Merge pull request #6221 from NixOS/build-paths-with-results

Add Store::buildPathsWithResults()

16 files changed, 405 insertions, 196 deletions

diff --git a/src/libstore/build-result.hh b/src/libstore/build-result.hh
index 018ba31b3..d39d23a76 100644
--- a/src/libstore/build-result.hh
+++ b/src/libstore/build-result.hh
@@ -28,6 +28,7 @@ struct BuildResult
         LogLimitExceeded,
         NotDeterministic,
         ResolvesToAlreadyValid,
+        NoSubstituters,
     } status = MiscFailure;
     std::string errorMsg;
 
@@ -63,15 +64,26 @@ struct BuildResult
        non-determinism.) */
     bool isNonDeterministic = false;
 
+    /* The derivation we built or the store path we substituted. */
+    DerivedPath path;
+
+    /* For derivations, the derivation path and the wanted outputs. */
+    std::optional<StorePath> drvPath;
     DrvOutputs builtOutputs;
 
     /* The start/stop times of the build (or one of the rounds, if it
        was repeated). */
     time_t startTime = 0, stopTime = 0;
 
-    bool success() {
+    bool success()
+    {
         return status == Built || status == Substituted || status == AlreadyValid || status == ResolvesToAlreadyValid;
     }
+
+    void rethrow()
+    {
+        throw Error("%s", errorMsg);
+    }
 };
 
 }
diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index ae250ffaf..325635e2e 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -66,7 +66,7 @@ namespace nix {
 
 DerivationGoal::DerivationGoal(const StorePath & drvPath,
     const StringSet & wantedOutputs, Worker & worker, BuildMode buildMode)
-    : Goal(worker)
+    : Goal(worker, DerivedPath::Built { .drvPath = drvPath, .outputs = wantedOutputs })
     , useDerivation(true)
     , drvPath(drvPath)
     , wantedOutputs(wantedOutputs)
@@ -85,7 +85,7 @@ DerivationGoal::DerivationGoal(const StorePath & drvPath,
 
 DerivationGoal::DerivationGoal(const StorePath & drvPath, const BasicDerivation & drv,
     const StringSet & wantedOutputs, Worker & worker, BuildMode buildMode)
-    : Goal(worker)
+    : Goal(worker, DerivedPath::Built { .drvPath = drvPath, .outputs = wantedOutputs })
     , useDerivation(false)
     , drvPath(drvPath)
     , wantedOutputs(wantedOutputs)
@@ -135,7 +135,7 @@ void DerivationGoal::killChild()
 void DerivationGoal::timedOut(Error && ex)
 {
     killChild();
-    done(BuildResult::TimedOut, ex);
+    done(BuildResult::TimedOut, {}, ex);
 }
 
 
@@ -182,7 +182,7 @@ void DerivationGoal::loadDerivation()
     trace("loading derivation");
 
     if (nrFailed != 0) {
-        done(BuildResult::MiscFailure, Error("cannot build missing derivation '%s'", worker.store.printStorePath(drvPath)));
+        done(BuildResult::MiscFailure, {}, Error("cannot build missing derivation '%s'", worker.store.printStorePath(drvPath)));
         return;
     }
 
@@ -215,28 +215,20 @@ void DerivationGoal::haveDerivation()
 
     auto outputHashes = staticOutputHashes(worker.evalStore, *drv);
     for (auto & [outputName, outputHash] : outputHashes)
-      initialOutputs.insert({
+        initialOutputs.insert({
             outputName,
-            InitialOutput{
+            InitialOutput {
                 .wanted = true, // Will be refined later
                 .outputHash = outputHash
             }
-          });
+        });
 
     /* Check what outputs paths are not already valid. */
-    checkPathValidity();
-    bool allValid = true;
-    for (auto & [_, status] : initialOutputs) {
-        if (!status.wanted) continue;
-        if (!status.known || !status.known->isValid()) {
-            allValid = false;
-            break;
-        }
-    }
+    auto [allValid, validOutputs] = checkPathValidity();
 
     /* If they are all valid, then we're done. */
     if (allValid && buildMode == bmNormal) {
-        done(BuildResult::AlreadyValid);
+        done(BuildResult::AlreadyValid, std::move(validOutputs));
         return;
     }
 
@@ -277,7 +269,7 @@ void DerivationGoal::outputsSubstitutionTried()
     trace("all outputs substituted (maybe)");
 
     if (nrFailed > 0 && nrFailed > nrNoSubstituters + nrIncompleteClosure && !settings.tryFallback) {
-        done(BuildResult::TransientFailure,
+        done(BuildResult::TransientFailure, {},
             Error("some substitutes for the outputs of derivation '%s' failed (usually happens due to networking issues); try '--fallback' to build derivation from source ",
                 worker.store.printStorePath(drvPath)));
         return;
@@ -301,23 +293,17 @@ void DerivationGoal::outputsSubstitutionTried()
         return;
     }
 
-    checkPathValidity();
-    size_t nrInvalid = 0;
-    for (auto & [_, status] : initialOutputs) {
-        if (!status.wanted) continue;
-        if (!status.known || !status.known->isValid())
-            nrInvalid++;
-    }
+    auto [allValid, validOutputs] = checkPathValidity();
 
-    if (buildMode == bmNormal && nrInvalid == 0) {
-        done(BuildResult::Substituted);
+    if (buildMode == bmNormal && allValid) {
+        done(BuildResult::Substituted, std::move(validOutputs));
         return;
     }
-    if (buildMode == bmRepair && nrInvalid == 0) {
+    if (buildMode == bmRepair && allValid) {
         repairClosure();
         return;
     }
-    if (buildMode == bmCheck && nrInvalid > 0)
+    if (buildMode == bmCheck && !allValid)
         throw Error("some outputs of '%s' are not valid, so checking is not possible",
             worker.store.printStorePath(drvPath));
 
@@ -409,7 +395,7 @@ void DerivationGoal::repairClosure()
     }
 
     if (waitees.empty()) {
-        done(BuildResult::AlreadyValid);
+        done(BuildResult::AlreadyValid, assertPathValidity());
         return;
     }
 
@@ -423,7 +409,7 @@ void DerivationGoal::closureRepaired()
     if (nrFailed > 0)
         throw Error("some paths in the output closure of derivation '%s' could not be repaired",
             worker.store.printStorePath(drvPath));
-    done(BuildResult::AlreadyValid);
+    done(BuildResult::AlreadyValid, assertPathValidity());
 }
 
 
@@ -434,7 +420,7 @@ void DerivationGoal::inputsRealised()
     if (nrFailed != 0) {
         if (!useDerivation)
             throw Error("some dependencies of '%s' are missing", worker.store.printStorePath(drvPath));
-        done(BuildResult::DependencyFailed, Error(
+        done(BuildResult::DependencyFailed, {}, Error(
                 "%s dependencies of derivation '%s' failed to build",
                 nrFailed, worker.store.printStorePath(drvPath)));
         return;
@@ -523,10 +509,11 @@ void DerivationGoal::inputsRealised()
     state = &DerivationGoal::tryToBuild;
     worker.wakeUp(shared_from_this());
 
-    result = BuildResult();
+    buildResult = BuildResult { .path = buildResult.path };
 }
 
-void DerivationGoal::started() {
+void DerivationGoal::started()
+{
     auto msg = fmt(
         buildMode == bmRepair ? "repairing outputs of '%s'" :
         buildMode == bmCheck ? "checking outputs of '%s'" :
@@ -588,19 +575,12 @@ void DerivationGoal::tryToBuild()
        omitted, but that would be less efficient.)  Note that since we
        now hold the locks on the output paths, no other process can
        build this derivation, so no further checks are necessary. */
-    checkPathValidity();
-    bool allValid = true;
-    for (auto & [_, status] : initialOutputs) {
-        if (!status.wanted) continue;
-        if (!status.known || !status.known->isValid()) {
-            allValid = false;
-            break;
-        }
-    }
+    auto [allValid, validOutputs] = checkPathValidity();
+
     if (buildMode != bmCheck && allValid) {
         debug("skipping build of derivation '%s', someone beat us to it", worker.store.printStorePath(drvPath));
         outputLocks.setDeletion(true);
-        done(BuildResult::AlreadyValid);
+        done(BuildResult::AlreadyValid, std::move(validOutputs));
         return;
     }
 
@@ -626,7 +606,7 @@ void DerivationGoal::tryToBuild()
                 /* Yes, it has started doing so.  Wait until we get
                    EOF from the hook. */
                 actLock.reset();
-                result.startTime = time(0); // inexact
+                buildResult.startTime = time(0); // inexact
                 state = &DerivationGoal::buildDone;
                 started();
                 return;
@@ -830,8 +810,8 @@ void DerivationGoal::buildDone()
 
     debug("builder process for '%s' finished", worker.store.printStorePath(drvPath));
 
-    result.timesBuilt++;
-    result.stopTime = time(0);
+    buildResult.timesBuilt++;
+    buildResult.stopTime = time(0);
 
     /* So the child is gone now. */
     worker.childTerminated(this);
@@ -876,11 +856,11 @@ void DerivationGoal::buildDone()
 
         /* Compute the FS closure of the outputs and register them as
            being valid. */
-        registerOutputs();
+        auto builtOutputs = registerOutputs();
 
         StorePathSet outputPaths;
-        for (auto & [_, path] : finalOutputs)
-            outputPaths.insert(path);
+        for (auto & [_, output] : buildResult.builtOutputs)
+            outputPaths.insert(output.outPath);
         runPostBuildHook(
             worker.store,
             *logger,
@@ -890,7 +870,7 @@ void DerivationGoal::buildDone()
 
         if (buildMode == bmCheck) {
             cleanupPostOutputsRegisteredModeCheck();
-            done(BuildResult::Built);
+            done(BuildResult::Built, std::move(builtOutputs));
             return;
         }
 
@@ -911,6 +891,8 @@ void DerivationGoal::buildDone()
         outputLocks.setDeletion(true);
         outputLocks.unlock();
 
+        done(BuildResult::Built, std::move(builtOutputs));
+
     } catch (BuildError & e) {
         outputLocks.unlock();
 
@@ -930,14 +912,13 @@ void DerivationGoal::buildDone()
                 BuildResult::PermanentFailure;
         }
 
-        done(st, e);
+        done(st, {}, e);
         return;
     }
-
-    done(BuildResult::Built);
 }
 
-void DerivationGoal::resolvedFinished() {
+void DerivationGoal::resolvedFinished()
+{
     assert(resolvedDrvGoal);
     auto resolvedDrv = *resolvedDrvGoal->drv;
 
@@ -950,11 +931,13 @@ void DerivationGoal::resolvedFinished() {
     if (realWantedOutputs.empty())
         realWantedOutputs = resolvedDrv.outputNames();
 
+    DrvOutputs builtOutputs;
+
     for (auto & wantedOutput : realWantedOutputs) {
         assert(initialOutputs.count(wantedOutput) != 0);
         assert(resolvedHashes.count(wantedOutput) != 0);
         auto realisation = worker.store.queryRealisation(
-                DrvOutput{resolvedHashes.at(wantedOutput), wantedOutput}
+            DrvOutput{resolvedHashes.at(wantedOutput), wantedOutput}
         );
         // We've just built it, but maybe the build failed, in which case the
         // realisation won't be there
@@ -966,10 +949,11 @@ void DerivationGoal::resolvedFinished() {
             signRealisation(newRealisation);
             worker.store.registerDrvOutput(newRealisation);
             outputPaths.insert(realisation->outPath);
+            builtOutputs.emplace(realisation->id, *realisation);
         } else {
             // If we don't have a realisation, then it must mean that something
             // failed when building the resolved drv
-            assert(!result.success());
+            assert(!buildResult.success());
         }
     }
 
@@ -981,7 +965,7 @@ void DerivationGoal::resolvedFinished() {
     );
 
     auto status = [&]() {
-        auto resolvedResult = resolvedDrvGoal->getResult();
+        auto & resolvedResult = resolvedDrvGoal->buildResult;
         switch (resolvedResult.status) {
             case BuildResult::AlreadyValid:
                 return BuildResult::ResolvesToAlreadyValid;
@@ -990,7 +974,7 @@ void DerivationGoal::resolvedFinished() {
         }
     }();
 
-    done(status);
+    done(status, std::move(builtOutputs));
 }
 
 HookReply DerivationGoal::tryBuildHook()
@@ -1100,7 +1084,7 @@ HookReply DerivationGoal::tryBuildHook()
 }
 
 
-void DerivationGoal::registerOutputs()
+DrvOutputs DerivationGoal::registerOutputs()
 {
     /* When using a build hook, the build hook can register the output
        as valid (by doing `nix-store --import').  If so we don't have
@@ -1109,21 +1093,7 @@ void DerivationGoal::registerOutputs()
        We can only early return when the outputs are known a priori. For
        floating content-addressed derivations this isn't the case.
      */
-    for (auto & [outputName, optOutputPath] : worker.store.queryPartialDerivationOutputMap(drvPath)) {
-        if (!wantOutput(outputName, wantedOutputs))
-            continue;
-        if (!optOutputPath)
-            throw BuildError(
-                "output '%s' from derivation '%s' does not have a known output path",
-                outputName, worker.store.printStorePath(drvPath));
-        auto & outputPath = *optOutputPath;
-        if (!worker.store.isValidPath(outputPath))
-            throw BuildError(
-                "output '%s' from derivation '%s' is supposed to be at '%s' but that path is not valid",
-                outputName, worker.store.printStorePath(drvPath), worker.store.printStorePath(outputPath));
-
-        finalOutputs.insert_or_assign(outputName, outputPath);
-    }
+    return assertPathValidity();
 }
 
 Path DerivationGoal::openLogFile()
@@ -1185,7 +1155,7 @@ void DerivationGoal::handleChildOutput(int fd, std::string_view data)
         if (settings.maxLogSize && logSize > settings.maxLogSize) {
             killChild();
             done(
-                BuildResult::LogLimitExceeded,
+                BuildResult::LogLimitExceeded, {},
                 Error("%s killed after writing more than %d bytes of log output",
                     getName(), settings.maxLogSize));
             return;
@@ -1274,10 +1244,12 @@ OutputPathMap DerivationGoal::queryDerivationOutputMap()
 }
 
 
-void DerivationGoal::checkPathValidity()
+std::pair<bool, DrvOutputs> DerivationGoal::checkPathValidity()
 {
     bool checkHash = buildMode == bmRepair;
     auto wantedOutputsLeft = wantedOutputs;
+    DrvOutputs validOutputs;
+
     for (auto & i : queryPartialDerivationOutputMap()) {
         InitialOutput & info = initialOutputs.at(i.first);
         info.wanted = wantOutput(i.first, wantedOutputs);
@@ -1294,26 +1266,28 @@ void DerivationGoal::checkPathValidity()
                     : PathStatus::Corrupt,
             };
         }
+        auto drvOutput = DrvOutput{initialOutputs.at(i.first).outputHash, i.first};
         if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
-            auto drvOutput = DrvOutput{initialOutputs.at(i.first).outputHash, i.first};
             if (auto real = worker.store.queryRealisation(drvOutput)) {
                 info.known = {
                     .path = real->outPath,
                     .status = PathStatus::Valid,
                 };
-            } else if (info.known && info.known->status == PathStatus::Valid) {
-                // We know the output because it' a static output of the
+            } else if (info.known && info.known->isValid()) {
+                // We know the output because it's a static output of the
                 // derivation, and the output path is valid, but we don't have
                 // its realisation stored (probably because it has been built
-                // without the `ca-derivations` experimental flag)
+                // without the `ca-derivations` experimental flag).
                 worker.store.registerDrvOutput(
-                    Realisation{
+                    Realisation {
                         drvOutput,
                         info.known->path,
                     }
                 );
             }
         }
+        if (info.wanted && info.known && info.known->isValid())
+            validOutputs.emplace(drvOutput, Realisation { drvOutput, info.known->path });
     }
     // If we requested all the outputs via the empty set, we are always fine.
     // If we requested specific elements, the loop above removes all the valid
@@ -1322,24 +1296,51 @@ void DerivationGoal::checkPathValidity()
         throw Error("derivation '%s' does not have wanted outputs %s",
             worker.store.printStorePath(drvPath),
             concatStringsSep(", ", quoteStrings(wantedOutputsLeft)));
+
+    bool allValid = true;
+    for (auto & [_, status] : initialOutputs) {
+        if (!status.wanted) continue;
+        if (!status.known || !status.known->isValid()) {
+            allValid = false;
+            break;
+        }
+    }
+
+    return { allValid, validOutputs };
+}
+
+
+DrvOutputs DerivationGoal::assertPathValidity()
+{
+    auto [allValid, validOutputs] = checkPathValidity();
+    if (!allValid)
+        throw Error("some outputs are unexpectedly invalid");
+    return validOutputs;
 }
 
 
-void DerivationGoal::done(BuildResult::Status status, std::optional<Error> ex)
+void DerivationGoal::done(
+    BuildResult::Status status,
+    DrvOutputs builtOutputs,
+    std::optional<Error> ex)
 {
-    result.status = status;
+    buildResult.drvPath = drvPath;
+    buildResult.status = status;
     if (ex)
-        result.errorMsg = ex->what();
-    amDone(result.success() ? ecSuccess : ecFailed, ex);
-    if (result.status == BuildResult::TimedOut)
+        // FIXME: strip: "error: "
+        buildResult.errorMsg = ex->what();
+    amDone(buildResult.success() ? ecSuccess : ecFailed, ex);
+    if (buildResult.status == BuildResult::TimedOut)
         worker.timedOut = true;
-    if (result.status == BuildResult::PermanentFailure)
+    if (buildResult.status == BuildResult::PermanentFailure)
         worker.permanentFailure = true;
 
     mcExpectedBuilds.reset();
     mcRunningBuilds.reset();
 
-    if (result.success()) {
+    if (buildResult.success()) {
+        assert(!builtOutputs.empty());
+        buildResult.builtOutputs = std::move(builtOutputs);
         if (status == BuildResult::Built)
             worker.doneBuilds++;
     } else {
@@ -1353,7 +1354,7 @@ void DerivationGoal::done(BuildResult::Status status, std::optional<Error> ex)
     if (traceBuiltOutputsFile != "") {
         std::fstream fs;
         fs.open(traceBuiltOutputsFile, std::fstream::out);
-        fs << worker.store.printStorePath(drvPath) << "\t" << result.toString() << std::endl;
+        fs << worker.store.printStorePath(drvPath) << "\t" << buildResult.toString() << std::endl;
     }
 }
 
diff --git a/src/libstore/build/derivation-goal.hh b/src/libstore/build/derivation-goal.hh
index 6f158bdbf..ea2db89b2 100644
--- a/src/libstore/build/derivation-goal.hh
+++ b/src/libstore/build/derivation-goal.hh
@@ -2,7 +2,6 @@
 
 #include "parsed-derivations.hh"
 #include "lock.hh"
-#include "build-result.hh"
 #include "store-api.hh"
 #include "pathlocks.hh"
 #include "goal.hh"
@@ -105,20 +104,8 @@ struct DerivationGoal : public Goal
     typedef void (DerivationGoal::*GoalState)();
     GoalState state;
 
-    /* The final output paths of the build.
-
-       - For input-addressed derivations, always the precomputed paths
-
-       - For content-addressed derivations, calcuated from whatever the hash
-         ends up being. (Note that fixed outputs derivations that produce the
-         "wrong" output still install that data under its true content-address.)
-     */
-    OutputPathMap finalOutputs;
-
     BuildMode buildMode;
 
-    BuildResult result;
-
     /* The current round, if we're building multiple times. */
     size_t curRound = 1;
 
@@ -153,8 +140,6 @@ struct DerivationGoal : public Goal
     /* Add wanted outputs to an already existing derivation goal. */
     void addWantedOutputs(const StringSet & outputs);
 
-    BuildResult getResult() { return result; }
-
     /* The states. */
     void getDerivation();
     void loadDerivation();
@@ -176,7 +161,7 @@ struct DerivationGoal : public Goal
 
     /* Check that the derivation outputs all exist and register them
        as valid. */
-    virtual void registerOutputs();
+    virtual DrvOutputs registerOutputs();
 
     /* Open a log file and a pipe to it. */
     Path openLogFile();
@@ -211,8 +196,17 @@ struct DerivationGoal : public Goal
     std::map<std::string, std::optional<StorePath>> queryPartialDerivationOutputMap();
     OutputPathMap queryDerivationOutputMap();
 
-    /* Return the set of (in)valid paths. */
-    void checkPathValidity();
+    /* Update 'initialOutputs' to determine the current status of the
+       outputs of the derivation. Also returns a Boolean denoting
+       whether all outputs are valid and non-corrupt, and a
+       'DrvOutputs' structure containing the valid and wanted
+       outputs. */
+    std::pair<bool, DrvOutputs> checkPathValidity();
+
+    /* Aborts if any output is not valid or corrupt, and otherwise
+       returns a 'DrvOutputs' structure containing the wanted
+       outputs. */
+    DrvOutputs assertPathValidity();
 
     /* Forcibly kill the child process, if any. */
     virtual void killChild();
@@ -223,6 +217,7 @@ struct DerivationGoal : public Goal
 
     void done(
         BuildResult::Status status,
+        DrvOutputs builtOutputs = {},
         std::optional<Error> ex = {});
 
     StorePathSet exportReferences(const StorePathSet & storePaths);
diff --git a/src/libstore/build/drv-output-substitution-goal.cc b/src/libstore/build/drv-output-substitution-goal.cc
index e6e810cdd..e50292c1e 100644
--- a/src/libstore/build/drv-output-substitution-goal.cc
+++ b/src/libstore/build/drv-output-substitution-goal.cc
@@ -6,8 +6,12 @@
 
 namespace nix {
 
-DrvOutputSubstitutionGoal::DrvOutputSubstitutionGoal(const DrvOutput& id, Worker & worker, RepairFlag repair, std::optional<ContentAddress> ca)
-    : Goal(worker)
+DrvOutputSubstitutionGoal::DrvOutputSubstitutionGoal(
+    const DrvOutput & id,
+    Worker & worker,
+    RepairFlag repair,
+    std::optional<ContentAddress> ca)
+    : Goal(worker, DerivedPath::Opaque { StorePath::dummy })
     , id(id)
 {
     state = &DrvOutputSubstitutionGoal::init;
@@ -32,7 +36,7 @@ void DrvOutputSubstitutionGoal::init()
 
 void DrvOutputSubstitutionGoal::tryNext()
 {
-    trace("Trying next substituter");
+    trace("trying next substituter");
 
     if (subs.size() == 0) {
         /* None left.  Terminate this goal and let someone else deal
@@ -119,7 +123,7 @@ void DrvOutputSubstitutionGoal::realisationFetched()
 void DrvOutputSubstitutionGoal::outPathValid()
 {
     assert(outputInfo);
-    trace("Output path substituted");
+    trace("output path substituted");
 
     if (nrFailed > 0) {
         debug("The output path of the derivation output '%s' could not be substituted", id.to_string());
diff --git a/src/libstore/build/entry-points.cc b/src/libstore/build/entry-points.cc
index 9b4cfd835..bea7363db 100644
--- a/src/libstore/build/entry-points.cc
+++ b/src/libstore/build/entry-points.cc
@@ -47,43 +47,51 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
     }
 }
 
+std::vector<BuildResult> Store::buildPathsWithResults(
+    const std::vector<DerivedPath> & reqs,
+    BuildMode buildMode,
+    std::shared_ptr<Store> evalStore)
+{
+    Worker worker(*this, evalStore ? *evalStore : *this);
+
+    Goals goals;
+    for (const auto & br : reqs) {
+        std::visit(overloaded {
+            [&](const DerivedPath::Built & bfd) {
+                goals.insert(worker.makeDerivationGoal(bfd.drvPath, bfd.outputs, buildMode));
+            },
+            [&](const DerivedPath::Opaque & bo) {
+                goals.insert(worker.makePathSubstitutionGoal(bo.path, buildMode == bmRepair ? Repair : NoRepair));
+            },
+        }, br.raw());
+    }
+
+    worker.run(goals);
+
+    std::vector<BuildResult> results;
+
+    for (auto & i : goals)
+        results.push_back(i->buildResult);
+
+    return results;
+}
+
 BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
     BuildMode buildMode)
 {
     Worker worker(*this, *this);
     auto goal = worker.makeBasicDerivationGoal(drvPath, drv, {}, buildMode);
 
-    BuildResult result;
-
     try {
         worker.run(Goals{goal});
-        result = goal->getResult();
+        return goal->buildResult;
     } catch (Error & e) {
-        result.status = BuildResult::MiscFailure;
-        result.errorMsg = e.msg();
-    }
-    // XXX: Should use `goal->queryPartialDerivationOutputMap()` once it's
-    // extended to return the full realisation for each output
-    auto staticDrvOutputs = drv.outputsAndOptPaths(*this);
-    auto outputHashes = staticOutputHashes(*this, drv);
-    for (auto & [outputName, staticOutput] : staticDrvOutputs) {
-        auto outputId = DrvOutput{outputHashes.at(outputName), outputName};
-        if (staticOutput.second)
-            result.builtOutputs.insert_or_assign(
-                    outputId,
-                    Realisation{ outputId, *staticOutput.second}
-                    );
-        if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations) && !derivationHasKnownOutputPaths(drv.type())) {
-            auto realisation = this->queryRealisation(outputId);
-            if (realisation)
-                result.builtOutputs.insert_or_assign(
-                        outputId,
-                        *realisation
-                        );
-        }
-    }
-
-    return result;
+        return BuildResult {
+            .status = BuildResult::MiscFailure,
+            .errorMsg = e.msg(),
+            .path = DerivedPath::Built { .drvPath = drvPath },
+        };
+    };
 }
 
 
diff --git a/src/libstore/build/goal.hh b/src/libstore/build/goal.hh
index 68e08bdf9..07c752bb9 100644
--- a/src/libstore/build/goal.hh
+++ b/src/libstore/build/goal.hh
@@ -2,6 +2,7 @@
 
 #include "types.hh"
 #include "store-api.hh"
+#include "build-result.hh"
 
 namespace nix {
 
@@ -55,10 +56,15 @@ struct Goal : public std::enable_shared_from_this<Goal>
     /* Whether the goal is finished. */
     ExitCode exitCode;
 
+    /* Build result. */
+    BuildResult buildResult;
+
     /* Exception containing an error message, if any. */
     std::optional<Error> ex;
 
-    Goal(Worker & worker) : worker(worker)
+    Goal(Worker & worker, DerivedPath path)
+        : worker(worker)
+        , buildResult { .path = std::move(path) }
     {
         nrFailed = nrNoSubstituters = nrIncompleteClosure = 0;
         exitCode = ecBusy;
diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 581d63d0e..a372728f5 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -194,7 +194,7 @@ void LocalDerivationGoal::tryLocalBuild() {
         outputLocks.unlock();
         buildUser.reset();
         worker.permanentFailure = true;
-        done(BuildResult::InputRejected, e);
+        done(BuildResult::InputRejected, {}, e);
         return;
     }
 
@@ -756,7 +756,7 @@ void LocalDerivationGoal::startBuilder()
     if (tcsetattr(builderOut.writeSide.get(), TCSANOW, &term))
         throw SysError("putting pseudoterminal into raw mode");
 
-    result.startTime = time(0);
+    buildResult.startTime = time(0);
 
     /* Fork a child to build the package. */
 
@@ -1261,6 +1261,16 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
 
     void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode, std::shared_ptr<Store> evalStore) override
     {
+        for (auto & result : buildPathsWithResults(paths, buildMode, evalStore))
+            if (!result.success())
+                result.rethrow();
+    }
+
+    std::vector<BuildResult> buildPathsWithResults(
+        const std::vector<DerivedPath> & paths,
+        BuildMode buildMode = bmNormal,
+        std::shared_ptr<Store> evalStore = nullptr) override
+    {
         assert(!evalStore);
 
         if (buildMode != bmNormal) throw Error("unsupported build mode");
@@ -1273,26 +1283,13 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
                 throw InvalidPath("cannot build '%s' in recursive Nix because path is unknown", req.to_string(*next));
         }
 
-        next->buildPaths(paths, buildMode);
-
-        for (auto & path : paths) {
-            auto p =  std::get_if<DerivedPath::Built>(&path);
-            if (!p) continue;
-            auto & bfd = *p;
-            auto drv = readDerivation(bfd.drvPath);
-            auto drvHashes = staticOutputHashes(*this, drv);
-            auto outputs = next->queryDerivationOutputMap(bfd.drvPath);
-            for (auto & [outputName, outputPath] : outputs)
-                if (wantOutput(outputName, bfd.outputs)) {
-                    newPaths.insert(outputPath);
-                    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
-                        auto thisRealisation = next->queryRealisation(
-                            DrvOutput{drvHashes.at(outputName), outputName}
-                        );
-                        assert(thisRealisation);
-                        newRealisations.insert(*thisRealisation);
-                    }
-                }
+        auto results = next->buildPathsWithResults(paths, buildMode);
+
+        for (auto & result : results) {
+            for (auto & [outputName, output] : result.builtOutputs) {
+                newPaths.insert(output.outPath);
+                newRealisations.insert(output);
+            }
         }
 
         StorePathSet closure;
@@ -1301,6 +1298,8 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
             goal.addDependency(path);
         for (auto & real : Realisation::closure(*next, newRealisations))
             goal.addedDrvOutputs.insert(real.id);
+
+        return results;
     }
 
     BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
@@ -2069,7 +2068,7 @@ void LocalDerivationGoal::runChild()
 }
 
 
-void LocalDerivationGoal::registerOutputs()
+DrvOutputs LocalDerivationGoal::registerOutputs()
 {
     /* When using a build hook, the build hook can register the output
        as valid (by doing `nix-store --import').  If so we don't have
@@ -2078,10 +2077,8 @@ void LocalDerivationGoal::registerOutputs()
        We can only early return when the outputs are known a priori. For
        floating content-addressed derivations this isn't the case.
      */
-    if (hook) {
-        DerivationGoal::registerOutputs();
-        return;
-    }
+    if (hook)
+        return DerivationGoal::registerOutputs();
 
     std::map<std::string, ValidPathInfo> infos;
 
@@ -2204,6 +2201,8 @@ void LocalDerivationGoal::registerOutputs()
 
     std::reverse(sortedOutputNames.begin(), sortedOutputNames.end());
 
+    OutputPathMap finalOutputs;
+
     for (auto & outputName : sortedOutputNames) {
         auto output = drv->outputs.at(outputName);
         auto & scratchPath = scratchOutputs.at(outputName);
@@ -2340,6 +2339,7 @@ void LocalDerivationGoal::registerOutputs()
         };
 
         ValidPathInfo newInfo = std::visit(overloaded {
+
             [&](const DerivationOutputInputAddressed & output) {
                 /* input-addressed case */
                 auto requiredFinalPath = output.path;
@@ -2359,6 +2359,7 @@ void LocalDerivationGoal::registerOutputs()
                     newInfo0.references.insert(newInfo0.path);
                 return newInfo0;
             },
+
             [&](const DerivationOutputCAFixed & dof) {
                 auto newInfo0 = newInfoFromCA(DerivationOutputCAFloating {
                     .method = dof.hash.method,
@@ -2381,14 +2382,17 @@ void LocalDerivationGoal::registerOutputs()
                 }
                 return newInfo0;
             },
-            [&](DerivationOutputCAFloating dof) {
+
+            [&](DerivationOutputCAFloating & dof) {
                 return newInfoFromCA(dof);
             },
+
             [&](DerivationOutputDeferred) -> ValidPathInfo {
                 // No derivation should reach that point without having been
                 // rewritten first
                 assert(false);
             },
+
         }, output.output);
 
         /* FIXME: set proper permissions in restorePath() so
@@ -2499,11 +2503,12 @@ void LocalDerivationGoal::registerOutputs()
     }
 
     if (buildMode == bmCheck) {
-        // In case of FOD mismatches on `--check` an error must be thrown as this is also
-        // a source for non-determinism.
+        /* In case of fixed-output derivations, if there are
+           mismatches on `--check` an error must be thrown as this is
+           also a source for non-determinism. */
         if (delayedException)
             std::rethrow_exception(delayedException);
-        return;
+        return assertPathValidity();
     }
 
     /* Apply output checks. */
@@ -2515,7 +2520,7 @@ void LocalDerivationGoal::registerOutputs()
         assert(prevInfos.size() == infos.size());
         for (auto i = prevInfos.begin(), j = infos.begin(); i != prevInfos.end(); ++i, ++j)
             if (!(*i == *j)) {
-                result.isNonDeterministic = true;
+                buildResult.isNonDeterministic = true;
                 Path prev = worker.store.printStorePath(i->second.path) + checkSuffix;
                 bool prevExists = keepPreviousRound && pathExists(prev);
                 hintformat hint = prevExists
@@ -2553,7 +2558,7 @@ void LocalDerivationGoal::registerOutputs()
 
     if (curRound < nrRounds) {
         prevInfos = std::move(infos);
-        return;
+        return {};
     }
 
     /* Remove the .check directories if we're done. FIXME: keep them
@@ -2588,17 +2593,24 @@ void LocalDerivationGoal::registerOutputs()
        means it's safe to link the derivation to the output hash. We must do
        that for floating CA derivations, which otherwise couldn't be cached,
        but it's fine to do in all cases. */
+    DrvOutputs builtOutputs;
 
-    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
-        for (auto& [outputName, newInfo] : infos) {
-            auto thisRealisation = Realisation{
-                .id = DrvOutput{initialOutputs.at(outputName).outputHash,
-                                outputName},
-                .outPath = newInfo.path};
+    for (auto & [outputName, newInfo] : infos) {
+        auto thisRealisation = Realisation {
+            .id = DrvOutput {
+                initialOutputs.at(outputName).outputHash,
+                outputName
+            },
+            .outPath = newInfo.path
+        };
+        if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
             signRealisation(thisRealisation);
             worker.store.registerDrvOutput(thisRealisation);
         }
+        builtOutputs.emplace(thisRealisation.id, thisRealisation);
     }
+
+    return builtOutputs;
 }
 
 void LocalDerivationGoal::signRealisation(Realisation & realisation)
@@ -2607,7 +2619,7 @@ void LocalDerivationGoal::signRealisation(Realisation & realisation)
 }
 
 
-void LocalDerivationGoal::checkOutputs(const std::map<Path, ValidPathInfo> & outputs)
+void LocalDerivationGoal::checkOutputs(const std::map<std::string, ValidPathInfo> & outputs)
 {
     std::map<Path, const ValidPathInfo &> outputsByPath;
     for (auto & output : outputs)
@@ -2679,8 +2691,8 @@ void LocalDerivationGoal::checkOutputs(const std::map<Path, ValidPathInfo> & out
                 for (auto & i : *value) {
                     if (worker.store.isStorePath(i))
                         spec.insert(worker.store.parseStorePath(i));
-                    else if (finalOutputs.count(i))
-                        spec.insert(finalOutputs.at(i));
+                    else if (outputs.count(i))
+                        spec.insert(outputs.at(i).path);
                     else throw BuildError("derivation contains an illegal reference specifier '%s'", i);
                 }
 
diff --git a/src/libstore/build/local-derivation-goal.hh b/src/libstore/build/local-derivation-goal.hh
index 95692c60d..d456e9cae 100644
--- a/src/libstore/build/local-derivation-goal.hh
+++ b/src/libstore/build/local-derivation-goal.hh
@@ -169,7 +169,7 @@ struct LocalDerivationGoal : public DerivationGoal
 
     /* Check that the derivation outputs all exist and register them
        as valid. */
-    void registerOutputs() override;
+    DrvOutputs registerOutputs() override;
 
     void signRealisation(Realisation &) override;
 
diff --git a/src/libstore/build/substitution-goal.cc b/src/libstore/build/substitution-goal.cc
index c1bb1941d..31e6dbc9f 100644
--- a/src/libstore/build/substitution-goal.cc
+++ b/src/libstore/build/substitution-goal.cc
@@ -6,7 +6,7 @@
 namespace nix {
 
 PathSubstitutionGoal::PathSubstitutionGoal(const StorePath & storePath, Worker & worker, RepairFlag repair, std::optional<ContentAddress> ca)
-    : Goal(worker)
+    : Goal(worker, DerivedPath::Opaque { storePath })
     , storePath(storePath)
     , repair(repair)
     , ca(ca)
@@ -24,6 +24,13 @@ PathSubstitutionGoal::~PathSubstitutionGoal()
 }
 
 
+void PathSubstitutionGoal::done(ExitCode result, BuildResult::Status status)
+{
+    buildResult.status = status;
+    amDone(result);
+}
+
+
 void PathSubstitutionGoal::work()
 {
     (this->*state)();
@@ -38,7 +45,7 @@ void PathSubstitutionGoal::init()
 
     /* If the path already exists we're done. */
     if (!repair && worker.store.isValidPath(storePath)) {
-        amDone(ecSuccess);
+        done(ecSuccess, BuildResult::AlreadyValid);
         return;
     }
 
@@ -65,7 +72,7 @@ void PathSubstitutionGoal::tryNext()
         /* Hack: don't indicate failure if there were no substituters.
            In that case the calling derivation should just do a
            build. */
-        amDone(substituterFailed ? ecFailed : ecNoSubstituters);
+        done(substituterFailed ? ecFailed : ecNoSubstituters, BuildResult::NoSubstituters);
 
         if (substituterFailed) {
             worker.failedSubstitutions++;
@@ -163,7 +170,9 @@ void PathSubstitutionGoal::referencesValid()
 
     if (nrFailed > 0) {
         debug("some references of path '%s' could not be realised", worker.store.printStorePath(storePath));
-        amDone(nrNoSubstituters > 0 || nrIncompleteClosure > 0 ? ecIncompleteClosure : ecFailed);
+        done(
+            nrNoSubstituters > 0 || nrIncompleteClosure > 0 ? ecIncompleteClosure : ecFailed,
+            BuildResult::DependencyFailed);
         return;
     }
 
@@ -268,7 +277,7 @@ void PathSubstitutionGoal::finished()
 
     worker.updateProgress();
 
-    amDone(ecSuccess);
+    done(ecSuccess, BuildResult::Substituted);
 }
 
 
diff --git a/src/libstore/build/substitution-goal.hh b/src/libstore/build/substitution-goal.hh
index d8399d2a8..946f13841 100644
--- a/src/libstore/build/substitution-goal.hh
+++ b/src/libstore/build/substitution-goal.hh
@@ -53,6 +53,8 @@ struct PathSubstitutionGoal : public Goal
     /* Content address for recomputing store path */
     std::optional<ContentAddress> ca;
 
+    void done(ExitCode result, BuildResult::Status status);
+
 public:
     PathSubstitutionGoal(const StorePath & storePath, Worker & worker, RepairFlag repair = NoRepair, std::optional<ContentAddress> ca = std::nullopt);
     ~PathSubstitutionGoal();
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 89d9487da..e6760664c 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -532,6 +532,25 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         break;
     }
 
+    case wopBuildPathsWithResults: {
+        auto drvs = readDerivedPaths(*store, clientVersion, from);
+        BuildMode mode = bmNormal;
+        mode = (BuildMode) readInt(from);
+
+        /* Repairing is not atomic, so disallowed for "untrusted"
+           clients.  */
+        if (mode == bmRepair && !trusted)
+            throw Error("repairing is not allowed because you are not in 'trusted-users'");
+
+        logger->startWork();
+        auto results = store->buildPathsWithResults(drvs, mode);
+        logger->stopWork();
+
+        worker_proto::write(*store, to, results);
+
+        break;
+    }
+
     case wopBuildDerivation: {
         auto drvPath = store->parseStorePath(readString(from));
         BasicDerivation drv;
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 16c2b90c6..dd34b19c6 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -279,7 +279,7 @@ public:
 
         conn->to.flush();
 
-        BuildResult status;
+        BuildResult status { .path = DerivedPath::Built { .drvPath = drvPath } };
         status.status = (BuildResult::Status) readInt(conn->from);
         conn->from >> status.errorMsg;
 
@@ -317,7 +317,7 @@ public:
 
         conn->to.flush();
 
-        BuildResult result;
+        BuildResult result { .path = DerivedPath::Opaque { StorePath::dummy } };
         result.status = (BuildResult::Status) readInt(conn->from);
 
         if (!result.success()) {
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index a25398ef2..347e32094 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -91,6 +91,35 @@ void write(const Store & store, Sink & out, const DrvOutput & drvOutput)
 }
 
 
+BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
+{
+    auto path = worker_proto::read(store, from, Phantom<DerivedPath> {});
+    BuildResult res { .path = path };
+    res.status = (BuildResult::Status) readInt(from);
+    from
+        >> res.errorMsg
+        >> res.timesBuilt
+        >> res.isNonDeterministic
+        >> res.startTime
+        >> res.stopTime;
+    res.builtOutputs = worker_proto::read(store, from, Phantom<DrvOutputs> {});
+    return res;
+}
+
+void write(const Store & store, Sink & to, const BuildResult & res)
+{
+    worker_proto::write(store, to, res.path);
+    to
+        << res.status
+        << res.errorMsg
+        << res.timesBuilt
+        << res.isNonDeterministic
+        << res.startTime
+        << res.stopTime;
+    worker_proto::write(store, to, res.builtOutputs);
+}
+
+
 std::optional<StorePath> read(const Store & store, Source & from, Phantom<std::optional<StorePath>> _)
 {
     auto s = readString(from);
@@ -747,17 +776,24 @@ static void writeDerivedPaths(RemoteStore & store, ConnectionHandle & conn, cons
     }
 }
 
-void RemoteStore::buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode, std::shared_ptr<Store> evalStore)
+void RemoteStore::copyDrvsFromEvalStore(
+    const std::vector<DerivedPath> & paths,
+    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)
+        for (auto & i : paths)
             if (auto p = std::get_if<DerivedPath::Built>(&i))
                 drvPaths2.insert(p->drvPath);
         copyClosure(*evalStore, *this, drvPaths2);
     }
+}
+
+void RemoteStore::buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMode buildMode, std::shared_ptr<Store> evalStore)
+{
+    copyDrvsFromEvalStore(drvPaths, evalStore);
 
     auto conn(getConnection());
     conn->to << wopBuildPaths;
@@ -774,6 +810,91 @@ void RemoteStore::buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMod
     readInt(conn->from);
 }
 
+std::vector<BuildResult> RemoteStore::buildPathsWithResults(
+    const std::vector<DerivedPath> & paths,
+    BuildMode buildMode,
+    std::shared_ptr<Store> evalStore)
+{
+    copyDrvsFromEvalStore(paths, evalStore);
+
+    std::optional<ConnectionHandle> conn_(getConnection());
+    auto & conn = *conn_;
+
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 34) {
+        conn->to << wopBuildPathsWithResults;
+        writeDerivedPaths(*this, conn, paths);
+        conn->to << buildMode;
+        conn.processStderr();
+        return worker_proto::read(*this, conn->from, Phantom<std::vector<BuildResult>> {});
+    } else {
+        // Avoid deadlock.
+        conn_.reset();
+
+        // Note: this throws an exception if a build/substitution
+        // fails, but meh.
+        buildPaths(paths, buildMode, evalStore);
+
+        std::vector<BuildResult> results;
+
+        for (auto & path : paths) {
+            std::visit(
+                overloaded {
+                    [&](const DerivedPath::Opaque & bo) {
+                        results.push_back(BuildResult {
+                            .status = BuildResult::Substituted,
+                            .path = bo,
+                        });
+                    },
+                    [&](const DerivedPath::Built & bfd) {
+                        BuildResult res {
+                            .status = BuildResult::Built,
+                            .path = bfd,
+                        };
+
+                        OutputPathMap outputs;
+                        auto drv = evalStore->readDerivation(bfd.drvPath);
+                        auto outputHashes = staticOutputHashes(*evalStore, drv); // FIXME: expensive
+                        auto drvOutputs = drv.outputsAndOptPaths(*this);
+                        for (auto & output : bfd.outputs) {
+                            if (!outputHashes.count(output))
+                                throw Error(
+                                    "the derivation '%s' doesn't have an output named '%s'",
+                                    printStorePath(bfd.drvPath), output);
+                            auto outputId =
+                                DrvOutput{outputHashes.at(output), output};
+                            if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
+                                auto realisation =
+                                    queryRealisation(outputId);
+                                if (!realisation)
+                                    throw Error(
+                                        "cannot operate on an output of unbuilt "
+                                        "content-addressed derivation '%s'",
+                                        outputId.to_string());
+                                res.builtOutputs.emplace(realisation->id, *realisation);
+                            } else {
+                                // If ca-derivations isn't enabled, assume that
+                                // the output path is statically known.
+                                assert(drvOutputs.count(output));
+                                assert(drvOutputs.at(output).second);
+                                res.builtOutputs.emplace(
+                                    outputId,
+                                    Realisation {
+                                        .id = outputId,
+                                        .outPath = *drvOutputs.at(output).second
+                                    });
+                            }
+                        }
+
+                        results.push_back(res);
+                    }
+                },
+                path.raw());
+        }
+
+        return results;
+    }
+}
+
 
 BuildResult RemoteStore::buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
     BuildMode buildMode)
@@ -783,7 +904,7 @@ BuildResult RemoteStore::buildDerivation(const StorePath & drvPath, const BasicD
     writeDerivation(conn->to, *this, drv);
     conn->to << buildMode;
     conn.processStderr();
-    BuildResult res;
+    BuildResult res { .path = DerivedPath::Built { .drvPath = drvPath } };
     res.status = (BuildResult::Status) readInt(conn->from);
     conn->from >> res.errorMsg;
     if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 29) {
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 2628206b1..9f6f50593 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -97,6 +97,11 @@ public:
 
     void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode, std::shared_ptr<Store> evalStore) override;
 
+    std::vector<BuildResult> buildPathsWithResults(
+        const std::vector<DerivedPath> & paths,
+        BuildMode buildMode,
+        std::shared_ptr<Store> evalStore) override;
+
     BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode) override;
 
@@ -171,6 +176,9 @@ private:
 
     std::atomic_bool failed{false};
 
+    void copyDrvsFromEvalStore(
+        const std::vector<DerivedPath> & paths,
+        std::shared_ptr<Store> evalStore);
 };
 
 
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 7bd21519c..e99a3f2cb 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -432,6 +432,16 @@ public:
         BuildMode buildMode = bmNormal,
         std::shared_ptr<Store> evalStore = nullptr);
 
+    /* Like `buildPaths()`, but return a vector of `BuildResult`s
+       corresponding to each element in `paths`. Note that in case of
+       a build/substitution error, this function won't throw an
+       exception, but return a `BuildResult` containing an error
+       message. */
+    virtual std::vector<BuildResult> buildPathsWithResults(
+        const std::vector<DerivedPath> & paths,
+        BuildMode buildMode = bmNormal,
+        std::shared_ptr<Store> evalStore = nullptr);
+
     /* Build a single non-materialized derivation (i.e. not from an
        on-disk .drv file).
 
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index c8332afe6..87088a3ac 100644
--- a/src/libstore/worker-protocol.hh
+++ b/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 | 33)
+#define PROTOCOL_VERSION (1 << 8 | 34)
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
@@ -57,6 +57,7 @@ typedef enum {
     wopQueryRealisation = 43,
     wopAddMultipleToStore = 44,
     wopAddBuildLog = 45,
+    wopBuildPathsWithResults = 46,
 } WorkerOp;
 
 
@@ -91,6 +92,7 @@ MAKE_WORKER_PROTO(, ContentAddress);
 MAKE_WORKER_PROTO(, DerivedPath);
 MAKE_WORKER_PROTO(, Realisation);
 MAKE_WORKER_PROTO(, DrvOutput);
+MAKE_WORKER_PROTO(, BuildResult);
 
 MAKE_WORKER_PROTO(template<typename T>, std::vector<T>);
 MAKE_WORKER_PROTO(template<typename T>, std::set<T>);