From e77bd30681952f001ebd02556ddfa1287bfcc793 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=A9mie=20Dimino?= <jeremie@dimino.org>
Date: Fri, 23 Feb 2018 15:46:35 +0700
Subject: [PATCH] prefix_rules should append rather than overwrite the prefix

---
 src/build_system.ml | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/build_system.ml b/src/build_system.ml
index 88cd7587..d8a05cce 100644
--- a/src/build_system.ml
+++ b/src/build_system.ml
@@ -1406,6 +1406,11 @@ let prefix_rules t prefix ~f =
     Sexp.code_error "Build_system.prefix_rules' prefix contains targets"
       ["targets", Path.Set.sexp_of_t (Build_interpret.Target.paths targets)]
   end;
+  let prefix =
+    match t.prefix with
+    | None -> prefix
+    | Some p -> Build.O.(>>>) p prefix
+  in
   prefix_rules' t (Some prefix) ~f
 
 let on_load_dir t ~dir ~f =