From 8f08c5d8a27f772e6ed45a7613f233563ee9ae19 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sat, 20 Apr 2013 20:03:53 -0600
Subject: [PATCH] Require Prepare to be called on Build

---
 packer/build.go      |  7 +++++++
 packer/build_test.go | 13 +++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/packer/build.go b/packer/build.go
index 8f93d1b31..67f9b80e8 100644
--- a/packer/build.go
+++ b/packer/build.go
@@ -7,6 +7,8 @@ package packer
 type Build struct {
 	name    string
 	builder Builder
+
+	prepareCalled bool
 }
 
 // Implementers of Builder are responsible for actually building images
@@ -42,10 +44,15 @@ func (NilBuilderFactory) CreateBuilder(name string) Builder {
 // Prepare prepares the build by doing some initialization for the builder
 // and any hooks. This _must_ be called prior to Run.
 func (b *Build) Prepare(config interface{}) {
+	b.prepareCalled = true
 	b.builder.Prepare(config)
 }
 
 // Runs the actual build. Prepare must be called prior to running this.
 func (b *Build) Run(ui Ui) {
+	if !b.prepareCalled {
+		panic("Prepare must be called first")
+	}
+
 	b.builder.Run(b, ui)
 }
diff --git a/packer/build_test.go b/packer/build_test.go
index cfa05f7ac..7359a05f2 100644
--- a/packer/build_test.go
+++ b/packer/build_test.go
@@ -49,6 +49,7 @@ func TestBuild_Run(t *testing.T) {
 	ui := testUi()
 
 	build := testBuild()
+	build.Prepare(nil)
 	build.Run(ui)
 
 	builder := build.builder.(*TestBuilder)
@@ -57,3 +58,15 @@ func TestBuild_Run(t *testing.T) {
 	assert.Equal(builder.runBuild, build, "run should be called with build")
 	assert.Equal(builder.runUi, ui, "run should be called with ui")
 }
+
+func TestBuild_RunBeforePrepare(t *testing.T) {
+	assert := asserts.NewTestingAsserts(t, true)
+
+	defer func() {
+		p := recover()
+		assert.NotNil(p, "should panic")
+		assert.Equal(p.(string), "Prepare must be called first", "right panic")
+	}()
+
+	testBuild().Run(testUi())
+}