diff --git a/flake.lock b/flake.lock
index fa71ceb5..d5c5e613 100644
--- a/flake.lock
+++ b/flake.lock
@@ -3,16 +3,15 @@
     "lowdown-src": {
       "flake": false,
       "locked": {
-        "lastModified": 1617481909,
-        "narHash": "sha256-SqnfOFuLuVRRNeVJr1yeEPJue/qWoCp5N6o5Kr///p4=",
+        "lastModified": 1633514407,
+        "narHash": "sha256-Dw32tiMjdK9t3ETl5fzGrutQTzh2rufgZV4A/BbxuD4=",
         "owner": "kristapsdz",
         "repo": "lowdown",
-        "rev": "148f9b2f586c41b7e36e73009db43ea68c7a1a4d",
+        "rev": "d2c2b44ff6c27b936ec27358a2653caaef8f73b8",
         "type": "github"
       },
       "original": {
         "owner": "kristapsdz",
-        "ref": "VERSION_0_8_4",
         "repo": "lowdown",
         "type": "github"
       }
@@ -20,28 +19,31 @@
     "nix": {
       "inputs": {
         "lowdown-src": "lowdown-src",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "nixpkgs-regression": "nixpkgs-regression"
       },
       "locked": {
-        "lastModified": 1628586117,
-        "narHash": "sha256-8hS4xy7fq3z9XZIMYm4sQi9SzhcYqEJfdbwgDePoWuc=",
+        "lastModified": 1646680282,
+        "narHash": "sha256-m8tqCS6uHveDon5GSro5yZor9H+sHeh+v/veF1IGw24=",
         "owner": "NixOS",
         "repo": "nix",
-        "rev": "a6ba313a0aac3b6e2fef434cb42d190a0849238e",
+        "rev": "ffe155abd36366a870482625543f9bf924a58281",
         "type": "github"
       },
       "original": {
-        "id": "nix",
-        "type": "indirect"
+        "owner": "NixOS",
+        "ref": "2.7.0",
+        "repo": "nix",
+        "type": "github"
       }
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1624862269,
-        "narHash": "sha256-JFcsh2+7QtfKdJFoPibLFPLgIW6Ycnv8Bts9a7RYme0=",
+        "lastModified": 1632864508,
+        "narHash": "sha256-d127FIvGR41XbVRDPVvozUPQ/uRHbHwvfyKHwEt5xFM=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "f77036342e2b690c61c97202bf48f2ce13acc022",
+        "rev": "82891b5e2c2359d7e58d08849e4c89511ab94234",
         "type": "github"
       },
       "original": {
@@ -50,6 +52,21 @@
         "type": "indirect"
       }
     },
+    "nixpkgs-regression": {
+      "locked": {
+        "lastModified": 1643052045,
+        "narHash": "sha256-uGJ0VXIhWKGXxkeNnq4TvV3CIOkUJ3PAoLZ3HMzNVMw=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
+        "type": "indirect"
+      }
+    },
     "root": {
       "inputs": {
         "nix": "nix",
diff --git a/flake.nix b/flake.nix
index 56cb2960..7c21b68d 100644
--- a/flake.nix
+++ b/flake.nix
@@ -2,6 +2,7 @@
   description = "A Nix-based continuous build system";
 
   inputs.nixpkgs.follows = "nix/nixpkgs";
+  inputs.nix.url = github:NixOS/nix/2.7.0;
 
   outputs = { self, nixpkgs, nix }:
     let
diff --git a/src/hydra-eval-jobs/hydra-eval-jobs.cc b/src/hydra-eval-jobs/hydra-eval-jobs.cc
index 44a273a9..ba92113e 100644
--- a/src/hydra-eval-jobs/hydra-eval-jobs.cc
+++ b/src/hydra-eval-jobs/hydra-eval-jobs.cc
@@ -63,13 +63,13 @@ struct MyArgs : MixEvalArgs, MixCommonArgs
 
 static MyArgs myArgs;
 
-static std::string queryMetaStrings(EvalState & state, DrvInfo & drv, const string & name, const string & subAttribute)
+static std::string queryMetaStrings(EvalState & state, DrvInfo & drv, const std::string & name, const std::string & subAttribute)
 {
     Strings res;
     std::function<void(Value & v)> rec;
 
     rec = [&](Value & v) {
-        state.forceValue(v);
+        state.forceValue(v, noPos);
         if (v.type() == nString)
             res.push_back(v.string.s);
         else if (v.isList())
@@ -78,7 +78,7 @@ static std::string queryMetaStrings(EvalState & state, DrvInfo & drv, const stri
         else if (v.type() == nAttrs) {
             auto a = v.attrs->find(state.symbols.create(subAttribute));
             if (a != v.attrs->end())
-                res.push_back(state.forceString(*a->value));
+                res.push_back(std::string(state.forceString(*a->value)));
         }
     };
 
@@ -113,7 +113,7 @@ static void worker(
         callFlake(state, lockedFlake, *vFlake);
 
         auto vOutputs = vFlake->attrs->get(state.symbols.create("outputs"))->value;
-        state.forceValue(*vOutputs);
+        state.forceValue(*vOutputs, noPos);
 
         auto aHydraJobs = vOutputs->attrs->get(state.symbols.create("hydraJobs"));
         if (!aHydraJobs)
@@ -157,7 +157,7 @@ static void worker(
                 if (drv->querySystem() == "unknown")
                     throw EvalError("derivation must have a 'system' attribute");
 
-                auto drvPath = drv->queryDrvPath();
+                auto drvPath = state.store->printStorePath(drv->requireDrvPath());
 
                 nlohmann::json job;
 
@@ -186,13 +186,13 @@ static void worker(
                     for (auto & i : context)
                         if (i.at(0) == '!') {
                             size_t index = i.find("!", 1);
-                            job["constituents"].push_back(string(i, index + 1));
+                            job["constituents"].push_back(std::string(i, index + 1));
                         }
 
                     state.forceList(*a->value, *a->pos);
                     for (unsigned int n = 0; n < a->value->listSize(); ++n) {
                         auto v = a->value->listElems()[n];
-                        state.forceValue(*v);
+                        state.forceValue(*v, noPos);
                         if (v->type() == nString)
                             job["namedConstituents"].push_back(state.forceStringNoCtx(*v));
                     }
@@ -210,7 +210,7 @@ static void worker(
 
                 nlohmann::json out;
                 for (auto & j : outputs)
-                    out[j.first] = j.second;
+                    out[j.first] = state.store->printStorePath(j.second);
                 job["outputs"] = std::move(out);
 
                 reply["job"] = std::move(job);
diff --git a/src/hydra-queue-runner/Makefile.am b/src/hydra-queue-runner/Makefile.am
index ea852334..57808608 100644
--- a/src/hydra-queue-runner/Makefile.am
+++ b/src/hydra-queue-runner/Makefile.am
@@ -2,7 +2,7 @@ bin_PROGRAMS = hydra-queue-runner
 
 hydra_queue_runner_SOURCES = hydra-queue-runner.cc queue-monitor.cc dispatcher.cc \
  builder.cc build-result.cc build-remote.cc \
- build-result.hh counter.hh state.hh db.hh \
+ hydra-build-result.hh counter.hh state.hh db.hh \
  nar-extractor.cc nar-extractor.hh
 hydra_queue_runner_LDADD = $(NIX_LIBS) -lpqxx
 hydra_queue_runner_CXXFLAGS = $(NIX_CFLAGS) -Wall -I ../libhydra -Wno-deprecated-declarations
diff --git a/src/hydra-queue-runner/build-remote.cc b/src/hydra-queue-runner/build-remote.cc
index 464a35c8..bdbd44b9 100644
--- a/src/hydra-queue-runner/build-remote.cc
+++ b/src/hydra-queue-runner/build-remote.cc
@@ -5,6 +5,7 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 
+#include "build-result.hh"
 #include "serve-protocol.hh"
 #include "state.hh"
 #include "util.hh"
@@ -49,7 +50,7 @@ static Strings extraStoreArgs(std::string & machine)
 
 static void openConnection(Machine::ptr machine, Path tmpDir, int stderrFD, Child & child)
 {
-    string pgmName;
+    std::string pgmName;
     Pipe to, from;
     to.create();
     from.create();
@@ -81,7 +82,7 @@ static void openConnection(Machine::ptr machine, Path tmpDir, int stderrFD, Chil
             if (machine->sshPublicHostKey != "") {
                 Path fileName = tmpDir + "/host-key";
                 auto p = machine->sshName.find("@");
-                string host = p != string::npos ? string(machine->sshName, p + 1) : machine->sshName;
+                std::string host = p != std::string::npos ? std::string(machine->sshName, p + 1) : machine->sshName;
                 writeFile(fileName, host + " " + machine->sshPublicHostKey + "\n");
                 append(argv, {"-oUserKnownHostsFile=" + fileName});
             }
@@ -185,8 +186,8 @@ void State::buildRemote(ref<Store> destStore,
 {
     assert(BuildResult::TimedOut == 8);
 
-    string base(step->drvPath.to_string());
-    result.logFile = logDir + "/" + string(base, 0, 2) + "/" + string(base, 2);
+    std::string base(step->drvPath.to_string());
+    result.logFile = logDir + "/" + std::string(base, 0, 2) + "/" + std::string(base, 2);
     AutoDelete autoDelete(result.logFile, false);
 
     createDirs(dirOf(result.logFile));
@@ -249,7 +250,7 @@ void State::buildRemote(ref<Store> destStore,
 
         } catch (EndOfFile & e) {
             child.pid.wait();
-            string s = chomp(readFile(result.logFile));
+            std::string s = chomp(readFile(result.logFile));
             throw Error("cannot connect to ‘%1%’: %2%", machine->sshName, s);
         }
 
@@ -287,9 +288,9 @@ void State::buildRemote(ref<Store> destStore,
            this will copy the inputs to the binary cache from the local
            store. */
         if (localStore != std::shared_ptr<Store>(destStore)) {
-            StorePathSet closure;
-            localStore->computeFSClosure(step->drv->inputSrcs, closure);
-            copyPaths(*localStore, *destStore, closure, NoRepair, NoCheckSigs, NoSubstitute);
+            copyClosure(*localStore, *destStore,
+                step->drv->inputSrcs,
+                NoRepair, NoCheckSigs, NoSubstitute);
         }
 
         {
diff --git a/src/hydra-queue-runner/build-result.cc b/src/hydra-queue-runner/build-result.cc
index f69bf0df..ea8b4a6a 100644
--- a/src/hydra-queue-runner/build-result.cc
+++ b/src/hydra-queue-runner/build-result.cc
@@ -1,4 +1,4 @@
-#include "build-result.hh"
+#include "hydra-build-result.hh"
 #include "store-api.hh"
 #include "util.hh"
 #include "fs-accessor.hh"
@@ -78,7 +78,7 @@ BuildOutput getBuildOutput(
             product.type = match[1];
             product.subtype = match[2];
             std::string s(match[3]);
-            product.path = s[0] == '"' ? string(s, 1, s.size() - 2) : s;
+            product.path = s[0] == '"' ? std::string(s, 1, s.size() - 2) : s;
             product.defaultPath = match[5];
 
             /* Ensure that the path exists and points into the Nix
diff --git a/src/hydra-queue-runner/builder.cc b/src/hydra-queue-runner/builder.cc
index 89aa7d15..37022522 100644
--- a/src/hydra-queue-runner/builder.cc
+++ b/src/hydra-queue-runner/builder.cc
@@ -1,7 +1,7 @@
 #include <cmath>
 
 #include "state.hh"
-#include "build-result.hh"
+#include "hydra-build-result.hh"
 #include "finally.hh"
 #include "binary-cache-store.hh"
 
diff --git a/src/hydra-queue-runner/build-result.hh b/src/hydra-queue-runner/hydra-build-result.hh
similarity index 100%
rename from src/hydra-queue-runner/build-result.hh
rename to src/hydra-queue-runner/hydra-build-result.hh
diff --git a/src/hydra-queue-runner/hydra-queue-runner.cc b/src/hydra-queue-runner/hydra-queue-runner.cc
index 3297730c..615e470b 100644
--- a/src/hydra-queue-runner/hydra-queue-runner.cc
+++ b/src/hydra-queue-runner/hydra-queue-runner.cc
@@ -7,7 +7,7 @@
 #include <fcntl.h>
 
 #include "state.hh"
-#include "build-result.hh"
+#include "hydra-build-result.hh"
 #include "store-api.hh"
 #include "remote-store.hh"
 
@@ -87,7 +87,7 @@ void State::parseMachines(const std::string & contents)
     }
 
     for (auto line : tokenizeString<Strings>(contents, "\n")) {
-        line = trim(string(line, 0, line.find('#')));
+        line = trim(std::string(line, 0, line.find('#')));
         auto tokens = tokenizeString<std::vector<std::string>>(line);
         if (tokens.size() < 3) continue;
         tokens.resize(8);
@@ -95,7 +95,7 @@ void State::parseMachines(const std::string & contents)
         auto machine = std::make_shared<Machine>();
         machine->sshName = tokens[0];
         machine->systemTypes = tokenizeString<StringSet>(tokens[1], ",");
-        machine->sshKey = tokens[2] == "-" ? string("") : tokens[2];
+        machine->sshKey = tokens[2] == "-" ? std::string("") : tokens[2];
         if (tokens[3] != "")
             machine->maxJobs = string2Int<decltype(machine->maxJobs)>(tokens[3]).value();
         else
@@ -149,7 +149,7 @@ void State::parseMachines(const std::string & contents)
 
 void State::monitorMachinesFile()
 {
-    string defaultMachinesFile = "/etc/nix/machines";
+    std::string defaultMachinesFile = "/etc/nix/machines";
     auto machinesFiles = tokenizeString<std::vector<Path>>(
         getEnv("NIX_REMOTE_SYSTEMS").value_or(pathExists(defaultMachinesFile) ? defaultMachinesFile : ""), ":");
 
@@ -191,7 +191,7 @@ void State::monitorMachinesFile()
 
         debug("reloading machines files");
 
-        string contents;
+        std::string contents;
         for (auto & machinesFile : machinesFiles) {
             try {
                 contents += readFile(machinesFile);
@@ -308,7 +308,7 @@ void State::finishBuildStep(pqxx::work & txn, const RemoteResult & result,
 
 
 int State::createSubstitutionStep(pqxx::work & txn, time_t startTime, time_t stopTime,
-    Build::ptr build, const StorePath & drvPath, const string & outputName, const StorePath & storePath)
+    Build::ptr build, const StorePath & drvPath, const std::string & outputName, const StorePath & storePath)
 {
  restart:
     auto stepNr = allocBuildStep(txn, build->id);
@@ -683,14 +683,14 @@ void State::showStatus()
     auto conn(dbPool.get());
     receiver statusDumped(*conn, "status_dumped");
 
-    string status;
+    std::string status;
     bool barf = false;
 
     /* Get the last JSON status dump from the database. */
     {
         pqxx::work txn(*conn);
         auto res = txn.exec("select status from SystemStatus where what = 'queue-runner'");
-        if (res.size()) status = res[0][0].as<string>();
+        if (res.size()) status = res[0][0].as<std::string>();
     }
 
     if (status != "") {
@@ -710,7 +710,7 @@ void State::showStatus()
         {
             pqxx::work txn(*conn);
             auto res = txn.exec("select status from SystemStatus where what = 'queue-runner'");
-            if (res.size()) status = res[0][0].as<string>();
+            if (res.size()) status = res[0][0].as<std::string>();
         }
 
     }
diff --git a/src/hydra-queue-runner/nar-extractor.cc b/src/hydra-queue-runner/nar-extractor.cc
index 260296c9..9f0eb431 100644
--- a/src/hydra-queue-runner/nar-extractor.cc
+++ b/src/hydra-queue-runner/nar-extractor.cc
@@ -64,7 +64,7 @@ struct Extractor : ParseSink
         }
     }
 
-    void createSymlink(const Path & path, const string & target) override
+    void createSymlink(const Path & path, const std::string & target) override
     {
         members.insert_or_assign(prefix + path, NarMemberData { .type = FSAccessor::Type::tSymlink });
     }
diff --git a/src/hydra-queue-runner/queue-monitor.cc b/src/hydra-queue-runner/queue-monitor.cc
index 49caf8e3..6a5a82db 100644
--- a/src/hydra-queue-runner/queue-monitor.cc
+++ b/src/hydra-queue-runner/queue-monitor.cc
@@ -1,5 +1,5 @@
 #include "state.hh"
-#include "build-result.hh"
+#include "hydra-build-result.hh"
 #include "globals.hh"
 
 #include <cstring>
@@ -111,12 +111,12 @@ bool State::getQueuedBuilds(Connection & conn,
             if (builds_->count(id)) continue;
 
             auto build = std::make_shared<Build>(
-                localStore->parseStorePath(row["drvPath"].as<string>()));
+                localStore->parseStorePath(row["drvPath"].as<std::string>()));
             build->id = id;
             build->jobsetId = row["jobset_id"].as<JobsetID>();
-            build->projectName = row["project"].as<string>();
-            build->jobsetName = row["jobset"].as<string>();
-            build->jobName = row["job"].as<string>();
+            build->projectName = row["project"].as<std::string>();
+            build->jobsetName = row["jobset"].as<std::string>();
+            build->jobName = row["job"].as<std::string>();
             build->maxSilentTime = row["maxsilent"].as<int>();
             build->buildTimeout = row["timeout"].as<int>();
             build->timestamp = row["timestamp"].as<time_t>();
@@ -513,9 +513,9 @@ Step::ptr State::createStep(ref<Store> destStore,
                         // FIXME: should copy directly from substituter to destStore.
                     }
 
-                    StorePathSet closure;
-                    localStore->computeFSClosure({*path}, closure);
-                    copyPaths(*localStore, *destStore, closure, NoRepair, CheckSigs, NoSubstitute);
+                    copyClosure(*localStore, *destStore,
+                        StorePathSet { *path },
+                        NoRepair, CheckSigs, NoSubstitute);
 
                     time_t stopTime = time(0);
 
@@ -620,7 +620,7 @@ void State::processJobsetSharesChange(Connection & conn)
     auto res = txn.exec("select project, name, schedulingShares from Jobsets");
     for (auto const & row : res) {
         auto jobsets_(jobsets.lock());
-        auto i = jobsets_->find(std::make_pair(row["project"].as<string>(), row["name"].as<string>()));
+        auto i = jobsets_->find(std::make_pair(row["project"].as<std::string>(), row["name"].as<std::string>()));
         if (i == jobsets_->end()) continue;
         i->second->setShares(row["schedulingShares"].as<unsigned int>());
     }
diff --git a/src/hydra-queue-runner/state.hh b/src/hydra-queue-runner/state.hh
index 8f303d28..7c375cb9 100644
--- a/src/hydra-queue-runner/state.hh
+++ b/src/hydra-queue-runner/state.hh
@@ -12,6 +12,7 @@
 #include "parsed-derivations.hh"
 #include "pathlocks.hh"
 #include "pool.hh"
+#include "build-result.hh"
 #include "store-api.hh"
 #include "sync.hh"
 #include "nar-extractor.hh"
diff --git a/src/libhydra/db.hh b/src/libhydra/db.hh
index 7d5bdc58..00e8f406 100644
--- a/src/libhydra/db.hh
+++ b/src/libhydra/db.hh
@@ -18,7 +18,7 @@ struct Connection : pqxx::connection
         std::string upper_prefix = "DBI:Pg:";
 
         if (hasPrefix(s, lower_prefix) || hasPrefix(s, upper_prefix)) {
-            return concatStringsSep(" ", tokenizeString<Strings>(string(s, lower_prefix.size()), ";"));
+            return concatStringsSep(" ", tokenizeString<Strings>(std::string(s, lower_prefix.size()), ";"));
         }
 
         throw Error("$HYDRA_DBI does not denote a PostgreSQL database");
diff --git a/src/libhydra/hydra-config.hh b/src/libhydra/hydra-config.hh
index bc989f74..1688c278 100644
--- a/src/libhydra/hydra-config.hh
+++ b/src/libhydra/hydra-config.hh
@@ -17,7 +17,7 @@ struct HydraConfig
         if (hydraConfigFile && pathExists(*hydraConfigFile)) {
 
             for (auto line : tokenizeString<Strings>(readFile(*hydraConfigFile), "\n")) {
-                line = trim(string(line, 0, line.find('#')));
+                line = trim(std::string(line, 0, line.find('#')));
 
                 auto eq = line.find('=');
                 if (eq == std::string::npos) continue;