common: process user variables in non-string config decodes [GH-598]

CHANGELOG.md

@@ -35,6 +35,7 @@ IMPROVEMENTS:
 BUG FIXES:
 
 * core: No colored output in machine-readable output. [GH-684]
+* core: User variables can now be used for non-string fields. [GH-598]
 * post-processor/vsphere: Uploads VM properly. [GH-694]
 * post-processor/vsphere: Process user variables.
 * provisioner/ansible-local: playbook paths are properly validated

common/config.go

@@ -7,6 +7,7 @@ import (
 	"net/url"
 	"os"
 	"path/filepath"
+	"reflect"
 	"runtime"
 	"sort"
 	"strings"
@@ -49,8 +50,14 @@ func CheckUnusedConfig(md *mapstructure.Metadata) *packer.MultiError {
 // If you need extra configuration for mapstructure, you should configure
 // it manually and not use this helper function.
 func DecodeConfig(target interface{}, raws ...interface{}) (*mapstructure.Metadata, error) {
+	decodeHook, err := decodeConfigHook(raws)
+	if err != nil {
+		return nil, err
+	}
+
 	var md mapstructure.Metadata
 	decoderConfig := &mapstructure.DecoderConfig{
+		DecodeHook:       decodeHook,
 		Metadata:         &md,
 		Result:           target,
 		WeaklyTypedInput: true,
@@ -149,3 +156,41 @@ func DownloadableURL(original string) (string, error) {
 
 	return url.String(), nil
 }
+
+// This returns a mapstructure.DecodeHookFunc that automatically template
+// processes any configuration values that aren't strings but have been
+// provided as strings.
+//
+// For example: "image_id" wants an int and the user uses a string with
+// a user variable like "{{user `image_id`}}". This decode hook makes that
+// work.
+func decodeConfigHook(raws []interface{}) (mapstructure.DecodeHookFunc, error) {
+	// First thing we do is decode PackerConfig so that we can have access
+	// to the user variables so that we can process some templates.
+	var pc PackerConfig
+	for _, raw := range raws {
+		if err := mapstructure.Decode(raw, &pc); err != nil {
+			return nil, err
+		}
+	}
+
+	tpl, err := packer.NewConfigTemplate()
+	if err != nil {
+		return nil, err
+	}
+	tpl.UserVars = pc.PackerUserVars
+
+	return func(f reflect.Kind, t reflect.Kind, v interface{}) (interface{}, error) {
+		if t != reflect.String {
+			if sv, ok := v.(string); ok {
+				var err error
+				v, err = tpl.Process(sv, nil)
+				if err != nil {
+					return nil, err
+				}
+			}
+		}
+
+		return v, nil
+	}, nil
+}

common/config_test.go

@@ -66,6 +66,32 @@ func TestDecodeConfig(t *testing.T) {
 	}
 }
 
+// This test tests the case that a user var is used for an integer
+// configuration.
+func TestDecodeConfig_userVarConversion(t *testing.T) {
+	type Local struct {
+		Val int
+	}
+
+	raw := map[string]interface{}{
+		"packer_user_variables": map[string]string{
+			"foo": "42",
+		},
+
+		"val": "{{user `foo`}}",
+	}
+
+	var result Local
+	_, err := DecodeConfig(&result, raw)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if result.Val != 42 {
+		t.Fatalf("invalid: %#v", result.Val)
+	}
+}
+
 func TestDownloadableURL(t *testing.T) {
 	// Invalid URL: has hex code in host
 	_, err := DownloadableURL("http://what%20.com")