Implement realisation operations on dummy store

src/libstore/dummy-store.cc

@@ -3,6 +3,7 @@
 #include "nix/util/callback.hh"
 #include "nix/util/memory-source-accessor.hh"
 #include "nix/store/dummy-store-impl.hh"
+#include "nix/store/realisation.hh"
 
 #include <boost/unordered/concurrent_flat_map.hpp>
 
@@ -251,7 +252,10 @@ struct DummyStoreImpl : DummyStore
 
     void registerDrvOutput(const Realisation & output) override
     {
-        unsupported("registerDrvOutput");
+        auto ref = make_ref<UnkeyedRealisation>(output);
+        buildTrace.insert_or_visit({output.id.drvHash, {{output.id.outputName, ref}}}, [&](auto & kv) {
+            kv.second.insert_or_assign(output.id.outputName, make_ref<UnkeyedRealisation>(output));
+        });
     }
 
     void narFromPath(const StorePath & path, Sink & sink) override
@@ -267,9 +271,18 @@ struct DummyStoreImpl : DummyStore
     }
 
     void queryRealisationUncached(
-        const DrvOutput &, Callback<std::shared_ptr<const UnkeyedRealisation>> callback) noexcept override
+        const DrvOutput & drvOutput, Callback<std::shared_ptr<const UnkeyedRealisation>> callback) noexcept override
     {
-        callback(nullptr);
+        bool visited = false;
+        buildTrace.cvisit(drvOutput.drvHash, [&](const auto & kv) {
+            if (auto it = kv.second.find(drvOutput.outputName); it != kv.second.end()) {
+                visited = true;
+                callback(it->second.get_ptr());
+            }
+        });
+
+        if (!visited)
+            callback(nullptr);
     }
 
     std::shared_ptr<SourceAccessor> getFSAccessor(const StorePath & path, bool requireValidPath) override

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

@@ -30,6 +30,18 @@ struct DummyStore : virtual Store
      */
     boost::concurrent_flat_map<StorePath, PathInfoAndContents> contents;
 
+    /**
+     * The build trace maps the pair of a content-addressing (fixed or
+     * floating) derivations an one of its output to a
+     * (content-addressed) store object.
+     *
+     * It is [curried](https://en.wikipedia.org/wiki/Currying), so we
+     * instead having a single output with a `DrvOutput` key, we have an
+     * outer map for the derivation, and inner maps for the outputs of a
+     * given derivation.
+     */
+    boost::concurrent_flat_map<Hash, std::map<std::string, ref<UnkeyedRealisation>>> buildTrace;
+
     DummyStore(ref<const Config> config)
         : Store{*config}
         , config(config)

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

@@ -3,6 +3,8 @@
 
 #include "nix/store/store-api.hh"
 
+#include <boost/unordered/concurrent_flat_map.hpp>
+
 namespace nix {
 
 struct DummyStore;