Revert "lib/promrelabel: show error message if labels not in prometheus exposition format (#4304)"

This reverts commit 193a9c3328.

Reason for revert: the commit doesn't fix the real issue with promutils.NewLabelsFromString()
function, which must return error when improperly formatted Prometheus metric with labels is passed to it.
See https://github.com/prometheus/docs/blob/main/content/docs/instrumenting/exposition_formats.md#text-format-example

E.g. the promutils.NewLabelsFromString() must return error when the following strings are passed to it:

- `{foo:"bar"}`, since `:` is disallowed in Prometheus text exposition format. The corect value is `{foo="bar"}`
- `{"foo":"bar"}`, since label name shouldn't be quoted. The correct value is `{foo="bar"}`.

The reverted commit introduces another set of bugs, which happily accept the following invalid input:

- `{foo=~"bar"}`
- `{foo!="bar"}`
- `{foo!~"bar"}`

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4284
See also https://github.com/VictoriaMetrics/VictoriaMetrics/pull/4304

docs/CHANGELOG.md

@@ -75,7 +75,6 @@ The following tip changes can be tested by building VictoriaMetrics components f
 * BUGFIX: [vmbackup](https://docs.victoriametrics.com/vmbackup.html): fix compatibility with Windows OS. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/70).
 * BUGFIX: [vmctl](https://docs.victoriametrics.com/vmctl.html): fix performance issue when migrating data from VictoriaMetrics according to [these docs](https://docs.victoriametrics.com/vmctl.html#migrating-data-from-victoriametrics). Add the ability to speed up the data migration via `--vm-native-disable-retries` command-line flag. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4092).
 * BUGFIX: [stream aggregation](https://docs.victoriametrics.com/stream-aggregation.html): fix bug with duplicated labels during stream aggregation via single-node VictoriaMetrics. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4277).
-* BUGFIX: [relabeling](https://docs.victoriametrics.com/relabeling.html): properly validate labels input on Metric Relabel Debug page in [VMUI](https://docs.victoriametrics.com/#vmui). See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4284).
 
 ## [v1.90.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.90.0)
 

lib/promrelabel/debug.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"io"
 
-	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/searchutils"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promutils"
 )
 
@@ -19,33 +18,20 @@ func WriteTargetRelabelDebug(w io.Writer, targetID, metric, relabelConfigs, form
 }
 
 func writeRelabelDebug(w io.Writer, isTargetRelabel bool, targetID, metric, relabelConfigs, format string, err error) {
-	targetURL := ""
 	if metric == "" {
-		WriteRelabelDebugSteps(w, targetURL, targetID, format, nil, metric, relabelConfigs, err)
-		return
+		metric = "{}"
 	}
+	targetURL := ""
 	if err != nil {
 		WriteRelabelDebugSteps(w, targetURL, targetID, format, nil, metric, relabelConfigs, err)
 		return
 	}
-	selectors, err := searchutils.ParseMetricSelector(metric)
+	labels, err := promutils.NewLabelsFromString(metric)
 	if err != nil {
 		err = fmt.Errorf("cannot parse metric: %s", err)
 		WriteRelabelDebugSteps(w, targetURL, targetID, format, nil, metric, relabelConfigs, err)
 		return
 	}
-
-	var labels promutils.Labels
-	for _, selector := range selectors {
-		key := string(selector.Key)
-		value := string(selector.Value)
-		if key == "" {
-			labels.Add("__name__", value)
-			continue
-		}
-		labels.Add(key, value)
-	}
-
 	pcs, err := ParseRelabelConfigsData([]byte(relabelConfigs))
 	if err != nil {
 		err = fmt.Errorf("cannot parse relabel configs: %s", err)
@@ -53,7 +39,7 @@ func writeRelabelDebug(w io.Writer, isTargetRelabel bool, targetID, metric, rela
 		return
 	}
 
-	dss, targetURL := newDebugRelabelSteps(pcs, &labels, isTargetRelabel)
+	dss, targetURL := newDebugRelabelSteps(pcs, labels, isTargetRelabel)
 	WriteRelabelDebugSteps(w, targetURL, targetID, format, dss, metric, relabelConfigs, nil)
 }