Define a type for onChange func instead of func pointer (#4656)

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## 🛑 Breaking changes 🛑
+
+- Define a type `WatcherFunc` for onChange func instead of func pointer (#4656)
+
 ## v0.42.0 Beta
 
 ## 🛑 Breaking changes 🛑

config/configmapprovider/env.go

@@ -36,7 +36,7 @@ func NewEnv(envName string) Provider {
 	}
 }
 
-func (emp *envMapProvider) Retrieve(_ context.Context, _ func(*ChangeEvent)) (Retrieved, error) {
+func (emp *envMapProvider) Retrieve(context.Context, WatcherFunc) (Retrieved, error) {
 	if emp.envName == "" {
 		return nil, errors.New("config environment not specified")
 	}

config/configmapprovider/file.go

@@ -36,7 +36,7 @@ func NewFile(fileName string) Provider {
 	}
 }
 
-func (fmp *fileMapProvider) Retrieve(_ context.Context, _ func(*ChangeEvent)) (Retrieved, error) {
+func (fmp *fileMapProvider) Retrieve(context.Context, WatcherFunc) (Retrieved, error) {
 	if fmp.fileName == "" {
 		return nil, errors.New("config file not specified")
 	}

config/configmapprovider/properties.go

@@ -40,7 +40,7 @@ func NewProperties(properties []string) Provider {
 	}
 }
 
-func (pmp *propertiesMapProvider) Retrieve(_ context.Context, onChange func(*ChangeEvent)) (Retrieved, error) {
+func (pmp *propertiesMapProvider) Retrieve(context.Context, WatcherFunc) (Retrieved, error) {
 	if len(pmp.properties) == 0 {
 		return NewRetrieved(func(ctx context.Context) (*config.Map, error) {
 			return config.NewMap(), nil

config/configmapprovider/provider.go

@@ -40,15 +40,15 @@ type Provider interface {
 	// contains the value to be injected in the configuration and the corresponding watcher that
 	// will be used to monitor for updates of the retrieved value.
 	//
-	// onChange callback is called when the config changes. onChange may be called from
-	// a different go routine. After onChange is called Retrieved.Get should be called
+	// watcher callback is called when the config changes. watcher may be called from
+	// a different go routine. After watcher is called Retrieved.Get should be called
 	// to get the new config. See description of Retrieved for more details.
-	// onChange may be nil, which indicates that the caller is not interested in
+	// watcher may be nil, which indicates that the caller is not interested in
 	// knowing about the changes.
 	//
 	// If ctx is cancelled should return immediately with an error.
 	// Should never be called concurrently with itself or with Shutdown.
-	Retrieve(ctx context.Context, onChange func(*ChangeEvent)) (Retrieved, error)
+	Retrieve(ctx context.Context, watcher WatcherFunc) (Retrieved, error)
 
 	// Shutdown signals that the configuration for which this Provider was used to
 	// retrieve values is no longer in use and the Provider should close and release
@@ -62,6 +62,8 @@ type Provider interface {
 	Shutdown(ctx context.Context) error
 }
 
+type WatcherFunc func(*ChangeEvent)
+
 // ChangeEvent describes the particular change event that happened with the config.
 // TODO: see if this can be eliminated.
 type ChangeEvent struct {

service/config_provider_test.go

@@ -38,14 +38,14 @@ type mockProvider struct {
 	errS error
 }
 
-func (m *mockProvider) Retrieve(_ context.Context, onChange func(*configmapprovider.ChangeEvent)) (configmapprovider.Retrieved, error) {
+func (m *mockProvider) Retrieve(_ context.Context, watcher configmapprovider.WatcherFunc) (configmapprovider.Retrieved, error) {
 	if m.errR != nil {
 		return nil, m.errR
 	}
 	if m.ret == nil {
 		return &fakeRetrieved{}, nil
 	}
-	m.ret.onChange = onChange
+	m.ret.watcher = watcher
 	return m.ret, nil
 }
 
@@ -63,16 +63,16 @@ func (ecu *errConfigUnmarshaler) Unmarshal(*config.Map, component.Factories) (*c
 
 type fakeRetrieved struct {
 	configmapprovider.Retrieved
-	retM     *config.Map
-	errG     error
-	errW     error
-	errC     error
-	onChange func(event *configmapprovider.ChangeEvent)
+	retM    *config.Map
+	errG    error
+	errW    error
+	errC    error
+	watcher configmapprovider.WatcherFunc
 }
 
 func (er *fakeRetrieved) Get(context.Context) (*config.Map, error) {
-	if er.onChange != nil {
-		er.onChange(&configmapprovider.ChangeEvent{Error: er.errW})
+	if er.watcher != nil {
+		er.watcher(&configmapprovider.ChangeEvent{Error: er.errW})
 	}
 	if er.errG != nil {
 		return nil, er.errG