From 78e47bafa84acfcaaa94ed114038e5e1c440f2cd Mon Sep 17 00:00:00 2001
From: Jeremie Dimino <jdimino@janestreet.com>
Date: Mon, 6 Mar 2017 15:33:03 +0000
Subject: [PATCH] Don't save the db if _build doesn't exist

---
 src/build_system.ml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/build_system.ml b/src/build_system.ml
index ebc26c2d..7d227240 100644
--- a/src/build_system.ml
+++ b/src/build_system.ml
@@ -384,7 +384,8 @@ module Trace = struct
         |> List.map ~f:(fun (path, hash) ->
           Sexp.List [ Atom (Path.to_string path); Atom (Digest.to_hex hash) ]))
     in
-    write_file file (Sexp.to_string sexp)
+    if Sys.file_exists "_build" then
+      write_file file (Sexp.to_string sexp)
 
   let load () =
     let trace = Hashtbl.create 1024 in