Store::addToStore bail out on no-op earlier in many cases

`BinaryCacheStore` and `LocalStore` already had this optimization. Now,
all the implementations do.

src/libstore/binary-cache-store.cc

@@ -296,8 +296,8 @@ void BinaryCacheStore::addToStore(
     const ValidPathInfo & info, Source & narSource, RepairFlag repair, CheckSigsFlag checkSigs)
 {
     if (!repair && isValidPath(info.path)) {
-        // FIXME: copyNAR -> null sink
-        narSource.drain();
+        NullFileSystemObjectSink s;
+        parseDump(s, narSource);
         return;
     }
 

src/libstore/dummy-store.cc

@@ -157,8 +157,13 @@ struct DummyStoreImpl : DummyStore
         unsupported("queryPathFromHashPart");
     }
 
-    void addToStore(const ValidPathInfo & info, Source & source, RepairFlag repair, CheckSigsFlag checkSigs) override
+    void
+    addToStore(const ValidPathInfo & info, const SourcePath & path, RepairFlag repair, CheckSigsFlag checkSigs) override
     {
+        if (!repair && isValidPath(info.path)) {
+            return;
+        }
+
         if (config->readOnly)
             unsupported("addToStore");
 
@@ -168,19 +173,19 @@ struct DummyStoreImpl : DummyStore
         if (checkSigs)
             throw Error("checking signatures is not supported for '%s' store", config->getHumanReadableURI());
 
-        auto temp = make_ref<MemorySourceAccessor>();
-        MemorySink tempSink{*temp};
-        parseDump(tempSink, source);
-        auto path = info.path;
+        auto accessor = make_ref<MemorySourceAccessor>();
+        {
+            MemorySink tempSink{*accessor};
+            copyRecursive(*path.accessor, path.path, tempSink, CanonPath::root);
+        }
 
-        auto accessor = make_ref<MemorySourceAccessor>(std::move(*temp));
         contents.insert(
-            {path,
+            {info.path,
              PathInfoAndContents{
-                 std::move(info),
+                 info,
                  accessor,
              }});
-        wholeStoreView->addObject(path.to_string(), accessor);
+        wholeStoreView->addObject(info.path.to_string(), accessor);
     }
 
     StorePath addToStoreFromDump(

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

@@ -511,13 +511,28 @@ public:
     virtual void querySubstitutablePathInfos(const StorePathCAMap & paths, SubstitutablePathInfos & infos);
 
     /**
-     * Import a path into the store.
+     * Import a path into the store, via NAR stream.
+     *
+     * One of these two must be overridden, as the defaults will
+     * infinitely mutually recur.
      */
     virtual void addToStore(
         const ValidPathInfo & info,
         Source & narSource,
         RepairFlag repair = NoRepair,
-        CheckSigsFlag checkSigs = CheckSigs) = 0;
+        CheckSigsFlag checkSigs = CheckSigs);
+
+    /**
+     * Import a path into the store, via arbitrary `SourcePath`.
+     *
+     * One of these two must be overridden, as the defaults will
+     * infinitely mutually recur.
+     */
+    virtual void addToStore(
+        const ValidPathInfo & info,
+        const SourcePath & path,
+        RepairFlag repair = NoRepair,
+        CheckSigsFlag checkSigs = CheckSigs);
 
     /**
      * A list of paths infos along with a source providing the content

src/libstore/legacy-ssh-store.cc

@@ -145,6 +145,12 @@ void LegacySSHStore::queryPathInfoUncached(
 
 void LegacySSHStore::addToStore(const ValidPathInfo & info, Source & source, RepairFlag repair, CheckSigsFlag checkSigs)
 {
+    if (!repair && isValidPath(info.path)) {
+        NullFileSystemObjectSink s;
+        parseDump(s, source);
+        return;
+    }
+
     debug("adding path '%s' to remote host '%s'", printStorePath(info.path), config->authority.host);
 
     auto conn(connections->get());

src/libstore/remote-store.cc

@@ -424,6 +424,12 @@ StorePath RemoteStore::addToStoreFromDump(
 
 void RemoteStore::addToStore(const ValidPathInfo & info, Source & source, RepairFlag repair, CheckSigsFlag checkSigs)
 {
+    if (!repair && isValidPath(info.path)) {
+        NullFileSystemObjectSink s;
+        parseDump(s, source);
+        return;
+    }
+
     auto conn(getConnection());
 
     conn->to << WorkerProto::Op::AddToStoreNar << printStorePath(info.path)

src/libstore/store-api.cc

@@ -1,6 +1,6 @@
 #include "nix/util/logging.hh"
 #include "nix/util/signature/local-keys.hh"
-#include "nix/util/source-accessor.hh"
+#include "nix/util/memory-source-accessor.hh"
 #include "nix/store/globals.hh"
 #include "nix/store/derived-path.hh"
 #include "nix/store/realisation.hh"
@@ -84,6 +84,30 @@ StorePath Store::followLinksToStorePath(std::string_view path) const
     return toStorePath(followLinksToStore(path)).first;
 }
 
+void Store::addToStore(const ValidPathInfo & info, Source & narSource, RepairFlag repair, CheckSigsFlag checkSigs)
+{
+    if (!repair && isValidPath(info.path)) {
+        NullFileSystemObjectSink s;
+        parseDump(s, narSource);
+        return;
+    }
+
+    auto temp = make_ref<MemorySourceAccessor>();
+    MemorySink tempSink{*temp};
+    parseDump(tempSink, narSource);
+    addToStore(info, {temp}, repair, checkSigs);
+}
+
+void Store::addToStore(const ValidPathInfo & info, const SourcePath & path, RepairFlag repair, CheckSigsFlag checkSigs)
+{
+    if (!repair && isValidPath(info.path)) {
+        return;
+    }
+
+    auto sink = sourceToSink([&](Source & source) { addToStore(info, source, repair, checkSigs); });
+    dumpPath(path, *sink, FileSerialisationMethod::NixArchive);
+}
+
 StorePath Store::addToStore(
     std::string_view name,
     const SourcePath & path,