vmagent: respect -usePromCompatibleNaming if no relabeling is set

See #3493

Signed-off-by: hagen1778 <roman@victoriametrics.com>

app/vmagent/remotewrite/relabel.go

@@ -86,7 +86,7 @@ func initLabelsGlobal() {
 }
 
 func (rctx *relabelCtx) applyRelabeling(tss []prompbmarshal.TimeSeries, extraLabels []prompbmarshal.Label, pcs *promrelabel.ParsedConfigs) []prompbmarshal.TimeSeries {
-	if len(extraLabels) == 0 && pcs.Len() == 0 {
+	if len(extraLabels) == 0 && pcs.Len() == 0 && !*usePromCompatibleNaming {
 		// Nothing to change.
 		return tss
 	}

app/vmagent/remotewrite/relabel_test.go

@@ -0,0 +1,48 @@
+package remotewrite
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompbmarshal"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promrelabel"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promutils"
+)
+
+func TestApplyRelabeling(t *testing.T) {
+	f := func(extraLabels []prompbmarshal.Label, pcs *promrelabel.ParsedConfigs, sTss, sExpTss string) {
+		rctx := &relabelCtx{}
+		tss, expTss := parseSeries(sTss), parseSeries(sExpTss)
+		gotTss := rctx.applyRelabeling(tss, extraLabels, pcs)
+		if !reflect.DeepEqual(gotTss, expTss) {
+			t.Fatalf("expected to have: \n%v;\ngot: \n%v", expTss, gotTss)
+		}
+	}
+
+	f(nil, nil, "up", "up")
+	f([]prompbmarshal.Label{{Name: "foo", Value: "bar"}}, nil, "up", `up{foo="bar"}`)
+	f([]prompbmarshal.Label{{Name: "foo", Value: "bar"}}, nil, `up{foo="baz"}`, `up{foo="bar"}`)
+
+	pcs, err := promrelabel.ParseRelabelConfigsData([]byte(`
+- target_label: "foo"
+  replacement: "aaa"
+- action: labeldrop
+  regex: "env.*"
+`))
+	if err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	f(nil, pcs, `up{foo="baz", env="prod"}`, `up{foo="aaa"}`)
+
+	*usePromCompatibleNaming = true
+	f(nil, nil, `foo.bar`, `foo_bar`)
+	*usePromCompatibleNaming = false
+}
+
+func parseSeries(data string) []prompbmarshal.TimeSeries {
+	var tss []prompbmarshal.TimeSeries
+	tss = append(tss, prompbmarshal.TimeSeries{
+		Labels: promutils.MustNewLabelsFromString(data).GetLabels(),
+	})
+	return tss
+}

docs/CHANGELOG.md

@@ -18,6 +18,7 @@ The following tip changes can be tested by building VictoriaMetrics components f
 **Update note 1:** This and newer releases of VictoriaMetrics may return gaps for `rate(m[d])` queries on short time ranges if `[d]` lookbehind window is set expliticly. For example, `rate(http_requests_total[$__interval])`. This reduces confusion level when the user expects the needed results from the query with explicitly set lookbehind window. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3483). The previous gap filling behaviour can be restored by removing explicit lookbehind window `[d]` from the query, e.g. by substituting the `rate(m[d])` with `rate(m)`. See [these docs](https://docs.victoriametrics.com/MetricsQL.html#implicit-query-conversions) for details.
 
 * BUGFIX: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): never extend explicitly set lookbehind window for [rate()](https://docs.victoriametrics.com/MetricsQL.html#rate) function. This reduces the level of confusion when the user expects the needed results after explicitly seting the lookbehind window `[d]` in the query `rate(m[d])`. Previously VictoriaMetrics could silently extend the lookbehind window, so it covers at least two raw samples. Now this behavior works only if the lookbehind window in square brackets isn't set explicitly, e.g. in the case of `rate(m)`. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3483) for details.
+* BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): respect `-usePromCompatibleNaming` flag if no relabeling or extra labels were set. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3511) for details.
 
 
 ## [v1.85.2](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.85.2)