fix: resolve lint issues and add changelog fragment

- append.go: apply De Morgan's law (QF1001)
- copy_fields.go: lowercase error string (ST1005)
- decompress_gzip_field.go: lowercase error string (ST1005)
- rename.go: lowercase error string (ST1005)
- extract_array.go: remove redundant embedded field selector (QF1008)
- Add changelog fragment

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: strawgate

changelog/fragments/1774840000-skip-unnecessary-event-clone.yaml

@@ -0,0 +1,5 @@
+kind: enhancement
+summary: Skip unnecessary event.Clone() in 11 processors for single-field operations
+component: libbeat
+pr:
+  - https://github.com/elastic/beats/pull/49777

libbeat/processors/actions/append.go

@@ -128,7 +128,7 @@ func (f *appendProcessor) appendValues(target string, fields []string, values []
 	}
 
 	// replace the existing target with new array
-	if err := event.Delete(target); err != nil && !(err.Error() == "key not found") {
+	if err := event.Delete(target); err != nil && err.Error() != "key not found" {
 		return fmt.Errorf("unable to delete the target field %s due to error: %w", target, err)
 	}
 	if _, err := event.PutValue(target, arr); err != nil {

libbeat/processors/actions/copy_fields.go

@@ -77,7 +77,7 @@ func (f *copyFields) Run(event *beat.Event) (*beat.Event, error) {
 	for _, field := range f.config.Fields {
 		err := f.copyField(field.From, field.To, event)
 		if err != nil {
-			errMsg := fmt.Errorf("Failed to copy fields in copy_fields processor: %w", err)
+			errMsg := fmt.Errorf("failed to copy fields in copy_fields processor: %w", err)
 			f.logger.Debugw(errMsg.Error(), logp.TypeKey, logp.EventType)
 
 			if f.config.FailOnError {

libbeat/processors/actions/decompress_gzip_field.go

@@ -69,7 +69,7 @@ func NewDecompressGzipFields(c *conf.C, log *logp.Logger) (beat.Processor, error
 func (f *decompressGzipField) Run(event *beat.Event) (*beat.Event, error) {
 	err := f.decompressGzipField(event)
 	if err != nil {
-		errMsg := fmt.Errorf("Failed to decompress field in decompress_gzip_field processor: %w", err)
+		errMsg := fmt.Errorf("failed to decompress field in decompress_gzip_field processor: %w", err)
 		f.log.Debugw(errMsg.Error(), logp.EventType, logp.TypeKey)
 
 		if f.config.FailOnError {

libbeat/processors/actions/rename.go

@@ -83,7 +83,7 @@ func (f *renameFields) Run(event *beat.Event) (*beat.Event, error) {
 	for _, field := range f.config.Fields {
 		err := f.renameField(field.From, field.To, event)
 		if err != nil {
-			errMsg := fmt.Errorf("Failed to rename fields in processor: %w", err)
+			errMsg := fmt.Errorf("failed to rename fields in processor: %w", err)
 			f.logger.Debugw(errMsg.Error(), logp.TypeKey, logp.EventType)
 
 			if f.config.FailOnError {

libbeat/processors/extract_array/extract_array.go

@@ -115,12 +115,12 @@ func isEmpty(v reflect.Value) bool {
 }
 
 func (f *extractArrayProcessor) Run(event *beat.Event) (*beat.Event, error) {
-	iValue, err := event.GetValue(f.config.Field)
+	iValue, err := event.GetValue(f.Field)
 	if err != nil {
-		if f.config.IgnoreMissing && errors.Is(err, mapstr.ErrKeyNotFound) {
+		if f.IgnoreMissing && errors.Is(err, mapstr.ErrKeyNotFound) {
 			return event, nil
 		}
-		return event, fmt.Errorf("could not fetch value for field %s: %w", f.config.Field, err)
+		return event, fmt.Errorf("could not fetch value for field %s: %w", f.Field, err)
 	}
 
 	array := reflect.ValueOf(iValue)