JSON impl and Schema for DummyStore

This is the "keystone" that puts most of the other store-layer JSON
formats together.

Also, add some documentation for JSON testing.

src/libstore/dummy-store.cc

@@ -2,6 +2,7 @@
 #include "nix/util/archive.hh"
 #include "nix/util/callback.hh"
 #include "nix/util/memory-source-accessor.hh"
+#include "nix/util/json-utils.hh"
 #include "nix/store/dummy-store-impl.hh"
 #include "nix/store/realisation.hh"
 
@@ -386,3 +387,100 @@ ref<DummyStore> DummyStore::Config::openDummyStore() const
 static RegisterStoreImplementation<DummyStore::Config> regDummyStore;
 
 } // namespace nix
+
+namespace nlohmann {
+
+using namespace nix;
+
+DummyStore::PathInfoAndContents adl_serializer<DummyStore::PathInfoAndContents>::from_json(const json & json)
+{
+    auto & obj = getObject(json);
+    return DummyStore::PathInfoAndContents{
+        .info = valueAt(obj, "info"),
+        .contents = make_ref<MemorySourceAccessor>(valueAt(obj, "contents")),
+    };
+}
+
+void adl_serializer<DummyStore::PathInfoAndContents>::to_json(json & json, const DummyStore::PathInfoAndContents & val)
+{
+    json = {
+        {"info", val.info},
+        {"contents", *val.contents},
+    };
+}
+
+ref<DummyStoreConfig> adl_serializer<ref<DummyStore::Config>>::from_json(const json & json)
+{
+    auto & obj = getObject(json);
+    auto cfg = make_ref<DummyStore::Config>(DummyStore::Config::Params{});
+    const_cast<PathSetting &>(cfg->storeDir_).set(getString(valueAt(obj, "store")));
+    cfg->readOnly = true;
+    return cfg;
+}
+
+void adl_serializer<DummyStoreConfig>::to_json(json & json, const DummyStoreConfig & val)
+{
+    json = {
+        {"store", val.storeDir},
+    };
+}
+
+ref<DummyStore> adl_serializer<ref<DummyStore>>::from_json(const json & json)
+{
+    auto & obj = getObject(json);
+    ref<DummyStore> res = adl_serializer<ref<DummyStoreConfig>>::from_json(valueAt(obj, "config"))->openDummyStore();
+    for (auto & [k, v] : getObject(valueAt(obj, "contents")))
+        res->contents.insert({StorePath{k}, v});
+    for (auto & [k, v] : getObject(valueAt(obj, "derivations")))
+        res->derivations.insert({StorePath{k}, v});
+    for (auto & [k0, v] : getObject(valueAt(obj, "buildTrace"))) {
+        for (auto & [k1, v2] : getObject(v)) {
+            UnkeyedRealisation realisation = v2;
+            res->buildTrace.insert_or_visit(
+                {
+                    Hash::parseExplicitFormatUnprefixed(k0, HashAlgorithm::SHA256, HashFormat::Base64),
+                    {{k1, realisation}},
+                },
+                [&](auto & kv) { kv.second.insert_or_assign(k1, realisation); });
+        }
+    }
+    return res;
+}
+
+void adl_serializer<DummyStore>::to_json(json & json, const DummyStore & val)
+{
+    json = {
+        {"config", *val.config},
+        {"contents",
+         [&] {
+             auto obj = json::object();
+             val.contents.cvisit_all([&](const auto & kv) {
+                 auto & [k, v] = kv;
+                 obj[k.to_string()] = v;
+             });
+             return obj;
+         }()},
+        {"derivations",
+         [&] {
+             auto obj = json::object();
+             val.derivations.cvisit_all([&](const auto & kv) {
+                 auto & [k, v] = kv;
+                 obj[k.to_string()] = v;
+             });
+             return obj;
+         }()},
+        {"buildTrace",
+         [&] {
+             auto obj = json::object();
+             val.buildTrace.cvisit_all([&](const auto & kv) {
+                 auto & [k, v] = kv;
+                 auto & obj2 = obj[k.to_string(HashFormat::Base64, false)] = json::object();
+                 for (auto & [k2, v2] : kv.second)
+                     obj2[k2] = v2;
+             });
+             return obj;
+         }()},
+    };
+}
+
+} // namespace nlohmann

src/libstore/include/nix/store/dummy-store-impl.hh

@@ -60,4 +60,10 @@ struct DummyStore : virtual Store
     bool operator==(const DummyStore &) const;
 };
 
+template<>
+struct json_avoids_null<DummyStore::PathInfoAndContents> : std::true_type
+{};
+
 } // namespace nix
+
+JSON_IMPL(nix::DummyStore::PathInfoAndContents)

src/libstore/include/nix/store/dummy-store.hh

@@ -2,6 +2,7 @@
 ///@file
 
 #include "nix/store/store-api.hh"
+#include "nix/util/json-impls.hh"
 
 #include <boost/unordered/concurrent_flat_map.hpp>
 
@@ -65,4 +66,33 @@ struct DummyStoreConfig : public std::enable_shared_from_this<DummyStoreConfig>,
     }
 };
 
+template<>
+struct json_avoids_null<nix::DummyStoreConfig> : std::true_type
+{};
+
+template<>
+struct json_avoids_null<ref<nix::DummyStoreConfig>> : std::true_type
+{};
+
+template<>
+struct json_avoids_null<nix::DummyStore> : std::true_type
+{};
+
+template<>
+struct json_avoids_null<ref<nix::DummyStore>> : std::true_type
+{};
+
 } // namespace nix
+
+namespace nlohmann {
+
+template<>
+JSON_IMPL_INNER_TO(nix::DummyStoreConfig);
+template<>
+JSON_IMPL_INNER_FROM(nix::ref<nix::DummyStoreConfig>);
+template<>
+JSON_IMPL_INNER_TO(nix::DummyStore);
+template<>
+JSON_IMPL_INNER_FROM(nix::ref<nix::DummyStore>);
+
+} // namespace nlohmann