From 507169375ec9f970e12f42df9cb73a05f76e3820 Mon Sep 17 00:00:00 2001
From: Andrea Leopardi <an.leopardi@gmail.com>
Date: Mon, 21 Nov 2016 12:19:47 +0100
Subject: [PATCH] Validate the :build_per_environment option in
 Mix.Project.build_path/1

---
 lib/mix/lib/mix/project.ex | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/lib/mix/lib/mix/project.ex b/lib/mix/lib/mix/project.ex
index 8723f1c35c0..9089b2ffcee 100644
--- a/lib/mix/lib/mix/project.ex
+++ b/lib/mix/lib/mix/project.ex
@@ -360,10 +360,13 @@ defmodule Mix.Project do
   defp env_path(config) do
     build = config[:build_path] || "_build"
 
-    if config[:build_per_environment] do
-      Path.expand("#{build}/#{Mix.env}")
-    else
-      Path.expand("#{build}/shared")
+    case config[:build_per_environment] do
+      true ->
+        Path.expand("#{build}/#{Mix.env}")
+      false ->
+        Path.expand("#{build}/shared")
+      other ->
+        Mix.raise "The :build_per_environment option should be a boolean, got: #{inspect(other)}"
     end
   end