From 41ba5135e0a2d9940c4e8cbedff44eb1a47af782 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 1 Apr 2019 21:09:49 +0200
Subject: [PATCH] primeCache(): Barf if builds are needed but not allowed

Fixes #2753.
---
 src/libstore/build.cc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 6b88b1307..53a0c743b 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -12,6 +12,7 @@
 #include "json.hh"
 #include "nar-info.hh"
 #include "parsed-derivations.hh"
+#include "machines.hh"
 
 #include <algorithm>
 #include <iostream>
@@ -4411,6 +4412,11 @@ static void primeCache(Store & store, const PathSet & paths)
     PathSet willBuild, willSubstitute, unknown;
     unsigned long long downloadSize, narSize;
     store.queryMissing(paths, willBuild, willSubstitute, unknown, downloadSize, narSize);
+
+    if (!willBuild.empty() && 0 == settings.maxBuildJobs && getMachines().empty())
+        throw Error(
+            "%d derivations need to be built, but neither local builds ('--max-jobs') "
+            "nor remote builds ('--builders') are enabled", willBuild.size());
 }