Kill builds when we get EOF on the log FD

This closes a long-time bug that allowed builds to hang Nix
indefinitely (regardless of timeouts) simply by doing

  exec > /dev/null 2>&1; while true; do true; done

Now, on EOF, we just send SIGKILL to the child to make sure it's
really gone.

1 files changed, 8 insertions, 0 deletions

diff --git a/tests/timeout.nix b/tests/timeout.nix
index 1f3f23f16a..540fba934f 100644
--- a/tests/timeout.nix
+++ b/tests/timeout.nix
@@ -17,4 +17,12 @@ with import ./config.nix;
     '';
   };
 
+  closeLog = mkDerivation {
+    name = "silent";
+    buildCommand = ''
+      exec > /dev/null 2>&1
+      sleep 1000000000
+    '';
+  };
+
 }