5 files changed, 40 insertions, 32 deletions

diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index ca4d509c2..124df34ea 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -12,7 +12,6 @@
 #include "eval-cache.hh"
 #include "url.hh"
 #include "registry.hh"
-#include "remote-store.hh"
 
 #include <regex>
 #include <queue>
@@ -393,31 +392,7 @@ DerivedPaths InstallableValue::toDerivedPaths()
     for (auto & i : drvsToOutputs)
         res.push_back(DerivedPath::Built { i.first, i.second });
 
-    // FIXME: Temporary hack
-    if (state->store != state->buildStore) {
-        RealisedPath::Set closure;
-        RealisedPath::closure(*state->store, drvsToCopy, closure);
-
-        if (dynamic_cast<RemoteStore *>(&*state->buildStore)) {
-            StorePathSet closure2;
-            for (auto & p : closure)
-                closure2.insert(p.path());
-
-            auto valid = state->buildStore->queryValidPaths(closure2);
-            StorePathSet missing;
-            for (auto & p : closure2)
-                if (!valid.count(p)) missing.insert(p);
-
-            if (!missing.empty()) {
-                auto source = sinkToSource([&](Sink & sink) {
-                    state->store->exportPaths(missing, sink);
-                });
-                state->buildStore->importPaths(*source, NoCheckSigs);
-            }
-
-        } else
-            copyPaths(state->store, state->buildStore, closure);
-    }
+    copyClosure(state->store, state->buildStore, drvsToCopy);
 
     return res;
 }
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 40a406468..d040560ca 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -9,6 +9,7 @@
 #include "url.hh"
 #include "archive.hh"
 #include "callback.hh"
+#include "remote-store.hh"
 
 #include <regex>
 
@@ -881,6 +882,16 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
     for (auto & path : storePaths)
         pathsMap.insert_or_assign(path, path);
 
+    // FIXME: Temporary hack to copy closures in a single round-trip.
+    if (dynamic_cast<RemoteStore *>(&*dstStore)) {
+        if (!missing.empty()) {
+            auto source = sinkToSource([&](Sink & sink) {
+                srcStore->exportPaths(missing, sink);
+            });
+            dstStore->importPaths(*source, NoCheckSigs);
+        }
+        return pathsMap;
+    }
 
     Activity act(*logger, lvlInfo, actCopyPaths, fmt("copying %d paths", missing.size()));
 
@@ -958,6 +969,22 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
     return pathsMap;
 }
 
+void copyClosure(
+    ref<Store> srcStore,
+    ref<Store> dstStore,
+    const RealisedPath::Set & paths,
+    RepairFlag repair,
+    CheckSigsFlag checkSigs,
+    SubstituteFlag substitute)
+{
+    if (srcStore == dstStore) return;
+
+    RealisedPath::Set closure;
+    RealisedPath::closure(*srcStore, paths, closure);
+
+    copyPaths(srcStore, dstStore, closure, repair, checkSigs, substitute);
+}
+
 std::optional<ValidPathInfo> decodeValidPathInfo(const Store & store, std::istream & str, std::optional<HashResult> hashGiven)
 {
     std::string path;
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 356ae615c..c39d9f894 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -773,6 +773,12 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
     CheckSigsFlag checkSigs = CheckSigs,
     SubstituteFlag substitute = NoSubstitute);
 
+/* Copy the closure of `paths` from `srcStore` to `dstStore`. */
+void copyClosure(ref<Store> srcStore, ref<Store> dstStore,
+    const RealisedPath::Set & paths,
+    RepairFlag repair = NoRepair,
+    CheckSigsFlag checkSigs = CheckSigs,
+    SubstituteFlag substitute = NoSubstitute);
 
 /* Remove the temporary roots file for this process.  Any temporary
    root becomes garbage after this point unless it has been registered
diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index 4305c0ac1..4ee471520 100755
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -532,6 +532,7 @@ static void main_nix_build(int argc, char * * argv)
 
         std::vector<StorePathWithOutputs> pathsToBuild;
         std::vector<std::pair<StorePath, std::string>> pathsToBuildOrdered;
+        RealisedPath::Set drvsToCopy;
 
         std::map<StorePath, std::pair<size_t, StringSet>> drvMap;
 
@@ -544,15 +545,17 @@ static void main_nix_build(int argc, char * * argv)
 
             pathsToBuild.push_back({drvPath, {outputName}});
             pathsToBuildOrdered.push_back({drvPath, {outputName}});
+            drvsToCopy.insert(drvPath);
 
             auto i = drvMap.find(drvPath);
             if (i != drvMap.end())
                 i->second.second.insert(outputName);
-            else {
+            else
                 drvMap[drvPath] = {drvMap.size(), {outputName}};
-            }
         }
 
+        copyClosure(state->store, state->buildStore, drvsToCopy);
+
         buildPaths(pathsToBuild);
 
         if (dryRun) return;
diff --git a/src/nix-copy-closure/nix-copy-closure.cc b/src/nix-copy-closure/nix-copy-closure.cc
index 02ccbe541..7c38e55e4 100755
--- a/src/nix-copy-closure/nix-copy-closure.cc
+++ b/src/nix-copy-closure/nix-copy-closure.cc
@@ -54,10 +54,7 @@ static int main_nix_copy_closure(int argc, char ** argv)
         for (auto & path : storePaths)
             storePaths2.insert(from->followLinksToStorePath(path));
 
-        RealisedPath::Set closure;
-        RealisedPath::closure(*from, storePaths2, closure);
-
-        copyPaths(from, to, closure, NoRepair, NoCheckSigs, useSubstitutes);
+        copyClosure(from, to, storePaths2, NoRepair, NoCheckSigs, useSubstitutes);
 
         return 0;
     }