Merge branch 'path-info' into ca-drv-exotic

29 files changed, 547 insertions, 265 deletions

diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index 9603a8caa..ca538b3cb 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -2,6 +2,7 @@
 
 #include "crypto.hh"
 #include "store-api.hh"
+#include "log-store.hh"
 
 #include "pool.hh"
 
@@ -28,7 +29,9 @@ struct BinaryCacheStoreConfig : virtual StoreConfig
         "other than -1 which we reserve to indicate Nix defaults should be used"};
 };
 
-class BinaryCacheStore : public virtual BinaryCacheStoreConfig, public virtual Store
+class BinaryCacheStore : public virtual BinaryCacheStoreConfig,
+    public virtual Store,
+    public virtual LogStore
 {
 
 private:
diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index afed9bf16..3d1c4fbc1 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -204,11 +204,9 @@ void DerivationGoal::haveDerivation()
 {
     trace("have derivation");
 
-    if (drv->type() == DerivationType::CAFloating)
+    if (!drv->type().hasKnownOutputPaths())
         settings.requireExperimentalFeature(Xp::CaDerivations);
 
-    retrySubstitution = false;
-
     for (auto & i : drv->outputsAndOptPaths(worker.store))
         if (i.second.second)
             worker.store.addTempRoot(*i.second.second);
@@ -311,14 +309,11 @@ void DerivationGoal::outputsSubstitutionTried()
     gaveUpOnSubstitution();
 }
 
+
 /* At least one of the output paths could not be
    produced using a substitute.  So we have to build instead. */
 void DerivationGoal::gaveUpOnSubstitution()
 {
-    /* Make sure checkPathValidity() from now on checks all
-       outputs. */
-    wantedOutputs.clear();
-
     /* The inputs must be built before we can build this goal. */
     if (useDerivation)
         for (auto & i : dynamic_cast<Derivation *>(drv.get())->inputDrvs)
@@ -426,7 +421,8 @@ void DerivationGoal::inputsRealised()
         return;
     }
 
-    if (retrySubstitution) {
+    if (retrySubstitution && !retriedSubstitution) {
+        retriedSubstitution = true;
         haveDerivation();
         return;
     }
@@ -440,9 +436,28 @@ void DerivationGoal::inputsRealised()
     if (useDerivation) {
         auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
 
-        if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations) &&
-            ((!fullDrv.inputDrvs.empty() && derivationIsCA(fullDrv.type()))
-            || fullDrv.type() == DerivationType::DeferredInputAddressed)) {
+        auto drvType = fullDrv.type();
+        bool resolveDrv = std::visit(overloaded {
+            [&](const DerivationType::InputAddressed & ia) {
+                /* must resolve if deferred. */
+                return ia.deferred;
+            },
+            [&](const DerivationType::ContentAddressed & ca) {
+                return !fullDrv.inputDrvs.empty() && (
+                    ca.fixed
+                    /* Can optionally resolve if fixed, which is good
+                       for avoiding unnecessary rebuilds. */
+                    ? settings.isExperimentalFeatureEnabled(Xp::CaDerivations)
+                    /* Must resolve if floating and there are any inputs
+                       drvs. */
+                    : true);
+            },
+        }, drvType.raw());
+
+        if (resolveDrv)
+        {
+            settings.requireExperimentalFeature(Xp::CaDerivations);
+
             /* We are be able to resolve this derivation based on the
                now-known results of dependencies. If so, we become a stub goal
                aliasing that resolved derivation goal */
@@ -501,7 +516,7 @@ void DerivationGoal::inputsRealised()
 
     /* Don't repeat fixed-output derivations since they're already
        verified by their output hash.*/
-    nrRounds = derivationIsFixed(derivationType) ? 1 : settings.buildRepeat + 1;
+    nrRounds = derivationType.isFixed() ? 1 : settings.buildRepeat + 1;
 
     /* Okay, try to build.  Note that here we don't wait for a build
        slot to become available, since we don't need one if there is a
@@ -908,7 +923,7 @@ void DerivationGoal::buildDone()
             st =
                 dynamic_cast<NotDeterministic*>(&e) ? BuildResult::NotDeterministic :
                 statusOk(status) ? BuildResult::OutputRejected :
-                derivationIsImpure(derivationType) || diskFull ? BuildResult::TransientFailure :
+                derivationType.isImpure() || diskFull ? BuildResult::TransientFailure :
                 BuildResult::PermanentFailure;
         }
 
@@ -1221,7 +1236,7 @@ void DerivationGoal::flushLine()
 
 std::map<std::string, std::optional<StorePath>> DerivationGoal::queryPartialDerivationOutputMap()
 {
-    if (!useDerivation || drv->type() != DerivationType::CAFloating) {
+    if (!useDerivation || drv->type().hasKnownOutputPaths()) {
         std::map<std::string, std::optional<StorePath>> res;
         for (auto & [name, output] : drv->outputs)
             res.insert_or_assign(name, output.path(worker.store, drv->name, name));
@@ -1233,7 +1248,7 @@ std::map<std::string, std::optional<StorePath>> DerivationGoal::queryPartialDeri
 
 OutputPathMap DerivationGoal::queryDerivationOutputMap()
 {
-    if (!useDerivation || drv->type() != DerivationType::CAFloating) {
+    if (!useDerivation || drv->type().hasKnownOutputPaths()) {
         OutputPathMap res;
         for (auto & [name, output] : drv->outputsAndOptPaths(worker.store))
             res.insert_or_assign(name, *output.second);
diff --git a/src/libstore/build/derivation-goal.hh b/src/libstore/build/derivation-goal.hh
index ea2db89b2..f556b6f25 100644
--- a/src/libstore/build/derivation-goal.hh
+++ b/src/libstore/build/derivation-goal.hh
@@ -61,8 +61,12 @@ struct DerivationGoal : public Goal
     bool needRestart = false;
 
     /* Whether to retry substituting the outputs after building the
-       inputs. */
-    bool retrySubstitution;
+       inputs. This is done in case of an incomplete closure. */
+    bool retrySubstitution = false;
+
+    /* Whether we've retried substitution, in which case we won't try
+       again. */
+    bool retriedSubstitution = false;
 
     /* The derivation stored at drvPath. */
     std::unique_ptr<Derivation> drv;
diff --git a/src/libstore/build/goal.cc b/src/libstore/build/goal.cc
index d2420b107..58e805f55 100644
--- a/src/libstore/build/goal.cc
+++ b/src/libstore/build/goal.cc
@@ -28,7 +28,7 @@ void Goal::addWaitee(GoalPtr waitee)
 
 void Goal::waiteeDone(GoalPtr waitee, ExitCode result)
 {
-    assert(waitees.find(waitee) != waitees.end());
+    assert(waitees.count(waitee));
     waitees.erase(waitee);
 
     trace(fmt("waitee '%s' done; %d left", waitee->name, waitees.size()));
diff --git a/src/libstore/build/goal.hh b/src/libstore/build/goal.hh
index 07c752bb9..35121c5d9 100644
--- a/src/libstore/build/goal.hh
+++ b/src/libstore/build/goal.hh
@@ -40,21 +40,21 @@ struct Goal : public std::enable_shared_from_this<Goal>
     WeakGoals waiters;
 
     /* Number of goals we are/were waiting for that have failed. */
-    unsigned int nrFailed;
+    size_t nrFailed = 0;
 
     /* Number of substitution goals we are/were waiting for that
        failed because there are no substituters. */
-    unsigned int nrNoSubstituters;
+    size_t nrNoSubstituters = 0;
 
     /* Number of substitution goals we are/were waiting for that
        failed because they had unsubstitutable references. */
-    unsigned int nrIncompleteClosure;
+    size_t nrIncompleteClosure = 0;
 
     /* Name of this goal for debugging purposes. */
     std::string name;
 
     /* Whether the goal is finished. */
-    ExitCode exitCode;
+    ExitCode exitCode = ecBusy;
 
     /* Build result. */
     BuildResult buildResult;
@@ -65,10 +65,7 @@ struct Goal : public std::enable_shared_from_this<Goal>
     Goal(Worker & worker, DerivedPath path)
         : worker(worker)
         , buildResult { .path = std::move(path) }
-    {
-        nrFailed = nrNoSubstituters = nrIncompleteClosure = 0;
-        exitCode = ecBusy;
-    }
+    { }
 
     virtual ~Goal()
     {
diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 14b1582f1..412c3df29 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -395,7 +395,7 @@ void LocalDerivationGoal::startBuilder()
         else if (settings.sandboxMode == smDisabled)
             useChroot = false;
         else if (settings.sandboxMode == smRelaxed)
-            useChroot = !(derivationIsImpure(derivationType)) && !noChroot;
+            useChroot = !(derivationType.isImpure()) && !noChroot;
     }
 
     auto & localStore = getLocalStore();
@@ -608,7 +608,7 @@ void LocalDerivationGoal::startBuilder()
                 "nogroup:x:65534:\n", sandboxGid()));
 
         /* Create /etc/hosts with localhost entry. */
-        if (!(derivationIsImpure(derivationType)))
+        if (!(derivationType.isImpure()))
             writeFile(chrootRootDir + "/etc/hosts", "127.0.0.1 localhost\n::1 localhost\n");
 
         /* Make the closure of the inputs available in the chroot,
@@ -796,7 +796,7 @@ void LocalDerivationGoal::startBuilder()
            us.
         */
 
-        if (!(derivationIsImpure(derivationType)))
+        if (!(derivationType.isImpure()))
             privateNetwork = true;
 
         userNamespaceSync.create();
@@ -1049,7 +1049,7 @@ void LocalDerivationGoal::initEnv()
        derivation, tell the builder, so that for instance `fetchurl'
        can skip checking the output.  On older Nixes, this environment
        variable won't be set, so `fetchurl' will do the check. */
-    if (derivationIsFixed(derivationType)) env["NIX_OUTPUT_CHECKED"] = "1";
+    if (derivationType.isFixed()) env["NIX_OUTPUT_CHECKED"] = "1";
 
     /* *Only* if this is a fixed-output derivation, propagate the
        values of the environment variables specified in the
@@ -1060,7 +1060,7 @@ void LocalDerivationGoal::initEnv()
        to the builder is generally impure, but the output of
        fixed-output derivations is by definition pure (since we
        already know the cryptographic hash of the output). */
-    if (derivationIsImpure(derivationType)) {
+    if (derivationType.isImpure()) {
         for (auto & i : parsedDrv->getStringsAttr("impureEnvVars").value_or(Strings()))
             env[i] = getEnv(i).value_or("");
     }
@@ -1340,6 +1340,12 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
         next->queryMissing(allowed, willBuild, willSubstitute,
             unknown, downloadSize, narSize);
     }
+
+    virtual std::optional<std::string> getBuildLog(const StorePath & path) override
+    { return std::nullopt; }
+
+    virtual void addBuildLog(const StorePath & path, std::string_view log) override
+    { unsupported("addBuildLog"); }
 };
 
 
@@ -1668,7 +1674,7 @@ void LocalDerivationGoal::runChild()
             /* Fixed-output derivations typically need to access the
                network, so give them access to /etc/resolv.conf and so
                on. */
-            if (derivationIsImpure(derivationType)) {
+            if (derivationType.isImpure()) {
                 // Only use nss functions to resolve hosts and
                 // services. Don’t use it for anything else that may
                 // be configured for this system. This limits the
@@ -1912,7 +1918,7 @@ void LocalDerivationGoal::runChild()
 
                 sandboxProfile += "(import \"sandbox-defaults.sb\")\n";
 
-                if (derivationIsImpure(derivationType))
+                if (derivationType.isImpure())
                     sandboxProfile += "(import \"sandbox-network.sb\")\n";
 
                 /* Add the output paths we'll use at build-time to the chroot */
@@ -2272,7 +2278,7 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
             return res;
         };
 
-        auto newInfoFromCA = [&](const DerivationOutputCAFloating outputHash) -> ValidPathInfo {
+        auto newInfoFromCA = [&](const DerivationOutput::CAFloating outputHash) -> ValidPathInfo {
             auto & st = outputStats.at(outputName);
             if (outputHash.method == ContentAddressMethod { FileIngestionMethod::Flat } ||
                 outputHash.method == ContentAddressMethod { TextHashMethod {} })
@@ -2340,7 +2346,7 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
 
         ValidPathInfo newInfo = std::visit(overloaded {
 
-            [&](const DerivationOutputInputAddressed & output) {
+            [&](const DerivationOutput::InputAddressed & output) {
                 /* input-addressed case */
                 auto requiredFinalPath = output.path;
                 /* Preemptively add rewrite rule for final hash, as that is
@@ -2357,7 +2363,7 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
                 return newInfo0;
             },
 
-            [&](const DerivationOutputCAFixed & dof) {
+            [&](const DerivationOutput::CAFixed & dof) {
                 auto wanted = getContentAddressHash(dof.ca);
 
                 auto newInfo0 = newInfoFromCA(DerivationOutputCAFloating {
@@ -2386,17 +2392,17 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
                 return newInfo0;
             },
 
-            [&](DerivationOutputCAFloating & dof) {
+            [&](const DerivationOutput::CAFloating & dof) {
                 return newInfoFromCA(dof);
             },
 
-            [&](DerivationOutputDeferred) -> ValidPathInfo {
+            [&](const DerivationOutput::Deferred &) -> ValidPathInfo {
                 // No derivation should reach that point without having been
                 // rewritten first
                 assert(false);
             },
 
-        }, output.output);
+        }, output.raw());
 
         /* FIXME: set proper permissions in restorePath() so
             we don't have to do another traversal. */
@@ -2610,7 +2616,8 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
             signRealisation(thisRealisation);
             worker.store.registerDrvOutput(thisRealisation);
         }
-        builtOutputs.emplace(thisRealisation.id, thisRealisation);
+        if (wantOutput(outputName, wantedOutputs))
+            builtOutputs.emplace(thisRealisation.id, thisRealisation);
     }
 
     return builtOutputs;
diff --git a/src/libstore/builtins/buildenv.cc b/src/libstore/builtins/buildenv.cc
index 25d015cb9..6f6ad57cb 100644
--- a/src/libstore/builtins/buildenv.cc
+++ b/src/libstore/builtins/buildenv.cc
@@ -47,9 +47,9 @@ static void createLinks(State & state, const Path & srcDir, const Path & dstDir,
             throw;
         }
 
-        /* The files below are special-cased to that they don't show up
-         * in user profiles, either because they are useless, or
-         * because they would cauase pointless collisions (e.g., each
+        /* The files below are special-cased to that they don't show
+         * up in user profiles, either because they are useless, or
+         * because they would cause pointless collisions (e.g., each
          * Python package brings its own
          * `$out/lib/pythonX.Y/site-packages/easy-install.pth'.)
          */
@@ -57,7 +57,9 @@ static void createLinks(State & state, const Path & srcDir, const Path & dstDir,
             hasSuffix(srcFile, "/nix-support") ||
             hasSuffix(srcFile, "/perllocal.pod") ||
             hasSuffix(srcFile, "/info/dir") ||
-            hasSuffix(srcFile, "/log"))
+            hasSuffix(srcFile, "/log") ||
+            hasSuffix(srcFile, "/manifest.nix") ||
+            hasSuffix(srcFile, "/manifest.json"))
             continue;
 
         else if (S_ISDIR(srcSt.st_mode)) {
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 4b5a57ff1..8271bc8d6 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -3,7 +3,9 @@
 #include "worker-protocol.hh"
 #include "build-result.hh"
 #include "store-api.hh"
+#include "store-cast.hh"
 #include "gc-store.hh"
+#include "log-store.hh"
 #include "path-with-outputs.hh"
 #include "finally.hh"
 #include "archive.hh"
@@ -562,6 +564,8 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         BuildMode buildMode = (BuildMode) readInt(from);
         logger->startWork();
 
+        auto drvType = drv.type();
+
         /* Content-addressed derivations are trustless because their output paths
            are verified by their content alone, so any derivation is free to
            try to produce such a path.
@@ -594,12 +598,12 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
            derivations, we throw out the precomputed output paths and just
            store the hashes, so there aren't two competing sources of truth an
            attacker could exploit. */
-        if (drv.type() == DerivationType::InputAddressed && !trusted)
+        if (!(drvType.isCA() || trusted))
             throw Error("you are not privileged to build input-addressed derivations");
 
         /* Make sure that the non-input-addressed derivations that got this far
            are in fact content-addressed if we don't trust them. */
-        assert(derivationIsCA(drv.type()) || trusted);
+        assert(drvType.isCA() || trusted);
 
         /* Recompute the derivation path when we cannot trust the original. */
         if (!trusted) {
@@ -608,7 +612,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                original not-necessarily-resolved derivation to verify the drv
                derivation as adequate claim to the input-addressed output
                paths. */
-            assert(derivationIsCA(drv.type()));
+            assert(drvType.isCA());
 
             Derivation drv2;
             static_cast<BasicDerivation &>(drv2) = drv;
@@ -649,7 +653,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         Path path = absPath(readString(from));
 
         logger->startWork();
-        auto & gcStore = requireGcStore(*store);
+        auto & gcStore = require<GcStore>(*store);
         gcStore.addIndirectRoot(path);
         logger->stopWork();
 
@@ -667,7 +671,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
 
     case wopFindRoots: {
         logger->startWork();
-        auto & gcStore = requireGcStore(*store);
+        auto & gcStore = require<GcStore>(*store);
         Roots roots = gcStore.findRoots(!trusted);
         logger->stopWork();
 
@@ -699,7 +703,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         if (options.ignoreLiveness)
             throw Error("you are not allowed to ignore liveness");
-        auto & gcStore = requireGcStore(*store);
+        auto & gcStore = require<GcStore>(*store);
         gcStore.collectGarbage(options, results);
         logger->stopWork();
 
@@ -957,11 +961,12 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         if (!trusted)
             throw Error("you are not privileged to add logs");
+        auto & logStore = require<LogStore>(*store);
         {
             FramedSource source(from);
             StringSink sink;
             source.drainInto(sink);
-            store->addBuildLog(path, sink.s);
+            logStore.addBuildLog(path, sink.s);
         }
         logger->stopWork();
         to << 1;
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index f6f41361b..00757abc8 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -12,25 +12,25 @@ namespace nix {
 std::optional<StorePath> DerivationOutput::path(const Store & store, std::string_view drvName, std::string_view outputName) const
 {
     return std::visit(overloaded {
-        [](const DerivationOutputInputAddressed & doi) -> std::optional<StorePath> {
+        [](const DerivationOutput::InputAddressed & doi) -> std::optional<StorePath> {
             return { doi.path };
         },
-        [&](const DerivationOutputCAFixed & dof) -> std::optional<StorePath> {
+        [&](const DerivationOutput::CAFixed & dof) -> std::optional<StorePath> {
             return {
                 dof.path(store, drvName, outputName)
             };
         },
-        [](const DerivationOutputCAFloating & dof) -> std::optional<StorePath> {
+        [](const DerivationOutput::CAFloating & dof) -> std::optional<StorePath> {
             return std::nullopt;
         },
-        [](const DerivationOutputDeferred &) -> std::optional<StorePath> {
+        [](const DerivationOutput::Deferred &) -> std::optional<StorePath> {
             return std::nullopt;
         },
-    }, output);
+    }, raw());
 }
 
 
-StorePath DerivationOutputCAFixed::path(const Store & store, std::string_view drvName, std::string_view outputName) const {
+StorePath DerivationOutput::CAFixed::path(const Store & store, std::string_view drvName, std::string_view outputName) const {
     return store.makeFixedOutputPathFromCA(StorePathDescriptor {
         .name = outputPathName(drvName, outputName),
         .info = ca,
@@ -38,47 +38,46 @@ StorePath DerivationOutputCAFixed::path(const Store & store, std::string_view dr
 }
 
 
-bool derivationIsCA(DerivationType dt) {
-    switch (dt) {
-    case DerivationType::InputAddressed: return false;
-    case DerivationType::CAFixed: return true;
-    case DerivationType::CAFloating: return true;
-    case DerivationType::DeferredInputAddressed: return false;
-    };
-    // Since enums can have non-variant values, but making a `default:` would
-    // disable exhaustiveness warnings.
-    assert(false);
+bool DerivationType::isCA() const {
+    /* Normally we do the full `std::visit` to make sure we have
+       exhaustively handled all variants, but so long as there is a
+       variant called `ContentAddressed`, it must be the only one for
+       which `isCA` is true for this to make sense!. */
+    return std::holds_alternative<ContentAddressed>(raw());
 }
 
-bool derivationIsFixed(DerivationType dt) {
-    switch (dt) {
-    case DerivationType::InputAddressed: return false;
-    case DerivationType::CAFixed: return true;
-    case DerivationType::CAFloating: return false;
-    case DerivationType::DeferredInputAddressed: return false;
-    };
-    assert(false);
+bool DerivationType::isFixed() const {
+    return std::visit(overloaded {
+        [](const InputAddressed & ia) {
+            return false;
+        },
+        [](const ContentAddressed & ca) {
+            return ca.fixed;
+        },
+    }, raw());
 }
 
-bool derivationHasKnownOutputPaths(DerivationType dt) {
-    switch (dt) {
-    case DerivationType::InputAddressed: return true;
-    case DerivationType::CAFixed: return true;
-    case DerivationType::CAFloating: return false;
-    case DerivationType::DeferredInputAddressed: return false;
-    };
-    assert(false);
+bool DerivationType::hasKnownOutputPaths() const {
+    return std::visit(overloaded {
+        [](const InputAddressed & ia) {
+            return !ia.deferred;
+        },
+        [](const ContentAddressed & ca) {
+            return ca.fixed;
+        },
+    }, raw());
 }
 
 
-bool derivationIsImpure(DerivationType dt) {
-    switch (dt) {
-    case DerivationType::InputAddressed: return false;
-    case DerivationType::CAFixed: return true;
-    case DerivationType::CAFloating: return false;
-    case DerivationType::DeferredInputAddressed: return false;
-    };
-    assert(false);
+bool DerivationType::isImpure() const {
+    return std::visit(overloaded {
+        [](const InputAddressed & ia) {
+            return false;
+        },
+        [](const ContentAddressed & ca) {
+            return !ca.pure;
+        },
+    }, raw());
 }
 
 
@@ -178,34 +177,26 @@ static DerivationOutput parseDerivationOutput(const Store & store,
         if (hashS != "") {
             validatePath(pathS);
             auto hash = Hash::parseNonSRIUnprefixed(hashS, hashType);
-            return DerivationOutput {
-                .output = DerivationOutputCAFixed {
-                    // FIXME non-trivial fixed refs set
-                    .ca = contentAddressFromMethodHashAndRefs(
-                        method, std::move(hash), {}),
-                },
+            return DerivationOutput::CAFixed {
+                // FIXME non-trivial fixed refs set
+                .ca = contentAddressFromMethodHashAndRefs(
+                    method, std::move(hash), {}),
             };
         } else {
             settings.requireExperimentalFeature(Xp::CaDerivations);
             assert(pathS == "");
-            return DerivationOutput {
-                .output = DerivationOutputCAFloating {
-                    .method = std::move(method),
-                    .hashType = std::move(hashType),
-                },
+            return DerivationOutput::CAFloating {
+                .method = std::move(method),
+                .hashType = std::move(hashType),
             };
         }
     } else {
         if (pathS == "") {
-            return DerivationOutput {
-                .output = DerivationOutputDeferred { }
-            };
+            return DerivationOutput::Deferred { };
         }
         validatePath(pathS);
-        return DerivationOutput {
-            .output = DerivationOutputInputAddressed {
-                .path = store.parseStorePath(pathS),
-            }
+        return DerivationOutput::InputAddressed {
+            .path = store.parseStorePath(pathS),
         };
     }
 }
@@ -333,27 +324,27 @@ std::string Derivation::unparse(const Store & store, bool maskOutputs,
         if (first) first = false; else s += ',';
         s += '('; printUnquotedString(s, i.first);
         std::visit(overloaded {
-            [&](const DerivationOutputInputAddressed & doi) {
+            [&](const DerivationOutput::InputAddressed & doi) {
                 s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(doi.path));
                 s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, "");
             },
-            [&](const DerivationOutputCAFixed & dof) {
+            [&](const DerivationOutput::CAFixed & dof) {
                 s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(dof.path(store, name, i.first)));
                 s += ','; printUnquotedString(s, printMethodAlgo(dof.ca));
                 s += ','; printUnquotedString(s, getContentAddressHash(dof.ca).to_string(Base16, false));
             },
-            [&](const DerivationOutputCAFloating & dof) {
+            [&](const DerivationOutput::CAFloating & dof) {
                 s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, makeContentAddressingPrefix(dof.method) + printHashType(dof.hashType));
                 s += ','; printUnquotedString(s, "");
             },
-            [&](const DerivationOutputDeferred &) {
+            [&](const DerivationOutput::Deferred &) {
                 s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, "");
             }
-        }, i.second.output);
+        }, i.second.raw());
         s += ')';
     }
 
@@ -421,13 +412,13 @@ DerivationType BasicDerivation::type() const
     std::optional<HashType> floatingHashType;
     for (auto & i : outputs) {
         std::visit(overloaded {
-            [&](const DerivationOutputInputAddressed &) {
+            [&](const DerivationOutput::InputAddressed &) {
                inputAddressedOutputs.insert(i.first);
             },
-            [&](const DerivationOutputCAFixed &) {
+            [&](const DerivationOutput::CAFixed &) {
                 fixedCAOutputs.insert(i.first);
             },
-            [&](const DerivationOutputCAFloating & dof) {
+            [&](const DerivationOutput::CAFloating & dof) {
                 floatingCAOutputs.insert(i.first);
                 if (!floatingHashType) {
                     floatingHashType = dof.hashType;
@@ -436,27 +427,37 @@ DerivationType BasicDerivation::type() const
                         throw Error("All floating outputs must use the same hash type");
                 }
             },
-            [&](const DerivationOutputDeferred &) {
+            [&](const DerivationOutput::Deferred &) {
                deferredIAOutputs.insert(i.first);
             },
-        }, i.second.output);
+        }, i.second.raw());
     }
 
     if (inputAddressedOutputs.empty() && fixedCAOutputs.empty() && floatingCAOutputs.empty() && deferredIAOutputs.empty()) {
         throw Error("Must have at least one output");
     } else if (! inputAddressedOutputs.empty() && fixedCAOutputs.empty() && floatingCAOutputs.empty() && deferredIAOutputs.empty()) {
-        return DerivationType::InputAddressed;
+        return DerivationType::InputAddressed {
+            .deferred = false,
+        };
     } else if (inputAddressedOutputs.empty() && ! fixedCAOutputs.empty() && floatingCAOutputs.empty() && deferredIAOutputs.empty()) {
         if (fixedCAOutputs.size() > 1)
             // FIXME: Experimental feature?
             throw Error("Only one fixed output is allowed for now");
         if (*fixedCAOutputs.begin() != "out")
             throw Error("Single fixed output must be named \"out\"");
-        return DerivationType::CAFixed;
+        return DerivationType::ContentAddressed {
+            .pure = false,
+            .fixed = true,
+        };
     } else if (inputAddressedOutputs.empty() && fixedCAOutputs.empty() && ! floatingCAOutputs.empty() && deferredIAOutputs.empty()) {
-        return DerivationType::CAFloating;
+        return DerivationType::ContentAddressed {
+            .pure = true,
+            .fixed = false,
+        };
     } else if (inputAddressedOutputs.empty() && fixedCAOutputs.empty() && floatingCAOutputs.empty() && !deferredIAOutputs.empty()) {
-        return DerivationType::DeferredInputAddressed;
+        return DerivationType::InputAddressed {
+            .deferred = true,
+        };
     } else {
         throw Error("Can't mix derivation output types");
     }
@@ -508,13 +509,13 @@ static const DrvHashModulo pathDerivationModulo(Store & store, const StorePath &
  */
 DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool maskOutputs)
 {
-    bool isDeferred = false;
+    auto type = drv.type();
+
     /* Return a fixed hash for fixed-output derivations. */
-    switch (drv.type()) {
-    case DerivationType::CAFixed: {
+    if (type.isFixed()) {
         std::map<std::string, Hash> outputHashes;
         for (const auto & i : drv.outputs) {
-            auto & dof = std::get<DerivationOutputCAFixed>(i.second.output);
+            auto & dof = std::get<DerivationOutput::CAFixed>(i.second.raw());
             auto hash = hashString(htSHA256, "fixed:out:"
                 + printMethodAlgo(dof.ca) + ":"
                 + getContentAddressHash(dof.ca).to_string(Base16, false) + ":"
@@ -523,33 +524,37 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
         }
         return outputHashes;
     }
-    case DerivationType::CAFloating:
-        isDeferred = true;
-        break;
-    case DerivationType::InputAddressed:
-        break;
-    case DerivationType::DeferredInputAddressed:
-        break;
-    }
+
+    auto kind = std::visit(overloaded {
+        [](const DerivationType::InputAddressed & ia) {
+            /* This might be a "pesimistically" deferred output, so we don't
+               "taint" the kind yet. */
+            return DrvHash::Kind::Regular;
+        },
+        [](const DerivationType::ContentAddressed & ca) {
+            return ca.fixed
+                ? DrvHash::Kind::Regular
+                : DrvHash::Kind::Deferred;
+        },
+    }, drv.type().raw());
 
     /* For other derivations, replace the inputs paths with recursive
        calls to this function. */
     std::map<std::string, StringSet> inputs2;
-    for (auto & i : drv.inputDrvs) {
-        const auto & res = pathDerivationModulo(store, i.first);
+    for (auto & [drvPath, inputOutputs0] : drv.inputDrvs) {
+        // Avoid lambda capture restriction with standard / Clang
+        auto & inputOutputs = inputOutputs0;
+        const auto & res = pathDerivationModulo(store, drvPath);
         std::visit(overloaded {
             // Regular non-CA derivation, replace derivation
-            [&](const Hash & drvHash) {
-                inputs2.insert_or_assign(drvHash.to_string(Base16, false), i.second);
-            },
-            [&](const DeferredHash & deferredHash) {
-                isDeferred = true;
-                inputs2.insert_or_assign(deferredHash.hash.to_string(Base16, false), i.second);
+            [&](const DrvHash & drvHash) {
+                kind |= drvHash.kind;
+                inputs2.insert_or_assign(drvHash.hash.to_string(Base16, false), inputOutputs);
             },
             // CA derivation's output hashes
             [&](const CaOutputHashes & outputHashes) {
                 std::set<std::string> justOut = { "out" };
-                for (auto & output : i.second) {
+                for (auto & output : inputOutputs) {
                     /* Put each one in with a single "out" output.. */
                     const auto h = outputHashes.at(output);
                     inputs2.insert_or_assign(
@@ -557,15 +562,24 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
                         justOut);
                 }
             },
-        }, res);
+        }, res.raw());
     }
 
     auto hash = hashString(htSHA256, drv.unparse(store, maskOutputs, &inputs2));
 
-    if (isDeferred)
-        return DeferredHash { hash };
-    else
-        return hash;
+    return DrvHash { .hash = hash, .kind = kind };
+}
+
+
+void operator |= (DrvHash::Kind & self, const DrvHash::Kind & other) noexcept
+{
+    switch (other) {
+    case DrvHash::Kind::Regular:
+        break;
+    case DrvHash::Kind::Deferred:
+        self = other;
+        break;
+    }
 }
 
 
@@ -573,20 +587,15 @@ std::map<std::string, Hash> staticOutputHashes(Store & store, const Derivation &
 {
     std::map<std::string, Hash> res;
     std::visit(overloaded {
-        [&](const Hash & drvHash) {
-            for (auto & outputName : drv.outputNames()) {
-                res.insert({outputName, drvHash});
-            }
-        },
-        [&](const DeferredHash & deferredHash) {
+        [&](const DrvHash & drvHash) {
             for (auto & outputName : drv.outputNames()) {
-                res.insert({outputName, deferredHash.hash});
+                res.insert({outputName, drvHash.hash});
             }
         },
         [&](const CaOutputHashes & outputHashes) {
             res = outputHashes;
         },
-    }, hashDerivationModulo(store, drv, true));
+    }, hashDerivationModulo(store, drv, true).raw());
     return res;
 }
 
@@ -667,27 +676,27 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
     for (auto & i : drv.outputs) {
         out << i.first;
         std::visit(overloaded {
-            [&](const DerivationOutputInputAddressed & doi) {
+            [&](const DerivationOutput::InputAddressed & doi) {
                 out << store.printStorePath(doi.path)
                     << ""
                     << "";
             },
-            [&](const DerivationOutputCAFixed & dof) {
+            [&](const DerivationOutput::CAFixed & dof) {
                 out << store.printStorePath(dof.path(store, drv.name, i.first))
                     << printMethodAlgo(dof.ca)
                     << getContentAddressHash(dof.ca).to_string(Base16, false);
             },
-            [&](const DerivationOutputCAFloating & dof) {
+            [&](const DerivationOutput::CAFloating & dof) {
                 out << ""
                     << (makeContentAddressingPrefix(dof.method) + printHashType(dof.hashType))
                     << "";
             },
-            [&](const DerivationOutputDeferred &) {
+            [&](const DerivationOutput::Deferred &) {
                 out << ""
                     << ""
                     << "";
             },
-        }, i.second.output);
+        }, i.second.raw());
     }
     worker_proto::write(store, out, drv.inputSrcs);
     out << drv.platform << drv.builder << drv.args;
@@ -735,45 +744,63 @@ static void rewriteDerivation(Store & store, BasicDerivation & drv, const String
 
     auto hashModulo = hashDerivationModulo(store, Derivation(drv), true);
     for (auto & [outputName, output] : drv.outputs) {
-        if (std::holds_alternative<DerivationOutputDeferred>(output.output)) {
-            Hash h = std::get<Hash>(hashModulo);
+        if (std::holds_alternative<DerivationOutput::Deferred>(output.raw())) {
+            auto & h = hashModulo.requireNoFixedNonDeferred();
             auto outPath = store.makeOutputPath(outputName, h, drv.name);
             drv.env[outputName] = store.printStorePath(outPath);
-            output = DerivationOutput {
-                .output = DerivationOutputInputAddressed {
-                    .path = std::move(outPath),
-                },
+            output = DerivationOutput::InputAddressed {
+                .path = std::move(outPath),
             };
         }
     }
 
 }
 
+const Hash & DrvHashModulo::requireNoFixedNonDeferred() const {
+    auto * drvHashOpt = std::get_if<DrvHash>(&raw());
+    assert(drvHashOpt);
+    assert(drvHashOpt->kind == DrvHash::Kind::Regular);
+    return drvHashOpt->hash;
+}
+
+static bool tryResolveInput(
+    Store & store, StorePathSet & inputSrcs, StringMap & inputRewrites,
+    const StorePath & inputDrv, const StringSet & inputOutputs)
+{
+    auto inputDrvOutputs = store.queryPartialDerivationOutputMap(inputDrv);
+
+    auto getOutput = [&](const std::string & outputName) {
+        auto & actualPathOpt = inputDrvOutputs.at(outputName);
+        if (!actualPathOpt)
+            warn("output %s of input %s missing, aborting the resolving",
+                outputName,
+                store.printStorePath(inputDrv)
+            );
+        return actualPathOpt;
+    };
+
+    for (auto & outputName : inputOutputs) {
+        auto actualPathOpt = getOutput(outputName);
+        if (!actualPathOpt) return false;
+        auto actualPath = *actualPathOpt;
+        inputRewrites.emplace(
+            downstreamPlaceholder(store, inputDrv, outputName),
+            store.printStorePath(actualPath));
+        inputSrcs.insert(std::move(actualPath));
+    }
+
+    return true;
+}
+
 std::optional<BasicDerivation> Derivation::tryResolve(Store & store) {
     BasicDerivation resolved { *this };
 
     // Input paths that we'll want to rewrite in the derivation
     StringMap inputRewrites;
 
-    for (auto & input : inputDrvs) {
-        auto inputDrvOutputs = store.queryPartialDerivationOutputMap(input.first);
-        StringSet newOutputNames;
-        for (auto & outputName : input.second) {
-            auto actualPathOpt = inputDrvOutputs.at(outputName);
-            if (!actualPathOpt) {
-                warn("output %s of input %s missing, aborting the resolving",
-                    outputName,
-                    store.printStorePath(input.first)
-                );
-                return std::nullopt;
-            }
-            auto actualPath = *actualPathOpt;
-            inputRewrites.emplace(
-                downstreamPlaceholder(store, input.first, outputName),
-                store.printStorePath(actualPath));
-            resolved.inputSrcs.insert(std::move(actualPath));
-        }
-    }
+    for (auto & [inputDrv, inputOutputs] : inputDrvs)
+        if (!tryResolveInput(store, resolved.inputSrcs, inputRewrites, inputDrv, inputOutputs))
+            return std::nullopt;
 
     rewriteDerivation(store, resolved, inputRewrites);
 
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index f59887465..f41a9d93b 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -4,6 +4,7 @@
 #include "types.hh"
 #include "hash.hh"
 #include "content-address.hh"
+#include "repair-flag.hh"
 #include "sync.hh"
 
 #include <map>
@@ -44,19 +45,31 @@ struct DerivationOutputCAFloating
  */
 struct DerivationOutputDeferred {};
 
-struct DerivationOutput
+typedef std::variant<
+    DerivationOutputInputAddressed,
+    DerivationOutputCAFixed,
+    DerivationOutputCAFloating,
+    DerivationOutputDeferred
+> _DerivationOutputRaw;
+
+struct DerivationOutput : _DerivationOutputRaw
 {
-    std::variant<
-        DerivationOutputInputAddressed,
-        DerivationOutputCAFixed,
-        DerivationOutputCAFloating,
-        DerivationOutputDeferred
-    > output;
+    using Raw = _DerivationOutputRaw;
+    using Raw::Raw;
+
+    using InputAddressed = DerivationOutputInputAddressed;
+    using CAFixed = DerivationOutputCAFixed;
+    using CAFloating = DerivationOutputCAFloating;
+    using Deferred = DerivationOutputDeferred;
 
     /* Note, when you use this function you should make sure that you're passing
        the right derivation name. When in doubt, you should use the safer
        interface provided by BasicDerivation::outputsAndOptPaths */
     std::optional<StorePath> path(const Store & store, std::string_view drvName, std::string_view outputName) const;
+
+    inline const Raw & raw() const {
+        return static_cast<const Raw &>(*this);
+    }
 };
 
 typedef std::map<std::string, DerivationOutput> DerivationOutputs;
@@ -72,30 +85,50 @@ typedef std::map<std::string, std::pair<DerivationOutput, std::optional<StorePat
    output IDs we are interested in. */
 typedef std::map<StorePath, StringSet> DerivationInputs;
 
-enum struct DerivationType : uint8_t {
-    InputAddressed,
-    DeferredInputAddressed,
-    CAFixed,
-    CAFloating,
+struct DerivationType_InputAddressed {
+    bool deferred;
 };
 
-/* Do the outputs of the derivation have paths calculated from their content,
-   or from the derivation itself? */
-bool derivationIsCA(DerivationType);
-
-/* Is the content of the outputs fixed a-priori via a hash? Never true for
-   non-CA derivations. */
-bool derivationIsFixed(DerivationType);
-
-/* Is the derivation impure and needs to access non-deterministic resources, or
-   pure and can be sandboxed? Note that whether or not we actually sandbox the
-   derivation is controlled separately. Never true for non-CA derivations. */
-bool derivationIsImpure(DerivationType);
+struct DerivationType_ContentAddressed {
+    bool pure;
+    bool fixed;
+};
 
-/* Does the derivation knows its own output paths?
- * Only true when there's no floating-ca derivation involved in the closure.
- */
-bool derivationHasKnownOutputPaths(DerivationType);
+typedef std::variant<
+    DerivationType_InputAddressed,
+    DerivationType_ContentAddressed
+> _DerivationTypeRaw;
+
+struct DerivationType : _DerivationTypeRaw {
+    using Raw = _DerivationTypeRaw;
+    using Raw::Raw;
+    using InputAddressed = DerivationType_InputAddressed;
+    using ContentAddressed = DerivationType_ContentAddressed;
+
+
+    /* Do the outputs of the derivation have paths calculated from their content,
+       or from the derivation itself? */
+    bool isCA() const;
+
+    /* Is the content of the outputs fixed a-priori via a hash? Never true for
+       non-CA derivations. */
+    bool isFixed() const;
+
+    /* Is the derivation impure and needs to access non-deterministic resources, or
+       pure and can be sandboxed? Note that whether or not we actually sandbox the
+       derivation is controlled separately. Never true for non-CA derivations. */
+    bool isImpure() const;
+
+    /* Does the derivation knows its own output paths?
+       Only true when there's no floating-ca derivation involved in the
+       closure, or if fixed output.
+     */
+    bool hasKnownOutputPaths() const;
+
+    inline const Raw & raw() const {
+        return static_cast<const Raw &>(*this);
+    }
+};
 
 struct BasicDerivation
 {
@@ -150,8 +183,6 @@ struct Derivation : BasicDerivation
 
 class Store;
 
-enum RepairFlag : bool { NoRepair = false, Repair = true };
-
 /* Write a derivation to the Nix store, and return its path. */
 StorePath writeDerivation(Store & store,
     const Derivation & drv,
@@ -175,13 +206,43 @@ std::string outputPathName(std::string_view drvName, std::string_view outputName
 // whose output hashes are always known since they are fixed up-front.
 typedef std::map<std::string, Hash> CaOutputHashes;
 
-struct DeferredHash { Hash hash; };
+struct DrvHash {
+    Hash hash;
+
+    enum struct Kind: bool {
+        // Statically determined derivations.
+        // This hash will be directly used to compute the output paths
+        Regular,
+        // Floating-output derivations (and their reverse dependencies).
+        Deferred,
+    };
+
+    Kind kind;
+};
+
+void operator |= (DrvHash::Kind & self, const DrvHash::Kind & other) noexcept;
 
 typedef std::variant<
-    Hash, // regular DRV normalized hash
-    CaOutputHashes, // Fixed-output derivation hashes
-    DeferredHash // Deferred hashes for floating outputs drvs and their dependencies
-> DrvHashModulo;
+    // Regular normalized derivation hash, and whether it was deferred (because
+    // an ancestor derivation is a floating content addressed derivation).
+    DrvHash,
+    // Fixed-output derivation hashes
+    CaOutputHashes
+> _DrvHashModuloRaw;
+
+struct DrvHashModulo : _DrvHashModuloRaw {
+    using Raw = _DrvHashModuloRaw;
+    using Raw::Raw;
+
+    /* Get hash, throwing if it is per-output CA hashes or a
+       deferred Drv hash.
+     */
+    const Hash & requireNoFixedNonDeferred() const;
+
+    inline const Raw & raw() const {
+        return static_cast<const Raw &>(*this);
+    }
+};
 
 /* Returns hashes with the details of fixed-output subderivations
    expunged.
diff --git a/src/libstore/derived-path.cc b/src/libstore/derived-path.cc
index 194489580..319b1c790 100644
--- a/src/libstore/derived-path.cc
+++ b/src/libstore/derived-path.cc
@@ -1,4 +1,5 @@
 #include "derived-path.hh"
+#include "derivations.hh"
 #include "store-api.hh"
 
 #include <nlohmann/json.hpp>
@@ -11,6 +12,21 @@ nlohmann::json DerivedPath::Opaque::toJSON(ref<Store> store) const {
     return res;
 }
 
+nlohmann::json DerivedPath::Built::toJSON(ref<Store> store) const {
+    nlohmann::json res;
+    res["drvPath"] = store->printStorePath(drvPath);
+    // Fallback for the input-addressed derivation case: We expect to always be
+    // able to print the output paths, so let’s do it
+    auto knownOutputs = store->queryPartialDerivationOutputMap(drvPath);
+    for (const auto& output : outputs) {
+        if (knownOutputs.at(output))
+            res["outputs"][output] = store->printStorePath(knownOutputs.at(output).value());
+        else
+            res["outputs"][output] = nullptr;
+    }
+    return res;
+}
+
 nlohmann::json BuiltPath::Built::toJSON(ref<Store> store) const {
     nlohmann::json res;
     res["drvPath"] = store->printStorePath(drvPath);
@@ -35,16 +51,22 @@ StorePathSet BuiltPath::outPaths() const
     );
 }
 
-nlohmann::json derivedPathsWithHintsToJSON(const BuiltPaths & buildables, ref<Store> store) {
+template<typename T>
+nlohmann::json stuffToJSON(const std::vector<T> & ts, ref<Store> store) {
     auto res = nlohmann::json::array();
-    for (const BuiltPath & buildable : buildables) {
-        std::visit([&res, store](const auto & buildable) {
-            res.push_back(buildable.toJSON(store));
-        }, buildable.raw());
+    for (const T & t : ts) {
+        std::visit([&res, store](const auto & t) {
+            res.push_back(t.toJSON(store));
+        }, t.raw());
     }
     return res;
 }
 
+nlohmann::json derivedPathsWithHintsToJSON(const BuiltPaths & buildables, ref<Store> store)
+{ return stuffToJSON<BuiltPath>(buildables, store); }
+nlohmann::json derivedPathsToJSON(const DerivedPaths & paths, ref<Store> store)
+{ return stuffToJSON<DerivedPath>(paths, store); }
+
 
 std::string DerivedPath::Opaque::to_string(const Store & store) const {
     return store.printStorePath(path);
diff --git a/src/libstore/derived-path.hh b/src/libstore/derived-path.hh
index ef7c5326c..5a38203ae 100644
--- a/src/libstore/derived-path.hh
+++ b/src/libstore/derived-path.hh
@@ -46,6 +46,7 @@ struct DerivedPathBuilt {
 
     std::string to_string(const Store & store) const;
     static DerivedPathBuilt parse(const Store & store, std::string_view);
+    nlohmann::json toJSON(ref<Store> store) const;
 };
 
 using _DerivedPathRaw = std::variant<
@@ -120,5 +121,6 @@ typedef std::vector<DerivedPath> DerivedPaths;
 typedef std::vector<BuiltPath> BuiltPaths;
 
 nlohmann::json derivedPathsWithHintsToJSON(const BuiltPaths & buildables, ref<Store> store);
+nlohmann::json derivedPathsToJSON(const DerivedPaths & , ref<Store> store);
 
 }
diff --git a/src/libstore/gc-store.cc b/src/libstore/gc-store.cc
deleted file mode 100644
index 3dbdec53b..000000000
--- a/src/libstore/gc-store.cc
+++ /dev/null
@@ -1,13 +0,0 @@
-#include "gc-store.hh"
-
-namespace nix {
-
-GcStore & requireGcStore(Store & store)
-{
-    auto * gcStore = dynamic_cast<GcStore *>(&store);
-    if (!gcStore)
-        throw UsageError("Garbage collection not supported by this store");
-    return *gcStore;
-}
-
-}
diff --git a/src/libstore/gc-store.hh b/src/libstore/gc-store.hh
index 829f70dc4..b3cbbad74 100644
--- a/src/libstore/gc-store.hh
+++ b/src/libstore/gc-store.hh
@@ -61,6 +61,8 @@ struct GCResults
 
 struct GcStore : public virtual Store
 {
+    inline static std::string operationName = "Garbage collection";
+
     /* Add an indirect root, which is merely a symlink to `path' from
        /nix/var/nix/gcroots/auto/<hash of `path'>.  `path' is supposed
        to be a symlink to a store path.  The garbage collector will
@@ -79,6 +81,4 @@ struct GcStore : public virtual Store
     virtual void collectGarbage(const GCOptions & options, GCResults & results) = 0;
 };
 
-GcStore & requireGcStore(Store & store);
-
 }
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 024da66c1..f65fb1b2e 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -678,7 +678,8 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
                 alive.insert(start);
                 try {
                     StorePathSet closure;
-                    computeFSClosure(*path, closure);
+                    computeFSClosure(*path, closure,
+                        /* flipDirection */ false, gcKeepOutputs, gcKeepDerivations);
                     for (auto & p : closure)
                         alive.insert(p);
                 } catch (InvalidPath &) { }
@@ -841,7 +842,8 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
             if (unlink(path.c_str()) == -1)
                 throw SysError("deleting '%1%'", path);
 
-            results.bytesFreed += st.st_size;
+            /* Do not accound for deleted file here. Rely on deletePath()
+               accounting.  */
         }
 
         struct stat st;
diff --git a/src/libstore/local-fs-store.hh b/src/libstore/local-fs-store.hh
index fbd49dc2c..e6fb3201a 100644
--- a/src/libstore/local-fs-store.hh
+++ b/src/libstore/local-fs-store.hh
@@ -2,6 +2,7 @@
 
 #include "store-api.hh"
 #include "gc-store.hh"
+#include "log-store.hh"
 
 namespace nix {
 
@@ -24,7 +25,10 @@ struct LocalFSStoreConfig : virtual StoreConfig
         "physical path to the Nix store"};
 };
 
-class LocalFSStore : public virtual LocalFSStoreConfig, public virtual Store, virtual GcStore
+class LocalFSStore : public virtual LocalFSStoreConfig,
+    public virtual Store,
+    public virtual GcStore,
+    public virtual LogStore
 {
 public:
 
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 52ca5a34a..9c0d482f7 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -698,11 +698,11 @@ void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivat
     std::optional<Hash> h;
     for (auto & i : drv.outputs) {
         std::visit(overloaded {
-            [&](const DerivationOutputInputAddressed & doia) {
+            [&](const DerivationOutput::InputAddressed & doia) {
                 if (!h) {
                     // somewhat expensive so we do lazily
-                    auto temp = hashDerivationModulo(*this, drv, true);
-                    h = std::get<Hash>(temp);
+                    auto h0 = hashDerivationModulo(*this, drv, true);
+                    h = h0.requireNoFixedNonDeferred();
                 }
                 StorePath recomputed = makeOutputPath(i.first, *h, drvName);
                 if (doia.path != recomputed)
@@ -710,16 +710,17 @@ void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivat
                         printStorePath(drvPath), printStorePath(doia.path), printStorePath(recomputed));
                 envHasRightPath(doia.path, i.first);
             },
-            [&](const DerivationOutputCAFixed & dof) {
+            [&](const DerivationOutput::CAFixed & dof) {
                 auto path = dof.path(*this, drvName, i.first);
                 envHasRightPath(path, i.first);
             },
-            [&](const DerivationOutputCAFloating &) {
+            [&](const DerivationOutput::CAFloating &) {
                 /* Nothing to check */
             },
-            [&](const DerivationOutputDeferred &) {
+            [&](const DerivationOutput::Deferred &) {
+                /* Nothing to check */
             },
-        }, i.second.output);
+        }, i.second.raw());
     }
 }
 
diff --git a/src/libstore/log-store.hh b/src/libstore/log-store.hh
new file mode 100644
index 000000000..ff1b92e17
--- /dev/null
+++ b/src/libstore/log-store.hh
@@ -0,0 +1,21 @@
+#pragma once
+
+#include "store-api.hh"
+
+
+namespace nix {
+
+struct LogStore : public virtual Store
+{
+    inline static std::string operationName = "Build log storage and retrieval";
+
+    /* Return the build log of the specified store path, if available,
+       or null otherwise. */
+    virtual std::optional<std::string> getBuildLog(const StorePath & path) = 0;
+
+    virtual void addBuildLog(const StorePath & path, std::string_view log) = 0;
+
+    static LogStore & require(Store & store);
+};
+
+}
diff --git a/src/libstore/make-content-addressed.cc b/src/libstore/make-content-addressed.cc
new file mode 100644
index 000000000..9655a0555
--- /dev/null
+++ b/src/libstore/make-content-addressed.cc
@@ -0,0 +1,83 @@
+#include "make-content-addressed.hh"
+#include "references.hh"
+
+namespace nix {
+
+std::map<StorePath, StorePath> makeContentAddressed(
+    Store & srcStore,
+    Store & dstStore,
+    const StorePathSet & storePaths)
+{
+    StorePathSet closure;
+    srcStore.computeFSClosure(storePaths, closure);
+
+    auto paths = srcStore.topoSortPaths(closure);
+
+    std::reverse(paths.begin(), paths.end());
+
+    std::map<StorePath, StorePath> remappings;
+
+    for (auto & path : paths) {
+        auto pathS = srcStore.printStorePath(path);
+        auto oldInfo = srcStore.queryPathInfo(path);
+        std::string oldHashPart(path.hashPart());
+
+        StringSink sink;
+        srcStore.narFromPath(path, sink);
+
+        StringMap rewrites;
+
+        PathReferences<StorePath> refs;
+        refs.hasSelfReference = oldInfo->hasSelfReference;
+        for (auto & ref : oldInfo->references) {
+            auto i = remappings.find(ref);
+            auto replacement = i != remappings.end() ? i->second : ref;
+            // FIXME: warn about unremapped paths?
+            if (replacement != ref) {
+                rewrites.insert_or_assign(srcStore.printStorePath(ref), srcStore.printStorePath(replacement));
+                refs.references.insert(std::move(replacement));
+            }
+        }
+
+        sink.s = rewriteStrings(sink.s, rewrites);
+
+        HashModuloSink hashModuloSink(htSHA256, oldHashPart);
+        hashModuloSink(sink.s);
+
+        auto narModuloHash = hashModuloSink.finish().first;
+
+        ValidPathInfo info {
+            dstStore,
+            StorePathDescriptor {
+                .name = std::string { path.name() },
+                .info = FixedOutputInfo {
+                    {
+                        .method = FileIngestionMethod::Recursive,
+                        .hash = narModuloHash,
+                    },
+                    std::move(refs),
+                },
+            },
+            Hash::dummy,
+        };
+
+        printInfo("rewriting '%s' to '%s'", pathS, dstStore.printStorePath(info.path));
+
+        StringSink sink2;
+        RewritingSink rsink2(oldHashPart, std::string(info.path.hashPart()), sink2);
+        rsink2(sink.s);
+        rsink2.flush();
+
+        info.narHash = hashString(htSHA256, sink2.s);
+        info.narSize = sink.s.size();
+
+        StringSource source(sink2.s);
+        dstStore.addToStore(info, source);
+
+        remappings.insert_or_assign(std::move(path), std::move(info.path));
+    }
+
+    return remappings;
+}
+
+}
diff --git a/src/libstore/make-content-addressed.hh b/src/libstore/make-content-addressed.hh
new file mode 100644
index 000000000..c4a66ed41
--- /dev/null
+++ b/src/libstore/make-content-addressed.hh
@@ -0,0 +1,12 @@
+#pragma once
+
+#include "store-api.hh"
+
+namespace nix {
+
+std::map<StorePath, StorePath> makeContentAddressed(
+    Store & srcStore,
+    Store & dstStore,
+    const StorePathSet & storePaths);
+
+}
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index e411cbe04..42965d66e 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -87,7 +87,7 @@ std::optional<ContentAddress> getDerivationCA(const BasicDerivation & drv)
     auto out = drv.outputs.find("out");
     if (out == drv.outputs.end())
         return std::nullopt;
-    if (auto dof = std::get_if<DerivationOutputCAFixed>(&out->second.output)) {
+    if (auto dof = std::get_if<DerivationOutput::CAFixed>(&out->second)) {
         return std::visit(overloaded {
             [&](const TextInfo & ti) -> std::optional<ContentAddress> {
                 if (!ti.references.empty())
diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index 8c65053e4..f2288a04e 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -93,7 +93,7 @@ StringSet ParsedDerivation::getRequiredSystemFeatures() const
     StringSet res;
     for (auto & i : getStringsAttr("requiredSystemFeatures").value_or(Strings()))
         res.insert(i);
-    if (!derivationHasKnownOutputPaths(drv.type()))
+    if (!drv.type().hasKnownOutputPaths())
         res.insert("ca-derivations");
     return res;
 }
diff --git a/src/libstore/parsed-derivations.hh b/src/libstore/parsed-derivations.hh
index effcf099d..95bec21e8 100644
--- a/src/libstore/parsed-derivations.hh
+++ b/src/libstore/parsed-derivations.hh
@@ -1,5 +1,6 @@
 #pragma once
 
+#include "derivations.hh"
 #include "store-api.hh"
 
 #include <nlohmann/json_fwd.hpp>
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index eb74d88c9..961d1bc08 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -5,6 +5,7 @@
 
 #include "store-api.hh"
 #include "gc-store.hh"
+#include "log-store.hh"
 
 
 namespace nix {
@@ -30,7 +31,10 @@ struct RemoteStoreConfig : virtual StoreConfig
 
 /* FIXME: RemoteStore is a misnomer - should be something like
    DaemonStore. */
-class RemoteStore : public virtual RemoteStoreConfig, public virtual Store, public virtual GcStore
+class RemoteStore : public virtual RemoteStoreConfig,
+    public virtual Store,
+    public virtual GcStore,
+    public virtual LogStore
 {
 public:
 
diff --git a/src/libstore/repair-flag.hh b/src/libstore/repair-flag.hh
new file mode 100644
index 000000000..a13cda312
--- /dev/null
+++ b/src/libstore/repair-flag.hh
@@ -0,0 +1,7 @@
+#pragma once
+
+namespace nix {
+
+enum RepairFlag : bool { NoRepair = false, Repair = true };
+
+}
diff --git a/src/libstore/ssh-store.cc b/src/libstore/ssh-store.cc
index bb03daef4..62daa838c 100644
--- a/src/libstore/ssh-store.cc
+++ b/src/libstore/ssh-store.cc
@@ -52,6 +52,10 @@ public:
     bool sameMachine() override
     { return false; }
 
+    // FIXME extend daemon protocol, move implementation to RemoteStore
+    std::optional<std::string> getBuildLog(const StorePath & path) override
+    { unsupported("getBuildLog"); }
+
 private:
 
     struct Connection : RemoteStore::Connection
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 6f4b6b98c..4362177f9 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -1,6 +1,7 @@
 #include "crypto.hh"
 #include "fs-accessor.hh"
 #include "globals.hh"
+#include "derivations.hh"
 #include "store-api.hh"
 #include "util.hh"
 #include "nar-info-disk-cache.hh"
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 1a320bcb1..5ea606886 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -10,8 +10,8 @@
 #include "sync.hh"
 #include "globals.hh"
 #include "config.hh"
-#include "derivations.hh"
 #include "path-info.hh"
+#include "repair-flag.hh"
 
 #include <atomic>
 #include <limits>
@@ -62,6 +62,8 @@ MakeError(BadStorePath, Error);
 
 MakeError(InvalidStoreURI, Error);
 
+struct BasicDerivation;
+struct Derivation;
 class FSAccessor;
 class NarInfoDiskCache;
 class Store;
@@ -601,14 +603,6 @@ public:
      */
     StorePathSet exportReferences(const StorePathSet & storePaths, const StorePathSet & inputPaths);
 
-    /* Return the build log of the specified store path, if available,
-       or null otherwise. */
-    virtual std::optional<std::string> getBuildLog(const StorePath & path)
-    { return std::nullopt; }
-
-    virtual void addBuildLog(const StorePath & path, std::string_view log)
-    { unsupported("addBuildLog"); }
-
     /* Hack to allow long-running processes like hydra-queue-runner to
        occasionally flush their path info cache. */
     void clearPathInfoCache()
diff --git a/src/libstore/store-cast.hh b/src/libstore/store-cast.hh
new file mode 100644
index 000000000..ff62fc359
--- /dev/null
+++ b/src/libstore/store-cast.hh
@@ -0,0 +1,16 @@
+#pragma once
+
+#include "store-api.hh"
+
+namespace nix {
+
+template<typename T>
+T & require(Store & store)
+{
+    auto * castedStore = dynamic_cast<T *>(&store);
+    if (!castedStore)
+        throw UsageError("%s not supported by store '%s'", T::operationName, store.getUri());
+    return *castedStore;
+}
+
+}