Don't return unexported types

pkg/plugin/builder/builder.go

@@ -42,7 +42,7 @@ type builder struct {
 }
 
 // Requires populated plugin config
-func NewPluginBuilder(gc config.Plugin) *builder {
+func NewPluginBuilder(gc config.Plugin) PluginBuilder {
 	return &builder{
 		GenConfig:  gc,
 		tmpVenDirs: make([]string, 0),

pkg/plugin/generator.go

@@ -36,7 +36,7 @@ type generator struct {
 }
 
 // Creates a new generator from a plugin and database config
-func NewGenerator(gc config.Plugin, dbc config.Database) (*generator, error) {
+func NewGenerator(gc config.Plugin, dbc config.Database) (Generator, error) {
 	if len(gc.Transformers) < 1 {
 		return nil, errors.New("plugin generator is not configured with any transformers")
 	}

pkg/plugin/manager/manager.go

@@ -41,7 +41,7 @@ type manager struct {
 }
 
 // Manager requires both filled in generator and database configs
-func NewMigrationManager(gc config.Plugin, dbc config.Database) *manager {
+func NewMigrationManager(gc config.Plugin, dbc config.Database) MigrationManager {
 	return &manager{
 		GenConfig: gc,
 		DBConfig:  dbc,

pkg/plugin/writer/writer.go

@@ -37,7 +37,7 @@ type writer struct {
 }
 
 // Requires populated plugin config
-func NewPluginWriter(gc config.Plugin) *writer {
+func NewPluginWriter(gc config.Plugin) PluginWriter {
 	return &writer{
 		GenConfig: gc,
 	}