chore(perf): Pre-allocate where possible (enable prealloc linter) (#88952)

* chore(perf): Pre-allocate where possible (enable prealloc linter)

Signed-off-by: Dave Henderson <dave.henderson@grafana.com>

* fix TestAlertManagers_buildRedactedAMs

Signed-off-by: Dave Henderson <dave.henderson@grafana.com>

* prealloc a slice that appeared after rebase

Signed-off-by: Dave Henderson <dave.henderson@grafana.com>

---------

Signed-off-by: Dave Henderson <dave.henderson@grafana.com>

pkg/tsdb/azuremonitor/resourcegraph/azure-resource-graph-datasource.go

@@ -88,9 +88,8 @@ type argJSONQuery struct {
 }
 
 func (e *AzureResourceGraphDatasource) buildQueries(queries []backend.DataQuery, dsInfo types.DatasourceInfo) ([]*AzureResourceGraphQuery, error) {
-	var azureResourceGraphQueries []*AzureResourceGraphQuery
-
-	for _, query := range queries {
+	azureResourceGraphQueries := make([]*AzureResourceGraphQuery, len(queries))
+	for i, query := range queries {
 		queryJSONModel := argJSONQuery{}
 		err := json.Unmarshal(query.JSON, &queryJSONModel)
 		if err != nil {
@@ -105,19 +104,18 @@ func (e *AzureResourceGraphDatasource) buildQueries(queries []backend.DataQuery,
 		}
 
 		interpolatedQuery, err := macros.KqlInterpolate(query, dsInfo, azureResourceGraphTarget.Query)
-
 		if err != nil {
 			return nil, err
 		}
 
-		azureResourceGraphQueries = append(azureResourceGraphQueries, &AzureResourceGraphQuery{
+		azureResourceGraphQueries[i] = &AzureResourceGraphQuery{
 			RefID:             query.RefID,
 			ResultFormat:      resultFormat,
 			JSON:              query.JSON,
 			InterpolatedQuery: interpolatedQuery,
 			TimeRange:         query.TimeRange,
 			QueryType:         query.QueryType,
-		})
+		}
 	}
 
 	return azureResourceGraphQueries, nil

pkg/tsdb/azuremonitor/types/types.go

@@ -129,8 +129,8 @@ type AzureMonitorDimensionFilterBackend struct {
 }
 
 func ConstructFiltersString(a dataquery.AzureMetricDimension) string {
-	var filterStrings []string
-	for _, filter := range a.Filters {
+	filterStrings := make([]string, len(a.Filters))
+	for i, filter := range a.Filters {
 		dimension := ""
 		operator := ""
 		if a.Dimension != nil {
@@ -139,11 +139,14 @@ func ConstructFiltersString(a dataquery.AzureMetricDimension) string {
 		if a.Operator != nil {
 			operator = *a.Operator
 		}
-		filterStrings = append(filterStrings, fmt.Sprintf("%v %v '%v'", dimension, operator, filter))
+
+		filterStrings[i] = fmt.Sprintf("%v %v '%v'", dimension, operator, filter)
 	}
+
 	if a.Operator != nil && *a.Operator == "eq" {
 		return strings.Join(filterStrings, " or ")
 	}
+
 	return strings.Join(filterStrings, " and ")
 }
 

pkg/tsdb/cloudwatch/services/utils.go

@@ -7,7 +7,7 @@ import (
 )
 
 func valuesToListMetricRespone[T any](values []T) []resources.ResourceResponse[T] {
-	var response []resources.ResourceResponse[T]
+	response := make([]resources.ResourceResponse[T], 0, len(values))
 	for _, value := range values {
 		response = append(response, resources.ResourceResponse[T]{Value: value})
 	}

pkg/tsdb/elasticsearch/querydata_test.go

@@ -84,15 +84,16 @@ func newFlowTestQueries(allJsonBytes []byte) ([]backend.DataQuery, error) {
 		return nil, fmt.Errorf("error unmarshaling query-json: %w", err)
 	}
 
-	var queries []backend.DataQuery
-
-	for _, jsonBytes := range jsonBytesArray {
+	queries := make([]backend.DataQuery, len(jsonBytesArray))
+	for i, jsonBytes := range jsonBytesArray {
 		// we need to extract some fields from the json-array
 		var jsonInfo queryDataTestQueryJSON
+
 		err = json.Unmarshal(jsonBytes, &jsonInfo)
 		if err != nil {
 			return nil, err
 		}
+
 		// we setup the DataQuery, with values loaded from the json
 		query := backend.DataQuery{
 			RefID:         jsonInfo.RefID,
@@ -101,7 +102,8 @@ func newFlowTestQueries(allJsonBytes []byte) ([]backend.DataQuery, error) {
 			TimeRange:     timeRange,
 			JSON:          jsonBytes,
 		}
-		queries = append(queries, query)
+
+		queries[i] = query
 	}
 	return queries, nil
 }

pkg/tsdb/elasticsearch/response_parser.go

@@ -873,16 +873,16 @@ func trimDatapoints(queryResult backend.DataResponse, target *Query) {
 // we sort the label's pairs by the label-key,
 // and return the label-values
 func getSortedLabelValues(labels data.Labels) []string {
-	var keys []string
+	keys := make([]string, 0, len(labels))
 	for key := range labels {
 		keys = append(keys, key)
 	}
 
 	sort.Strings(keys)
 
-	var values []string
-	for _, key := range keys {
-		values = append(values, labels[key])
+	values := make([]string, len(keys))
+	for i, key := range keys {
+		values[i] = labels[key]
 	}
 
 	return values

pkg/tsdb/influxdb/fsql/arrow_test.go

@@ -60,7 +60,7 @@ func TestNewQueryDataResponse(t *testing.T) {
 		newJSONArray(`[0, 1, 2]`, &arrow.TimestampType{}),
 	}
 
-	var arr []arrow.Array
+	arr := make([]arrow.Array, 0, len(strValues))
 	for _, v := range strValues {
 		tarr, _, err := array.FromJSON(
 			alloc,

pkg/tsdb/influxdb/influxql/buffered/response_parser.go

@@ -269,12 +269,12 @@ func transformRowsForTimeSeries(rows []models.Row, query models.Query) data.Fram
 }
 
 func newFrameWithTimeField(row models.Row, column string, colIndex int, query models.Query, frameName []byte) *data.Frame {
-	var timeArray []time.Time
 	var floatArray []*float64
 	var stringArray []*string
 	var boolArray []*bool
 	valType := util.Typeof(row.Values, colIndex)
 
+	timeArray := make([]time.Time, 0, len(row.Values))
 	for _, valuePair := range row.Values {
 		timestamp, timestampErr := util.ParseTimestamp(valuePair[0])
 		// we only add this row if the timestamp is valid

pkg/tsdb/tempo/trace_transform_test.go

@@ -136,10 +136,11 @@ func rootSpan(frame *BetterFrame) Row {
 }
 
 func fieldNames(frame *data.Frame) []string {
-	var names []string
-	for _, f := range frame.Fields {
-		names = append(names, f.Name)
+	names := make([]string, len(frame.Fields))
+	for i, f := range frame.Fields {
+		names[i] = f.Name
 	}
+
 	return names
 }