From 9e3389c3378df026dcbf66adef8e52002c7b9d2a Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Mon, 24 Nov 2014 16:44:35 +0100
Subject: [PATCH] Don't create unnecessary substitution goals for derivations

---
 src/libstore/build.cc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 24576f670..72694cfbb 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -924,6 +924,11 @@ void DerivationGoal::init()
     /* The first thing to do is to make sure that the derivation
        exists.  If it doesn't, it may be created through a
        substitute. */
+    if (buildMode == bmNormal && worker.store.isValidPath(drvPath)) {
+        haveDerivation();
+        return;
+    }
+
     addWaitee(worker.makeSubstitutionGoal(drvPath));
 
     state = &DerivationGoal::haveDerivation;