fallback when arg is empty

cmd/prometheus/main.go

@@ -432,7 +432,7 @@ func main() {
 	a.Flag("scrape.discovery-reload-interval", "Interval used by scrape manager to throttle target groups updates.").
 		Hidden().Default("5s").SetValue(&cfg.scrape.DiscoveryReloadInterval)
 
-	a.Flag("scrape.name-escaping-scheme", "method to escape legacy invalid names when sending to an old version of prometheus.  can be one of values (default), underscores, or dots").Default(model.DefaultNameEscapingScheme.String()).StringVar(&cfg.scrape.NameEscapingScheme)
+	a.Flag("scrape.name-escaping-scheme", "method to escape legacy invalid names when sending to an old version of prometheus.  can be one of values (default), underscores, or dots").Default(scrape.DefaultNameEscapingScheme.String()).StringVar(&cfg.scrape.NameEscapingScheme)
 
 	a.Flag("enable-feature", "Comma separated feature names to enable. Valid options: agent, exemplar-storage, expand-external-labels, memory-snapshot-on-shutdown, promql-at-modifier, promql-negative-offset, promql-per-step-stats, promql-experimental-functions, remote-write-receiver (DEPRECATED), extra-scrape-metrics, new-service-discovery-manager, auto-gomaxprocs, no-default-scrape-port, native-histograms, otlp-write-receiver, utf8-names. See https://prometheus.io/docs/prometheus/latest/feature_flags/ for more details.").
 		Default("").StringsVar(&cfg.featureList)

scrape/manager.go

@@ -91,6 +91,8 @@ type Options struct {
 	skipOffsetting bool
 }
 
+const DefaultNameEscapingScheme = model.ValueEncodingEscaping
+
 // Manager maintains a set of scrape pools and manages start/stop cycles
 // when receiving new target groups from the discovery manager.
 type Manager struct {
@@ -160,12 +162,16 @@ func (m *Manager) reload() {
 	m.mtxScrape.Lock()
 	defer m.mtxScrape.Unlock()
 	var err error
-	model.DefaultNameEscapingScheme, err = model.ToEscapingScheme(m.opts.NameEscapingScheme)
-	level.Info(m.logger).Log("msg", "ESCAPING SCHEME UPDATED", "scheme", m.opts.NameEscapingScheme)
-	if err != nil {
-		level.Error(m.logger).Log("msg", "error setting escaping scheme", "err", err)
-		return
+	if m.opts.NameEscapingScheme != "" {
+		model.NameEscapingScheme, err = model.ToEscapingScheme(m.opts.NameEscapingScheme)
+		if err != nil {
+			level.Error(m.logger).Log("msg", "error setting escaping scheme", "err", err)
+			return
+		}
+	} else {
+		model.NameEscapingScheme = DefaultNameEscapingScheme
 	}
+	level.Info(m.logger).Log("msg", "ESCAPING SCHEME", "scheme", model.NameEscapingScheme.String(), "arg", m.opts.NameEscapingScheme)
 
 	var wg sync.WaitGroup
 	for setName, groups := range m.targetSets {