buildPaths(): Add an evalStore argument

With this, we don't have to copy the entire .drv closure to the
destination store ahead of time (or at all). Instead, buildPaths()
reads .drv files from the eval store and copies inputSrcs to the
destination store if it needs to build a derivation.

Issue #5025.

src/libcmd/installables.cc

@@ -766,7 +766,7 @@ BuiltPaths build(ref<Store> evalStore, 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(evalStore, store, pathsToBuild);
 }

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 +337,16 @@ 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, inputClosure;
+        for (auto & i : drv->inputSrcs)
+            inputSrcs.insert(i);
+        RealisedPath::closure(worker.evalStore, inputSrcs, inputClosure);
+        copyClosure(worker.evalStore, worker.store, inputClosure);
+    }
+
     for (auto & i : drv->inputSrcs) {
         if (worker.store.isValidPath(i)) continue;
         if (!settings.useSubstitutes)
@@ -478,8 +488,8 @@ 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/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/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/remote-store.cc

@@ -705,8 +705,11 @@ 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)
+        throw Error("building on a remote store is incompatible with '--eval-store'");
+
     auto conn(getConnection());
     conn->to << wopBuildPaths;
     assert(GET_PROTOCOL_MINOR(conn->daemonVersion) >= 13);

src/libstore/remote-store.hh

@@ -85,7 +85,7 @@ 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;

src/libstore/store-api.hh

@@ -497,7 +497,8 @@ 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).

src/nix-build/nix-build.cc

@@ -341,7 +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) {
@@ -397,8 +397,6 @@ static void main_nix_build(int argc, char * * argv)
             pathsToCopy.insert(src);
         }
 
-        copyClosure(*evalStore, *store, pathsToCopy);
-
         buildPaths(pathsToBuild);
 
         if (dryRun) return;
@@ -449,7 +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);
@@ -564,8 +562,6 @@ static void main_nix_build(int argc, char * * argv)
                 drvMap[drvPath] = {drvMap.size(), {outputName}};
         }
 
-        copyClosure(*evalStore, *store, drvsToCopy);
-
         buildPaths(pathsToBuild);
 
         if (dryRun) return;
@@ -578,7 +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/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));
@@ -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};
     }
 };