packer: min_packer_version [GH-487]

CHANGELOG.md

@@ -8,6 +8,8 @@ FEATURES:
     command, which talks to a Chef Server. [GH-855]
   * **New provisioner:** `puppet-server` - Provision using Puppet by
     communicating to a Puppet master. [GH-796]
+  * `min_packer_version` can be specified in a Packer template to force
+    a minimum version. [GH-487]
 
 IMPROVEMENTS:
 

packer/template.go

@@ -3,6 +3,7 @@ package packer
 import (
 	"bytes"
 	"fmt"
+	"github.com/hashicorp/go-version"
 	"github.com/mitchellh/mapstructure"
 	jsonutil "github.com/mitchellh/packer/common/json"
 	"io"
@@ -18,12 +19,14 @@ import (
 // "interface{}" pointers since we actually don't know what their contents
 // are until we read the "type" field.
 type rawTemplate struct {
+	MinimumPackerVersion string `mapstructure:"min_packer_version"`
+
 	Description    string
-	Variables      map[string]interface{}
 	Builders       []map[string]interface{}
 	Hooks          map[string][]string
-	Provisioners   []map[string]interface{}
 	PostProcessors []interface{} `mapstructure:"post-processors"`
+	Provisioners   []map[string]interface{}
+	Variables      map[string]interface{}
 }
 
 // The Template struct represents a parsed template, parsed into the most
@@ -115,6 +118,25 @@ func ParseTemplate(data []byte, vars map[string]string) (t *Template, err error)
 		return
 	}
 
+	if rawTpl.MinimumPackerVersion != "" {
+		vCur, err := version.NewVersion(Version)
+		if err != nil {
+			panic(err)
+		}
+		vReq, err := version.NewVersion(rawTpl.MinimumPackerVersion)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"'minimum_packer_version' error: %s", err)
+		}
+
+		if vCur.LessThan(vReq) {
+			return nil, fmt.Errorf(
+				"Template requires Packer version %s. " +
+				"Running version is %s.",
+				vReq, vCur)
+		}
+	}
+
 	errors := make([]error, 0)
 
 	if len(md.Unused) > 0 {

packer/template_test.go

@@ -60,6 +60,69 @@ func TestParseTemplateFile_basic(t *testing.T) {
 	}
 }
 
+func TestParseTemplateFile_minPackerVersionBad(t *testing.T) {
+	data := `
+	{
+		"min_packer_version": "27.0.0",
+		"builders": [{"type": "something"}]
+	}
+	`
+
+	tf, err := ioutil.TempFile("", "packer")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	tf.Write([]byte(data))
+	tf.Close()
+
+	_, err = ParseTemplateFile(tf.Name(), nil)
+	if err == nil {
+		t.Fatal("expects error")
+	}
+}
+
+func TestParseTemplateFile_minPackerVersionFormat(t *testing.T) {
+	data := `
+	{
+		"min_packer_version": "NOPE NOPE NOPE",
+		"builders": [{"type": "something"}]
+	}
+	`
+
+	tf, err := ioutil.TempFile("", "packer")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	tf.Write([]byte(data))
+	tf.Close()
+
+	_, err = ParseTemplateFile(tf.Name(), nil)
+	if err == nil {
+		t.Fatal("expects error")
+	}
+}
+
+func TestParseTemplateFile_minPackerVersionGood(t *testing.T) {
+	data := `
+	{
+		"min_packer_version": "0.1",
+		"builders": [{"type": "something"}]
+	}
+	`
+
+	tf, err := ioutil.TempFile("", "packer")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	tf.Write([]byte(data))
+	tf.Close()
+
+	_, err = ParseTemplateFile(tf.Name(), nil)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+}
+
 func TestParseTemplateFile_stdin(t *testing.T) {
 	data := `
 	{

website/source/docs/templates/introduction.html.markdown

@@ -43,6 +43,12 @@ Along with each key, it is noted whether it is required or not.
   information on what post-processors do and how they're defined, read the
   sub-section on [configuring post-processors in templates](/docs/templates/post-processors.html).
 
+* `min_packer_version` (optional) is a string that has a minimum Packer
+  version that is required to parse the template. This can be used to
+  ensure that proper versions of Packer are used with the template. A
+  max version can't be specified because Packer retains backwards
+  compatibility with `packer fix`.
+
 ## Example Template
 
 Below is an example of a basic template that is nearly fully functional. It is just