[9.4] .golangci.yml: enable the modernize linter

Enable the modernize linter from golangci-lint's suite. It flags
outdated Go syntax and rewrites it to modern equivalents: min/max
builtins, range-over-int loops, slices/maps helpers, any, t.Context()
in tests, fmt.Appendf, strings.CutPrefix, and more. Keeping it enabled
stops outdated patterns from re-entering the codebase, which matters
more now that much code is produced by AI agents trained on older Go,
and it often yields simpler, more efficient code.

The omitzero analyzer is disabled: it rewrites ,omitempty struct tags to
,omitzero, which changes JSON marshaling semantics and is not a
mechanical, behavior-preserving fix.

The loop also runs `go fix -inline`, which applies //go:fix inline
directives. modernize marks its own pointer helpers with the directive,
and dependencies/stdlib carry it on deprecated APIs, so this pulls in
mechanical migrations such as io/ioutil -> io and reflect.Ptr ->
reflect.Pointer. `go fix` inlines the call sites but never deletes the
now-dead helper declarations; a follow-up commit removes those.

Every Go change here is a linter/`go fix` auto-fix, restricted to the
files owned by @elastic/elastic-agent-data-plane; the rest of the
repository is modernized in a stacked follow-up PR so each team reviews
only its own code.

The .golangci.yml change is made by hand. The Go changes (except for
some manual changes that were highlighted in the review) are then fully
reproducible by running this with bash from the repository root:

set -euo pipefail

OWNER="@elastic/elastic-agent-data-plane"
export CGO_ENABLED=1
MAX_PASSES=10

modernize() {
	golangci-lint run --enable-only modernize \
		--max-issues-per-linter 0 --max-same-issues 0 --timeout=90m --fix ./...
}

for pass in $(seq "$MAX_PASSES"); do
	echo ">>> pass $pass: fmt"
	before="$(git diff | git hash-object --stdin)"
	golangci-lint fmt ./...
	echo ">>> pass $pass: modernize --fix"
	if modernize; then :; fi
	echo ">>> pass $pass: go fix -inline"
	if go fix -inline ./...; then :; fi
	echo ">>> pass $pass done: $(git diff --name-only | wc -l) files changed"
	[ "$before" = "$(git diff | git hash-object --stdin)" ] && { echo ">>> fixpoint at pass $pass"; break; }
done
golangci-lint fmt ./...

changed="$(mktemp)"
keep="$(mktemp)"
trap 'rm -f "$changed" "$keep"' EXIT
git diff --name-only -- '*.go' | sort -u >"$changed"
git diff --name-only -- '*.go' | xargs -r codeowners -o "$OWNER" \
	| awk '{print $1}' | sort -u >"$keep"
comm -23 "$changed" "$keep" | tr '\n' '\0' | xargs -0 -r git checkout --

echo "PR1 data-plane .go files: $(git diff --name-only -- '*.go' | wc -l)"

Author: orestisfl

dev-tools/cmd/license/license_generate.go

@@ -173,7 +173,7 @@ func usageFlag() {
 	flag.PrintDefaults()
 }
 
-var Template = template.Must(template.New("normalizations").Funcs(map[string]interface{}{
+var Template = template.Must(template.New("normalizations").Funcs(map[string]any{
 	"trim": strings.TrimSpace,
 }).Parse(`
 {{ .License | trim }}

dev-tools/cmd/module_include_list/module_include_list.go

@@ -20,7 +20,6 @@ package main
 import (
 	"flag"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"strings"
 )
@@ -51,7 +50,7 @@ func main() {
 }
 
 func getGoVersion() string {
-	version, err := ioutil.ReadFile(".go-version")
+	version, err := os.ReadFile(".go-version")
 	checkErr(err)
 	return strings.TrimRight(string(version), "\r\n")
 }
@@ -65,10 +64,10 @@ func checkErr(err error) {
 func updateGoVersion(oldVersion, newVersion string) {
 	for _, file := range files {
 		fmt.Printf("Updating Go version from %s to %s in %s\n", oldVersion, newVersion, file)
-		content, err := ioutil.ReadFile(file)
+		content, err := os.ReadFile(file)
 		checkErr(err)
 		updatedContent := strings.ReplaceAll(string(content), oldVersion, newVersion)
-		err = ioutil.WriteFile(file, []byte(updatedContent), 0644)
+		err = os.WriteFile(file, []byte(updatedContent), 0644)
 		checkErr(err)
 	}
 }

dev-tools/cmd/update_go/update_go_version.go

@@ -22,9 +22,11 @@ import (
 	"fmt"
 	"go/build"
 	"log"
+	"maps"
 	"os"
 	"path/filepath"
 	"regexp"
+	"slices"
 	"strings"
 
 	"github.com/josephspurrier/goversioninfo"
@@ -114,9 +116,7 @@ func DefaultBuildArgs() BuildArgs {
 			args.ExtraFlags = append(args.ExtraFlags, "-tags="+tag)
 		}
 		args.CGO = args.CGO || FIPSConfig.Compile.CGO
-		for varName, value := range FIPSConfig.Compile.Env {
-			args.Env[varName] = value
-		}
+		maps.Copy(args.Env, FIPSConfig.Compile.Env)
 	}
 
 	return args
@@ -138,12 +138,7 @@ func positionIndependentCodeSupported() bool {
 }
 
 func oneOf(value string, lst ...string) bool {
-	for _, other := range lst {
-		if other == value {
-			return true
-		}
-	}
-	return false
+	return slices.Contains(lst, value)
 }
 
 // DefaultGolangCrossBuildArgs returns the default BuildArgs for use in

dev-tools/mage/build.go

@@ -22,7 +22,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
+
 	"log"
 	"os"
 	"os/exec"
@@ -230,7 +230,7 @@ func CheckDashboardsFormat() error {
 
 	hasErrors := false
 	for _, file := range dashboardFiles {
-		d, err := ioutil.ReadFile(file)
+		d, err := os.ReadFile(file)
 		if err != nil {
 			return fmt.Errorf("failed to read dashboard file %s: %w", file, err)
 		}

dev-tools/mage/check.go

@@ -33,6 +33,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"maps"
 	"net/http"
 	"os"
 	"os/exec"
@@ -54,13 +55,13 @@ import (
 )
 
 // Expand expands the given Go text/template string.
-func Expand(in string, args ...map[string]interface{}) (string, error) {
+func Expand(in string, args ...map[string]any) (string, error) {
 	return expandTemplate("inline", in, FuncMap, EnvMap(args...))
 }
 
 // MustExpand expands the given Go text/template string. It panics if there is
 // an error.
-func MustExpand(in string, args ...map[string]interface{}) string {
+func MustExpand(in string, args ...map[string]any) string {
 	out, err := Expand(in, args...)
 	if err != nil {
 		panic(err)
@@ -70,19 +71,19 @@ func MustExpand(in string, args ...map[string]interface{}) string {
 
 // ExpandFile expands the Go text/template read from src and writes the output
 // to dst.
-func ExpandFile(src, dst string, args ...map[string]interface{}) error {
+func ExpandFile(src, dst string, args ...map[string]any) error {
 	return expandFile(src, dst, EnvMap(args...))
 }
 
 // MustExpandFile expands the Go text/template read from src and writes the
 // output to dst. It panics if there is an error.
-func MustExpandFile(src, dst string, args ...map[string]interface{}) {
+func MustExpandFile(src, dst string, args ...map[string]any) {
 	if err := ExpandFile(src, dst, args...); err != nil {
 		panic(err)
 	}
 }
 
-func expandTemplate(name, tmpl string, funcs template.FuncMap, args ...map[string]interface{}) (string, error) {
+func expandTemplate(name, tmpl string, funcs template.FuncMap, args ...map[string]any) (string, error) {
 	t := template.New(name).Option("missingkey=error")
 	if len(funcs) > 0 {
 		t = t.Funcs(funcs)
@@ -107,24 +108,22 @@ func expandTemplate(name, tmpl string, funcs template.FuncMap, args ...map[strin
 	return buf.String(), nil
 }
 
-func joinMaps(args ...map[string]interface{}) map[string]interface{} {
+func joinMaps(args ...map[string]any) map[string]any {
 	switch len(args) {
 	case 0:
 		return nil
 	case 1:
 		return args[0]
 	}
 
-	out := map[string]interface{}{}
+	out := map[string]any{}
 	for _, m := range args {
-		for k, v := range m {
-			out[k] = v
-		}
+		maps.Copy(out, m)
 	}
 	return out
 }
 
-func expandFile(src, dst string, args ...map[string]interface{}) error {
+func expandFile(src, dst string, args ...map[string]any) error {
 	tmplData, err := os.ReadFile(src)
 	if err != nil {
 		return fmt.Errorf("failed reading from template %v: %w", src, err)
@@ -662,7 +661,7 @@ func numParallel() int {
 // ParallelCtx runs the given functions in parallel with an upper limit set
 // based on GOMAXPROCS. The provided ctx is passed to the functions (if they
 // accept it as a param).
-func ParallelCtx(ctx context.Context, fns ...interface{}) {
+func ParallelCtx(ctx context.Context, fns ...any) {
 	var fnWrappers []func(context.Context) error
 	for _, f := range fns {
 		fnWrapper := funcTypeWrap(f)
@@ -707,12 +706,12 @@ func ParallelCtx(ctx context.Context, fns ...interface{}) {
 
 // Parallel runs the given functions in parallel with an upper limit set based
 // on GOMAXPROCS.
-func Parallel(fns ...interface{}) {
+func Parallel(fns ...any) {
 	ParallelCtx(context.TODO(), fns...)
 }
 
 // funcTypeWrap wraps a valid FuncType to FuncContextError
-func funcTypeWrap(fn interface{}) func(context.Context) error {
+func funcTypeWrap(fn any) func(context.Context) error {
 	switch f := fn.(type) {
 	case func():
 		return func(context.Context) error {
@@ -1019,9 +1018,9 @@ func ListMatchingEnvVars(prefixes ...string) []string {
 	for _, v := range os.Environ() {
 		for _, prefix := range prefixes {
 			if strings.HasPrefix(v, prefix) {
-				eqIdx := strings.Index(v, "=")
-				if eqIdx != -1 {
-					vars = append(vars, v[:eqIdx])
+				before, _, ok := strings.Cut(v, "=")
+				if ok {
+					vars = append(vars, before)
 				}
 				break
 			}
@@ -1072,8 +1071,8 @@ func ReadGLIBCRequirement(elfFile string) (*SemanticVersion, error) {
 
 	versionSet := map[SemanticVersion]struct{}{}
 	for _, sym := range symbols {
-		if strings.HasPrefix(sym.Version, "GLIBC_") {
-			semver, err := NewSemanticVersion(strings.TrimPrefix(sym.Version, "GLIBC_"))
+		if after, ok := strings.CutPrefix(sym.Version, "GLIBC_"); ok {
+			semver, err := NewSemanticVersion(after)
 			if err != nil {
 				continue
 			}

dev-tools/mage/common.go

@@ -66,19 +66,19 @@ func (t ConfigFileType) IsDocker() bool { return t&DockerConfigType > 0 }
 // ConfigFileParams defines the files that make up each config file.
 type ConfigFileParams struct {
 	Templates                []string // List of files or globs to load.
-	ExtraVars                map[string]interface{}
+	ExtraVars                map[string]any
 	Short, Reference, Docker ConfigParams
 }
 
 type ConfigParams struct {
 	Template string
-	Deps     []interface{}
+	Deps     []any
 }
 
 func DefaultConfigFileParams() ConfigFileParams {
 	return ConfigFileParams{
 		Templates: []string{LibbeatDir("_meta/config/*.tmpl")},
-		ExtraVars: map[string]interface{}{},
+		ExtraVars: map[string]any{},
 		Short: ConfigParams{
 			Template: LibbeatDir("_meta/config/default.short.yml.tmpl"),
 		},
@@ -124,17 +124,17 @@ func Config(types ConfigFileType, args ConfigFileParams, targetDir string) error
 func makeConfigTemplate(destination string, mode os.FileMode, confParams ConfigFileParams, typ ConfigFileType) error {
 	// Determine what type to build and set some parameters.
 	var confFile ConfigParams
-	var tmplParams map[string]interface{}
+	var tmplParams map[string]any
 	switch typ {
 	case ShortConfigType:
 		confFile = confParams.Short
-		tmplParams = map[string]interface{}{}
+		tmplParams = map[string]any{}
 	case ReferenceConfigType:
 		confFile = confParams.Reference
-		tmplParams = map[string]interface{}{"Reference": true}
+		tmplParams = map[string]any{"Reference": true}
 	case DockerConfigType:
 		confFile = confParams.Docker
-		tmplParams = map[string]interface{}{"Docker": true}
+		tmplParams = map[string]any{"Docker": true}
 	default:
 		panic(fmt.Errorf("Invalid config file type: %v", typ))
 	}
@@ -146,7 +146,7 @@ func makeConfigTemplate(destination string, mode os.FileMode, confParams ConfigF
 	// Rather than adding more "ExcludeX"/"UseX" options consider overwriting
 	// one of the libbeat templates in your project by adding a file with the
 	// same name to your _meta/config directory.
-	params := map[string]interface{}{
+	params := map[string]any{
 		"GOOS":                           EnvOr("DEV_OS", "linux"),
 		"GOARCH":                         EnvOr("DEV_ARCH", "amd64"),
 		"CI":                             EnvOr("CI", ""),
@@ -172,7 +172,7 @@ func makeConfigTemplate(destination string, mode os.FileMode, confParams ConfigF
 		// include is necessary because you cannot pipe 'template' to a function
 		// since 'template' is an action. This allows you to include a
 		// template and indent it (e.g. {{ include "x.tmpl" . | indent 4 }}).
-		"include": func(name string, data interface{}) (string, error) {
+		"include": func(name string, data any) (string, error) {
 			buf := bytes.NewBuffer(nil)
 			if err := tmpl.ExecuteTemplate(buf, name, data); err != nil {
 				return "", err
@@ -196,7 +196,7 @@ func makeConfigTemplate(destination string, mode os.FileMode, confParams ConfigF
 		}
 	}
 
-	data, err := ioutil.ReadFile(confFile.Template)
+	data, err := os.ReadFile(confFile.Template)
 	if err != nil {
 		return fmt.Errorf("failed to read config template %q: %w", confFile.Template, err)
 	}
@@ -265,7 +265,7 @@ type moduleFieldsYmlData []struct {
 }
 
 func readModuleFieldsYml(path string) (title string, useShort bool, err error) {
-	data, err := ioutil.ReadFile(path)
+	data, err := os.ReadFile(path)
 	if err != nil {
 		return "", false, err
 	}
@@ -327,7 +327,7 @@ func GenerateModuleReferenceConfig(out string, moduleDirs ...string) error {
 
 			var data []byte
 			for _, f := range files {
-				data, err = ioutil.ReadFile(f)
+				data, err = os.ReadFile(f)
 				if err != nil {
 					if os.IsNotExist(err) {
 						continue
@@ -361,9 +361,9 @@ func GenerateModuleReferenceConfig(out string, moduleDirs ...string) error {
 		return moduleConfigs[i].ID < moduleConfigs[j].ID
 	})
 
-	config := MustExpand(moduleConfigTemplate, map[string]interface{}{
+	config := MustExpand(moduleConfigTemplate, map[string]any{
 		"Modules": moduleConfigs,
 	})
 
-	return ioutil.WriteFile(createDir(out), []byte(config), 0644)
+	return os.WriteFile(createDir(out), []byte(config), 0644)
 }

dev-tools/mage/config.go

@@ -54,7 +54,7 @@ var Platforms = BuildPlatforms.Defaults()
 // values are ignored.
 func ParsePackageTypes(packageTypes string) []PackageType {
 	var parsed []PackageType
-	for _, packageType := range strings.Split(packageTypes, ",") {
+	for packageType := range strings.SplitSeq(packageTypes, ",") {
 		packageType = strings.TrimSpace(packageType)
 		if packageType == "" {
 			continue
@@ -199,7 +199,7 @@ func CrossBuild(options ...CrossBuildOption) error {
 	mg.Deps(buildMage)
 
 	log.Println("crossBuild: Platform list =", params.Platforms)
-	var deps []interface{}
+	var deps []any
 	for _, buildPlatform := range params.Platforms {
 		if !buildPlatform.Flags.CanCrossBuild() {
 			return fmt.Errorf("unsupported cross build platform %v", buildPlatform.Name)
@@ -501,7 +501,7 @@ func gitAlternateObjectDirMounts(objectsDir, containerObjectsDir string, alterna
 	var mounts []dockerVolumeMount
 	seen := map[string]struct{}{}
 
-	for _, line := range strings.Split(string(alternates), "\n") {
+	for line := range strings.SplitSeq(string(alternates), "\n") {
 		alternate := strings.TrimSpace(line)
 		if alternate == "" || strings.HasPrefix(alternate, "#") {
 			continue

dev-tools/mage/crossbuild.go

@@ -71,7 +71,7 @@ func ExportDashboard() error {
 // - KIBANA_INSECURE: Disable TLS verification.
 // - KIBANA_ALWAYS: Connect to Kibana without checking ES version. Default true.
 // - ES_URL: URL of Elasticsearch (only used with KIBANA_ALWAYS=false).
-func ImportDashboards(buildDep, dashboardDep interface{}) error {
+func ImportDashboards(buildDep, dashboardDep any) error {
 	mg.Deps(buildDep, dashboardDep)
 
 	setupDashboards := sh.RunCmd(CWD(BeatName+binaryExtension(GOOS)),