common: config strings to slices [GH-950]

CHANGELOG.md

@@ -14,6 +14,9 @@ FEATURES:
 IMPROVEMENTS:
 
   * core: RPC transport between plugins switched to MessagePack
+  * core: Templates array values can now be comma separated strings.
+      Most importantly, this allows for user variables to fill
+      array configurations. [GH-950]
   * builder/amazon: Added `ssh_private_key_file` option [GH-971]
   * builder/amazon: Added `ami_virtualization_type` option [GH-1021]
   * builder/googlecompute: Configurable instance name. [GH-1065]

common/config.go

@@ -68,7 +68,10 @@ func DecodeConfig(target interface{}, raws ...interface{}) (*mapstructure.Metada
 
 	var md mapstructure.Metadata
 	decoderConfig := &mapstructure.DecoderConfig{
-		DecodeHook:       decodeHook,
+		DecodeHook:       mapstructure.ComposeDecodeHookFunc(
+			decodeHook,
+			mapstructure.StringToSliceHookFunc(","),
+		),
 		Metadata:         &md,
 		Result:           target,
 		WeaklyTypedInput: true,

common/config_test.go

@@ -95,6 +95,33 @@ func TestDecodeConfig(t *testing.T) {
 	}
 }
 
+// This test tests the case that a user var is used for an integer
+// configuration.
+func TestDecodeConfig_stringToSlice(t *testing.T) {
+	type Local struct {
+		Val []string
+	}
+
+	raw := map[string]interface{}{
+		"packer_user_variables": map[string]string{
+			"foo": "bar",
+		},
+
+		"val": "foo,{{user `foo`}}",
+	}
+
+	var result Local
+	_, err := DecodeConfig(&result, raw)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	expected := []string{"foo", "bar"}
+	if !reflect.DeepEqual(result.Val, expected) {
+		t.Fatalf("invalid: %#v", result.Val)
+	}
+}
+
 // This test tests the case that a user var is used for an integer
 // configuration.
 func TestDecodeConfig_userVarConversion(t *testing.T) {