chore(processors.regex): Inform and warn user on operation modus (#14084)

plugins/processors/regex/converter.go

@@ -9,7 +9,46 @@ import (
 	"github.com/influxdata/telegraf/filter"
 )
 
-func (c *converter) setup(ct converterType) error {
+type converterType int
+
+const (
+	convertTags = iota
+	convertFields
+	convertTagRename
+	convertFieldRename
+	convertMetricRename
+)
+
+func (ct converterType) String() string {
+	switch ct {
+	case convertTags:
+		return "tags"
+	case convertFields:
+		return "fields"
+	case convertTagRename:
+		return "tag_rename"
+	case convertFieldRename:
+		return "field_rename"
+	case convertMetricRename:
+		return "metric_rename"
+	}
+	return fmt.Sprintf("unknown %d", int(ct))
+}
+
+type converter struct {
+	Key         string `toml:"key"`
+	Pattern     string `toml:"pattern"`
+	Replacement string `toml:"replacement"`
+	ResultKey   string `toml:"result_key"`
+	Append      bool   `toml:"append"`
+
+	filter filter.Filter
+	re     *regexp.Regexp
+	groups []string
+	apply  func(m telegraf.Metric)
+}
+
+func (c *converter) setup(ct converterType, log telegraf.Logger) error {
 	// Compile the pattern
 	re, err := regexp.Compile(c.Pattern)
 	if err != nil {
@@ -39,8 +78,15 @@ func (c *converter) setup(ct converterType) error {
 				}
 			}
 			if allNamed {
+				log.Infof("%s: Using named-group mode...", ct)
 				c.groups = groups[1:]
+			} else {
+				msg := "Neither 'result_key' nor 'replacement' given with unnamed or mixed groups;"
+				msg += " using explicit, empty replacement!"
+				log.Warnf("%s: %s", ct, msg)
 			}
+		} else {
+			log.Infof("%s: Using explicit mode...", ct)
 		}
 	case convertTagRename, convertFieldRename:
 		switch c.ResultKey {

plugins/processors/regex/regex.go

@@ -4,26 +4,14 @@ package regex
 import (
 	_ "embed"
 	"fmt"
-	"regexp"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/filter"
 	"github.com/influxdata/telegraf/plugins/processors"
 )
 
 //go:embed sample.conf
 var sampleConfig string
 
-type converterType int
-
-const (
-	convertTags = iota
-	convertFields
-	convertTagRename
-	convertFieldRename
-	convertMetricRename
-)
-
 type Regex struct {
 	Tags         []converter     `toml:"tags"`
 	Fields       []converter     `toml:"fields"`
@@ -33,19 +21,6 @@ type Regex struct {
 	Log          telegraf.Logger `toml:"-"`
 }
 
-type converter struct {
-	Key         string `toml:"key"`
-	Pattern     string `toml:"pattern"`
-	Replacement string `toml:"replacement"`
-	ResultKey   string `toml:"result_key"`
-	Append      bool   `toml:"append"`
-
-	filter filter.Filter
-	re     *regexp.Regexp
-	groups []string
-	apply  func(m telegraf.Metric)
-}
-
 func (*Regex) SampleConfig() string {
 	return sampleConfig
 }
@@ -53,12 +28,12 @@ func (*Regex) SampleConfig() string {
 func (r *Regex) Init() error {
 	// Compile the regular expressions
 	for i := range r.Tags {
-		if err := r.Tags[i].setup(convertTags); err != nil {
+		if err := r.Tags[i].setup(convertTags, r.Log); err != nil {
 			return fmt.Errorf("'tags' %w", err)
 		}
 	}
 	for i := range r.Fields {
-		if err := r.Fields[i].setup(convertFields); err != nil {
+		if err := r.Fields[i].setup(convertFields, r.Log); err != nil {
 			return fmt.Errorf("'fields' %w", err)
 		}
 	}
@@ -67,7 +42,7 @@ func (r *Regex) Init() error {
 		if c.Key != "" {
 			r.Log.Info("'tag_rename' section contains a key which is ignored during processing")
 		}
-		if err := r.TagRename[i].setup(convertTagRename); err != nil {
+		if err := r.TagRename[i].setup(convertTagRename, r.Log); err != nil {
 			return fmt.Errorf("'tag_rename' %w", err)
 		}
 	}
@@ -77,7 +52,7 @@ func (r *Regex) Init() error {
 			r.Log.Info("'field_rename' section contains a key which is ignored during processing")
 		}
 
-		if err := r.FieldRename[i].setup(convertFieldRename); err != nil {
+		if err := r.FieldRename[i].setup(convertFieldRename, r.Log); err != nil {
 			return fmt.Errorf("'field_rename' %w", err)
 		}
 	}
@@ -91,7 +66,7 @@ func (r *Regex) Init() error {
 			r.Log.Info("'metric_rename' section contains a 'result_key' ignored during processing as metrics will ALWAYS the name")
 		}
 
-		if err := r.MetricRename[i].setup(convertMetricRename); err != nil {
+		if err := r.MetricRename[i].setup(convertMetricRename, r.Log); err != nil {
 			return fmt.Errorf("'metric_rename' %w", err)
 		}
 	}