4 files changed, 68 insertions, 17 deletions

diff --git a/src/db.cc b/src/db.cc
index 89cee32ba4a9..64f9813a400f 100644
--- a/src/db.cc
+++ b/src/db.cc
@@ -65,7 +65,10 @@ bool queryDB(const string & filename, const string & dbname,
         err = db->get(0, &kt, &dt, 0);
         if (err) return false;
 
-        data = string((char *) dt.get_data(), dt.get_size());
+        if (!dt.get_data())
+            data = "";
+        else
+            data = string((char *) dt.get_data(), dt.get_size());
     
     } catch (DbException e) { rethrow(e); }
 
diff --git a/src/fix.cc b/src/fix.cc
index d954abfe4be2..f55074907fbb 100644
--- a/src/fix.cc
+++ b/src/fix.cc
@@ -111,6 +111,14 @@ static Expr evalExpr(Expr e)
         ATmatch(e, "FSId(<str>)", &s1))
         return e;
 
+    if (ATgetType(e) == AT_APPL && 
+        ((string) ATgetName(ATgetAFun(e)) == "Slice" ||
+         (string) ATgetName(ATgetAFun(e)) == "Derive"))
+    {
+        return ATmake("FSId(<str>)", 
+            ((string) writeTerm(e, "", 0)).c_str());
+    }
+
     /* Application. */
     if (ATmatch(e, "App(<term>, [<list>])", &e1, &e2)) {
         e1 = evalExpr(e1);
diff --git a/src/fstate.cc b/src/fstate.cc
index cdd620cf1042..11a91cffcb87 100644
--- a/src/fstate.cc
+++ b/src/fstate.cc
@@ -21,15 +21,22 @@ typedef map<string, string> Environment;
 class AutoDelete
 {
     string path;
+    bool del;
 public:
 
     AutoDelete(const string & p) : path(p) 
     {
+        del = true;
     }
 
     ~AutoDelete()
     {
-        deletePath(path);
+        if (del) deletePath(path);
+    }
+
+    void cancel()
+    {
+        del = false;
     }
 };
 
@@ -114,8 +121,10 @@ static void runProgram(const string & program, Environment env)
     if (waitpid(pid, &status, 0) != pid)
         throw Error("unable to wait for child");
     
-    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
+    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+        delTmpDir.cancel();
         throw Error("unable to build package");
+    }
 }
 
 
@@ -336,7 +345,7 @@ static Slice normaliseFState2(FSId id, StringSet & usedPaths)
         bnds = ATgetNext(bnds);
     }
 
-    /* Check that none of the output paths exist. */
+    /* Parse the outputs. */
     typedef map<string, FSId> OutPaths;
     OutPaths outPaths;
     while (!ATisEmpty(outs)) {
@@ -349,14 +358,36 @@ static Slice normaliseFState2(FSId id, StringSet & usedPaths)
         outs = ATgetNext(outs);
     }
 
+    /* We can skip running the builder if we can expand all output
+       paths from their ids. */
+    bool fastBuild = false;
+#if 0
     for (OutPaths::iterator i = outPaths.begin(); 
          i != outPaths.end(); i++)
-        if (pathExists(i->first))
-            throw Error(format("path `%1%' exists") % i->first);
+    {
+        try {
+            expandId(i->second, i->first);
+        } catch (...) {
+            fastBuild = false;
+            break;
+        }
+    }
+#endif
+
+    if (!fastBuild) {
 
-    /* Run the builder. */
-    runProgram(builder, env);
+        /* Check that none of the outputs exist. */
+        for (OutPaths::iterator i = outPaths.begin(); 
+             i != outPaths.end(); i++)
+            if (pathExists(i->first))
+                throw Error(format("path `%1%' exists") % i->first);
+
+        /* Run the builder. */
+        runProgram(builder, env);
         
+    } else
+        debug(format("skipping build"));
+
     Slice slice;
 
     /* Check whether the output paths were created, and register each
diff --git a/src/store.cc b/src/store.cc
index c8b3bd37f4e5..d75458d8a55b 100644
--- a/src/store.cc
+++ b/src/store.cc
@@ -86,6 +86,7 @@ void copyPath(string src, string dst)
 
 void registerSubstitute(const FSId & srcId, const FSId & subId)
 {
+#if 0
     Strings subs;
     queryListDB(nixDB, dbSubstitutes, srcId, subs); /* non-existence = ok */
 
@@ -95,6 +96,12 @@ void registerSubstitute(const FSId & srcId, const FSId & subId)
     subs.push_back(subId);
     
     setListDB(nixDB, dbSubstitutes, srcId, subs);
+#endif
+
+    /* For now, accept only one substitute per id. */
+    Strings subs;
+    subs.push_back(subId);
+    setListDB(nixDB, dbSubstitutes, srcId, subs);
 }
 
 
@@ -126,6 +133,8 @@ void unregisterPath(const string & _path)
         return;
     FSId id(parseHash(_id));
 
+    delDB(nixDB, dbPath2Id, path);
+
     /* begin transaction */
     
     Strings paths, paths2;
@@ -140,6 +149,7 @@ void unregisterPath(const string & _path)
         setListDB(nixDB, dbId2Paths, id, paths2);
 
     /* end transaction */
+
 }
 
 
@@ -189,32 +199,31 @@ string expandId(const FSId & id, const string & target,
         }
     }
 
-#if 0
     /* Try to realise the substitutes. */
 
     Strings subs;
     queryListDB(nixDB, dbSubstitutes, id, subs); /* non-existence = ok */
 
     for (Strings::iterator it = subs.begin(); it != subs.end(); it++) {
-        realiseSlice(normaliseFState(*it));
+        FSId subId = parseHash(*it);
+        Slice slice = normaliseFState(subId);
+        realiseSlice(slice);
         
-        FState nf = realiseFState(hash2fstate(parseHash(*it)), dummy);
-        string path = fstatePath(nf);
-
-        if (hashPath(path) != hash)
-            throw Error(format("bad substitute in `%1%'") % (string) path);
+        Strings paths = fstatePaths(subId, true);
+        if (paths.size() != 1) 
+            throw Error("substitute created more than 1 path");
+        string path = *(paths.begin());
 
         if (target.empty())
             return path; /* !!! prefix */
         else {
             if (path != target) {
                 copyPath(path, target);
-                registerPath(target, hash);
+                registerPath(target, id);
             }
             return target;
         }
     }
-#endif
     
     throw Error(format("cannot expand id `%1%'") % (string) id);
 }