lib/config: Decouple VerifyConfiguration from Committer (syncthing#7939)

... and remove 8/10 implementations, which were no-ops. This saves code
and time copying configurations.

lib/api/api.go

@@ -94,6 +94,8 @@ type service struct {
 	systemLog logger.Recorder
 }
 
+var _ config.Verifier = &service{}
+
 type Service interface {
 	suture.Service
 	config.Committer

lib/config/wrapper.go

@@ -31,14 +31,14 @@ const (
 
 var errTooManyModifications = errors.New("too many concurrent config modifications")
 
-// The Committer interface is implemented by objects that need to know about
-// or have a say in configuration changes.
+// The Committer and Verifier interfaces are implemented by objects
+// that need to know about or have a say in configuration changes.
 //
 // When the configuration is about to be changed, VerifyConfiguration() is
-// called for each subscribing object, with the old and new configuration. A
-// nil error is returned if the new configuration is acceptable (i.e. does not
-// contain any errors that would prevent it from being a valid config).
-// Otherwise an error describing the problem is returned.
+// called for each subscribing object that implements it, with copies of the
+// old and new configuration. A nil error is returned if the new configuration
+// is acceptable (i.e., does not contain any errors that would prevent it from
+// being a valid config). Otherwise an error describing the problem is returned.
 //
 // If any subscriber returns an error from VerifyConfiguration(), the
 // configuration change is not committed and an error is returned to whoever
@@ -55,11 +55,16 @@ var errTooManyModifications = errors.New("too many concurrent config modificatio
 // configuration (e.g. calling Wrapper.SetFolder), that are also acquired in any
 // methods of the Committer interface.
 type Committer interface {
-	VerifyConfiguration(from, to Configuration) error
 	CommitConfiguration(from, to Configuration) (handled bool)
 	String() string
 }
 
+// A Verifier can determine if a new configuration is acceptable.
+// See the description for Committer, above.
+type Verifier interface {
+	VerifyConfiguration(from, to Configuration) error
+}
+
 // Waiter allows to wait for the given config operation to complete.
 type Waiter interface {
 	Wait()
@@ -300,6 +305,10 @@ func (w *wrapper) replaceLocked(to Configuration) (Waiter, error) {
 	}
 
 	for _, sub := range w.subs {
+		sub, ok := sub.(Verifier)
+		if !ok {
+			continue
+		}
 		l.Debugln(sub, "verifying configuration")
 		if err := sub.VerifyConfiguration(from.Copy(), to.Copy()); err != nil {
 			l.Debugln(sub, "rejected config:", err)

lib/connections/limiter.go

@@ -122,10 +122,6 @@ func (lim *limiter) processDevicesConfigurationLocked(from, to config.Configurat
 	}
 }
 
-func (lim *limiter) VerifyConfiguration(from, to config.Configuration) error {
-	return nil
-}
-
 func (lim *limiter) CommitConfiguration(from, to config.Configuration) bool {
 	// to ensure atomic update of configuration
 	lim.mu.Lock()

lib/connections/service.go

@@ -706,10 +706,6 @@ func (s *service) logListenAddressesChangedEvent(l ListenerAddresses) {
 	})
 }
 
-func (s *service) VerifyConfiguration(from, to config.Configuration) error {
-	return nil
-}
-
 func (s *service) CommitConfiguration(from, to config.Configuration) bool {
 	newDevices := make(map[protocol.DeviceID]bool, len(to.Devices))
 	for _, dev := range to.Devices {

lib/discover/manager.go

@@ -227,10 +227,6 @@ func (m *manager) Cache() map[protocol.DeviceID]CacheEntry {
 	return res
 }
 
-func (m *manager) VerifyConfiguration(_, _ config.Configuration) error {
-	return nil
-}
-
 func (m *manager) CommitConfiguration(_, to config.Configuration) (handled bool) {
 	m.mut.Lock()
 	defer m.mut.Unlock()

lib/model/model.go

@@ -168,6 +168,8 @@ type model struct {
 	foldersRunning int32
 }
 
+var _ config.Verifier = &model{}
+
 type folderFactory func(*model, *db.FileSet, *ignore.Matcher, config.FolderConfiguration, versioner.Versioner, events.Logger, *util.Semaphore) service
 
 var (

lib/model/progressemitter.go

@@ -212,11 +212,6 @@ func (t *ProgressEmitter) computeProgressUpdates() []progressUpdate {
 	return progressUpdates
 }
 
-// VerifyConfiguration implements the config.Committer interface
-func (t *ProgressEmitter) VerifyConfiguration(from, to config.Configuration) error {
-	return nil
-}
-
 // CommitConfiguration implements the config.Committer interface
 func (t *ProgressEmitter) CommitConfiguration(_, to config.Configuration) bool {
 	t.mut.Lock()

lib/nat/service.go

@@ -45,10 +45,6 @@ func NewService(id protocol.DeviceID, cfg config.Wrapper) *Service {
 	return s
 }
 
-func (s *Service) VerifyConfiguration(from, to config.Configuration) error {
-	return nil
-}
-
 func (s *Service) CommitConfiguration(from, to config.Configuration) bool {
 	s.mut.Lock()
 	if !s.enabled && to.Options.NATEnabled {

lib/ur/failurereporting.go

@@ -188,10 +188,6 @@ func (h *failureHandler) addReport(data FailureData, evTime time.Time) {
 	}
 }
 
-func (h *failureHandler) VerifyConfiguration(_, _ config.Configuration) error {
-	return nil
-}
-
 func (h *failureHandler) CommitConfiguration(from, to config.Configuration) bool {
 	if from.Options.CREnabled != to.Options.CREnabled || from.Options.CRURL != to.Options.CRURL {
 		h.optsChan <- to.Options

lib/ur/usage_report.go

@@ -390,10 +390,6 @@ func (s *Service) Serve(ctx context.Context) error {
 	}
 }
 
-func (s *Service) VerifyConfiguration(from, to config.Configuration) error {
-	return nil
-}
-
 func (s *Service) CommitConfiguration(from, to config.Configuration) bool {
 	if from.Options.URAccepted != to.Options.URAccepted || from.Options.URUniqueID != to.Options.URUniqueID || from.Options.URURL != to.Options.URURL {
 		select {

lib/watchaggregator/aggregator.go

@@ -419,10 +419,6 @@ func (a *aggregator) String() string {
 	return fmt.Sprintf("aggregator/%s:", a.folderCfg.Description())
 }
 
-func (a *aggregator) VerifyConfiguration(from, to config.Configuration) error {
-	return nil
-}
-
 func (a *aggregator) CommitConfiguration(from, to config.Configuration) bool {
 	for _, folderCfg := range to.Folders {
 		if folderCfg.ID == a.folderID {