linter: prealloc (#2315)

.golangci.yml

@@ -25,7 +25,7 @@ linters:
     - errname
     - gofmt
     # - misspell (lots to fix, but we should)
-    # - prealloc (15 to fix)
+    - prealloc
     # - predeclared (20 to fix)
     # - stylecheck (quite a lot to fix, but we should definitely work on this)
     # - unconvert (not at all critical, but makes for cleaner code)

cache_test.go

@@ -6,7 +6,7 @@ import (
 	"reflect"
 	"testing"
 
-	"github.com/featurebasedb/featurebase/v3"
+	pilosa "github.com/featurebasedb/featurebase/v3"
 )
 
 // Ensure cache stays constrained to its configured size.
@@ -62,7 +62,7 @@ func TestCache_Rank_Dirty(t *testing.T) {
 		cache.Add(v.ID, v.Count)
 	}
 
-	var got []pair
+	var got []pair //nolint:prealloc
 	for _, p := range cache.Top() {
 		got = append(got, pair(p))
 	}

dax/table.go

@@ -459,7 +459,7 @@ func (t *Table) HasValidPrimaryKey() bool {
 
 // FieldNames returns the list of field names associated with the table.
 func (t *Table) FieldNames() []FieldName {
-	var ret []FieldName
+	ret := make([]FieldName, 0, len(t.Fields))
 	for _, f := range t.Fields {
 		ret = append(ret, f.Name)
 	}

debugstats/stats.go

@@ -57,7 +57,7 @@ func (c *CallStats) Report(title string) (r string) {
 	r = fmt.Sprintf("CallStats: (%v)\n", title)
 	c.mu.Lock()
 	defer c.mu.Unlock()
-	var lines []*LineSorter
+	lines := make([]*LineSorter, 0, len(c.elap))
 	for id, elap := range c.elap {
 		slc := elap.dur
 		n := len(slc)

etcd/embed.go

@@ -134,8 +134,9 @@ func (e *EmbeddedEtcd) Shutdown() {
 }
 
 func (e *EmbeddedEtcd) Peers() []*disco.Peer {
-	var peers []*disco.Peer
-	for _, member := range e.e.Server.Cluster().Members() {
+	members := e.e.Server.Cluster().Members()
+	peers := make([]*disco.Peer, 0, len(members))
+	for _, member := range members {
 		peers = append(peers, &disco.Peer{ID: member.ID.String(), URL: member.PickPeerURL()})
 	}
 	return peers

executor.go

@@ -2321,7 +2321,7 @@ func (e *executor) executeTopKShardTime(ctx context.Context, tx Tx, filter *Row,
 	}
 
 	// Fetch fragments.
-	var fragments []*fragment
+	fragments := make([]*fragment, 0, len(views))
 	for _, view := range views {
 		f := e.Holder.fragment(index, field, view, shard)
 		if f == nil {

executor_test.go

@@ -7620,7 +7620,7 @@ func variousQueriesOnPercentiles(t *testing.T, c *test.Cluster) {
 	}
 
 	// generate string-set entries for index
-	var stringEntries [][2]string
+	stringEntries := make([][2]string, 0, len(testValues))
 	for _, v := range testValues {
 		stringEntries = append(stringEntries,
 			[2]string{v.rowKey, v.colKey})
@@ -7657,7 +7657,7 @@ func variousQueriesOnPercentiles(t *testing.T, c *test.Cluster) {
 
 	// generate test cases per each nth argument
 	nthsFloat := []float64{0, 10, 25, 50, 75, 90, 99}
-	var tests []testCase
+	tests := make([]testCase, 0, len(nthsFloat))
 	for _, nth := range nthsFloat {
 		query := fmt.Sprintf(`Percentile(field="net_worth", filter=Row(val="foo"), nth=%f)`, nth)
 		expectedPercentile := getExpectedPercentile(nums, nth)

field.go

@@ -1018,8 +1018,9 @@ func (f *Field) viewsByTimeRange(from, to time.Time) (views []string, err error)
 	}
 
 	// Get min/max based on existing views.
-	var vs []string
-	for _, v := range f.views() {
+	fv := f.views()
+	vs := make([]string, 0, len(fv))
+	for _, v := range fv {
 		vs = append(vs, v.name)
 	}
 	min, max := minMaxViews(vs, q)

http_handler.go

@@ -2907,8 +2907,9 @@ const (
 
 // parseUint64Slice returns a slice of uint64s from a comma-delimited string.
 func parseUint64Slice(s string) ([]uint64, error) {
-	var a []uint64
-	for _, str := range strings.Split(s, ",") {
+	ss := strings.Split(s, ",")
+	a := make([]uint64, 0, len(ss))
+	for _, str := range ss {
 		// Ignore blanks.
 		if str == "" {
 			continue

rbf/cursor.go

@@ -493,7 +493,7 @@ func (c *Cursor) putLeafCell(in leafCell) (err error) {
 
 	// Write each group to a separate page.
 	newRoot := (len(groups) > 1) && (c.stack.top == 0)
-	var parents []branchCell
+	parents := make([]branchCell, 0, len(groups))
 	origPgno := elem.pgno
 	// newRoot if split occured and bottom of the stack
 	for i, group := range groups {
@@ -724,7 +724,7 @@ func (c *Cursor) putBranchCells(stackIndex int, newCells []branchCell) (err erro
 	}
 
 	// Write each group to a separate page.
-	var parents []branchCell
+	parents := make([]branchCell, 0, len(groups))
 	origPgno := readPageNo(page)
 	newRoot := len(groups) > 1 && stackIndex == 0
 	for i, group := range groups {

rbf/cursor_internal_test.go

@@ -332,7 +332,7 @@ func TestCursor_putBranchCellsHandlesLotsOfNewBranchesAtTheRoot(t *testing.T) {
 
 	groups := splitLeafCells(leafcells)
 
-	var branches []branchCell
+	branches := make([]branchCell, 0, len(groups))
 
 	for i, group := range groups {
 		_ = i

sql/select.go

@@ -206,7 +206,7 @@ func (h handlerSelectFieldsFromTableWhere) Apply(stmt *sqlparser.Select, qm Quer
 		return nil, errors.Wrap(err, "extracting select fields")
 	}
 
-	var fields []string
+	var fields []string //nolint:prealloc
 	for _, fld := range selectFields {
 		if _, ok := fld.(*StarColumn); ok {
 			pflds := index.Fields()

sql3/planner/inbuiltfunctionsstring.go

@@ -706,7 +706,7 @@ func (n *callPlanExpression) EvaluateFormat(currentRow []interface{}) (interface
 		return nil, sql3.NewErrUnexpectedTypeConversion(0, 0, argEval)
 	}
 
-	var args []interface{}
+	args := make([]interface{}, 0, len(n.args)-1)
 
 	// loop, since args can be of any length.
 	for _, arg := range n.args[1:] {

view.go

@@ -134,7 +134,7 @@ func (v *view) openWithShardSet(ss *shardSet) error {
 
 	shards := ss.CloneMaybe()
 
-	var frags []*fragment
+	frags := make([]*fragment, 0, len(shards))
 	for shard := range shards {
 		frag := v.newFragment(shard)
 		frags = append(frags, frag)