packer: add ParseTemplateFile since that is useful

packer/template.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"github.com/mitchellh/mapstructure"
+	"io/ioutil"
 	"sort"
 )
 
@@ -255,6 +256,17 @@ func ParseTemplate(data []byte) (t *Template, err error) {
 	return
 }
 
+// ParseTemplateFile takes the given template file and parses it into
+// a single template.
+func ParseTemplateFile(path string) (*Template, error) {
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	return ParseTemplate(data)
+}
+
 func parsePostProvisioner(i int, rawV interface{}) (result []map[string]interface{}, errors []error) {
 	switch v := rawV.(type) {
 	case string:

packer/template_test.go

@@ -2,6 +2,7 @@ package packer
 
 import (
 	"cgl.tideland.biz/asserts"
+	"io/ioutil"
 	"reflect"
 	"sort"
 	"testing"
@@ -18,6 +19,30 @@ func testComponentFinder() *ComponentFinder {
 	}
 }
 
+func TestParseTemplateFile_basic(t *testing.T) {
+	data := `
+	{
+		"builders": [{"type": "something"}]
+	}
+	`
+
+	tf, err := ioutil.TempFile("", "packer")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	tf.Write([]byte(data))
+	tf.Close()
+
+	result, err := ParseTemplateFile(tf.Name())
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if len(result.Builders) != 1 {
+		t.Fatalf("bad: %#v", result.Builders)
+	}
+}
+
 func TestParseTemplate_Basic(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)