Merge pull request #5048 from tweag/flox-eval-store

--eval-store and faster closure copying

src/build-remote/build-remote.cc

@@ -270,7 +270,7 @@ connected:
 
         {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri));
-            copyPaths(store, ref<Store>(sshStore), store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute);
+            copyPaths(*store, *sshStore, store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute);
         }
 
         uploadLock = -1;
@@ -321,7 +321,7 @@ connected:
             if (auto localStore = store.dynamic_pointer_cast<LocalStore>())
                 for (auto & path : missingPaths)
                     localStore->locksHeld.insert(store->printStorePath(path)); /* FIXME: ugly */
-            copyPaths(ref<Store>(sshStore), store, missingPaths, NoRepair, NoCheckSigs, NoSubstitute);
+            copyPaths(*sshStore, *store, missingPaths, NoRepair, NoCheckSigs, NoSubstitute);
         }
         // XXX: Should be done as part of `copyPaths`
         for (auto & realisation : missingRealisations) {

src/libcmd/command.cc

@@ -54,6 +54,30 @@ void StoreCommand::run()
     run(getStore());
 }
 
+EvalCommand::EvalCommand()
+{
+}
+
+EvalCommand::~EvalCommand()
+{
+    if (evalState)
+        evalState->printStats();
+}
+
+ref<Store> EvalCommand::getEvalStore()
+{
+    if (!evalStore)
+        evalStore = evalStoreUrl ? openStore(*evalStoreUrl) : getStore();
+    return ref<Store>(evalStore);
+}
+
+ref<EvalState> EvalCommand::getEvalState()
+{
+    if (!evalState)
+        evalState = std::make_shared<EvalState>(searchPath, getEvalStore(), getStore());
+    return ref<EvalState>(evalState);
+}
+
 BuiltPathsCommand::BuiltPathsCommand(bool recursive)
     : recursive(recursive)
 {
@@ -91,7 +115,7 @@ void BuiltPathsCommand::run(ref<Store> store)
         for (auto & p : store->queryAllValidPaths())
             paths.push_back(BuiltPath::Opaque{p});
     } else {
-        paths = toBuiltPaths(store, realiseMode, operateOn, installables);
+        paths = toBuiltPaths(getEvalStore(), store, realiseMode, operateOn, installables);
         if (recursive) {
             // XXX: This only computes the store path closure, ignoring
             // intermediate realisations

src/libcmd/command.hh

@@ -45,11 +45,18 @@ private:
 
 struct EvalCommand : virtual StoreCommand, MixEvalArgs
 {
-    ref<EvalState> getEvalState();
+    EvalCommand();
-
-    std::shared_ptr<EvalState> evalState;
 
     ~EvalCommand();
+
+    ref<Store> getEvalStore();
+
+    ref<EvalState> getEvalState();
+
+private:
+    std::shared_ptr<Store> evalStore;
+
+    std::shared_ptr<EvalState> evalState;
 };
 
 struct MixFlakeOptions : virtual Args, EvalCommand
@@ -216,15 +223,21 @@ static RegisterCommand registerCommand2(std::vector<std::string> && name)
     return RegisterCommand(std::move(name), [](){ return make_ref<T>(); });
 }
 
-BuiltPaths build(ref<Store> store, Realise mode,
+BuiltPaths build(ref<Store> evalStore, ref<Store> store, Realise mode,
     std::vector<std::shared_ptr<Installable>> installables, BuildMode bMode = bmNormal);
 
-std::set<StorePath> toStorePaths(ref<Store> store,
+std::set<StorePath> toStorePaths(
-    Realise mode, OperateOn operateOn,
+    ref<Store> evalStore,
+    ref<Store> store,
+    Realise mode,
+    OperateOn operateOn,
     std::vector<std::shared_ptr<Installable>> installables);
 
-StorePath toStorePath(ref<Store> store,
+StorePath toStorePath(
-    Realise mode, OperateOn operateOn,
+    ref<Store> evalStore,
+    ref<Store> store,
+    Realise mode,
+    OperateOn operateOn,
     std::shared_ptr<Installable> installable);
 
 std::set<StorePath> toDerivations(ref<Store> store,
@@ -232,6 +245,7 @@ std::set<StorePath> toDerivations(ref<Store> store,
     bool useDeriver = false);
 
 BuiltPaths toBuiltPaths(
+    ref<Store> evalStore,
     ref<Store> store,
     Realise mode,
     OperateOn operateOn,

src/libcmd/installables.cc

@@ -289,19 +289,6 @@ void completeFlakeRefWithFragment(
     completeFlakeRef(evalState->store, prefix);
 }
 
-ref<EvalState> EvalCommand::getEvalState()
-{
-    if (!evalState)
-        evalState = std::make_shared<EvalState>(searchPath, getStore());
-    return ref<EvalState>(evalState);
-}
-
-EvalCommand::~EvalCommand()
-{
-    if (evalState)
-        evalState->printStats();
-}
-
 void completeFlakeRef(ref<Store> store, std::string_view prefix)
 {
     if (prefix == "")
@@ -391,6 +378,7 @@ DerivedPaths InstallableValue::toDerivedPaths()
     DerivedPaths res;
 
     std::map<StorePath, std::set<std::string>> drvsToOutputs;
+    RealisedPath::Set drvsToCopy;
 
     // Group by derivation, helps with .all in particular
     for (auto & drv : toDerivations()) {
@@ -398,6 +386,7 @@ DerivedPaths InstallableValue::toDerivedPaths()
         if (outputName == "")
             throw Error("derivation '%s' lacks an 'outputName' attribute", state->store->printStorePath(drv.drvPath));
         drvsToOutputs[drv.drvPath].insert(outputName);
+        drvsToCopy.insert(drv.drvPath);
     }
 
     for (auto & i : drvsToOutputs)
@@ -712,7 +701,7 @@ std::shared_ptr<Installable> SourceExprCommand::parseInstallable(
     return installables.front();
 }
 
-BuiltPaths getBuiltPaths(ref<Store> store, DerivedPaths hopefullyBuiltPaths)
+BuiltPaths getBuiltPaths(ref<Store> evalStore, ref<Store> store, const DerivedPaths & hopefullyBuiltPaths)
 {
     BuiltPaths res;
     for (auto & b : hopefullyBuiltPaths)
@@ -723,14 +712,13 @@ BuiltPaths getBuiltPaths(ref<Store> store, DerivedPaths hopefullyBuiltPaths)
                 },
                 [&](DerivedPath::Built bfd) {
                     OutputPathMap outputs;
-                    auto drv = store->readDerivation(bfd.drvPath);
+                    auto drv = evalStore->readDerivation(bfd.drvPath);
-                    auto outputHashes = staticOutputHashes(*store, drv);
+                    auto outputHashes = staticOutputHashes(*evalStore, drv); // FIXME: expensive
                     auto drvOutputs = drv.outputsAndOptPaths(*store);
                     for (auto & output : bfd.outputs) {
                         if (!outputHashes.count(output))
                             throw Error(
-                                "the derivation '%s' doesn't have an output "
+                                "the derivation '%s' doesn't have an output named '%s'",
-                                "named '%s'",
                                 store->printStorePath(bfd.drvPath), output);
                         if (settings.isExperimentalFeatureEnabled(
                                 "ca-derivations")) {
@@ -762,7 +750,7 @@ BuiltPaths getBuiltPaths(ref<Store> store, DerivedPaths hopefullyBuiltPaths)
     return res;
 }
 
-BuiltPaths build(ref<Store> store, Realise mode,
+BuiltPaths build(ref<Store> evalStore, ref<Store> store, Realise mode,
     std::vector<std::shared_ptr<Installable>> installables, BuildMode bMode)
 {
     if (mode == Realise::Nothing)
@@ -778,20 +766,21 @@ BuiltPaths build(ref<Store> store, Realise mode,
     if (mode == Realise::Nothing)
         printMissing(store, pathsToBuild, lvlError);
     else if (mode == Realise::Outputs)
-        store->buildPaths(pathsToBuild, bMode);
+        store->buildPaths(pathsToBuild, bMode, evalStore);
 
-    return getBuiltPaths(store, pathsToBuild);
+    return getBuiltPaths(evalStore, store, pathsToBuild);
 }
 
 BuiltPaths toBuiltPaths(
+    ref<Store> evalStore,
     ref<Store> store,
     Realise mode,
     OperateOn operateOn,
     std::vector<std::shared_ptr<Installable>> installables)
 {
-    if (operateOn == OperateOn::Output) {
+    if (operateOn == OperateOn::Output)
-        return build(store, mode, installables);
+        return build(evalStore, store, mode, installables);
-    } else {
+    else {
         if (mode == Realise::Nothing)
             settings.readOnlyMode = true;
 
@@ -802,23 +791,27 @@ BuiltPaths toBuiltPaths(
     }
 }
 
-StorePathSet toStorePaths(ref<Store> store,
+StorePathSet toStorePaths(
+    ref<Store> evalStore,
+    ref<Store> store,
     Realise mode, OperateOn operateOn,
     std::vector<std::shared_ptr<Installable>> installables)
 {
     StorePathSet outPaths;
-    for (auto & path : toBuiltPaths(store, mode, operateOn, installables)) {
+    for (auto & path : toBuiltPaths(evalStore, store, mode, operateOn, installables)) {
         auto thisOutPaths = path.outPaths();
         outPaths.insert(thisOutPaths.begin(), thisOutPaths.end());
     }
     return outPaths;
 }
 
-StorePath toStorePath(ref<Store> store,
+StorePath toStorePath(
+    ref<Store> evalStore,
+    ref<Store> store,
     Realise mode, OperateOn operateOn,
     std::shared_ptr<Installable> installable)
 {
-    auto paths = toStorePaths(store, mode, operateOn, {installable});
+    auto paths = toStorePaths(evalStore, store, mode, operateOn, {installable});
 
     if (paths.size() != 1)
         throw Error("argument '%s' should evaluate to one store path", installable->what());

src/libcmd/installables.hh

@@ -26,7 +26,7 @@ struct App
 struct UnresolvedApp
 {
     App unresolved;
-    App resolve(ref<Store>);
+    App resolve(ref<Store> evalStore, ref<Store> store);
 };
 
 struct Installable

src/libexpr/common-eval-args.cc

@@ -61,6 +61,14 @@ MixEvalArgs::MixEvalArgs()
             fetchers::overrideRegistry(from.input, to.input, extraAttrs);
         }}
     });
+
+    addFlag({
+        .longName = "eval-store",
+        .description = "The Nix store to use for evaluations.",
+        .category = category,
+        .labels = {"store-url"},
+        .handler = {&evalStoreUrl},
+    });
 }
 
 Bindings * MixEvalArgs::getAutoArgs(EvalState & state)

src/libexpr/common-eval-args.hh

@@ -16,8 +16,9 @@ struct MixEvalArgs : virtual Args
 
     Strings searchPath;
 
-private:
+    std::optional<std::string> evalStoreUrl;
 
+private:
     std::map<std::string, std::string> autoArgs;
 };
 

src/libexpr/eval.cc

@@ -378,7 +378,10 @@ static Strings parseNixPath(const string & s)
 }
 
 
-EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
+EvalState::EvalState(
+    const Strings & _searchPath,
+    ref<Store> store,
+    std::shared_ptr<Store> buildStore)
     : sWith(symbols.create("<with>"))
     , sOutPath(symbols.create("outPath"))
     , sDrvPath(symbols.create("drvPath"))
@@ -411,6 +414,7 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
     , sEpsilon(symbols.create(""))
     , repair(NoRepair)
     , store(store)
+    , buildStore(buildStore ? buildStore : store)
     , regexCache(makeRegexCache())
     , baseEnv(allocEnv(128))
     , staticBaseEnv(false, 0)

src/libexpr/eval.hh

@@ -94,8 +94,12 @@ public:
 
     Value vEmptySet;
 
+    /* Store used to materialise .drv files. */
     const ref<Store> store;
 
+    /* Store used to build stuff. */
+    const ref<Store> buildStore;
+
 
 private:
     SrcToStore srcToStore;
@@ -128,7 +132,10 @@ private:
 
 public:
 
-    EvalState(const Strings & _searchPath, ref<Store> store);
+    EvalState(
+        const Strings & _searchPath,
+        ref<Store> store,
+        std::shared_ptr<Store> buildStore = nullptr);
     ~EvalState();
 
     void addToSearchPath(const string & s);

src/libstore/build/derivation-goal.cc

@@ -165,7 +165,7 @@ void DerivationGoal::getDerivation()
     /* The first thing to do is to make sure that the derivation
        exists.  If it doesn't, it may be created through a
        substitute. */
-    if (buildMode == bmNormal && worker.store.isValidPath(drvPath)) {
+    if (buildMode == bmNormal && worker.evalStore.isValidPath(drvPath)) {
         loadDerivation();
         return;
     }
@@ -188,12 +188,12 @@ void DerivationGoal::loadDerivation()
     /* `drvPath' should already be a root, but let's be on the safe
        side: if the user forgot to make it a root, we wouldn't want
        things being garbage collected while we're busy. */
-    worker.store.addTempRoot(drvPath);
+    worker.evalStore.addTempRoot(drvPath);
 
-    assert(worker.store.isValidPath(drvPath));
+    assert(worker.evalStore.isValidPath(drvPath));
 
     /* Get the derivation. */
-    drv = std::make_unique<Derivation>(worker.store.derivationFromPath(drvPath));
+    drv = std::make_unique<Derivation>(worker.evalStore.derivationFromPath(drvPath));
 
     haveDerivation();
 }
@@ -212,7 +212,7 @@ void DerivationGoal::haveDerivation()
         if (i.second.second)
             worker.store.addTempRoot(*i.second.second);
 
-    auto outputHashes = staticOutputHashes(worker.store, *drv);
+    auto outputHashes = staticOutputHashes(worker.evalStore, *drv);
     for (auto & [outputName, outputHash] : outputHashes)
       initialOutputs.insert({
             outputName,
@@ -337,6 +337,15 @@ void DerivationGoal::gaveUpOnSubstitution()
         for (auto & i : dynamic_cast<Derivation *>(drv.get())->inputDrvs)
             addWaitee(worker.makeDerivationGoal(i.first, i.second, buildMode == bmRepair ? bmRepair : bmNormal));
 
+    /* Copy the input sources from the eval store to the build
+       store. */
+    if (&worker.evalStore != &worker.store) {
+        RealisedPath::Set inputSrcs;
+        for (auto & i : drv->inputSrcs)
+            inputSrcs.insert(i);
+        copyClosure(worker.evalStore, worker.store, inputSrcs);
+    }
+
     for (auto & i : drv->inputSrcs) {
         if (worker.store.isValidPath(i)) continue;
         if (!settings.useSubstitutes)
@@ -478,8 +487,8 @@ void DerivationGoal::inputsRealised()
             /* Add the relevant output closures of the input derivation
                `i' as input paths.  Only add the closures of output paths
                that are specified as inputs. */
-            assert(worker.store.isValidPath(drvPath));
+            assert(worker.evalStore.isValidPath(drvPath));
-            auto outputs = worker.store.queryPartialDerivationOutputMap(depDrvPath);
+            auto outputs = worker.evalStore.queryPartialDerivationOutputMap(depDrvPath);
             for (auto & j : wantedDepOutputs) {
                 if (outputs.count(j) > 0) {
                     auto optRealizedInput = outputs.at(j);

src/libstore/build/entry-points.cc

@@ -6,9 +6,9 @@
 
 namespace nix {
 
-void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMode)
+void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMode, std::shared_ptr<Store> evalStore)
 {
-    Worker worker(*this);
+    Worker worker(*this, evalStore ? *evalStore : *this);
 
     Goals goals;
     for (auto & br : reqs) {
@@ -51,7 +51,7 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
 BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
     BuildMode buildMode)
 {
-    Worker worker(*this);
+    Worker worker(*this, *this);
     auto goal = worker.makeBasicDerivationGoal(drvPath, drv, {}, buildMode);
 
     BuildResult result;
@@ -93,7 +93,7 @@ void Store::ensurePath(const StorePath & path)
     /* If the path is already valid, we're done. */
     if (isValidPath(path)) return;
 
-    Worker worker(*this);
+    Worker worker(*this, *this);
     GoalPtr goal = worker.makePathSubstitutionGoal(path);
     Goals goals = {goal};
 
@@ -111,7 +111,7 @@ void Store::ensurePath(const StorePath & path)
 
 void LocalStore::repairPath(const StorePath & path)
 {
-    Worker worker(*this);
+    Worker worker(*this, *this);
     GoalPtr goal = worker.makePathSubstitutionGoal(path, Repair);
     Goals goals = {goal};
 

src/libstore/build/local-derivation-goal.cc

@@ -1254,8 +1254,10 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
         return next->queryRealisation(id);
     }
 
-    void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode) override
+    void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode, std::shared_ptr<Store> evalStore) override
     {
+        assert(!evalStore);
+
         if (buildMode != bmNormal) throw Error("unsupported build mode");
 
         StorePathSet newPaths;

src/libstore/build/substitution-goal.cc

@@ -204,7 +204,7 @@ void PathSubstitutionGoal::tryToRun()
             Activity act(*logger, actSubstitute, Logger::Fields{worker.store.printStorePath(storePath), sub->getUri()});
             PushActivity pact(act.id);
 
-            copyStorePath(ref<Store>(sub), ref<Store>(worker.store.shared_from_this()),
+            copyStorePath(*sub, worker.store,
                 subPath ? *subPath : storePath, repair, sub->isTrusted ? NoCheckSigs : CheckSigs);
 
             promise.set_value();

src/libstore/build/worker.cc

@@ -9,11 +9,12 @@
 
 namespace nix {
 
-Worker::Worker(Store & store)
+Worker::Worker(Store & store, Store & evalStore)
     : act(*logger, actRealise)
     , actDerivations(*logger, actBuilds)
     , actSubstitutions(*logger, actCopyPaths)
     , store(store)
+    , evalStore(evalStore)
 {
     /* Debugging: prevent recursive workers. */
     nrLocalBuilds = 0;

src/libstore/build/worker.hh

@@ -110,6 +110,7 @@ public:
     bool checkMismatch;
 
     Store & store;
+    Store & evalStore;
 
     std::unique_ptr<HookInstance> hook;
 
@@ -131,7 +132,7 @@ public:
        it answers with "decline-permanently", we don't try again. */
     bool tryBuildHook = true;
 
-    Worker(Store & store);
+    Worker(Store & store, Store & evalStore);
     ~Worker();
 
     /* Make a goal (with caching). */

src/libstore/daemon.cc

@@ -243,23 +243,6 @@ struct ClientSettings
     }
 };
 
-static void writeValidPathInfo(
-    ref<Store> store,
-    unsigned int clientVersion,
-    Sink & to,
-    std::shared_ptr<const ValidPathInfo> info)
-{
-    to << (info->deriver ? store->printStorePath(*info->deriver) : "")
-       << info->narHash.to_string(Base16, false);
-    worker_proto::write(*store, to, info->references);
-    to << info->registrationTime << info->narSize;
-    if (GET_PROTOCOL_MINOR(clientVersion) >= 16) {
-        to << info->ultimate
-           << info->sigs
-           << renderContentAddress(info->ca);
-    }
-}
-
 static std::vector<DerivedPath> readDerivedPaths(Store & store, unsigned int clientVersion, Source & from)
 {
     std::vector<DerivedPath> reqs;
@@ -422,9 +405,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
             }();
             logger->stopWork();
 
-            to << store->printStorePath(pathInfo->path);
+            pathInfo->write(to, *store, GET_PROTOCOL_MINOR(clientVersion));
-            writeValidPathInfo(store, clientVersion, to, pathInfo);
-
         } else {
             HashType hashAlgo;
             std::string baseName;
@@ -471,6 +452,21 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         break;
     }
 
+    case wopAddMultipleToStore: {
+        bool repair, dontCheckSigs;
+        from >> repair >> dontCheckSigs;
+        if (!trusted && dontCheckSigs)
+            dontCheckSigs = false;
+
+        logger->startWork();
+        FramedSource source(from);
+        store->addMultipleToStore(source,
+            RepairFlag{repair},
+            dontCheckSigs ? NoCheckSigs : CheckSigs);
+        logger->stopWork();
+        break;
+    }
+
     case wopAddTextToStore: {
         string suffix = readString(from);
         string s = readString(from);
@@ -770,7 +766,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (info) {
             if (GET_PROTOCOL_MINOR(clientVersion) >= 17)
                 to << 1;
-            writeValidPathInfo(store, clientVersion, to, info);
+            info->write(to, *store, GET_PROTOCOL_MINOR(clientVersion), false);
         } else {
             assert(GET_PROTOCOL_MINOR(clientVersion) >= 17);
             to << 0;

src/libstore/dummy-store.cc

@@ -43,11 +43,6 @@ struct DummyStore : public virtual DummyStoreConfig, public virtual Store
         RepairFlag repair, CheckSigsFlag checkSigs) override
     { unsupported("addToStore"); }
 
-    StorePath addToStore(const string & name, const Path & srcPath,
-        FileIngestionMethod method, HashType hashAlgo,
-        PathFilter & filter, RepairFlag repair) override
-    { unsupported("addToStore"); }
-
     StorePath addTextToStore(const string & name, const string & s,
         const StorePathSet & references, RepairFlag repair) override
     { unsupported("addTextToStore"); }

src/libstore/legacy-ssh-store.cc

@@ -267,8 +267,11 @@ public:
         return status;
     }
 
-    void buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode) override
+    void buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode, std::shared_ptr<Store> evalStore) override
     {
+        if (evalStore && evalStore.get() != this)
+            throw Error("building on an SSH store is incompatible with '--eval-store'");
+
         auto conn(connections->get());
 
         conn->to << cmdBuildPaths;

src/libstore/path-info.cc

@@ -0,0 +1,46 @@
+#include "path-info.hh"
+#include "worker-protocol.hh"
+
+namespace nix {
+
+ValidPathInfo ValidPathInfo::read(Source & source, const Store & store, unsigned int format)
+{
+    return read(source, store, format, store.parseStorePath(readString(source)));
+}
+
+ValidPathInfo ValidPathInfo::read(Source & source, const Store & store, unsigned int format, StorePath && path)
+{
+    auto deriver = readString(source);
+    auto narHash = Hash::parseAny(readString(source), htSHA256);
+    ValidPathInfo info(path, narHash);
+    if (deriver != "") info.deriver = store.parseStorePath(deriver);
+    info.references = worker_proto::read(store, source, Phantom<StorePathSet> {});
+    source >> info.registrationTime >> info.narSize;
+    if (format >= 16) {
+        source >> info.ultimate;
+        info.sigs = readStrings<StringSet>(source);
+        info.ca = parseContentAddressOpt(readString(source));
+    }
+    return info;
+}
+
+void ValidPathInfo::write(
+    Sink & sink,
+    const Store & store,
+    unsigned int format,
+    bool includePath) const
+{
+    if (includePath)
+        sink << store.printStorePath(path);
+    sink << (deriver ? store.printStorePath(*deriver) : "")
+         << narHash.to_string(Base16, false);
+    worker_proto::write(store, sink, references);
+    sink << registrationTime << narSize;
+    if (format >= 16) {
+        sink << ultimate
+             << sigs
+             << renderContentAddress(ca);
+    }
+}
+
+}

src/libstore/path-info.hh

@@ -105,6 +105,11 @@ struct ValidPathInfo
     ValidPathInfo(const StorePath & path, Hash narHash) : path(path), narHash(narHash) { };
 
     virtual ~ValidPathInfo() { }
+
+    static ValidPathInfo read(Source & source, const Store & store, unsigned int format);
+    static ValidPathInfo read(Source & source, const Store & store, unsigned int format, StorePath && path);
+
+    void write(Sink & sink, const Store & store, unsigned int format, bool includePath = true) const;
 };
 
 typedef std::map<StorePath, ValidPathInfo> ValidPathInfos;

src/libstore/remote-store.cc

@@ -386,23 +386,6 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, S
 }
 
 
-ref<const ValidPathInfo> RemoteStore::readValidPathInfo(ConnectionHandle & conn, const StorePath & path)
-{
-    auto deriver = readString(conn->from);
-    auto narHash = Hash::parseAny(readString(conn->from), htSHA256);
-    auto info = make_ref<ValidPathInfo>(path, narHash);
-    if (deriver != "") info->deriver = parseStorePath(deriver);
-    info->references = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
-    conn->from >> info->registrationTime >> info->narSize;
-    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 16) {
-        conn->from >> info->ultimate;
-        info->sigs = readStrings<StringSet>(conn->from);
-        info->ca = parseContentAddressOpt(readString(conn->from));
-    }
-    return info;
-}
-
-
 void RemoteStore::queryPathInfoUncached(const StorePath & path,
     Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept
 {
@@ -423,7 +406,8 @@ void RemoteStore::queryPathInfoUncached(const StorePath & path,
                 bool valid; conn->from >> valid;
                 if (!valid) throw InvalidPath("path '%s' is not valid", printStorePath(path));
             }
-            info = readValidPathInfo(conn, path);
+            info = std::make_shared<ValidPathInfo>(
+                ValidPathInfo::read(conn->from, *this, GET_PROTOCOL_MINOR(conn->daemonVersion), StorePath{path}));
         }
         callback(std::move(info));
     } catch (...) { callback.rethrow(); }
@@ -525,8 +509,8 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
             });
         }
 
-        auto path = parseStorePath(readString(conn->from));
+        return make_ref<ValidPathInfo>(
-        return readValidPathInfo(conn, path);
+            ValidPathInfo::read(conn->from, *this, GET_PROTOCOL_MINOR(conn->daemonVersion)));
     }
     else {
         if (repair) throw Error("repairing is not supported when building through the Nix daemon protocol < 1.25");
@@ -642,6 +626,25 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
 }
 
 
+void RemoteStore::addMultipleToStore(
+    Source & source,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs)
+{
+    if (GET_PROTOCOL_MINOR(getConnection()->daemonVersion) >= 32) {
+        auto conn(getConnection());
+        conn->to
+            << wopAddMultipleToStore
+            << repair
+            << !checkSigs;
+        conn.withFramedSink([&](Sink & sink) {
+            source.drainInto(sink);
+        });
+    } else
+        Store::addMultipleToStore(source, repair, checkSigs);
+}
+
+
 StorePath RemoteStore::addTextToStore(const string & name, const string & s,
     const StorePathSet & references, RepairFlag repair)
 {
@@ -705,8 +708,18 @@ static void writeDerivedPaths(RemoteStore & store, ConnectionHandle & conn, cons
     }
 }
 
-void RemoteStore::buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode)
+void RemoteStore::buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode, std::shared_ptr<Store> evalStore)
 {
+    if (evalStore && evalStore.get() != this) {
+        /* The remote doesn't have a way to access evalStore, so copy
+           the .drvs. */
+        RealisedPath::Set drvPaths2;
+        for (auto & i : drvPaths)
+            if (auto p = std::get_if<DerivedPath::Built>(&i))
+                drvPaths2.insert(p->drvPath);
+        copyClosure(*evalStore, *this, drvPaths2);
+    }
+
     auto conn(getConnection());
     conn->to << wopBuildPaths;
     assert(GET_PROTOCOL_MINOR(conn->daemonVersion) >= 13);
@@ -1007,8 +1020,8 @@ void ConnectionHandle::withFramedSink(std::function<void(Sink &sink)> fun)
 
     std::exception_ptr ex;
 
-    /* Handle log messages / exceptions from the remote on a
+    /* Handle log messages / exceptions from the remote on a separate
-        separate thread. */
+       thread. */
     std::thread stderrThread([&]()
     {
         try {
@@ -1041,7 +1054,6 @@ void ConnectionHandle::withFramedSink(std::function<void(Sink &sink)> fun)
     stderrThread.join();
     if (ex)
         std::rethrow_exception(ex);
-
 }
 
 }

src/libstore/remote-store.hh

@@ -78,6 +78,11 @@ public:
     void addToStore(const ValidPathInfo & info, Source & nar,
         RepairFlag repair, CheckSigsFlag checkSigs) override;
 
+    void addMultipleToStore(
+        Source & source,
+        RepairFlag repair,
+        CheckSigsFlag checkSigs) override;
+
     StorePath addTextToStore(const string & name, const string & s,
         const StorePathSet & references, RepairFlag repair) override;
 
@@ -85,7 +90,7 @@ public:
 
     std::optional<const Realisation> queryRealisation(const DrvOutput &) override;
 
-    void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode) override;
+    void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode, std::shared_ptr<Store> evalStore) override;
 
     BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode) override;
@@ -151,8 +156,6 @@ protected:
 
     virtual void narFromPath(const StorePath & path, Sink & sink) override;
 
-    ref<const ValidPathInfo> readValidPathInfo(ConnectionHandle & conn, const StorePath & path);
-
 private:
 
     std::atomic_bool failed{false};

src/libstore/store-api.cc

@@ -9,6 +9,7 @@
 #include "url.hh"
 #include "archive.hh"
 #include "callback.hh"
+#include "remote-store.hh"
 
 #include <regex>
 
@@ -249,6 +250,20 @@ StorePath Store::addToStore(const string & name, const Path & _srcPath,
 }
 
 
+void Store::addMultipleToStore(
+    Source & source,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs)
+{
+    auto expected = readNum<uint64_t>(source);
+    for (uint64_t i = 0; i < expected; ++i) {
+        auto info = ValidPathInfo::read(source, *this, 16);
+        info.ultimate = false;
+        addToStore(info, source, repair, checkSigs);
+    }
+}
+
+
 /*
 The aim of this function is to compute in one pass the correct ValidPathInfo for
 the files that we are trying to add to the store. To accomplish that in one
@@ -770,30 +785,43 @@ const Store::Stats & Store::getStats()
 }
 
 
-void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
+static std::string makeCopyPathMessage(
-    const StorePath & storePath, RepairFlag repair, CheckSigsFlag checkSigs)
+    std::string_view srcUri,
+    std::string_view dstUri,
+    std::string_view storePath)
 {
-    auto srcUri = srcStore->getUri();
+    return srcUri == "local" || srcUri == "daemon"
-    auto dstUri = dstStore->getUri();
+        ? fmt("copying path '%s' to '%s'", storePath, dstUri)
-
-    Activity act(*logger, lvlInfo, actCopyPath,
-        srcUri == "local" || srcUri == "daemon"
-        ? fmt("copying path '%s' to '%s'", srcStore->printStorePath(storePath), dstUri)
         : dstUri == "local" || dstUri == "daemon"
-        ? fmt("copying path '%s' from '%s'", srcStore->printStorePath(storePath), srcUri)
+        ? fmt("copying path '%s' from '%s'", storePath, srcUri)
-          : fmt("copying path '%s' from '%s' to '%s'", srcStore->printStorePath(storePath), srcUri, dstUri),
+        : fmt("copying path '%s' from '%s' to '%s'", storePath, srcUri, dstUri);
-        {srcStore->printStorePath(storePath), srcUri, dstUri});
+}
+
+
+void copyStorePath(
+    Store & srcStore,
+    Store & dstStore,
+    const StorePath & storePath,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs)
+{
+    auto srcUri = srcStore.getUri();
+    auto dstUri = dstStore.getUri();
+    auto storePathS = srcStore.printStorePath(storePath);
+    Activity act(*logger, lvlInfo, actCopyPath,
+        makeCopyPathMessage(srcUri, dstUri, storePathS),
+        {storePathS, srcUri, dstUri});
     PushActivity pact(act.id);
 
-    auto info = srcStore->queryPathInfo(storePath);
+    auto info = srcStore.queryPathInfo(storePath);
 
     uint64_t total = 0;
 
     // recompute store path on the chance dstStore does it differently
     if (info->ca && info->references.empty()) {
         auto info2 = make_ref<ValidPathInfo>(*info);
-        info2->path = dstStore->makeFixedOutputPathFromCA(info->path.name(), *info->ca);
+        info2->path = dstStore.makeFixedOutputPathFromCA(info->path.name(), *info->ca);
-        if (dstStore->storeDir == srcStore->storeDir)
+        if (dstStore.storeDir == srcStore.storeDir)
             assert(info->path == info2->path);
         info = info2;
     }
@@ -810,17 +838,22 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
             act.progress(total, info->narSize);
         });
         TeeSink tee { sink, progressSink };
-        srcStore->narFromPath(storePath, tee);
+        srcStore.narFromPath(storePath, tee);
     }, [&]() {
-           throw EndOfFile("NAR for '%s' fetched from '%s' is incomplete", srcStore->printStorePath(storePath), srcStore->getUri());
+           throw EndOfFile("NAR for '%s' fetched from '%s' is incomplete", srcStore.printStorePath(storePath), srcStore.getUri());
     });
 
-    dstStore->addToStore(*info, *source, repair, checkSigs);
+    dstStore.addToStore(*info, *source, repair, checkSigs);
 }
 
 
-std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore, const RealisedPath::Set & paths,
+std::map<StorePath, StorePath> copyPaths(
-    RepairFlag repair, CheckSigsFlag checkSigs, SubstituteFlag substitute)
+    Store & srcStore,
+    Store & dstStore,
+    const RealisedPath::Set & paths,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs,
+    SubstituteFlag substitute)
 {
     StorePathSet storePaths;
     std::set<Realisation> toplevelRealisations;
@@ -838,11 +871,11 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
     try {
         // Copy the realisation closure
         processGraph<Realisation>(
-            pool, Realisation::closure(*srcStore, toplevelRealisations),
+            pool, Realisation::closure(srcStore, toplevelRealisations),
             [&](const Realisation & current) -> std::set<Realisation> {
                 std::set<Realisation> children;
                 for (const auto & [drvOutput, _] : current.dependentRealisations) {
-                    auto currentChild = srcStore->queryRealisation(drvOutput);
+                    auto currentChild = srcStore.queryRealisation(drvOutput);
                     if (!currentChild)
                         throw Error(
                             "incomplete realisation closure: '%s' is a "
@@ -853,7 +886,7 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
                 return children;
             },
             [&](const Realisation& current) -> void {
-                dstStore->registerDrvOutput(current, checkSigs);
+                dstStore.registerDrvOutput(current, checkSigs);
             });
     } catch (MissingExperimentalFeature & e) {
         // Don't fail if the remote doesn't support CA derivations is it might
@@ -868,10 +901,15 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
     return pathsMap;
 }
 
-std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore, const StorePathSet & storePaths,
+std::map<StorePath, StorePath> copyPaths(
-    RepairFlag repair, CheckSigsFlag checkSigs, SubstituteFlag substitute)
+    Store & srcStore,
+    Store & dstStore,
+    const StorePathSet & storePaths,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs,
+    SubstituteFlag substitute)
 {
-    auto valid = dstStore->queryValidPaths(storePaths, substitute);
+    auto valid = dstStore.queryValidPaths(storePaths, substitute);
 
     StorePathSet missing;
     for (auto & path : storePaths)
@@ -881,9 +919,31 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
     for (auto & path : storePaths)
         pathsMap.insert_or_assign(path, path);
 
-
     Activity act(*logger, lvlInfo, actCopyPaths, fmt("copying %d paths", missing.size()));
 
+    auto sorted = srcStore.topoSortPaths(missing);
+    std::reverse(sorted.begin(), sorted.end());
+
+    auto source = sinkToSource([&](Sink & sink) {
+        sink << sorted.size();
+        for (auto & storePath : sorted) {
+            auto srcUri = srcStore.getUri();
+            auto dstUri = dstStore.getUri();
+            auto storePathS = srcStore.printStorePath(storePath);
+            Activity act(*logger, lvlInfo, actCopyPath,
+                makeCopyPathMessage(srcUri, dstUri, storePathS),
+                {storePathS, srcUri, dstUri});
+            PushActivity pact(act.id);
+
+            auto info = srcStore.queryPathInfo(storePath);
+            info->write(sink, srcStore, 16);
+            srcStore.narFromPath(storePath, sink);
+        }
+    });
+
+    dstStore.addMultipleToStore(*source, repair, checkSigs);
+
+    #if 0
     std::atomic<size_t> nrDone{0};
     std::atomic<size_t> nrFailed{0};
     std::atomic<uint64_t> bytesExpected{0};
@@ -899,18 +959,21 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
         StorePathSet(missing.begin(), missing.end()),
 
         [&](const StorePath & storePath) {
-            auto info = srcStore->queryPathInfo(storePath);
+            auto info = srcStore.queryPathInfo(storePath);
             auto storePathForDst = storePath;
             if (info->ca && info->references.empty()) {
-                storePathForDst = dstStore->makeFixedOutputPathFromCA(storePath.name(), *info->ca);
+                storePathForDst = dstStore.makeFixedOutputPathFromCA(storePath.name(), *info->ca);
-                if (dstStore->storeDir == srcStore->storeDir)
+                if (dstStore.storeDir == srcStore.storeDir)
                     assert(storePathForDst == storePath);
                 if (storePathForDst != storePath)
-                    debug("replaced path '%s' to '%s' for substituter '%s'", srcStore->printStorePath(storePath), dstStore->printStorePath(storePathForDst), dstStore->getUri());
+                    debug("replaced path '%s' to '%s' for substituter '%s'",
+                        srcStore.printStorePath(storePath),
+                        dstStore.printStorePath(storePathForDst),
+                        dstStore.getUri());
             }
             pathsMap.insert_or_assign(storePath, storePathForDst);
 
-            if (dstStore->isValidPath(storePath)) {
+            if (dstStore.isValidPath(storePath)) {
                 nrDone++;
                 showProgress();
                 return StorePathSet();
@@ -925,19 +988,22 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
         [&](const StorePath & storePath) {
             checkInterrupt();
 
-            auto info = srcStore->queryPathInfo(storePath);
+            auto info = srcStore.queryPathInfo(storePath);
 
             auto storePathForDst = storePath;
             if (info->ca && info->references.empty()) {
-                storePathForDst = dstStore->makeFixedOutputPathFromCA(storePath.name(), *info->ca);
+                storePathForDst = dstStore.makeFixedOutputPathFromCA(storePath.name(), *info->ca);
-                if (dstStore->storeDir == srcStore->storeDir)
+                if (dstStore.storeDir == srcStore.storeDir)
                     assert(storePathForDst == storePath);
                 if (storePathForDst != storePath)
-                    debug("replaced path '%s' to '%s' for substituter '%s'", srcStore->printStorePath(storePath), dstStore->printStorePath(storePathForDst), dstStore->getUri());
+                    debug("replaced path '%s' to '%s' for substituter '%s'",
+                        srcStore.printStorePath(storePath),
+                        dstStore.printStorePath(storePathForDst),
+                        dstStore.getUri());
             }
             pathsMap.insert_or_assign(storePath, storePathForDst);
 
-            if (!dstStore->isValidPath(storePathForDst)) {
+            if (!dstStore.isValidPath(storePathForDst)) {
                 MaintainCount<decltype(nrRunning)> mc(nrRunning);
                 showProgress();
                 try {
@@ -946,7 +1012,7 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
                     nrFailed++;
                     if (!settings.keepGoing)
                         throw e;
-                    logger->log(lvlError, fmt("could not copy %s: %s", dstStore->printStorePath(storePath), e.what()));
+                    logger->log(lvlError, fmt("could not copy %s: %s", dstStore.printStorePath(storePath), e.what()));
                     showProgress();
                     return;
                 }
@@ -955,9 +1021,27 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
             nrDone++;
             showProgress();
         });
+    #endif
+
     return pathsMap;
 }
 
+void copyClosure(
+    Store & srcStore,
+    Store & dstStore,
+    const RealisedPath::Set & paths,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs,
+    SubstituteFlag substitute)
+{
+    if (&srcStore == &dstStore) return;
+
+    RealisedPath::Set closure;
+    RealisedPath::closure(srcStore, paths, closure);
+
+    copyPaths(srcStore, dstStore, closure, repair, checkSigs, substitute);
+}
+
 std::optional<ValidPathInfo> decodeValidPathInfo(const Store & store, std::istream & str, std::optional<HashResult> hashGiven)
 {
     std::string path;

src/libstore/store-api.hh

@@ -440,6 +440,12 @@ public:
     virtual void addToStore(const ValidPathInfo & info, Source & narSource,
         RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs) = 0;
 
+    /* Import multiple paths into the store. */
+    virtual void addMultipleToStore(
+        Source & source,
+        RepairFlag repair = NoRepair,
+        CheckSigsFlag checkSigs = CheckSigs);
+
     /* Copy the contents of a path to the store and register the
        validity the resulting path.  The resulting path is returned.
        The function object `filter' can be used to exclude files (see
@@ -497,7 +503,8 @@ public:
        not derivations, substitute them. */
     virtual void buildPaths(
         const std::vector<DerivedPath> & paths,
-        BuildMode buildMode = bmNormal);
+        BuildMode buildMode = bmNormal,
+        std::shared_ptr<Store> evalStore = nullptr);
 
     /* Build a single non-materialized derivation (i.e. not from an
        on-disk .drv file).
@@ -751,8 +758,12 @@ protected:
 
 
 /* Copy a path from one store to another. */
-void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
+void copyStorePath(
-    const StorePath & storePath, RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs);
+    Store & srcStore,
+    Store & dstStore,
+    const StorePath & storePath,
+    RepairFlag repair = NoRepair,
+    CheckSigsFlag checkSigs = CheckSigs);
 
 
 /* Copy store paths from one store to another. The paths may be copied
@@ -761,17 +772,27 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
    of store paths is not automatically closed; use copyClosure() for
    that. Returns a map of what each path was copied to the dstStore
    as. */
-std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore,
+std::map<StorePath, StorePath> copyPaths(
+    Store & srcStore, Store & dstStore,
     const RealisedPath::Set &,
     RepairFlag repair = NoRepair,
     CheckSigsFlag checkSigs = CheckSigs,
     SubstituteFlag substitute = NoSubstitute);
-std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore,
+
+std::map<StorePath, StorePath> copyPaths(
+    Store & srcStore, Store & dstStore,
     const StorePathSet & paths,
     RepairFlag repair = NoRepair,
     CheckSigsFlag checkSigs = CheckSigs,
     SubstituteFlag substitute = NoSubstitute);
 
+/* Copy the closure of `paths` from `srcStore` to `dstStore`. */
+void copyClosure(
+    Store & srcStore, Store & dstStore,
+    const RealisedPath::Set & paths,
+    RepairFlag repair = NoRepair,
+    CheckSigsFlag checkSigs = CheckSigs,
+    SubstituteFlag substitute = NoSubstitute);
 
 /* Remove the temporary roots file for this process.  Any temporary
    root becomes garbage after this point unless it has been registered

src/libstore/worker-protocol.hh

@@ -9,7 +9,7 @@ namespace nix {
 #define WORKER_MAGIC_1 0x6e697863
 #define WORKER_MAGIC_2 0x6478696f
 
-#define PROTOCOL_VERSION (1 << 8 | 31)
+#define PROTOCOL_VERSION (1 << 8 | 32)
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
@@ -55,6 +55,7 @@ typedef enum {
     wopQueryDerivationOutputMap = 41,
     wopRegisterDrvOutput = 42,
     wopQueryRealisation = 43,
+    wopAddMultipleToStore = 44,
 } WorkerOp;
 
 

src/nix-build/nix-build.cc

@@ -250,8 +250,9 @@ static void main_nix_build(int argc, char * * argv)
         throw UsageError("'-p' and '-E' are mutually exclusive");
 
     auto store = openStore();
+    auto evalStore = myArgs.evalStoreUrl ? openStore(*myArgs.evalStoreUrl) : store;
 
-    auto state = std::make_unique<EvalState>(myArgs.searchPath, store);
+    auto state = std::make_unique<EvalState>(myArgs.searchPath, evalStore, store);
     state->repair = repair;
 
     auto autoArgs = myArgs.getAutoArgs(*state);
@@ -301,8 +302,8 @@ static void main_nix_build(int argc, char * * argv)
                     absolute = canonPath(absPath(i), true);
                 } catch (Error & e) {};
                 auto [path, outputNames] = parsePathWithOutputs(absolute);
-                if (store->isStorePath(path) && hasSuffix(path, ".drv"))
+                if (evalStore->isStorePath(path) && hasSuffix(path, ".drv"))
-                    drvs.push_back(DrvInfo(*state, store, absolute));
+                    drvs.push_back(DrvInfo(*state, evalStore, absolute));
                 else
                     /* If we're in a #! script, interpret filenames
                        relative to the script. */
@@ -340,7 +341,7 @@ static void main_nix_build(int argc, char * * argv)
             printMissing(ref<Store>(store), willBuild, willSubstitute, unknown, downloadSize, narSize);
 
         if (!dryRun)
-            store->buildPaths(paths, buildMode);
+            store->buildPaths(paths, buildMode, evalStore);
     };
 
     if (runEnv) {
@@ -348,9 +349,10 @@ static void main_nix_build(int argc, char * * argv)
             throw UsageError("nix-shell requires a single derivation");
 
         auto & drvInfo = drvs.front();
-        auto drv = store->derivationFromPath(store->parseStorePath(drvInfo.queryDrvPath()));
+        auto drv = evalStore->derivationFromPath(evalStore->parseStorePath(drvInfo.queryDrvPath()));
 
         std::vector<StorePathWithOutputs> pathsToBuild;
+        RealisedPath::Set pathsToCopy;
 
         /* Figure out what bash shell to use. If $NIX_BUILD_SHELL
            is not set, then build bashInteractive from
@@ -369,7 +371,9 @@ static void main_nix_build(int argc, char * * argv)
                 if (!drv)
                     throw Error("the 'bashInteractive' attribute in <nixpkgs> did not evaluate to a derivation");
 
-                pathsToBuild.push_back({store->parseStorePath(drv->queryDrvPath())});
+                auto bashDrv = store->parseStorePath(drv->queryDrvPath());
+                pathsToBuild.push_back({bashDrv});
+                pathsToCopy.insert(bashDrv);
 
                 shell = drv->queryOutPath() + "/bin/bash";
 
@@ -384,9 +388,14 @@ static void main_nix_build(int argc, char * * argv)
         for (const auto & input : drv.inputDrvs)
             if (std::all_of(envExclude.cbegin(), envExclude.cend(),
                     [&](const string & exclude) { return !std::regex_search(store->printStorePath(input.first), std::regex(exclude)); }))
+            {
                 pathsToBuild.push_back({input.first, input.second});
-        for (const auto & src : drv.inputSrcs)
+                pathsToCopy.insert(input.first);
+            }
+        for (const auto & src : drv.inputSrcs) {
             pathsToBuild.push_back({src});
+            pathsToCopy.insert(src);
+        }
 
         buildPaths(pathsToBuild);
 
@@ -438,7 +447,7 @@ static void main_nix_build(int argc, char * * argv)
         if (env.count("__json")) {
             StorePathSet inputs;
             for (auto & [depDrvPath, wantedDepOutputs] : drv.inputDrvs) {
-                auto outputs = store->queryPartialDerivationOutputMap(depDrvPath);
+                auto outputs = evalStore->queryPartialDerivationOutputMap(depDrvPath);
                 for (auto & i : wantedDepOutputs) {
                     auto o = outputs.at(i);
                     store->computeFSClosure(*o, inputs);
@@ -531,6 +540,7 @@ static void main_nix_build(int argc, char * * argv)
 
         std::vector<StorePathWithOutputs> pathsToBuild;
         std::vector<std::pair<StorePath, std::string>> pathsToBuildOrdered;
+        RealisedPath::Set drvsToCopy;
 
         std::map<StorePath, std::pair<size_t, StringSet>> drvMap;
 
@@ -543,14 +553,14 @@ static void main_nix_build(int argc, char * * argv)
 
             pathsToBuild.push_back({drvPath, {outputName}});
             pathsToBuildOrdered.push_back({drvPath, {outputName}});
+            drvsToCopy.insert(drvPath);
 
             auto i = drvMap.find(drvPath);
             if (i != drvMap.end())
                 i->second.second.insert(outputName);
-            else {
+            else
                 drvMap[drvPath] = {drvMap.size(), {outputName}};
         }
-        }
 
         buildPaths(pathsToBuild);
 
@@ -564,7 +574,7 @@ static void main_nix_build(int argc, char * * argv)
             if (counter)
                 drvPrefix += fmt("-%d", counter + 1);
 
-            auto builtOutputs = store->queryPartialDerivationOutputMap(drvPath);
+            auto builtOutputs = evalStore->queryPartialDerivationOutputMap(drvPath);
 
             auto maybeOutputPath = builtOutputs.at(outputName);
             assert(maybeOutputPath);

src/nix-copy-closure/nix-copy-closure.cc

@@ -54,10 +54,7 @@ static int main_nix_copy_closure(int argc, char ** argv)
         for (auto & path : storePaths)
             storePaths2.insert(from->followLinksToStorePath(path));
 
-        RealisedPath::Set closure;
+        copyClosure(*from, *to, storePaths2, NoRepair, NoCheckSigs, useSubstitutes);
-        RealisedPath::closure(*from, storePaths2, closure);
-
-        copyPaths(from, to, closure, NoRepair, NoCheckSigs, useSubstitutes);
 
         return 0;
     }

src/nix-instantiate/nix-instantiate.cc

@@ -153,8 +153,9 @@ static int main_nix_instantiate(int argc, char * * argv)
             settings.readOnlyMode = true;
 
         auto store = openStore();
+        auto evalStore = myArgs.evalStoreUrl ? openStore(*myArgs.evalStoreUrl) : store;
 
-        auto state = std::make_unique<EvalState>(myArgs.searchPath, store);
+        auto state = std::make_unique<EvalState>(myArgs.searchPath, evalStore, store);
         state->repair = repair;
 
         Bindings & autoArgs = *myArgs.getAutoArgs(*state);

src/nix/app.cc

@@ -100,7 +100,8 @@ UnresolvedApp Installable::toApp(EvalState & state)
         throw Error("attribute '%s' has unsupported type '%s'", attrPath, type);
 }
 
-App UnresolvedApp::resolve(ref<Store> store)
+// FIXME: move to libcmd
+App UnresolvedApp::resolve(ref<Store> evalStore, ref<Store> store)
 {
     auto res = unresolved;
 
@@ -110,7 +111,7 @@ App UnresolvedApp::resolve(ref<Store> store)
         installableContext.push_back(
             std::make_shared<InstallableDerivedPath>(store, ctxElt.toDerivedPath()));
 
-    auto builtContext = build(store, Realise::Outputs, installableContext);
+    auto builtContext = build(evalStore, store, Realise::Outputs, installableContext);
     res.program = resolveString(*store, unresolved.program, builtContext);
     if (!store->isInStore(res.program))
         throw Error("app program '%s' is not in the Nix store", res.program);

src/nix/build.cc

@@ -52,7 +52,10 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
 
     void run(ref<Store> store) override
     {
-        auto buildables = build(store, dryRun ? Realise::Nothing : Realise::Outputs, installables, buildMode);
+        auto buildables = build(
+            getEvalStore(), store,
+            dryRun ? Realise::Nothing : Realise::Outputs,
+            installables, buildMode);
 
         if (json) logger->cout("%s", derivedPathsWithHintsToJSON(buildables, store).dump());
 

src/nix/bundle.cc

@@ -69,7 +69,7 @@ struct CmdBundle : InstallableCommand
     {
         auto evalState = getEvalState();
 
-        auto app = installable->toApp(*evalState).resolve(store);
+        auto app = installable->toApp(*evalState).resolve(getEvalStore(), store);
 
         auto [bundlerFlakeRef, bundlerName] = parseFlakeRefWithFragment(bundler, absPath("."));
         const flake::LockFlags lockFlags{ .writeLockFile = false };

src/nix/copy.cc

@@ -90,7 +90,7 @@ struct CmdCopy : BuiltPathsCommand
         }
 
         copyPaths(
-            srcStore, dstStore, stuffToCopy, NoRepair, checkSigs, substitute);
+            *srcStore, *dstStore, stuffToCopy, NoRepair, checkSigs, substitute);
     }
 };
 

src/nix/develop.cc

@@ -171,15 +171,15 @@ const static std::string getEnvSh =
    modified derivation with the same dependencies and nearly the same
    initial environment variables, that just writes the resulting
    environment to a file and exits. */
-StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
+static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore, const StorePath & drvPath)
 {
-    auto drv = store->derivationFromPath(drvPath);
+    auto drv = evalStore->derivationFromPath(drvPath);
 
     auto builder = baseNameOf(drv.builder);
     if (builder != "bash")
         throw Error("'nix develop' only works on derivations that use 'bash' as their builder");
 
-    auto getEnvShPath = store->addTextToStore("get-env.sh", getEnvSh, {});
+    auto getEnvShPath = evalStore->addTextToStore("get-env.sh", getEnvSh, {});
 
     drv.args = {store->printStorePath(getEnvShPath)};
 
@@ -205,7 +205,7 @@ StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
             output.second = { .output = DerivationOutputInputAddressed { .path = StorePath::dummy } };
             drv.env[output.first] = "";
         }
-        Hash h = std::get<0>(hashDerivationModulo(*store, drv, true));
+        Hash h = std::get<0>(hashDerivationModulo(*evalStore, drv, true));
 
         for (auto & output : drv.outputs) {
             auto outPath = store->makeOutputPath(output.first, h, drv.name);
@@ -214,12 +214,12 @@ StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
         }
     }
 
-    auto shellDrvPath = writeDerivation(*store, drv);
+    auto shellDrvPath = writeDerivation(*evalStore, drv);
 
     /* Build the derivation. */
-    store->buildPaths({DerivedPath::Built{shellDrvPath}});
+    store->buildPaths({DerivedPath::Built{shellDrvPath}}, bmNormal, evalStore);
 
-    for (auto & [_0, optPath] : store->queryPartialDerivationOutputMap(shellDrvPath)) {
+    for (auto & [_0, optPath] : evalStore->queryPartialDerivationOutputMap(shellDrvPath)) {
         assert(optPath);
         auto & outPath = *optPath;
         assert(store->isValidPath(outPath));
@@ -307,7 +307,7 @@ struct Common : InstallableCommand, MixProfile
             auto dir = absPath(dir_);
             auto installable = parseInstallable(store, installable_);
             auto builtPaths = toStorePaths(
-                store, Realise::Nothing, OperateOn::Output, {installable});
+                getEvalStore(), store, Realise::Nothing, OperateOn::Output, {installable});
             for (auto & path: builtPaths) {
                 auto from = store->printStorePath(path);
                 if (script.find(from) == std::string::npos)
@@ -347,7 +347,7 @@ struct Common : InstallableCommand, MixProfile
 
             auto & drvPath = *drvs.begin();
 
-            return getDerivationEnvironment(store, drvPath);
+            return getDerivationEnvironment(store, getEvalStore(), drvPath);
         }
     }
 
@@ -361,7 +361,7 @@ struct Common : InstallableCommand, MixProfile
 
         debug("reading environment file '%s'", strPath);
 
-        return {BuildEnvironment::fromJSON(readFile(strPath)), strPath};
+        return {BuildEnvironment::fromJSON(readFile(store->toRealPath(shellOutPath))), strPath};
     }
 };
 
@@ -495,8 +495,8 @@ struct CmdDevelop : Common, MixEnvironment
                 Strings{"legacyPackages." + settings.thisSystem.get() + "."},
                 nixpkgsLockFlags);
 
-            shell = state->store->printStorePath(
+            shell = store->printStorePath(
-                toStorePath(state->store, Realise::Outputs, OperateOn::Output, bashInstallable)) + "/bin/bash";
+                toStorePath(getEvalStore(), store, Realise::Outputs, OperateOn::Output, bashInstallable)) + "/bin/bash";
         } catch (Error &) {
             ignoreException();
         }

src/nix/diff-closures.cc

@@ -131,9 +131,9 @@ struct CmdDiffClosures : SourceExprCommand
     void run(ref<Store> store) override
     {
         auto before = parseInstallable(store, _before);
-        auto beforePath = toStorePath(store, Realise::Outputs, operateOn, before);
+        auto beforePath = toStorePath(getEvalStore(), store, Realise::Outputs, operateOn, before);
         auto after = parseInstallable(store, _after);
-        auto afterPath = toStorePath(store, Realise::Outputs, operateOn, after);
+        auto afterPath = toStorePath(getEvalStore(), store, Realise::Outputs, operateOn, after);
         printClosureDiff(store, beforePath, afterPath, "");
     }
 };

src/nix/flake.cc

@@ -841,7 +841,7 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
 
         if (!dryRun && !dstUri.empty()) {
             ref<Store> dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
-            copyPaths(store, dstStore, sources);
+            copyPaths(*store, *dstStore, sources);
         }
     }
 };

src/nix/profile.cc

@@ -253,7 +253,7 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
 
                 manifest.elements.emplace_back(std::move(element));
             } else {
-                auto buildables = build(store, Realise::Outputs, {installable}, bmNormal);
+                auto buildables = build(getEvalStore(), store, Realise::Outputs, {installable}, bmNormal);
 
                 for (auto & buildable : buildables) {
                     ProfileElement element;

src/nix/run.cc

@@ -93,7 +93,7 @@ struct CmdShell : InstallablesCommand, RunCommon, MixEnvironment
 
     void run(ref<Store> store) override
     {
-        auto outPaths = toStorePaths(store, Realise::Outputs, OperateOn::Output, installables);
+        auto outPaths = toStorePaths(getEvalStore(), store, Realise::Outputs, OperateOn::Output, installables);
 
         auto accessor = store->getFSAccessor();
 
@@ -178,7 +178,7 @@ struct CmdRun : InstallableCommand, RunCommon
     {
         auto state = getEvalState();
 
-        auto app = installable->toApp(*state).resolve(store);
+        auto app = installable->toApp(*state).resolve(getEvalStore(), store);
 
         Strings allArgs{app.program};
         for (auto & i : args) allArgs.push_back(i);

src/nix/why-depends.cc

@@ -62,9 +62,9 @@ struct CmdWhyDepends : SourceExprCommand
     void run(ref<Store> store) override
     {
         auto package = parseInstallable(store, _package);
-        auto packagePath = toStorePath(store, Realise::Outputs, operateOn, package);
+        auto packagePath = toStorePath(getEvalStore(), store, Realise::Outputs, operateOn, package);
         auto dependency = parseInstallable(store, _dependency);
-        auto dependencyPath = toStorePath(store, Realise::Derivation, operateOn, dependency);
+        auto dependencyPath = toStorePath(getEvalStore(), store, Realise::Derivation, operateOn, dependency);
         auto dependencyPathHash = dependencyPath.hashPart();
 
         StorePathSet closure;

tests/eval-store.sh

@@ -0,0 +1,26 @@
+source common.sh
+
+eval_store=$TEST_ROOT/eval-store
+
+clearStore
+rm -rf "$eval_store"
+
+nix build -f dependencies.nix --eval-store "$eval_store" -o "$TEST_ROOT/result"
+[[ -e $TEST_ROOT/result/foobar ]]
+(! ls $NIX_STORE_DIR/*.drv)
+ls $eval_store/nix/store/*.drv
+
+clearStore
+rm -rf "$eval_store"
+
+nix-instantiate dependencies.nix --eval-store "$eval_store"
+(! ls $NIX_STORE_DIR/*.drv)
+ls $eval_store/nix/store/*.drv
+
+clearStore
+rm -rf "$eval_store"
+
+nix-build dependencies.nix --eval-store "$eval_store" -o "$TEST_ROOT/result"
+[[ -e $TEST_ROOT/result/foobar ]]
+(! ls $NIX_STORE_DIR/*.drv)
+ls $eval_store/nix/store/*.drv

tests/local.mk

@@ -56,7 +56,8 @@ nix_tests = \
   ca/nix-run.sh \
   ca/recursive.sh \
   ca/concurrent-builds.sh \
-  ca/nix-copy.sh
+  ca/nix-copy.sh \
+  eval-store.sh
   # parallel.sh
 
 install-tests += $(foreach x, $(nix_tests), tests/$(x))