provisioner/file: add "generated" key to allow files created on-the-fly.

provisioner/file/provisioner.go

@@ -26,6 +26,9 @@ type Config struct {
 	// Direction
 	Direction string
 
+	// False if the sources have to exist.
+	Generated bool
+
 	ctx interpolate.Context
 }
 
@@ -61,7 +64,7 @@ func (p *Provisioner) Prepare(raws ...interface{}) error {
 
 	if p.config.Direction == "upload" {
 		for _, src := range p.config.Sources {
-			if _, err := os.Stat(src); err != nil {
+			if _, err := os.Stat(src); p.config.Generated == false && err != nil {
 				errs = packer.MultiErrorAppend(errs,
 					fmt.Errorf("Bad source '%s': %s", src, err))
 			}

provisioner/file/provisioner_test.go

@@ -45,6 +45,12 @@ func TestProvisionerPrepare_InvalidSource(t *testing.T) {
 	if err == nil {
 		t.Fatalf("should require existing file")
 	}
+
+	config["generated"] = false
+	err = p.Prepare(config)
+	if err == nil {
+		t.Fatalf("should required existing file")
+	}
 }
 
 func TestProvisionerPrepare_ValidSource(t *testing.T) {
@@ -58,13 +64,30 @@ func TestProvisionerPrepare_ValidSource(t *testing.T) {
 
 	config := testConfig()
 	config["source"] = tf.Name()
+	err = p.Prepare(config)
+	if err != nil {
+		t.Fatalf("should allow valid file: %s", err)
+	}
 
+	config["generated"] = false
 	err = p.Prepare(config)
 	if err != nil {
 		t.Fatalf("should allow valid file: %s", err)
 	}
 }
 
+func TestProvisionerPrepare_GeneratedSource(t *testing.T) {
+	var p Provisioner
+
+	config := testConfig()
+	config["source"] = "/this/should/not/exist"
+	config["generated"] = true
+	err := p.Prepare(config)
+	if err != nil {
+		t.Fatalf("should allow non-existing file: %s", err)
+	}
+}
+
 func TestProvisionerPrepare_EmptyDestination(t *testing.T) {
 	var p Provisioner