NilBuilderFactory

packer/build.go

@@ -31,3 +31,10 @@ type Builder interface {
 type BuilderFactory interface {
 	CreateBuilder(name string) Builder
 }
+
+// This implements BuilderFactory to return nil for every builder.
+type NilBuilderFactory byte
+
+func (NilBuilderFactory) CreateBuilder(name string) Builder {
+	return nil
+}

packer/environment.go

@@ -51,6 +51,7 @@ type EnvironmentConfig struct {
 // be used to create a new enviroment with NewEnvironment with sane defaults.
 func DefaultEnvironmentConfig() *EnvironmentConfig {
 	config := &EnvironmentConfig{}
+	config.BuilderFactory = new(NilBuilderFactory)
 	config.Ui = &ReaderWriterUi{os.Stdin, os.Stdout}
 	return config
 }