Add Store::readDerivation() convenience function

src/build-remote/build-remote.cc

@@ -241,7 +241,7 @@ connected:
 
         uploadLock = -1;
 
-        BasicDerivation drv(readDerivation(*store, store->realStoreDir + "/" + std::string(drvPath->to_string())));
+        auto drv = store->readDerivation(*drvPath);
         drv.inputSrcs = store->parseStorePathSet(inputs);
 
         auto result = sshStore->buildDerivation(*drvPath, drv);

src/libexpr/primops.cc

@@ -688,7 +688,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
             for (auto & j : refs) {
                 drv.inputSrcs.insert(j.clone());
                 if (j.isDerivation())
-                    drv.inputDrvs[j.clone()] = readDerivation(*state.store, state.store->toRealPath(j)).outputNames();
+                    drv.inputDrvs[j.clone()] = state.store->readDerivation(j).outputNames();
             }
         }
 

src/libstore/daemon.cc

@@ -329,7 +329,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case wopQueryDerivationOutputNames: {
         auto path = store->parseStorePath(readString(from));
         logger->startWork();
-        auto names = readDerivation(*store, store->toRealPath(path)).outputNames();
+        auto names = store->readDerivation(path).outputNames();
         logger->stopWork();
         to << names;
         break;

src/libstore/derivations.cc

@@ -204,6 +204,12 @@ Derivation readDerivation(const Store & store, const Path & drvPath)
 Derivation Store::derivationFromPath(const StorePath & drvPath)
 {
     ensurePath(drvPath);
+    return readDerivation(drvPath);
+}
+
+
+Derivation Store::readDerivation(const StorePath & drvPath)
+{
     auto accessor = getFSAccessor();
     try {
         return parseDerivation(*this, accessor->readFile(printStorePath(drvPath)));
@@ -378,7 +384,7 @@ Hash hashDerivationModulo(Store & store, const Derivation & drv, bool maskOutput
         if (h == drvHashes.end()) {
             assert(store.isValidPath(i.first));
             h = drvHashes.insert_or_assign(i.first.clone(), hashDerivationModulo(store,
-                readDerivation(store, store.toRealPath(i.first)), false)).first;
+                store.readDerivation(i.first), false)).first;
         }
         inputs2.insert_or_assign(h->second.to_string(Base16, false), i.second);
     }

src/libstore/local-store.cc

@@ -595,7 +595,7 @@ uint64_t LocalStore::addValidPath(State & state,
        efficiently query whether a path is an output of some
        derivation. */
     if (info.path.isDerivation()) {
-        auto drv = readDerivation(*this, realStoreDir + "/" + std::string(info.path.to_string()));
+        auto drv = readDerivation(info.path);
 
         /* Verify that the output paths in the derivation are correct
            (i.e., follow the scheme for computing output paths from
@@ -911,8 +911,7 @@ void LocalStore::registerValidPaths(const ValidPathInfos & infos)
         for (auto & i : infos)
             if (i.path.isDerivation()) {
                 // FIXME: inefficient; we already loaded the derivation in addValidPath().
-                checkDerivationOutputs(i.path,
+                checkDerivationOutputs(i.path, readDerivation(i.path));
-                    readDerivation(*this, realStoreDir + "/" + std::string(i.path.to_string())));
             }
 
         /* Do a topological sort of the paths.  This will throw an

src/libstore/store-api.hh

@@ -583,6 +583,9 @@ public:
        ensurePath(). */
     Derivation derivationFromPath(const StorePath & drvPath);
 
+    /* Read a derivation (which must already be valid). */
+    Derivation readDerivation(const StorePath & drvPath);
+
     /* Place in `out' the set of all store paths in the file system
        closure of `storePath'; that is, all paths than can be directly
        or indirectly reached from it.  `out' is not cleared.  If

src/nix/show-derivation.cc

@@ -61,11 +61,9 @@ struct CmdShowDerivation : InstallablesCommand
         for (auto & drvPath : drvPaths) {
             if (!drvPath.isDerivation()) continue;
 
-            auto drvPathS = store->printStorePath(drvPath);
+            auto drvObj(jsonRoot.object(store->printStorePath(drvPath)));
 
-            auto drvObj(jsonRoot.object(drvPathS));
+            auto drv = store->readDerivation(drvPath);
-
-            auto drv = readDerivation(*store, drvPathS);
 
             {
                 auto outputsObj(drvObj.object("outputs"));