std::to_string(i));
-                CHECK(element.second.payload == i);
-                ++i;
-            }
-        };
-
-        SECTION("emplace")
-        {
-            fill([](ordered_map<std::string, counted>& m, int i)
-            {
-                m.emplace(std::to_string(i), counted(i));
-            });
-            CHECK(growths >= 3);
-            CHECK(value_copies == 0);
-            check_contents();
-        }
-
-        SECTION("operator[]")
-        {
-            fill([](ordered_map<std::string, counted>& m, int i)
-            {
-                m[std::to_string(i)] = counted(i);
-            });
-            CHECK(growths >= 3);
-            CHECK(value_copies == 0);
-            check_contents();
-        }
-
-        SECTION("insert(value_type&&)")
-        {
-            fill([](ordered_map<std::string, counted>& m, int i)
-            {
-                m.insert({std::to_string(i), counted(i)});
-            });
-            CHECK(growths >= 3);
-            CHECK(value_copies == 0);
-            check_contents();
-        }
-
-        SECTION("insert(const value_type&)")
-        {
-            fill([](ordered_map<std::string, counted>& m, int i)
-            {
-                const std::pair<const std::string, counted> value(std::to_string(i), counted(i));
-                m.insert(value);
-            });
-            CHECK(growths >= 3);
-            // only the inserted values are copied
-            CHECK(value_copies == 100);
-            check_contents();
-        }
-
-        SECTION("insert(first, last)")
-        {
-            std::vector<std::pair<const std::string, counted>> values;
-            values.reserve(100);
-            for (int i = 0; i < 100; ++i)
-            {
-                values.emplace_back(std::to_string(i), counted(i));
-            }
-            value_copies = 0;
-
-            om.insert(values.cbegin(), values.cend());
-            // only the inserted values are copied
-            CHECK(value_copies == 100);
-            check_contents();
-        }
-    }
-
-    SECTION("elements keep their order and values over many growths")
-    {
-        ordered_map<std::string, counted> om;
-        for (int i = 0; i < 1000; ++i)
-        {
-            om.emplace(std::to_string(i), counted(i));
-        }
-
-        CHECK(om.size() == 1000);
-        int i = 0;
-        for (const auto& element : om)
-        {
-            CHECK(element.first == std::to_string(i));
-            CHECK(element.second.payload == i);
-            ++i;
-        }
-    }
-
-    SECTION("arguments may refer to elements of the full container")
-    {
-        SECTION("moving a value out of the container")
-        {
-            ordered_map<std::string, counted> om;
-            om.reserve(4);
-            while (om.size() < om.capacity())
-            {
-                const auto i = static_cast<int>(om.size());
-                om.emplace(std::to_string(i), counted(i));
-            }
-            const auto size = om.size();
-
-            om.emplace("new", std::move(om.at("0")));
-            CHECK(om.size() == size + 1);
-            CHECK(om.at("new").payload == 0);
-            CHECK(om.at("0").payload == -1);
-        }
-
-        SECTION("using a value as key")
-        {
-            ordered_map<std::string, std::string> om;
-            om.reserve(4);
-            while (om.size() < om.capacity())
-            {
-                const auto i = std::to_string(om.size());
-                om.emplace("k" + i, "v" + i);
-            }
-            const auto size = om.size();
-
-            om.emplace(om.at("k0"), std::string("x"));
-            CHECK(om.size() == size + 1);
-            CHECK(om.at("k0") == "v0");
-            CHECK(om.at("v0") == "x");
-        }
-
-        SECTION("ordered_json")
-        {
-            auto j = nlohmann::ordered_json::object();
-            auto& object = j.get_ref<nlohmann::ordered_json::object_t&>();
-            object.reserve(4);
-            while (object.size() < object.capacity())
-            {
-                const auto i = std::to_string(object.size());
-                j[i] = "a value that is too long for the small string optimization " + i;
-            }
-            const auto size = j.size();
-
-            j.emplace("new", std::move(j["0"]));
-            CHECK(j.size() == size + 1);
-            CHECK(j["new"] == "a value that is too long for the small string optimization 0");
-            CHECK(j["0"].is_null());
-        }
-    }
-
-#if !defined(JSON_NOEXCEPTION) && !defined(JSON_TEST_PAIR_MOVE_IS_NOEXCEPT)
-    SECTION("the container is unchanged if growing it throws")
-    {
-        ordered_map<throwing_key, counted> om;
-        om.reserve(4);
-        while (om.size() < om.capacity())
-        {
-            const auto i = static_cast<int>(om.size());
-            om.emplace(throwing_key(i), counted(i));
-        }
-        const auto size = om.size();
-        const auto capacity = om.capacity();
-
-        // checks that the elements are unchanged
-        const auto check_unchanged = [&om, size, capacity]
-        {
-            CHECK(om.size() == size);
-            CHECK(om.capacity() == capacity);
-            int i = 0;
-            for (const auto& element : om)
-            {
-                CHECK(element.first.id == i);
-                CHECK(element.second.payload == i);
-                ++i;
-            }
-        };
-
-        SECTION("emplace")
-        {
-            // growing copies the existing keys and then the new one; let each of these copies throw
-            for (std::size_t k = 0; k <= size; ++k)
-            {
-                counted value(100);
-                key_copies_until_throw = static_cast<int>(k);
-                CHECK_THROWS_AS(om.emplace(throwing_key(100), std::move(value)), std::runtime_error);
-                key_copies_until_throw = -1;
-
-                check_unchanged();
-                CHECK(value.payload == 100); // NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
-            }
-
-            om.emplace(throwing_key(100), counted(100));
-            CHECK(om.size() == size + 1);
-            CHECK(om.capacity() > capacity);
-            CHECK(om.at(throwing_key(100)).payload == 100);
-        }
-
-        SECTION("insert(const value_type&)")
-        {
-            const std::pair<const throwing_key, counted> value(throwing_key(100), counted(100));
-            value_copies = 0;
-
-            key_copies_until_throw = static_cast<int>(size / 2);
-            CHECK_THROWS_AS(om.insert(value), std::runtime_error);
-            key_copies_until_throw = -1;
-
-            check_unchanged();
-            CHECK(value_copies == 0);
-        }
-    }
-#endif
-
-    SECTION("elements that std::vector moves, or that cannot be moved back")
-    {
-        SECTION("nothrow move-constructible elements")
-        {
-            ordered_map<int, counted> om;
-            value_copies = 0;
-            for (int i = 0; i < 100; ++i)
-            {
-                om.emplace(i, counted(i));
-            }
-            CHECK(om.size() == 100);
-            CHECK(value_copies == 0);
-        }
-
-        SECTION("mapped type without default constructor")
-        {
-            ordered_map<std::string, no_default> om;
-            for (int i = 0; i < 100; ++i)
-            {
-                om.emplace(std::to_string(i), no_default(i));
-            }
-
-            CHECK(om.size() == 100);
-            int i = 0;
-            for (const auto& element : om)
-            {
-                CHECK(element.first == std::to_string(i));
-                CHECK(element.second.value == i);
-                ++i;
-            }
-        }
-    }
-}

tools/amalgamate/CHANGES.md

@@ -8,3 +8,6 @@ The following changes have been made to the code with respect to <https://github
   - membership check
   - made function from `_is_within`
   - removed unused variable `actual_path`
+- Added the optional config key `external`: include paths listed there are kept as
+  `#include` directives instead of being inlined (the first directive per path; the
+  repeated ones are commented out).

tools/amalgamate/README.md

@@ -57,6 +57,11 @@ Python v.2.7.0 or higher is required.
    amalgamation. Have a look at `test/source.c.json` and `test/include.h.json`
    to see two examples.
 
+   The optional `external` list names include paths that are kept as `#include`
+   directives instead of being inlined, e.g. `["nlohmann/json.hpp"]` for a header
+   that includes another amalgamated header. Only the first directive for each
+   of these paths is kept; the repeated ones are commented out.
+
  * The `-s, --source` option should specify the path to the source directory.
    This is useful for supporting separate source and build directories.
 

tools/amalgamate/amalgamate.py

@@ -62,6 +62,10 @@ class Amalgamation(object):
         return None
 
     def __init__(self, args):
+        # include paths that are kept as #include directives instead of
+        # being inlined (e.g. a header amalgamated on its own)
+        self.external = []
+        self.included_external = []
         with open(args.config, 'r') as f:
             config = json.loads(f.read())
             for key in config:
@@ -220,11 +224,14 @@ class TranslationUnit(object):
         while include_match:
             if not _is_within(include_match, skippable_contexts):
                 include_path = include_match.group("path")
-                search_same_dir = include_match.group(1) == '"'
-                found_included_path = self.amalgamation.find_included_file(
-                    include_path, self.file_dir if search_same_dir else None)
-                if found_included_path:
-                    includes.append((include_match, found_included_path))
+                if include_path in self.amalgamation.external:
+                    includes.append((include_match, None))
+                else:
+                    search_same_dir = include_match.group(1) == '"'
+                    found_included_path = self.amalgamation.find_included_file(
+                        include_path, self.file_dir if search_same_dir else None)
+                    if found_included_path:
+                        includes.append((include_match, found_included_path))
 
             include_match = self.include_pattern.search(self.content,
                                                         include_match.end())
@@ -235,6 +242,17 @@ class TranslationUnit(object):
         for include in includes:
             include_match, found_included_path = include
             tmp_content += self.content[prev_end:include_match.start()]
+            if found_included_path is None:
+                # an external header: keep the first directive and comment
+                # out the repeated ones
+                include_path = include_match.group("path")
+                if include_path in self.amalgamation.included_external:
+                    tmp_content += "// {0}".format(include_match.group(0))
+                else:
+                    self.amalgamation.included_external.append(include_path)
+                    tmp_content += include_match.group(0)
+                prev_end = include_match.end()
+                continue
             tmp_content += "// {0}\n".format(include_match.group(0))
             if found_included_path not in self.amalgamation.included_files:
                 t = TranslationUnit(found_included_path, self.amalgamation, False)

tools/amalgamate/config_json_view.json

@@ -0,0 +1,9 @@
+{
+	"project": "JSON for Modern C++",
+	"target": "single_include/nlohmann/json_view.hpp",
+	"sources": [
+		"include/nlohmann/json_view.hpp"
+	],
+	"include_paths": ["include"],
+	"external": ["nlohmann/json.hpp"]
+}