Make building only require a LocalFSStore

This is the crucial first step to allowing client-side building --- i.e.
building locally but using some form of RPC to manipulate metadata
rather than interact with a concrete form of persisting metadata like
the SQLite database.

To facilitate this, a few methods were hastily moved from `LocalStore`
to `LocalFSStore`. We should not just accept that as good enough to
merge, but carefully consider the trust/security implications of this,
and the proper division of labor between the less-trusted "builder" and
the more-trusted "store".

src/libstore/build/derivation-goal.cc

@@ -668,7 +668,7 @@ void DerivationGoal::tryToBuild()
     PathSet lockFiles;
     /* FIXME: Should lock something like the drv itself so we don't build same
        CA drv concurrently */
-    if (dynamic_cast<LocalStore *>(&worker.store)) {
+    if (dynamic_cast<LocalFSStore *>(&worker.store)) {
         /* If we aren't a local store, we might need to use the local store as
            a build remote, but that would cause a deadlock. */
         /* FIXME: Make it so we can use ourselves as a build remote even if we
@@ -1240,7 +1240,7 @@ Path DerivationGoal::openLogFile()
 
     /* Create a log file. */
     Path logDir;
-    if (auto localStore = dynamic_cast<LocalStore *>(&worker.store))
+    if (auto localStore = dynamic_cast<LocalFSStore *>(&worker.store))
         logDir = localStore->logDir;
     else
         logDir = settings.nixLogDir;

src/libstore/build/local-derivation-goal.cc

@@ -121,9 +121,9 @@ inline bool LocalDerivationGoal::needsHashRewrite()
 }
 
 
-LocalStore & LocalDerivationGoal::getLocalStore()
+LocalFSStore & LocalDerivationGoal::getLocalFSStore()
 {
-    auto p = dynamic_cast<LocalStore *>(&worker.store);
+    auto p = dynamic_cast<LocalFSStore *>(&worker.store);
     assert(p);
     return *p;
 }
@@ -204,7 +204,7 @@ void LocalDerivationGoal::tryLocalBuild()
             useChroot = derivationType->isSandboxed() && !noChroot;
     }
 
-    auto & localStore = getLocalStore();
+    auto & localStore = getLocalFSStore();
     if (localStore.storeDir != localStore.realStoreDir.get()) {
         #if __linux__
             useChroot = true;
@@ -343,7 +343,7 @@ bool LocalDerivationGoal::cleanupDecideWhetherDiskFull()
        so, we don't mark this build as a permanent failure. */
 #if HAVE_STATVFS
     {
-        auto & localStore = getLocalStore();
+        auto & localStore = getLocalFSStore();
         uint64_t required = 8ULL * 1024 * 1024; // FIXME: make configurable
         struct statvfs st;
         if (statvfs(localStore.realStoreDir.get().c_str(), &st) == 0 &&
@@ -1223,16 +1223,16 @@ struct RestrictedStoreConfig : virtual LocalFSStoreConfig
     const std::string name() { return "Restricted Store"; }
 };
 
-/* A wrapper around LocalStore that only allows building/querying of
+/* A wrapper around LocalFSStore that only allows building/querying of
    paths that are in the input closures of the build or were added via
    recursive Nix calls. */
 struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual IndirectRootStore, public virtual GcStore
 {
-    ref<LocalStore> next;
+    ref<LocalFSStore> next;
 
     LocalDerivationGoal & goal;
 
-    RestrictedStore(const Params & params, ref<LocalStore> next, LocalDerivationGoal & goal)
+    RestrictedStore(const Params & params, ref<LocalFSStore> next, LocalDerivationGoal & goal)
         : StoreConfig(params)
         , LocalFSStoreConfig(params)
         , RestrictedStoreConfig(params)
@@ -1459,12 +1459,12 @@ void LocalDerivationGoal::startDaemon()
     Store::Params params;
     params["path-info-cache-size"] = "0";
     params["store"] = worker.store.storeDir;
-    if (auto & optRoot = getLocalStore().rootDir.get())
+    if (auto & optRoot = getLocalFSStore().rootDir.get())
         params["root"] = *optRoot;
     params["state"] = "/no-such-path";
     params["log"] = "/no-such-path";
     auto store = make_ref<RestrictedStore>(params,
-        ref<LocalStore>(std::dynamic_pointer_cast<LocalStore>(worker.store.shared_from_this())),
+        ref<LocalFSStore>(std::dynamic_pointer_cast<LocalFSStore>(worker.store.shared_from_this())),
         *this);
 
     addedPaths.clear();
@@ -2632,7 +2632,7 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
             }
         }
 
-        auto & localStore = getLocalStore();
+        auto & localStore = getLocalFSStore();
 
         if (buildMode == bmCheck) {
 
@@ -2709,7 +2709,7 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
        paths referenced by each of them.  If there are cycles in the
        outputs, this will fail. */
     {
-        auto & localStore = getLocalStore();
+        auto & localStore = getLocalFSStore();
 
         ValidPathInfos infos2;
         for (auto & [outputName, newInfo] : infos) {
@@ -2754,7 +2754,7 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
 
 void LocalDerivationGoal::signRealisation(Realisation & realisation)
 {
-    getLocalStore().signRealisation(realisation);
+    getLocalFSStore().signRealisation(realisation);
 }
 
 

src/libstore/build/local-derivation-goal.hh

@@ -2,14 +2,14 @@
 ///@file
 
 #include "derivation-goal.hh"
-#include "local-store.hh"
+#include "local-fs-store.hh"
 #include "processes.hh"
 
 namespace nix {
 
 struct LocalDerivationGoal : public DerivationGoal
 {
-    LocalStore & getLocalStore();
+    LocalFSStore & getLocalFSStore();
 
     /**
      * User selected for running the builder.

src/libstore/build/worker.cc

@@ -3,6 +3,8 @@
 #include "substitution-goal.hh"
 #include "drv-output-substitution-goal.hh"
 #include "local-derivation-goal.hh"
+// Just for `autoGC`, which should have own interface, don't add more usage!
+#include "local-store.hh"
 #include "hook-instance.hh"
 #include "signals.hh"
 
@@ -64,7 +66,7 @@ std::shared_ptr<DerivationGoal> Worker::makeDerivationGoal(const StorePath & drv
     const OutputsSpec & wantedOutputs, BuildMode buildMode)
 {
     return makeDerivationGoalCommon(drvPath, wantedOutputs, [&]() -> std::shared_ptr<DerivationGoal> {
-        return !dynamic_cast<LocalStore *>(&store)
+        return !dynamic_cast<LocalFSStore *>(&store)
             ? std::make_shared</* */DerivationGoal>(drvPath, wantedOutputs, *this, buildMode)
             : std::make_shared<LocalDerivationGoal>(drvPath, wantedOutputs, *this, buildMode);
     });
@@ -75,7 +77,7 @@ std::shared_ptr<DerivationGoal> Worker::makeBasicDerivationGoal(const StorePath
     const BasicDerivation & drv, const OutputsSpec & wantedOutputs, BuildMode buildMode)
 {
     return makeDerivationGoalCommon(drvPath, wantedOutputs, [&]() -> std::shared_ptr<DerivationGoal> {
-        return !dynamic_cast<LocalStore *>(&store)
+        return !dynamic_cast<LocalFSStore *>(&store)
             ? std::make_shared</* */DerivationGoal>(drvPath, drv, wantedOutputs, *this, buildMode)
             : std::make_shared<LocalDerivationGoal>(drvPath, drv, wantedOutputs, *this, buildMode);
     });

src/libstore/local-fs-store.hh

@@ -71,6 +71,40 @@ public:
 
     std::optional<std::string> getBuildLogExact(const StorePath & path) override;
 
+    /**
+     * @todo this was moved to `LocalFSStore` from `LocalStore` because
+     * building needed it. Instead of just blindly moving it, we should
+     * should consider the division of labor and trust between the
+     * builder and the store.
+     */
+    virtual void registerValidPaths(const ValidPathInfos & infos)
+    { unsupported("registerValidPaths"); }
+
+    /**
+     * Optimise a single store path. Optionally, test the encountered
+     * symlinks for corruption.
+     *
+     * @todo this was moved to `LocalFSStore` from `LocalStore` because
+     * building needed it. Instead of just blindly moving it, we should
+     * should consider the division of labor and trust between the
+     * builder and the store.
+     */
+    virtual void optimisePath(const Path & path, RepairFlag repair)
+    { unsupported("optimisePath"); }
+
+    /**
+     * Add signatures to a ValidPathInfo or Realisation using the secret keys
+     * specified by the ‘secret-key-files’ option.
+     *
+     * @todo this was moved to `LocalFSStore` from `LocalStore` because
+     * building needed it. Instead of just blindly moving it, we should
+     * should consider the division of labor and trust between the
+     * builder and the store.
+     */
+    virtual void signPathInfo(ValidPathInfo & info)
+    { unsupported("signPathInfo"); }
+    virtual void signRealisation(Realisation &)
+    { unsupported("signRealisation"); }
 };
 
 }

src/libstore/local-store.hh

@@ -237,11 +237,7 @@ public:
 
     void optimiseStore() override;
 
-    /**
-     * Optimise a single store path. Optionally, test the encountered
-     * symlinks for corruption.
-     */
-    void optimisePath(const Path & path, RepairFlag repair);
+    void optimisePath(const Path & path, RepairFlag repair) override;
 
     bool verifyStore(bool checkContents, RepairFlag repair) override;
 
@@ -255,7 +251,7 @@ public:
      */
     void registerValidPath(const ValidPathInfo & info);
 
-    void registerValidPaths(const ValidPathInfos & infos);
+    void registerValidPaths(const ValidPathInfos & infos) override;
 
     unsigned int getProtocol() override;
 
@@ -343,12 +339,8 @@ private:
     bool isValidPath_(State & state, const StorePath & path);
     void queryReferrers(State & state, const StorePath & path, StorePathSet & referrers);
 
-    /**
-     * Add signatures to a ValidPathInfo or Realisation using the secret keys
-     * specified by the ‘secret-key-files’ option.
-     */
-    void signPathInfo(ValidPathInfo & info);
-    void signRealisation(Realisation &);
+    void signPathInfo(ValidPathInfo & info) override;
+    void signRealisation(Realisation &) override;
 
     // XXX: Make a generic `Store` method
     ContentAddress hashCAPath(