3 files changed, 18 insertions, 7 deletions
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 3785c7da7924..e71201785e1d 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1502,7 +1502,8 @@ void SubstitutionGoal::finished()
 
     Transaction txn;
     createStoreTransaction(txn);
-    registerValidPath(txn, storePath, contentHash, references, "");
+    registerValidPath(txn, storePath, contentHash,
+        references, sub.deriver);
     txn.commit();
 
     outputLock->setDeletion(true);
diff --git a/src/libstore/store.cc b/src/libstore/store.cc
index 83577e4fb744..5516dc8016c1 100644
--- a/src/libstore/store.cc
+++ b/src/libstore/store.cc
@@ -391,6 +391,9 @@ Path queryDeriver(const Transaction & txn, const Path & storePath)
 }
 
 
+const int substituteVersion = 2;
+
+
 static Substitutes readSubstitutes(const Transaction & txn,
     const Path & srcPath)
 {
@@ -406,13 +409,15 @@ static Substitutes readSubstitutes(const Transaction & txn,
             break;
         }
         Strings ss2 = unpackStrings(*i);
-        if (ss2.size() == 3) {
-            /* Another old-style substitute. */
-            continue;
-        }
-        if (ss2.size() != 2) throw Error("malformed substitute");
+        if (ss2.size() == 0) continue;
+        int version;
+        if (!string2Int(ss2.front(), version)) continue;
+        if (version != substituteVersion) continue;
+        if (ss2.size() != 4) throw Error("malformed substitute");
         Strings::iterator j = ss2.begin();
+        j++;
         Substitute sub;
+        sub.deriver = *j++;
         sub.program = *j++;
         sub.args = unpackStrings(*j++);
         subs.push_back(sub);
@@ -431,6 +436,8 @@ static void writeSubstitutes(const Transaction & txn,
          i != subs.end(); ++i)
     {
         Strings ss2;
+        ss2.push_back((format("%1%") % substituteVersion).str());
+        ss2.push_back(i->deriver);
         ss2.push_back(i->program);
         ss2.push_back(packStrings(i->args));
         ss.push_back(packStrings(ss2));
diff --git a/src/libstore/store.hh b/src/libstore/store.hh
index 082fc9de498d..3b18664de646 100644
--- a/src/libstore/store.hh
+++ b/src/libstore/store.hh
@@ -16,7 +16,10 @@ const int nixSchemaVersion = 2;
    path (typically by fetching it from somewhere, e.g., from the
    network). */
 struct Substitute
-{
+{       
+    /* The derivation that built this store path (empty if none). */
+    Path deriver;
+    
     /* Program to be executed to create the store path.  Must be in
        the output path of `storeExpr'. */
     Path program;