From 6d3d2b2eb4909d9a4d94a53d6d3310dbd5ab9a1a Mon Sep 17 00:00:00 2001
From: Alex Shabalin <alex.shabalin@pm.me>
Date: Tue, 19 Mar 2024 12:26:18 +0100
Subject: [PATCH] Try auto-archive with type conversion

---
 immer/extra/archive/champ/traits.hpp          |   9 +-
 .../extra/archive/json/json_with_archive.hpp  |  10 ++
 .../archive/json/json_with_archive_auto.hpp   |  85 ++++++++++---
 .../archive/test_special_archive_auto.cpp     | 120 ++++++++++++++++++
 test/extra/archive/utils.hpp                  |  13 ++
 5 files changed, 217 insertions(+), 20 deletions(-)

diff --git a/immer/extra/archive/champ/traits.hpp b/immer/extra/archive/champ/traits.hpp
index 05811723..0f4b24a4 100644
--- a/immer/extra/archive/champ/traits.hpp
+++ b/immer/extra/archive/champ/traits.hpp
@@ -42,6 +42,13 @@ template <typename T,
           immer::detail::hamts::bits_t B>
 struct container_traits<immer::table<T, KeyFn, Hash, Equal, MemoryPolicy, B>>
     : champ_traits<immer::table<T, KeyFn, Hash, Equal, MemoryPolicy, B>>
-{};
+{
+    template <class F>
+    static auto transform(F&& func)
+    {
+        using U = std::decay_t<decltype(func(std::declval<T>()))>;
+        return immer::table<U, KeyFn, Hash, Equal, MemoryPolicy, B>{};
+    }
+};
 
 } // namespace immer::archive
diff --git a/immer/extra/archive/json/json_with_archive.hpp b/immer/extra/archive/json/json_with_archive.hpp
index 76e655aa..7794dcae 100644
--- a/immer/extra/archive/json/json_with_archive.hpp
+++ b/immer/extra/archive/json/json_with_archive.hpp
@@ -28,6 +28,9 @@ class error_no_archive_for_the_given_type_check_get_archives_types_function;
 template <class T>
 class error_duplicate_archive_name_found;
 
+template <class T>
+class error_missing_archive_for_type;
+
 /**
  * Archives and functions to serialize types that contain archivable data
  * structures.
@@ -112,6 +115,13 @@ struct archives_load
     template <class Container>
     auto& get_loader()
     {
+        using Contains =
+            decltype(hana::contains(storage, hana::type_c<Container>));
+        constexpr bool contains = hana::value<Contains>();
+        if constexpr (!contains) {
+            auto err = error_missing_archive_for_type<Container>{};
+        }
+
         auto& load = storage[hana::type_c<Container>];
         if (!load.loader) {
             load.loader.emplace(load.archive);
diff --git a/immer/extra/archive/json/json_with_archive_auto.hpp b/immer/extra/archive/json/json_with_archive_auto.hpp
index 59003503..a344c27e 100644
--- a/immer/extra/archive/json/json_with_archive_auto.hpp
+++ b/immer/extra/archive/json/json_with_archive_auto.hpp
@@ -226,22 +226,13 @@ auto load_initial_auto_archives(std::istream& is, WrapF wrap)
     return archives;
 }
 
-template <typename T, class ArchivesTypes>
-T from_json_with_auto_archive(std::istream& is,
-                              const ArchivesTypes& archives_types)
-{
-    namespace hana      = boost::hana;
-    constexpr auto wrap = wrap_for_loading;
-    using WrapF         = std::decay_t<decltype(wrap)>;
-
-    using Archives =
-        std::decay_t<decltype(detail::generate_archives_load(archives_types))>;
-
-    constexpr auto reload_archive_auto = [wrap](std::istream& is,
-                                                auto archives) {
-        auto restore  = util::istream_snapshot{is};
-        auto previous = immer::archive::json_immer_input_archive<Archives>{
-            std::move(archives), is};
+constexpr auto reload_archive_auto = [](auto wrap) {
+    return [wrap](std::istream& is, auto archives) {
+        using Archives = std::decay_t<decltype(archives)>;
+        using WrapF    = std::decay_t<decltype(wrap)>;
+        auto restore   = util::istream_snapshot{is};
+        auto previous =
+            json_immer_input_archive<Archives>{std::move(archives), is};
         auto ar = json_immer_auto_input_archive<decltype(previous), WrapF>{
             previous, wrap};
         /**
@@ -253,14 +244,25 @@ T from_json_with_auto_archive(std::istream& is,
         ar(CEREAL_NVP(archives));
         return archives;
     };
+};
+
+template <typename T, class ArchivesTypes>
+T from_json_with_auto_archive(std::istream& is,
+                              const ArchivesTypes& archives_types)
+{
+    namespace hana      = boost::hana;
+    constexpr auto wrap = wrap_for_loading;
+    using WrapF         = std::decay_t<decltype(wrap)>;
+
+    using Archives =
+        std::decay_t<decltype(detail::generate_archives_load(archives_types))>;
 
     auto archives =
         load_archives(is,
                       load_initial_auto_archives<Archives>(is, wrap),
-                      reload_archive_auto);
+                      reload_archive_auto(wrap));
 
-    auto previous = immer::archive::json_immer_input_archive<Archives>{
-        std::move(archives), is};
+    auto previous = json_immer_input_archive<Archives>{std::move(archives), is};
     auto ar = json_immer_auto_input_archive<decltype(previous), WrapF>{previous,
                                                                        wrap};
     auto r  = T{};
@@ -276,4 +278,49 @@ T from_json_with_auto_archive(const std::string& input,
     return from_json_with_auto_archive<T>(is, archives_types);
 }
 
+template <typename T,
+          typename OldType,
+          typename ConversionsMap,
+          class ArchivesTypes>
+T from_json_with_auto_archive_with_conversion(
+    std::istream& is,
+    const ConversionsMap& map,
+    const ArchivesTypes& archives_types)
+{
+    constexpr auto wrap = wrap_for_loading;
+    using WrapF         = std::decay_t<decltype(wrap)>;
+
+    // Load the archives part for the old type
+    using OldArchives =
+        std::decay_t<decltype(detail::generate_archives_load(archives_types))>;
+    auto archives_old =
+        load_archives(is,
+                      load_initial_auto_archives<OldArchives>(is, wrap),
+                      reload_archive_auto(wrap));
+
+    auto archives  = archives_old.transform(map);
+    using Archives = decltype(archives);
+
+    auto previous = json_immer_input_archive<Archives>{std::move(archives), is};
+    auto ar = json_immer_auto_input_archive<decltype(previous), WrapF>{previous,
+                                                                       wrap};
+    auto r  = T{};
+    ar(r);
+    return r;
+}
+
+template <typename T,
+          typename OldType,
+          typename ConversionsMap,
+          class ArchivesTypes>
+T from_json_with_auto_archive_with_conversion(
+    const std::string& input,
+    const ConversionsMap& map,
+    const ArchivesTypes& archives_types)
+{
+    auto is = std::istringstream{input};
+    return from_json_with_auto_archive_with_conversion<T, OldType>(
+        is, map, archives_types);
+}
+
 } // namespace immer::archive
diff --git a/test/extra/archive/test_special_archive_auto.cpp b/test/extra/archive/test_special_archive_auto.cpp
index cd336c72..1479fa9e 100644
--- a/test/extra/archive/test_special_archive_auto.cpp
+++ b/test/extra/archive/test_special_archive_auto.cpp
@@ -250,3 +250,123 @@ TEST_CASE("Test save and load small type")
         REQUIRE(loaded == value);
     }
 }
+
+namespace {
+
+using test::new_type;
+using test::old_type;
+
+template <class V>
+using map_t = immer::map<std::string, V, immer::archive::xx_hash<std::string>>;
+
+template <class T>
+using table_t =
+    immer::table<T, immer::table_key_fn, immer::archive::xx_hash<std::string>>;
+
+// Some type that an application would serialize. Contains multiple vectors and
+// maps to demonstrate structural sharing.
+struct old_app_type
+{
+    BOOST_HANA_DEFINE_STRUCT(old_app_type,
+                             (test::vector_one<old_type>, vec),
+                             (test::vector_one<old_type>, vec2),
+                             (map_t<old_type>, map),
+                             (map_t<old_type>, map2),
+                             (table_t<old_type>, table)
+
+    );
+
+    template <class Archive>
+    void serialize(Archive& ar)
+    {
+        serialize_members(ar, *this);
+    }
+};
+
+struct new_app_type
+{
+    BOOST_HANA_DEFINE_STRUCT(new_app_type,
+                             (test::vector_one<new_type>, vec),
+                             (test::vector_one<new_type>, vec2),
+                             (map_t<new_type>, map),
+                             (map_t<new_type>, map2),
+                             (table_t<new_type>, table)
+
+    );
+
+    template <class Archive>
+    void serialize(Archive& ar)
+    {
+        serialize_members(ar, *this);
+    }
+};
+
+} // namespace
+
+TEST_CASE("Test conversion with auto-archive")
+{
+    const auto vec1 = test::vector_one<old_type>{
+        old_type{.data = 123},
+        old_type{.data = 234},
+    };
+    const auto vec2 = vec1.push_back(old_type{.data = 345});
+
+    const auto map1 = [] {
+        auto map = map_t<old_type>{};
+        for (auto i = 0; i < 30; ++i) {
+            map =
+                std::move(map).set(fmt::format("x{}x", i), old_type{.data = i});
+        }
+        return map;
+    }();
+    const auto map2 = map1.set("345", old_type{.data = 345});
+
+    // Prepare a value of the old type that uses some structural sharing
+    // internally.
+    const auto value = old_app_type{
+        .vec  = vec1,
+        .vec2 = vec2,
+        .map  = map1,
+        .map2 = map2,
+        .table =
+            {
+                old_type{"_51_", 51},
+                old_type{"_52_", 52},
+                old_type{"_53_", 53},
+            },
+    };
+
+    constexpr auto old_names = [] {
+        return immer::archive::get_archives_for_types(
+            hana::tuple_t<old_app_type>, hana::make_map());
+    };
+
+    using OldArchiveTypes            = decltype(old_names());
+    constexpr auto old_archive_types = OldArchiveTypes{};
+    const auto [json_str, archives] =
+        immer::archive::to_json_with_auto_archive(value, old_archive_types);
+    // REQUIRE(json_str == "");
+
+    // Describe how to go from the old archive to the desired new archive.
+    // Convert all old archives with convert_old_type.
+    const auto archives_conversions = hana::unpack(
+        hana::transform(hana::keys(old_archive_types),
+                        [&](auto key) {
+                            return hana::make_pair(key, test::convert_old_type);
+                        }),
+        hana::make_map);
+
+    // Having a JSON from serializing old_app_type and a conversion function,
+    // we need to somehow load new_app_type.
+    const new_app_type full_load = immer::archive::
+        from_json_with_auto_archive_with_conversion<new_app_type, old_app_type>(
+            json_str, archives_conversions, old_archive_types);
+
+    {
+        REQUIRE(full_load.vec == transform_vec(value.vec));
+        REQUIRE(full_load.vec2 == transform_vec(value.vec2));
+        REQUIRE(full_load.map == transform_map(value.map));
+        REQUIRE(full_load.map2 == transform_map(value.map2));
+        REQUIRE(full_load.table == transform_table(value.table));
+    }
+}
diff --git a/test/extra/archive/utils.hpp b/test/extra/archive/utils.hpp
index 807c91ff..647fa196 100644
--- a/test/extra/archive/utils.hpp
+++ b/test/extra/archive/utils.hpp
@@ -4,6 +4,8 @@
 #include <immer/extra/archive/rbts/load.hpp>
 #include <immer/extra/archive/xxhash/xxhash.hpp>
 
+#include <immer/table.hpp>
+
 #include <sstream>
 
 #include <cereal/archives/json.hpp>
@@ -151,6 +153,17 @@ inline auto transform_map(const auto& map)
     return result;
 }
 
+inline auto transform_table(const auto& table)
+{
+    auto result = immer::table<new_type,
+                               immer::table_key_fn,
+                               immer::archive::xx_hash<std::string>>{};
+    for (const auto& item : table) {
+        result = std::move(result).insert(convert_old_type(item));
+    }
+    return result;
+}
+
 } // namespace test
 
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