Deduplicate the Store downcasting with a template

src/libstore/daemon.cc

@@ -3,6 +3,7 @@
 #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"
@@ -646,7 +647,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         Path path = absPath(readString(from));
 
         logger->startWork();
-        auto & gcStore = GcStore::require(*store);
+        auto & gcStore = require<GcStore>(*store);
         gcStore.addIndirectRoot(path);
         logger->stopWork();
 
@@ -664,7 +665,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
 
     case wopFindRoots: {
         logger->startWork();
-        auto & gcStore = GcStore::require(*store);
+        auto & gcStore = require<GcStore>(*store);
         Roots roots = gcStore.findRoots(!trusted);
         logger->stopWork();
 
@@ -696,7 +697,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         if (options.ignoreLiveness)
             throw Error("you are not allowed to ignore liveness");
-        auto & gcStore = GcStore::require(*store);
+        auto & gcStore = require<GcStore>(*store);
         gcStore.collectGarbage(options, results);
         logger->stopWork();
 
@@ -954,7 +955,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         if (!trusted)
             throw Error("you are not privileged to add logs");
-        auto & logStore = LogStore::require(*store);
+        auto & logStore = require<LogStore>(*store);
         {
             FramedSource source(from);
             StringSink sink;

src/libstore/gc-store.cc

@@ -1,13 +0,0 @@
-#include "gc-store.hh"
-
-namespace nix {
-
-GcStore & GcStore::require(Store & store)
-{
-    auto * gcStore = dynamic_cast<GcStore *>(&store);
-    if (!gcStore)
-        throw UsageError("Garbage collection not supported by store '%s'", store.getUri());
-    return *gcStore;
-}
-
-}

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
@@ -77,8 +79,6 @@ struct GcStore : public virtual Store
 
     /* Perform a garbage collection. */
     virtual void collectGarbage(const GCOptions & options, GCResults & results) = 0;
-
-    static GcStore & require(Store & store);
 };
 
 }

src/libstore/log-store.cc

@@ -1,13 +0,0 @@
-#include "log-store.hh"
-
-namespace nix {
-
-LogStore & LogStore::require(Store & store)
-{
-    auto * gcStore = dynamic_cast<LogStore *>(&store);
-    if (!gcStore)
-        throw UsageError("Build log storage and retrieval not supported by store '%s'", store.getUri());
-    return *gcStore;
-}
-
-}

src/libstore/log-store.hh

@@ -7,6 +7,8 @@ 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;

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;
+}
+
+}