Relegate toRealPath to LocalFSStore

Fix #14480

This method is not well-defined for arbitrary stores, which do not have
a notion of a "real path" -- it is only well-defined for local file
systems stores, which do have exactly that notion, and so it is moved to
that sub-interface instead.

Some call-sites had to be fixed up for this, but in all cases the
changes are positive. Using `getFSSourceAccessor` allows for more other
stores to work properly. `nix-channel` was straight-up wrong in the case
of redirected local stores. And the building logic with remote building
and a non-local store is also fixed, properly gating some deletions on
store type.

Co-authored-by: Robert Hensing <robert@roberthensing.nl>

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

@@ -286,7 +286,7 @@ Goal::Co DerivationBuildingGoal::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 (auto * localStore = dynamic_cast<LocalStore *>(&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
@@ -296,9 +296,9 @@ Goal::Co DerivationBuildingGoal::tryToBuild()
                */
             for (auto & i : drv->outputsAndOptPaths(worker.store)) {
                 if (i.second.second)
-                    lockFiles.insert(worker.store.Store::toRealPath(*i.second.second));
+                    lockFiles.insert(localStore->toRealPath(*i.second.second));
                 else
-                    lockFiles.insert(worker.store.Store::toRealPath(drvPath) + "." + i.first);
+                    lockFiles.insert(localStore->toRealPath(drvPath) + "." + i.first);
             }
         }
 
@@ -331,12 +331,14 @@ Goal::Co DerivationBuildingGoal::tryToBuild()
 
         /* If any of the outputs already exist but are not valid, delete
            them. */
-        for (auto & [_, status] : initialOutputs) {
-            if (!status.known || status.known->isValid())
-                continue;
-            auto storePath = status.known->path;
-            debug("removing invalid path '%s'", worker.store.printStorePath(status.known->path));
-            deletePath(worker.store.Store::toRealPath(storePath));
+        if (auto * localStore = dynamic_cast<LocalFSStore *>(&worker.store)) {
+            for (auto & [_, status] : initialOutputs) {
+                if (!status.known || status.known->isValid())
+                    continue;
+                auto storePath = status.known->path;
+                debug("removing invalid path '%s'", worker.store.printStorePath(status.known->path));
+                deletePath(localStore->toRealPath(storePath));
+            }
         }
 
         /* Don't do a remote build if the derivation has the attribute

src/libstore/daemon.cc

@@ -896,7 +896,7 @@ static void performOp(
         auto path = WorkerProto::Serialise<StorePath>::read(*store, rconn);
         logger->startWork();
         logger->stopWork();
-        dumpPath(store->toRealPath(path), conn.to);
+        store->narFromPath(path, conn.to);
         break;
     }
 

src/libstore/include/nix/store/local-fs-store.hh

@@ -102,7 +102,12 @@ struct LocalFSStore : virtual Store, virtual GcStore, virtual LogStore
         return config.realStoreDir;
     }
 
-    Path toRealPath(const Path & storePath) override
+    Path toRealPath(const StorePath & storePath)
+    {
+        return toRealPath(printStorePath(storePath));
+    }
+
+    Path toRealPath(const Path & storePath)
     {
         assert(isInStore(storePath));
         return getRealStoreDir() + "/" + std::string(storePath, storeDir.size() + 1);

src/libstore/include/nix/store/store-api.hh

@@ -895,16 +895,6 @@ public:
      */
     virtual std::optional<TrustedFlag> isTrustedClient() = 0;
 
-    virtual Path toRealPath(const Path & storePath)
-    {
-        return storePath;
-    }
-
-    Path toRealPath(const StorePath & storePath)
-    {
-        return toRealPath(printStorePath(storePath));
-    }
-
     /**
      * Synchronises the options of the client with those of the daemon
      * (a no-op when there’s no daemon)

src/libstore/local-overlay-store.cc

@@ -246,7 +246,7 @@ void LocalOverlayStore::optimiseStore()
         if (lowerStore->isValidPath(path)) {
             uint64_t bytesFreed = 0;
             // Deduplicate store path
-            deleteStorePath(Store::toRealPath(path), bytesFreed);
+            deleteStorePath(toRealPath(path), bytesFreed);
         }
         done++;
         act.progress(done, paths.size());

src/libstore/local-store.cc

@@ -1063,7 +1063,7 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source, RepairF
 
             PathLocks outputLock;
 
-            auto realPath = Store::toRealPath(info.path);
+            auto realPath = toRealPath(info.path);
 
             /* Lock the output path.  But don't lock if we're being called
             from a build hook (whose parent process already acquired a
@@ -1262,7 +1262,7 @@ StorePath LocalStore::addToStoreFromDump(
         /* The first check above is an optimisation to prevent
            unnecessary lock acquisition. */
 
-        auto realPath = Store::toRealPath(dstPath);
+        auto realPath = toRealPath(dstPath);
 
         PathLocks outputLock({realPath});
 
@@ -1413,7 +1413,7 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
 
                 auto hashSink = HashSink(info->narHash.algo);
 
-                dumpPath(Store::toRealPath(i), hashSink);
+                dumpPath(toRealPath(i), hashSink);
                 auto current = hashSink.finish();
 
                 if (info->narHash != nullHash && info->narHash != current.hash) {

src/libstore/unix/build/chroot-derivation-builder.cc

@@ -58,7 +58,7 @@ struct ChrootDerivationBuilder : virtual DerivationBuilderImpl
            environment using bind-mounts.  We put it in the Nix store
            so that the build outputs can be moved efficiently from the
            chroot to their final location. */
-        auto chrootParentDir = store.Store::toRealPath(drvPath) + ".chroot";
+        auto chrootParentDir = store.toRealPath(drvPath) + ".chroot";
         deletePath(chrootParentDir);
 
         /* Clean up the chroot directory automatically. */
@@ -171,7 +171,7 @@ struct ChrootDerivationBuilder : virtual DerivationBuilderImpl
                     continue;
                 if (buildMode != bmCheck && status.known->isValid())
                     continue;
-                auto p = store.Store::toRealPath(status.known->path);
+                auto p = store.toRealPath(status.known->path);
                 if (pathExists(chrootRootDir + p))
                     std::filesystem::rename((chrootRootDir + p), p);
             }
@@ -185,7 +185,7 @@ struct ChrootDerivationBuilder : virtual DerivationBuilderImpl
 
         debug("materialising '%s' in the sandbox", store.printStorePath(path));
 
-        Path source = store.Store::toRealPath(path);
+        Path source = store.toRealPath(path);
         Path target = chrootRootDir + store.printStorePath(path);
 
         if (pathExists(target)) {

src/libstore/unix/build/derivation-builder.cc

@@ -1887,7 +1887,7 @@ void DerivationBuilderImpl::cleanupBuild(bool force)
     if (force) {
         /* Delete unused redirected outputs (when doing hash rewriting). */
         for (auto & i : redirectedOutputs)
-            deletePath(store.Store::toRealPath(i.second));
+            deletePath(store.toRealPath(i.second));
     }
 
     if (topTmpDir != "") {