GODRIVER-2156 Enable prealloc linter. (#799)

Author: matthewdale

.golangci.yml

@@ -16,6 +16,7 @@ linters:
     - makezero
     # - misspell
     - nakedret
+    - prealloc
     - revive
     - staticcheck
     - structcheck

internal/string_util.go

@@ -33,7 +33,7 @@ func StringSliceFromRawValue(name string, val bson.RawValue) ([]string, error) {
 		return nil, err
 	}
 
-	var strs []string
+	strs := make([]string, 0, len(arrayValues))
 	for _, arrayVal := range arrayValues {
 		str, ok := arrayVal.StringValueOK()
 		if !ok {

internal/testutil/ops.go

@@ -24,7 +24,7 @@ import (
 
 // AutoCreateIndexes creates an index in the test cluster.
 func AutoCreateIndexes(t *testing.T, keys []string) {
-	var elems [][]byte
+	elems := make([][]byte, 0, len(keys))
 	for _, k := range keys {
 		elems = append(elems, bsoncore.AppendInt32Element(nil, k, 1))
 	}

mongo/integration/gridfs_spec_test.go

@@ -194,7 +194,7 @@ func arrangeGridfsCollections(mt *mtest.T, arrange gridfsArrange) {
 		return
 	}
 
-	var arrangeCmds []interface{}
+	arrangeCmds := make([]interface{}, 0, len(arrange.Data))
 	for _, cmd := range arrange.Data {
 		if cmd[0].Key != "update" {
 			arrangeCmds = append(arrangeCmds, cmd)
@@ -230,7 +230,7 @@ func arrangeGridfsCollections(mt *mtest.T, arrange gridfsArrange) {
 func executeUploadAssert(mt *mtest.T, fileID primitive.ObjectID, assert gridfsAssert) {
 	fileIDVal := bsonx.ObjectID(fileID)
 
-	var assertCommands []interface{}
+	assertCommands := make([]interface{}, 0, len(assert.Data))
 	for _, data := range assert.Data {
 		documentsIdx := data.IndexOf("documents")
 		if documentsIdx == -1 {
@@ -412,7 +412,7 @@ func executeGridfsDelete(mt *mtest.T, test gridfsTest, bucket *gridfs.Bucket) {
 		compareGridfsAssertError(mt, test.Assert.Error, err)
 		return
 	}
-	var cmds []interface{}
+	cmds := make([]interface{}, 0, len(test.Assert.Data))
 	for _, cmd := range test.Assert.Data {
 		cmds = append(cmds, cmd)
 	}
@@ -432,7 +432,7 @@ func setupGridfsTest(mt *mtest.T, data gridfsData) int32 {
 			break
 		}
 	}
-	var chunksDocs []interface{}
+	chunksDocs := make([]interface{}, 0, len(data.Chunks))
 	for _, chunk := range data.Chunks {
 		if hexStr, err := chunk.LookupErr("data", "$hex"); err == nil {
 			hexBytes := hexStringToBytes(mt, hexStr.StringValue())

mongo/integration/mtest/mongotest.go

@@ -794,7 +794,7 @@ func (t *T) verifyConstraints() error {
 
 	// Stop once we find a RunOnBlock that matches the current environment. Record all errors as we go because if we
 	// don't find any matching blocks, we want to report the comparison errors for each block.
-	var runOnErrors []error
+	runOnErrors := make([]error, 0, len(t.runOn))
 	for _, runOn := range t.runOn {
 		err := verifyRunOnBlockConstraint(runOn)
 		if err == nil {

x/mongo/driver/auth/internal/awsv4/signer.go

@@ -234,7 +234,7 @@ func (ctx *signingCtx) buildCredentialString() {
 }
 
 func (ctx *signingCtx) buildCanonicalHeaders(r rule, header http.Header) {
-	var headers []string
+	headers := make([]string, 0, len(header))
 	headers = append(headers, "host")
 	for k, v := range header {
 		if !r.IsValid(k) {

x/mongo/driver/dns/dns.go

@@ -86,7 +86,7 @@ func (r *Resolver) fetchSeedlistFromSRV(host string, srvName string, stopOnErr b
 
 	trimmedHost := strings.TrimSuffix(host, ".")
 
-	var parsedHosts []string
+	parsedHosts := make([]string, 0, len(addresses))
 	for _, address := range addresses {
 		trimmedAddressTarget := strings.TrimSuffix(address.Target, ".")
 		err := validateSRVResult(trimmedAddressTarget, trimmedHost)