feat(tvix): Write even more build logs to client r/1767

Write *all* build logs (essentially everything that wasn't a DLOG), not
just the stdout of the builder, to the client-bound log_sink_ that's
threaded through build.cc. These logs are significantly more useful on
the client, both when debugging tvix itself and (more importantly) when
building things with it.

To make this all work, this commit also refactors the passing-around of
the log sink in build.cc slightly - the main reference is now owned by
the Worker class, which already stores pointers to itself on the Goals
it creates, so those Goals can then load the log sink from the Worker.
This change was originally made to allow for logging to the log_sink
from instance methods of the worker, but actually feels significantly
more natural than storing the sink on the goal anyway.

Change-Id: I461685bc7f5c0a326054940ac5971b568dd43f8e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1925
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

1 files changed, 84 insertions, 89 deletions

diff --git a/third_party/nix/src/libstore/build.cc b/third_party/nix/src/libstore/build.cc
index b7d7c1d431ab..502281d0051c 100644
--- a/third_party/nix/src/libstore/build.cc
+++ b/third_party/nix/src/libstore/build.cc
@@ -144,10 +144,9 @@ class Goal : public std::enable_shared_from_this<Goal> {
 
   // Output stream for build logs.
   // TODO(tazjin): Rename all build_log instances to log_sink.
-  std::ostream& log_sink_;
+  std::ostream& log_sink() const;
 
-  Goal(Worker& worker, std::ostream& log_sink)
-      : worker(worker), log_sink_(log_sink) {
+  explicit Goal(Worker& worker) : worker(worker) {
     nrFailed = nrNoSubstituters = nrIncompleteClosure = 0;
     exitCode = ecBusy;
   }
@@ -242,6 +241,8 @@ class Worker {
   /* Cache for pathContentsGood(). */
   std::map<Path, bool> pathContentsGoodCache;
 
+  std::ostream& log_sink_;
+
  public:
   /* Set if at least one derivation had a BuildError (i.e. permanent
      failure). */
@@ -278,19 +279,18 @@ class Worker {
      it answers with "decline-permanently", we don't try again. */
   bool tryBuildHook = true;
 
-  explicit Worker(LocalStore& store);
+  Worker(LocalStore& store, std::ostream& log_sink);
   ~Worker();
 
   /* Make a goal (with caching). */
-  GoalPtr makeDerivationGoal(std::ostream& log_sink, const Path& drvPath,
+  GoalPtr makeDerivationGoal(const Path& drvPath,
                              const StringSet& wantedOutputs,
                              BuildMode buildMode);
 
   std::shared_ptr<DerivationGoal> makeBasicDerivationGoal(
-      std::ostream& log_sink, const Path& drvPath, const BasicDerivation& drv,
-      BuildMode buildMode);
+      const Path& drvPath, const BasicDerivation& drv, BuildMode buildMode);
 
-  GoalPtr makeSubstitutionGoal(std::ostream& log_sink, const Path& storePath,
+  GoalPtr makeSubstitutionGoal(const Path& storePath,
                                RepairFlag repair = NoRepair);
 
   /* Remove a dead goal. */
@@ -342,6 +342,8 @@ class Worker {
   bool pathContentsGood(const Path& path);
 
   void markContentsGood(const Path& path);
+
+  std::ostream& log_sink() const { return log_sink_; };
 };
 
 //////////////////////////////////////////////////////////////////////
@@ -357,6 +359,8 @@ void addToWeakGoals(WeakGoals& goals, const GoalPtr& p) {
   goals.push_back(p);
 }
 
+std::ostream& Goal::log_sink() const { return worker.log_sink(); }
+
 void Goal::addWaitee(const GoalPtr& waitee) {
   waitees.insert(waitee);
   addToWeakGoals(waitee->waiters, shared_from_this());
@@ -455,7 +459,7 @@ static void commonChildInit(Pipe& logPipe) {
 }
 
 void handleDiffHook(uid_t uid, uid_t gid, Path tryA, Path tryB, Path drvPath,
-                    Path tmpDir) {
+                    Path tmpDir, std::ostream& log_sink) {
   auto diffHook = settings.diffHook;
   if (diffHook != "" && settings.runDiffHook) {
     try {
@@ -475,10 +479,10 @@ void handleDiffHook(uid_t uid, uid_t gid, Path tryA, Path tryB, Path drvPath,
       }
 
       if (!diffRes.second.empty()) {
-        LOG(ERROR) << absl::StripTrailingAsciiWhitespace(diffRes.second);
+        log_sink << absl::StripTrailingAsciiWhitespace(diffRes.second);
       }
     } catch (Error& error) {
-      LOG(ERROR) << "diff hook execution failed: " << error.what();
+      log_sink << "diff hook execution failed: " << error.what();
     }
   }
 }
@@ -887,10 +891,10 @@ class DerivationGoal : public Goal {
   std::string machineName;
 
  public:
-  DerivationGoal(Worker& worker, std::ostream& log_sink, const Path& drvPath,
-                 StringSet wantedOutputs, BuildMode buildMode);
+  DerivationGoal(Worker& worker, const Path& drvPath, StringSet wantedOutputs,
+                 BuildMode buildMode);
 
-  DerivationGoal(Worker& worker, std::ostream& log_sink, const Path& drvPath,
+  DerivationGoal(Worker& worker, const Path& drvPath,
                  const BasicDerivation& drv, BuildMode buildMode);
 
   ~DerivationGoal() override;
@@ -997,10 +1001,9 @@ class DerivationGoal : public Goal {
 
 const Path DerivationGoal::homeDir = "/homeless-shelter";
 
-DerivationGoal::DerivationGoal(Worker& worker, std::ostream& log_sink,
-                               const Path& drvPath, StringSet wantedOutputs,
-                               BuildMode buildMode)
-    : Goal(worker, log_sink),
+DerivationGoal::DerivationGoal(Worker& worker, const Path& drvPath,
+                               StringSet wantedOutputs, BuildMode buildMode)
+    : Goal(worker),
       useDerivation(true),
       drvPath(drvPath),
       wantedOutputs(std::move(wantedOutputs)),
@@ -1013,10 +1016,9 @@ DerivationGoal::DerivationGoal(Worker& worker, std::ostream& log_sink,
       std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
 }
 
-DerivationGoal::DerivationGoal(Worker& worker, std::ostream& log_sink,
-                               const Path& drvPath, const BasicDerivation& drv,
-                               BuildMode buildMode)
-    : Goal(worker, log_sink),
+DerivationGoal::DerivationGoal(Worker& worker, const Path& drvPath,
+                               const BasicDerivation& drv, BuildMode buildMode)
+    : Goal(worker),
       useDerivation(false),
       drvPath(drvPath),
       buildMode(buildMode) {
@@ -1116,7 +1118,7 @@ void DerivationGoal::getDerivation() {
     return;
   }
 
-  addWaitee(worker.makeSubstitutionGoal(log_sink_, drvPath));
+  addWaitee(worker.makeSubstitutionGoal(drvPath));
 
   state = &DerivationGoal::loadDerivation;
 }
@@ -1125,7 +1127,7 @@ void DerivationGoal::loadDerivation() {
   trace("loading derivation");
 
   if (nrFailed != 0) {
-    LOG(ERROR) << "cannot build missing derivation '" << drvPath << "'";
+    log_sink() << "cannot build missing derivation '" << drvPath << "'";
     done(BuildResult::MiscFailure);
     return;
   }
@@ -1170,7 +1172,7 @@ void DerivationGoal::haveDerivation() {
   if (settings.useSubstitutes && parsedDrv->substitutesAllowed()) {
     for (auto& i : invalidOutputs) {
       addWaitee(worker.makeSubstitutionGoal(
-          log_sink_, i, buildMode == bmRepair ? Repair : NoRepair));
+          i, buildMode == bmRepair ? Repair : NoRepair));
     }
   }
 
@@ -1236,8 +1238,7 @@ void DerivationGoal::outputsSubstituted() {
   if (useDerivation) {
     for (auto& i : dynamic_cast<Derivation*>(drv.get())->inputDrvs) {
       addWaitee(worker.makeDerivationGoal(
-          log_sink_, i.first, i.second,
-          buildMode == bmRepair ? bmRepair : bmNormal));
+          i.first, i.second, buildMode == bmRepair ? bmRepair : bmNormal));
     }
   }
 
@@ -1250,7 +1251,7 @@ void DerivationGoal::outputsSubstituted() {
                          "substitution is disabled") %
                   i % drvPath);
     }
-    addWaitee(worker.makeSubstitutionGoal(log_sink_, i));
+    addWaitee(worker.makeSubstitutionGoal(i));
   }
 
   if (waitees.empty()) { /* to prevent hang (no wake-up event) */
@@ -1303,14 +1304,13 @@ void DerivationGoal::repairClosure() {
     if (worker.pathContentsGood(i)) {
       continue;
     }
-    LOG(ERROR) << "found corrupted or missing path '" << i
+    log_sink() << "found corrupted or missing path '" << i
                << "' in the output closure of '" << drvPath << "'";
     Path drvPath2 = outputsToDrv[i];
     if (drvPath2.empty()) {
-      addWaitee(worker.makeSubstitutionGoal(log_sink_, i, Repair));
+      addWaitee(worker.makeSubstitutionGoal(i, Repair));
     } else {
-      addWaitee(
-          worker.makeDerivationGoal(log_sink_, drvPath2, PathSet(), bmRepair));
+      addWaitee(worker.makeDerivationGoal(drvPath2, PathSet(), bmRepair));
     }
   }
 
@@ -1339,7 +1339,7 @@ void DerivationGoal::inputsRealised() {
     if (!useDerivation) {
       throw Error(format("some dependencies of '%1%' are missing") % drvPath);
     }
-    LOG(ERROR) << "cannot build derivation '" << drvPath << "': " << nrFailed
+    log_sink() << "cannot build derivation '" << drvPath << "': " << nrFailed
                << " dependencies couldn't be built";
     done(BuildResult::DependencyFailed);
     return;
@@ -1355,7 +1355,7 @@ void DerivationGoal::inputsRealised() {
 
   /* The outputs are referenceable paths. */
   for (auto& i : drv->outputs) {
-    DLOG(INFO) << "building path " << i.second.path;
+    log_sink() << "building path " << i.second.path;
     allPaths.insert(i.second.path);
   }
 
@@ -1473,7 +1473,7 @@ void DerivationGoal::tryToBuild() {
     if (hook) {
       msg += fmt(" on '%s'", machineName);
     }
-    log_sink_ << absl::StrCat(msg, "[", drvPath, "]\n");
+    log_sink() << absl::StrCat(msg, "[", drvPath, "]\n");
     mcRunningBuilds =
         std::make_unique<MaintainCount<uint64_t>>(worker.runningBuilds);
   };
@@ -1515,7 +1515,7 @@ void DerivationGoal::tryToBuild() {
     startBuilder();
 
   } catch (BuildError& e) {
-    LOG(ERROR) << e.msg();
+    log_sink() << e.msg();
     outputLocks.unlock();
     buildUser.reset();
     worker.permanentFailure = true;
@@ -1653,8 +1653,8 @@ void DerivationGoal::buildDone() {
     registerOutputs();
 
     if (settings.postBuildHook != "") {
-      LOG(INFO) << "running post-build-hook '" << settings.postBuildHook
-                << "' [" << drvPath << "]";
+      log_sink() << "running post-build-hook '" << settings.postBuildHook
+                 << "' [" << drvPath << "]";
       auto outputPaths = drv->outputPaths();
       std::map<std::string, std::string> hookEnvironment = getEnv();
 
@@ -1733,7 +1733,7 @@ void DerivationGoal::buildDone() {
     outputLocks.unlock();
 
   } catch (BuildError& e) {
-    LOG(ERROR) << e.msg();
+    log_sink() << e.msg();
 
     outputLocks.unlock();
 
@@ -1808,7 +1808,7 @@ HookReply DerivationGoal::tryBuildHook() {
     }
   } catch (SysError& e) {
     if (e.errNo == EPIPE) {
-      LOG(ERROR) << "build hook died unexpectedly: "
+      log_sink() << "build hook died unexpectedly: "
                  << absl::StripTrailingAsciiWhitespace(
                         drainFD(worker.hook->fromHook.readSide.get()));
       worker.hook = nullptr;
@@ -3407,7 +3407,7 @@ void DerivationGoal::registerOutputs() {
 
           handleDiffHook(buildUser ? buildUser->getUID() : getuid(),
                          buildUser ? buildUser->getGID() : getgid(), path, dst,
-                         drvPath, tmpDir);
+                         drvPath, tmpDir, log_sink());
 
           throw NotDeterministic(
               format("derivation '%1%' may not be deterministic: output '%2%' "
@@ -3489,13 +3489,13 @@ void DerivationGoal::registerOutputs() {
 
         handleDiffHook(buildUser ? buildUser->getUID() : getuid(),
                        buildUser ? buildUser->getGID() : getgid(), prev,
-                       i->second.path, drvPath, tmpDir);
+                       i->second.path, drvPath, tmpDir, log_sink());
 
         if (settings.enforceDeterminism) {
           throw NotDeterministic(msg);
         }
 
-        LOG(ERROR) << msg;
+        log_sink() << msg;
         curRound = nrRounds;  // we know enough, bail out early
       }
     }
@@ -3775,7 +3775,7 @@ void DerivationGoal::deleteTmpDir(bool force) {
     /* Don't keep temporary directories for builtins because they
        might have privileged stuff (like a copy of netrc). */
     if (settings.keepFailed && !force && !drv->isBuiltin()) {
-      LOG(INFO) << "note: keeping build directory '" << tmpDir << "'";
+      log_sink() << "note: keeping build directory '" << tmpDir << "'";
       chmod(tmpDir.c_str(), 0755);
     } else {
       deletePath(tmpDir);
@@ -3790,9 +3790,8 @@ void DerivationGoal::handleChildOutput(int fd, const std::string& data) {
       (!hook && fd == builderOut.readSide.get())) {
     logSize += data.size();
     if (settings.maxLogSize && logSize > settings.maxLogSize) {
-      LOG(ERROR) << getName()
-                 << " killed after writing more than %2% bytes of log output"
-                 << settings.maxLogSize;
+      log_sink() << getName() << " killed after writing more than "
+                 << settings.maxLogSize << " bytes of log output";
       killChild();
       done(BuildResult::LogLimitExceeded);
       return;
@@ -3837,7 +3836,7 @@ void DerivationGoal::handleEOF(int /* fd */) {
 void DerivationGoal::flushLine() {
   if (settings.verboseBuild &&
       (settings.printRepeatedBuilds || curRound == 1)) {
-    log_sink_ << absl::StrCat(currentLogLine, "\n");
+    log_sink() << absl::StrCat(currentLogLine, "\n");
   } else {
     logTail.push_back(currentLogLine);
     if (logTail.size() > settings.logLines) {
@@ -3949,8 +3948,8 @@ class SubstitutionGoal : public Goal {
   GoalState state;
 
  public:
-  SubstitutionGoal(Worker& worker, std::ostream& log_sink,
-                   const Path& storePath, RepairFlag repair = NoRepair);
+  SubstitutionGoal(Worker& worker, const Path& storePath,
+                   RepairFlag repair = NoRepair);
 
   ~SubstitutionGoal() override;
 
@@ -3981,9 +3980,9 @@ class SubstitutionGoal : public Goal {
   void amDone(ExitCode result) override { Goal::amDone(result); }
 };
 
-SubstitutionGoal::SubstitutionGoal(Worker& worker, std::ostream& log_sink,
-                                   const Path& storePath, RepairFlag repair)
-    : Goal(worker, log_sink), repair(repair) {
+SubstitutionGoal::SubstitutionGoal(Worker& worker, const Path& storePath,
+                                   RepairFlag repair)
+    : Goal(worker), repair(repair) {
   this->storePath = storePath;
   state = &SubstitutionGoal::init;
   name = absl::StrCat("substitution of ", storePath);
@@ -4074,7 +4073,7 @@ void SubstitutionGoal::tryNext() {
     throw;
   } catch (Error& e) {
     if (settings.tryFallback) {
-      LOG(ERROR) << e.what();
+      log_sink() << e.what();
       tryNext();
       return;
     }
@@ -4099,9 +4098,9 @@ void SubstitutionGoal::tryNext() {
   if (worker.store.requireSigs && !sub->isTrusted &&
       (info->checkSignatures(worker.store, worker.store.getPublicKeys()) ==
        0u)) {
-    LOG(WARNING) << "substituter '" << sub->getUri()
-                 << "' does not have a valid signature for path '" << storePath
-                 << "'";
+    log_sink() << "substituter '" << sub->getUri()
+               << "' does not have a valid signature for path '" << storePath
+               << "'";
     tryNext();
     return;
   }
@@ -4110,7 +4109,7 @@ void SubstitutionGoal::tryNext() {
      paths referenced by this one. */
   for (auto& i : info->references) {
     if (i != storePath) { /* ignore self-references */
-      addWaitee(worker.makeSubstitutionGoal(log_sink_, i));
+      addWaitee(worker.makeSubstitutionGoal(i));
     }
   }
 
@@ -4192,7 +4191,7 @@ void SubstitutionGoal::finished() {
   try {
     promise.get_future().get();
   } catch (std::exception& e) {
-    LOG(ERROR) << e.what();
+    log_sink() << e.what();
 
     /* Cause the parent build to fail unless --fallback is given,
        or the substitute has disappeared. The latter case behaves
@@ -4244,7 +4243,8 @@ void SubstitutionGoal::handleEOF(int fd) {
 
 static bool working = false;
 
-Worker::Worker(LocalStore& store) : store(store) {
+Worker::Worker(LocalStore& store, std::ostream& log_sink)
+    : log_sink_(log_sink), store(store) {
   /* Debugging: prevent recursive workers. */
   if (working) {
     abort();
@@ -4272,13 +4272,13 @@ Worker::~Worker() {
   assert(expectedNarSize == 0);
 }
 
-GoalPtr Worker::makeDerivationGoal(std::ostream& log_sink, const Path& drv_path,
+GoalPtr Worker::makeDerivationGoal(const Path& drv_path,
                                    const StringSet& wantedOutputs,
                                    BuildMode buildMode) {
   GoalPtr goal = derivationGoals[drv_path].lock();
   if (!goal) {
-    goal = std::make_shared<DerivationGoal>(*this, log_sink, drv_path,
-                                            wantedOutputs, buildMode);
+    goal = std::make_shared<DerivationGoal>(*this, drv_path, wantedOutputs,
+                                            buildMode);
     derivationGoals[drv_path] = goal;
     wakeUp(goal);
   } else {
@@ -4289,19 +4289,17 @@ GoalPtr Worker::makeDerivationGoal(std::ostream& log_sink, const Path& drv_path,
 }
 
 std::shared_ptr<DerivationGoal> Worker::makeBasicDerivationGoal(
-    std::ostream& log_sink, const Path& drvPath, const BasicDerivation& drv,
-    BuildMode buildMode) {
-  std::shared_ptr<DerivationGoal> goal = std::make_shared<DerivationGoal>(
-      *this, log_sink, drvPath, drv, buildMode);
+    const Path& drvPath, const BasicDerivation& drv, BuildMode buildMode) {
+  std::shared_ptr<DerivationGoal> goal =
+      std::make_shared<DerivationGoal>(*this, drvPath, drv, buildMode);
   wakeUp(goal);
   return goal;
 }
 
-GoalPtr Worker::makeSubstitutionGoal(std::ostream& log_sink, const Path& path,
-                                     RepairFlag repair) {
+GoalPtr Worker::makeSubstitutionGoal(const Path& path, RepairFlag repair) {
   GoalPtr goal = substitutionGoals[path].lock();
   if (!goal) {
-    goal = std::make_shared<SubstitutionGoal>(*this, log_sink, path, repair);
+    goal = std::make_shared<SubstitutionGoal>(*this, path, repair);
     substitutionGoals[path] = goal;
     wakeUp(goal);
   }
@@ -4604,8 +4602,8 @@ void Worker::waitForInput() {
     if (goal->getExitCode() == Goal::ecBusy && 0 != settings.maxSilentTime &&
         j->respectTimeouts &&
         after - j->lastOutput >= std::chrono::seconds(settings.maxSilentTime)) {
-      LOG(ERROR) << goal->getName() << " timed out after "
-                 << settings.maxSilentTime << " seconds of silence";
+      log_sink_ << goal->getName() << " timed out after "
+                << settings.maxSilentTime << " seconds of silence";
       goal->timedOut();
     }
 
@@ -4613,8 +4611,8 @@ void Worker::waitForInput() {
              0 != settings.buildTimeout && j->respectTimeouts &&
              after - j->timeStarted >=
                  std::chrono::seconds(settings.buildTimeout)) {
-      LOG(ERROR) << goal->getName() << " timed out after "
-                 << settings.buildTimeout << " seconds";
+      log_sink_ << goal->getName() << " timed out after "
+                << settings.buildTimeout << " seconds";
       goal->timedOut();
     }
   }
@@ -4667,7 +4665,7 @@ bool Worker::pathContentsGood(const Path& path) {
   if (i != pathContentsGoodCache.end()) {
     return i->second;
   }
-  LOG(INFO) << "checking path '" << path << "'...";
+  log_sink_ << "checking path '" << path << "'...";
   auto info = store.queryPathInfo(path);
   bool res;
   if (!pathExists(path)) {
@@ -4679,7 +4677,7 @@ bool Worker::pathContentsGood(const Path& path) {
   }
   pathContentsGoodCache[path] = res;
   if (!res) {
-    LOG(ERROR) << "path '" << path << "' is corrupted or missing!";
+    log_sink_ << "path '" << path << "' is corrupted or missing!";
   }
   return res;
 }
@@ -4712,7 +4710,7 @@ static void primeCache(Store& store, const PathSet& paths) {
 absl::Status LocalStore::buildPaths(std::ostream& log_sink,
                                     const PathSet& drvPaths,
                                     BuildMode build_mode) {
-  Worker worker(*this);
+  Worker worker(*this, log_sink);
 
   primeCache(*this, drvPaths);
 
@@ -4720,11 +4718,10 @@ absl::Status LocalStore::buildPaths(std::ostream& log_sink,
   for (auto& i : drvPaths) {
     DrvPathWithOutputs i2 = parseDrvPathWithOutputs(i);
     if (isDerivation(i2.first)) {
-      goals.insert(
-          worker.makeDerivationGoal(log_sink, i2.first, i2.second, build_mode));
+      goals.insert(worker.makeDerivationGoal(i2.first, i2.second, build_mode));
     } else {
       goals.insert(worker.makeSubstitutionGoal(
-          log_sink, i, build_mode == bmRepair ? Repair : NoRepair));
+          i, build_mode == bmRepair ? Repair : NoRepair));
     }
   }
 
@@ -4754,10 +4751,9 @@ absl::Status LocalStore::buildPaths(std::ostream& log_sink,
 BuildResult LocalStore::buildDerivation(const Path& drvPath,
                                         const BasicDerivation& drv,
                                         BuildMode buildMode) {
-  Worker worker(*this);
   auto discard_logs = DiscardLogsSink();
-  auto goal =
-      worker.makeBasicDerivationGoal(discard_logs, drvPath, drv, buildMode);
+  Worker worker(*this, discard_logs);
+  auto goal = worker.makeBasicDerivationGoal(drvPath, drv, buildMode);
 
   BuildResult result;
 
@@ -4780,9 +4776,9 @@ void LocalStore::ensurePath(const Path& path) {
 
   primeCache(*this, {path});
 
-  Worker worker(*this);
   auto discard_logs = DiscardLogsSink();
-  GoalPtr goal = worker.makeSubstitutionGoal(discard_logs, path);
+  Worker worker(*this, discard_logs);
+  GoalPtr goal = worker.makeSubstitutionGoal(path);
   Goals goals = {goal};
 
   worker.run(goals);
@@ -4794,9 +4790,9 @@ void LocalStore::ensurePath(const Path& path) {
 }
 
 void LocalStore::repairPath(const Path& path) {
-  Worker worker(*this);
   auto discard_logs = DiscardLogsSink();
-  GoalPtr goal = worker.makeSubstitutionGoal(discard_logs, path, Repair);
+  Worker worker(*this, discard_logs);
+  GoalPtr goal = worker.makeSubstitutionGoal(path, Repair);
   Goals goals = {goal};
 
   worker.run(goals);
@@ -4807,8 +4803,7 @@ void LocalStore::repairPath(const Path& path) {
     auto deriver = queryPathInfo(path)->deriver;
     if (!deriver.empty() && isValidPath(deriver)) {
       goals.clear();
-      goals.insert(worker.makeDerivationGoal(discard_logs, deriver, StringSet(),
-                                             bmRepair));
+      goals.insert(worker.makeDerivationGoal(deriver, StringSet(), bmRepair));
       worker.run(goals);
     } else {
       throw Error(worker.exitStatus(), "cannot repair path '%s'", path);