chore: Fix linter findings for prealloc (part3) (#12246)

.golangci.yml

@@ -19,6 +19,7 @@ linters:
     - lll
     - nakedret
     - nilerr
+    - prealloc
     - predeclared
     - revive
     - sqlclosecheck
@@ -77,6 +78,10 @@ linters-settings:
     # Tab width in spaces.
     # Default: 1
     tab-width: 4
+  prealloc:
+    # Report pre-allocation suggestions only on simple loops that have no returns/breaks/continues/gotos in them.
+    # Default: true
+    simple: false
   revive:
     rules:
       - name: argument-limit

plugins/inputs/hddtemp/go-hddtemp/hddtemp.go

@@ -28,7 +28,6 @@ func (h *hddtemp) Fetch(address string) ([]Disk, error) {
 		err    error
 		conn   net.Conn
 		buffer bytes.Buffer
-		disks  []Disk
 	)
 
 	if conn, err = net.Dial("tcp", address); err != nil {
@@ -41,7 +40,9 @@ func (h *hddtemp) Fetch(address string) ([]Disk, error) {
 
 	fields := strings.Split(buffer.String(), "|")
 
-	for index := 0; index < len(fields)/5; index++ {
+	size := len(fields) / 5
+	disks := make([]Disk, 0, size)
+	for index := 0; index < size; index++ {
 		status := ""
 		offset := index * 5
 		device := fields[offset+1]

plugins/inputs/modbus/modbus_test.go

@@ -3473,8 +3473,7 @@ func generateRequestDefinitions(ranges []rangeDefinition) []requestFieldDefiniti
 }
 
 func generateExpectation(defs []requestExpectation) []request {
-	var requests []request
+	requests := make([]request, 0, len(defs))
-
 	for _, def := range defs {
 		r := def.req
 		r.fields = make([]field, 0)

plugins/inputs/pgbouncer/pgbouncer.go

@@ -138,7 +138,6 @@ type scanner interface {
 
 func (p *PgBouncer) accRow(row scanner, columns []string) (map[string]string,
 	map[string]*interface{}, error) {
-	var columnVars []interface{}
 	var dbname bytes.Buffer
 
 	// this is where we'll store the column name with its *interface{}
@@ -148,6 +147,7 @@ func (p *PgBouncer) accRow(row scanner, columns []string) (map[string]string,
 		columnMap[column] = new(interface{})
 	}
 
+	columnVars := make([]interface{}, 0, len(columnMap))
 	// populate the array of interface{} with the pointers in the right order
 	for i := 0; i < len(columnMap); i++ {
 		columnVars = append(columnVars, columnMap[columns[i]])

plugins/inputs/postgresql/postgresql.go

@@ -105,7 +105,6 @@ type scanner interface {
 }
 
 func (p *Postgresql) accRow(row scanner, acc telegraf.Accumulator, columns []string) error {
-	var columnVars []interface{}
 	var dbname bytes.Buffer
 
 	// this is where we'll store the column name with its *interface{}
@@ -115,6 +114,7 @@ func (p *Postgresql) accRow(row scanner, acc telegraf.Accumulator, columns []str
 		columnMap[column] = new(interface{})
 	}
 
+	columnVars := make([]interface{}, 0, len(columnMap))
 	// populate the array of interface{} with the pointers in the right order
 	for i := 0; i < len(columnMap); i++ {
 		columnVars = append(columnVars, columnMap[columns[i]])

plugins/inputs/postgresql_extensible/postgresql_extensible.go

@@ -170,7 +170,6 @@ type scanner interface {
 func (p *Postgresql) accRow(measName string, row scanner, acc telegraf.Accumulator, columns []string) error {
 	var (
 		err        error
-		columnVars []interface{}
 		dbname     bytes.Buffer
 		tagAddress string
 		timestamp  time.Time
@@ -183,6 +182,7 @@ func (p *Postgresql) accRow(measName string, row scanner, acc telegraf.Accumulat
 		columnMap[column] = new(interface{})
 	}
 
+	columnVars := make([]interface{}, 0, len(columnMap))
 	// populate the array of interface{} with the pointers in the right order
 	for i := 0; i < len(columnMap); i++ {
 		columnVars = append(columnVars, columnMap[columns[i]])

plugins/inputs/sqlserver/sqlserver.go

@@ -325,7 +325,6 @@ func (s *SQLServer) gatherServer(pool *sql.DB, query Query, acc telegraf.Accumul
 }
 
 func (s *SQLServer) accRow(query Query, acc telegraf.Accumulator, row scanner) error {
-	var columnVars []interface{}
 	var fields = make(map[string]interface{})
 
 	// store the column name with its *interface{}
@@ -333,6 +332,8 @@ func (s *SQLServer) accRow(query Query, acc telegraf.Accumulator, row scanner) e
 	for _, column := range query.OrderedColumns {
 		columnMap[column] = new(interface{})
 	}
+
+	columnVars := make([]interface{}, 0, len(columnMap))
 	// populate the array of interface{} with the pointers in the right order
 	for i := 0; i < len(columnMap); i++ {
 		columnVars = append(columnVars, columnMap[query.OrderedColumns[i]])

plugins/inputs/zipkin/cmd/thrift_serialize/thrift_serialize.go

@@ -31,6 +31,7 @@ import (
 	"os"
 
 	"github.com/apache/thrift/lib/go/thrift"
+
 	"github.com/influxdata/telegraf/plugins/inputs/zipkin/codec/thrift/gen-go/zipkincore"
 )
 
@@ -122,31 +123,27 @@ func jsonToZipkinThrift(jsonRaw []byte) ([]byte, error) {
 func thriftToJSONSpans(thriftData []byte) ([]byte, error) {
 	buffer := thrift.NewTMemoryBuffer()
 	if _, err := buffer.Write(thriftData); err != nil {
-		err = fmt.Errorf("error in buffer write: %v", err)
+		return nil, fmt.Errorf("error in buffer write: %w", err)
-		return nil, err
 	}
 
 	transport := thrift.NewTBinaryProtocolConf(buffer, nil)
 	_, size, err := transport.ReadListBegin(context.Background())
 	if err != nil {
-		err = fmt.Errorf("error in ReadListBegin: %v", err)
+		return nil, fmt.Errorf("error in ReadListBegin: %w", err)
-		return nil, err
 	}
 
-	var spans []*zipkincore.Span
+	spans := make([]*zipkincore.Span, 0, size)
 	for i := 0; i < size; i++ {
 		zs := &zipkincore.Span{}
 		if err = zs.Read(context.Background(), transport); err != nil {
-			err = fmt.Errorf("Error reading into zipkin struct: %v", err)
+			return nil, fmt.Errorf("error reading into zipkin struct: %w", err)
-			return nil, err
 		}
 		spans = append(spans, zs)
 	}
 
 	err = transport.ReadListEnd(context.Background())
 	if err != nil {
-		err = fmt.Errorf("error ending thrift read: %v", err)
+		return nil, fmt.Errorf("error ending thrift read: %w", err)
-		return nil, err
 	}
 
 	out, _ := json.MarshalIndent(spans, "", "    ")

plugins/outputs/timestream/timestream.go

@@ -357,7 +357,7 @@ func (t *Timestream) createTable(tableName *string) error {
 			MemoryStoreRetentionPeriodInHours:  t.CreateTableMemoryStoreRetentionPeriodInHours,
 		},
 	}
-	var tags []types.Tag
+	tags := make([]types.Tag, 0, len(t.CreateTableTags))
 	for key, val := range t.CreateTableTags {
 		tags = append(tags, types.Tag{
 			Key:   aws.String(key),
@@ -434,7 +434,7 @@ func (t *Timestream) TransformMetrics(metrics []telegraf.Metric) []*timestreamwr
 }
 
 func (t *Timestream) buildDimensions(point telegraf.Metric) []types.Dimension {
-	var dimensions []types.Dimension
+	dimensions := make([]types.Dimension, 0, len(point.Tags()))
 	for tagName, tagValue := range point.Tags() {
 		dimension := types.Dimension{
 			Name:  aws.String(tagName),
@@ -464,10 +464,8 @@ func (t *Timestream) buildWriteRecords(point telegraf.Metric) []types.Record {
 }
 
 func (t *Timestream) buildSingleWriteRecords(point telegraf.Metric) []types.Record {
-	var records []types.Record
-
 	dimensions := t.buildDimensions(point)
-
+	records := make([]types.Record, 0, len(point.Fields()))
 	for fieldName, fieldValue := range point.Fields() {
 		stringFieldValue, stringFieldValueType, ok := convertValue(fieldValue)
 		if !ok {
@@ -501,8 +499,7 @@ func (t *Timestream) buildMultiMeasureWriteRecords(point telegraf.Metric) []type
 		multiMeasureName = point.Name()
 	}
 
-	var multiMeasures []types.MeasureValue
+	multiMeasures := make([]types.MeasureValue, 0, len(point.Fields()))
-
 	for fieldName, fieldValue := range point.Fields() {
 		stringFieldValue, stringFieldValueType, ok := convertValue(fieldValue)
 		if !ok {

plugins/outputs/timestream/timestream_test.go

@@ -231,8 +231,7 @@ func TestWriteMultiMeasuresSingleTableMode(t *testing.T) {
 
 	localTime, _ := strconv.Atoi(time1Epoch)
 
-	var inputs []telegraf.Metric
+	inputs := make([]telegraf.Metric, 0, recordCount+1)
-
 	for i := 1; i <= recordCount+1; i++ {
 		localTime++
 
@@ -289,8 +288,7 @@ func TestWriteMultiMeasuresMultiTableMode(t *testing.T) {
 
 	localTime, _ := strconv.Atoi(time1Epoch)
 
-	var inputs []telegraf.Metric
+	inputs := make([]telegraf.Metric, 0, recordCount)
-
 	for i := 1; i <= recordCount; i++ {
 		localTime++
 
@@ -584,8 +582,7 @@ func TestWriteWhenRequestsGreaterThanMaxWriteGoRoutinesCount(t *testing.T) {
 
 	require.NoError(t, plugin.Connect())
 
-	var inputs []telegraf.Metric
+	inputs := make([]telegraf.Metric, 0, totalRecords)
-
 	for i := 1; i <= totalRecords; i++ {
 		fieldName := "value_supported" + strconv.Itoa(i)
 		inputs = append(inputs, testutil.MustMetric(
@@ -624,8 +621,7 @@ func TestWriteWhenRequestsLesserThanMaxWriteGoRoutinesCount(t *testing.T) {
 	}
 	require.NoError(t, plugin.Connect())
 
-	var inputs []telegraf.Metric
+	inputs := make([]telegraf.Metric, 0, totalRecords)
-
 	for i := 1; i <= totalRecords; i++ {
 		fieldName := "value_supported" + strconv.Itoa(i)
 		inputs = append(inputs, testutil.MustMetric(
@@ -724,7 +720,7 @@ func TestTransformMetricsSkipEmptyMetric(t *testing.T) {
 func TestTransformMetricsRequestsAboveLimitAreSplit(t *testing.T) {
 	const maxRecordsInWriteRecordsCall = 100
 
-	var inputs []telegraf.Metric
+	inputs := make([]telegraf.Metric, 0, maxRecordsInWriteRecordsCall+1)
 	for i := 1; i <= maxRecordsInWriteRecordsCall+1; i++ {
 		fieldName := "value_supported" + strconv.Itoa(i)
 		inputs = append(inputs, testutil.MustMetric(
@@ -781,8 +777,7 @@ func TestTransformMetricsRequestsAboveLimitAreSplitSingleTable(t *testing.T) {
 
 	localTime, _ := strconv.Atoi(time1Epoch)
 
-	var inputs []telegraf.Metric
+	inputs := make([]telegraf.Metric, 0, maxRecordsInWriteRecordsCall+1)
-
 	for i := 1; i <= maxRecordsInWriteRecordsCall+1; i++ {
 		localTime++
 
@@ -1275,7 +1270,7 @@ type SimpleInput struct {
 }
 
 func buildExpectedInput(i SimpleInput) *timestreamwrite.WriteRecordsInput {
-	var tsDimensions []types.Dimension
+	tsDimensions := make([]types.Dimension, 0, len(i.dimensions))
 	for k, v := range i.dimensions {
 		tsDimensions = append(tsDimensions, types.Dimension{
 			Name:  aws.String(k),
@@ -1283,7 +1278,7 @@ func buildExpectedInput(i SimpleInput) *timestreamwrite.WriteRecordsInput {
 		})
 	}
 
-	var tsRecords []types.Record
+	tsRecords := make([]types.Record, 0, len(i.measureValues))
 	for k, v := range i.measureValues {
 		tsRecords = append(tsRecords, types.Record{
 			MeasureName:      aws.String(k),
@@ -1316,10 +1311,7 @@ func buildRecords(inputs []SimpleInput) []types.Record {
 }
 
 func buildRecord(input SimpleInput) []types.Record {
-	var tsRecords []types.Record
+	tsDimensions := make([]types.Dimension, 0, len(input.dimensions))
-
-	var tsDimensions []types.Dimension
-
 	for k, v := range input.dimensions {
 		tsDimensions = append(tsDimensions, types.Dimension{
 			Name:  aws.String(k),
@@ -1327,6 +1319,7 @@ func buildRecord(input SimpleInput) []types.Record {
 		})
 	}
 
+	tsRecords := make([]types.Record, 0, len(input.measureValues))
 	for k, v := range input.measureValues {
 		tsRecords = append(tsRecords, types.Record{
 			MeasureName:      aws.String(k),
@@ -1342,11 +1335,9 @@ func buildRecord(input SimpleInput) []types.Record {
 }
 
 func buildMultiRecords(inputs []SimpleInput, multiMeasureName string, measureType types.MeasureValueType) []types.Record {
-	var tsRecords []types.Record
+	tsRecords := make([]types.Record, 0, len(inputs))
 	for _, input := range inputs {
-		var multiMeasures []types.MeasureValue
+		tsDimensions := make([]types.Dimension, 0, len(input.dimensions))
-		var tsDimensions []types.Dimension
-
 		for k, v := range input.dimensions {
 			tsDimensions = append(tsDimensions, types.Dimension{
 				Name:  aws.String(k),
@@ -1354,6 +1345,7 @@ func buildMultiRecords(inputs []SimpleInput, multiMeasureName string, measureTyp
 			})
 		}
 
+		multiMeasures := make([]types.MeasureValue, 0, len(input.measureValues))
 		for k, v := range input.measureValues {
 			multiMeasures = append(multiMeasures, types.MeasureValue{
 				Name:  aws.String(k),

plugins/parsers/influx/machine_test.go

@@ -2158,7 +2158,7 @@ func TestStreamMachine(t *testing.T) {
 		err     error
 	}
 
-	var tc []testcase
+	tc := make([]testcase, 0, len(tests))
 	for _, tt := range tests {
 		tc = append(tc, testcase{
 			name:    tt.name,
@@ -2197,7 +2197,7 @@ func TestStreamMachinePosition(t *testing.T) {
 		column int
 	}
 
-	var tc []testcase
+	tc := make([]testcase, 0, len(positionTests))
 	for _, tt := range positionTests {
 		tc = append(tc, testcase{
 			name:   tt.name,

plugins/parsers/json_v2/parser.go

@@ -161,8 +161,7 @@ func (p *Parser) processMetric(input []byte, data []json_v2.DataSet, tag bool, t
 	}
 
 	p.iterateObjects = false
-	var metrics [][]telegraf.Metric
+	metrics := make([][]telegraf.Metric, 0, len(data))
-
 	for _, c := range data {
 		if c.Path == "" {
 			return nil, fmt.Errorf("GJSON path is required")

plugins/parsers/prometheus/parser.go

@@ -120,7 +120,7 @@ func (p *Parser) SetDefaultTags(tags map[string]string) {
 
 // Get Quantiles for summary metric & Buckets for histogram
 func makeQuantiles(m *dto.Metric, tags map[string]string, metricName string, metricType dto.MetricType, t time.Time) []telegraf.Metric {
-	var metrics []telegraf.Metric
+	metrics := make([]telegraf.Metric, 0, len(m.GetSummary().Quantile)+1)
 	fields := make(map[string]interface{})
 
 	fields[metricName+"_count"] = float64(m.GetSummary().GetSampleCount())
@@ -143,7 +143,7 @@ func makeQuantiles(m *dto.Metric, tags map[string]string, metricName string, met
 
 // Get Buckets  from histogram metric
 func makeBuckets(m *dto.Metric, tags map[string]string, metricName string, metricType dto.MetricType, t time.Time) []telegraf.Metric {
-	var metrics []telegraf.Metric
+	metrics := make([]telegraf.Metric, 0, len(m.GetHistogram().Bucket)+2)
 	fields := make(map[string]interface{})
 
 	fields[metricName+"_count"] = float64(m.GetHistogram().GetSampleCount())

plugins/serializers/graphite/graphite.go

@@ -205,9 +205,8 @@ func SerializeBucketName(
 }
 
 func InitGraphiteTemplates(templates []string) ([]*GraphiteTemplate, string, error) {
-	var graphiteTemplates []*GraphiteTemplate
 	defaultTemplate := ""
-
+	graphiteTemplates := make([]*GraphiteTemplate, 0, len(templates))
 	for i, t := range templates {
 		parts := strings.Fields(t)
 
@@ -299,7 +298,7 @@ func InsertField(bucket, fieldName string) string {
 }
 
 func buildTags(tags map[string]string) string {
-	var keys []string
+	keys := make([]string, 0, len(tags))
 	for k := range tags {
 		keys = append(keys, k)
 	}

plugins/serializers/nowmetric/nowmetric.go

@@ -77,9 +77,8 @@ func (s *serializer) createObject(metric telegraf.Metric) ([]byte, error) {
 		 ** ci2metric_id:	List of key-value pairs to identify the CI.
 		 ** source:			Data source monitoring the metric type
 	*/
-	var allmetrics OIMetrics
+	var allmetrics OIMetrics //nolint:prealloc // Pre-allocating may change format of marshaled JSON
 	var oimetric OIMetric
-
 	oimetric.Source = "Telegraf"
 
 	// Process Tags to extract node & resource name info

testutil/container.go

@@ -42,8 +42,7 @@ type Container struct {
 func (c *Container) Start() error {
 	c.ctx = context.Background()
 
-	var containerMounts []testcontainers.ContainerMount
+	containerMounts := make([]testcontainers.ContainerMount, 0, len(c.BindMounts))
-
 	for k, v := range c.BindMounts {
 		containerMounts = append(containerMounts, testcontainers.BindMount(v, testcontainers.ContainerMountTarget(k)))
 	}