Modernize Go

.golangci.yml

@@ -11,6 +11,7 @@ linters:
     - govet
     - loggercheck
     - misspell
+    - modernize
     - nilnesserr
     # TODO(bwplotka): Enable once https://github.com/golangci/golangci-lint/issues/3228 is fixed.
     # - nolintlint
@@ -43,6 +44,9 @@ linters:
       - linters:
           - gocritic
         text: "appendAssign"
+      - linters:
+          - errcheck
+        path: _test.go
     warn-unused: true
   settings:
     depguard:
@@ -77,6 +81,15 @@ linters:
         - shadow
         - fieldalignment
       enable-all: true
+    modernize:
+      disable:
+        # Suggest replacing omitempty with omitzero for struct fields.
+        # Disable this check for now since it introduces too many changes in our existing codebase.
+        # See https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/modernize#hdr-Analyzer_omitzero for more details.
+        - omitzero
+        # Disable newexpr check for now since it introduces too many changes in our existing codebase.
+        # To be re-enabled as a part of https://github.com/prometheus/prometheus/issues/18066.
+        - newexpr
     perfsprint:
       # Optimizes even if it requires an int or uint type cast.
       int-conversion: true

config/config.go

@@ -33,7 +33,7 @@ type Secret string
 var MarshalSecretValue = false
 
 // MarshalYAML implements the yaml.Marshaler interface for Secrets.
-func (s Secret) MarshalYAML() (interface{}, error) {
+func (s Secret) MarshalYAML() (any, error) {
 	if MarshalSecretValue {
 		return string(s), nil
 	}
@@ -44,7 +44,7 @@ func (s Secret) MarshalYAML() (interface{}, error) {
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface for Secrets.
-func (s *Secret) UnmarshalYAML(unmarshal func(interface{}) error) error {
+func (s *Secret) UnmarshalYAML(unmarshal func(any) error) error {
 	type plain Secret
 	return unmarshal((*plain)(s))
 }

config/http_config.go

@@ -22,6 +22,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"maps"
 	"net"
 	"net/http"
 	"net/url"
@@ -76,7 +77,7 @@ var TLSVersions = map[string]TLSVersion{
 	"TLS10": (TLSVersion)(tls.VersionTLS10),
 }
 
-func (tv *TLSVersion) UnmarshalYAML(unmarshal func(interface{}) error) error {
+func (tv *TLSVersion) UnmarshalYAML(unmarshal func(any) error) error {
 	var s string
 	err := unmarshal(&s)
 	if err != nil {
@@ -89,7 +90,7 @@ func (tv *TLSVersion) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	return fmt.Errorf("unknown TLS version: %s", s)
 }
 
-func (tv TLSVersion) MarshalYAML() (interface{}, error) {
+func (tv TLSVersion) MarshalYAML() (any, error) {
 	for s, v := range TLSVersions {
 		if tv == v {
 			return s, nil
@@ -178,7 +179,7 @@ type URL struct {
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface for URLs.
-func (u *URL) UnmarshalYAML(unmarshal func(interface{}) error) error {
+func (u *URL) UnmarshalYAML(unmarshal func(any) error) error {
 	var s string
 	if err := unmarshal(&s); err != nil {
 		return err
@@ -193,7 +194,7 @@ func (u *URL) UnmarshalYAML(unmarshal func(interface{}) error) error {
 }
 
 // MarshalYAML implements the yaml.Marshaler interface for URLs.
-func (u URL) MarshalYAML() (interface{}, error) {
+func (u URL) MarshalYAML() (any, error) {
 	if u.URL != nil {
 		return u.Redacted(), nil
 	}
@@ -269,16 +270,16 @@ type OAuth2 struct {
 	Audience string `yaml:"audience,omitempty" json:"audience,omitempty"`
 	// Claims is a map of claims to be added to the JWT token. Only used if
 	// GrantType is set to "urn:ietf:params:oauth:grant-type:jwt-bearer".
-	Claims         map[string]interface{} `yaml:"claims,omitempty" json:"claims,omitempty"`
-	Scopes         []string               `yaml:"scopes,omitempty" json:"scopes,omitempty"`
-	TokenURL       string                 `yaml:"token_url,omitempty" json:"token_url,omitempty"`
-	EndpointParams map[string]string      `yaml:"endpoint_params,omitempty" json:"endpoint_params,omitempty"`
-	TLSConfig      TLSConfig              `yaml:"tls_config,omitempty"`
+	Claims         map[string]any    `yaml:"claims,omitempty" json:"claims,omitempty"`
+	Scopes         []string          `yaml:"scopes,omitempty" json:"scopes,omitempty"`
+	TokenURL       string            `yaml:"token_url,omitempty" json:"token_url,omitempty"`
+	EndpointParams map[string]string `yaml:"endpoint_params,omitempty" json:"endpoint_params,omitempty"`
+	TLSConfig      TLSConfig         `yaml:"tls_config,omitempty"`
 	ProxyConfig    `yaml:",inline"`
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
-func (o *OAuth2) UnmarshalYAML(unmarshal func(interface{}) error) error {
+func (o *OAuth2) UnmarshalYAML(unmarshal func(any) error) error {
 	type plain OAuth2
 	if err := unmarshal((*plain)(o)); err != nil {
 		return err
@@ -463,7 +464,7 @@ func (c *HTTPClientConfig) Validate() error {
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
-func (c *HTTPClientConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
+func (c *HTTPClientConfig) UnmarshalYAML(unmarshal func(any) error) error {
 	type plain HTTPClientConfig
 	*c = DefaultHTTPClientConfig
 	if err := unmarshal((*plain)(c)); err != nil {
@@ -483,7 +484,7 @@ func (c *HTTPClientConfig) UnmarshalJSON(data []byte) error {
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
-func (a *BasicAuth) UnmarshalYAML(unmarshal func(interface{}) error) error {
+func (a *BasicAuth) UnmarshalYAML(unmarshal func(any) error) error {
 	type plain BasicAuth
 	return unmarshal((*plain)(a))
 }
@@ -1130,10 +1131,7 @@ func cloneRequest(r *http.Request) *http.Request {
 	r2 := new(http.Request)
 	*r2 = *r
 	// Deep copy of the Header.
-	r2.Header = make(http.Header)
-	for k, s := range r.Header {
-		r2.Header[k] = s
-	}
+	maps.Copy(r.Header, r2.Header)
 	return r2
 }
 
@@ -1256,7 +1254,7 @@ func (c *TLSConfig) SetDirectory(dir string) {
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
-func (c *TLSConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
+func (c *TLSConfig) UnmarshalYAML(unmarshal func(any) error) error {
 	type plain TLSConfig
 	if err := unmarshal((*plain)(c)); err != nil {
 		return err

config/http_config_test.go

@@ -1128,7 +1128,6 @@ func TestTLSRoundTripper(t *testing.T) {
 
 	var c *http.Client
 	for i, tc := range testCases {
-		tc := tc
 		t.Run(strconv.Itoa(i), func(t *testing.T) {
 			writeCertificate(bs, tc.ca, ca)
 			writeCertificate(bs, tc.cert, cert)
@@ -1239,7 +1238,6 @@ func TestTLSRoundTripper_Inline(t *testing.T) {
 	}
 
 	for i, tc := range testCases {
-		tc := tc
 		t.Run(strconv.Itoa(i), func(t *testing.T) {
 			cfg := HTTPClientConfig{
 				TLSConfig: TLSConfig{
@@ -1316,10 +1314,8 @@ func TestTLSRoundTripperRaces(t *testing.T) {
 	ch := make(chan struct{})
 	var total, ok int64
 	// Spawn 10 Go routines polling the server concurrently.
-	for i := 0; i < 10; i++ {
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
+	for range 10 {
+		wg.Go(func() {
 			for {
 				select {
 				case <-ch:
@@ -1333,13 +1329,11 @@ func TestTLSRoundTripperRaces(t *testing.T) {
 					}
 				}
 			}
-		}()
+		})
 	}
 
 	// Change the CA file every 10ms for 1 second.
-	wg.Add(1)
-	go func() {
-		defer wg.Done()
+	wg.Go(func() {
 		i := 0
 		for {
 			tick := time.NewTicker(10 * time.Millisecond)
@@ -1355,7 +1349,7 @@ func TestTLSRoundTripperRaces(t *testing.T) {
 				return
 			}
 		}
-	}()
+	})
 
 	wg.Wait()
 	require.NotEqualf(t, ok, total, "Expecting some requests to fail but got %d/%d successful requests", ok, total)
@@ -1788,7 +1782,7 @@ endpoint_params:
 		Scopes:                   []string{"A", "B"},
 		TokenURL:                 ts.tokenURL(),
 		EndpointParams:           map[string]string{"hi": "hello"},
-		Claims: map[string]interface{}{
+		Claims: map[string]any{
 			"iss":     "https://example.com",
 			"aud":     "common-test",
 			"sub":     "common",

config/oauth_assertion.go

@@ -18,6 +18,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"maps"
 	"net/http"
 	"net/url"
 	"strings"
@@ -133,9 +134,7 @@ func (js jwtSource) Token() (*oauth2.Token, error) {
 		claims["scope"] = scopes
 	}
 
-	for k, v := range js.conf.PrivateClaims {
-		claims[k] = v
-	}
+	maps.Copy(claims, js.conf.PrivateClaims)
 
 	assertion := jwt.NewWithClaims(js.conf.SigningAlgorithm, claims)
 	if js.conf.PrivateKeyID != "" {

expfmt/expfmt.go

@@ -122,7 +122,7 @@ func NewOpenMetricsFormat(version string) (Format, error) {
 // removed.
 func (f Format) WithEscapingScheme(s model.EscapingScheme) Format {
 	var terms []string
-	for _, p := range strings.Split(string(f), ";") {
+	for p := range strings.SplitSeq(string(f), ";") {
 		toks := strings.Split(p, "=")
 		if len(toks) != 2 {
 			trimmed := strings.TrimSpace(p)
@@ -194,7 +194,7 @@ func (f Format) FormatType() FormatType {
 // "escaping" term exists, that will be used. Otherwise, the global default will
 // be returned.
 func (f Format) ToEscapingScheme() model.EscapingScheme {
-	for _, p := range strings.Split(string(f), ";") {
+	for p := range strings.SplitSeq(string(f), ";") {
 		toks := strings.Split(p, "=")
 		if len(toks) != 2 {
 			continue

expfmt/text_create.go

@@ -42,12 +42,12 @@ const (
 
 var (
 	bufPool = sync.Pool{
-		New: func() interface{} {
+		New: func() any {
 			return bufio.NewWriter(io.Discard)
 		},
 	}
 	numBufPool = sync.Pool{
-		New: func() interface{} {
+		New: func() any {
 			b := make([]byte, 0, initialNumBufSize)
 			return &b
 		},

helpers/templates/time.go

@@ -25,7 +25,7 @@ import (
 
 var errNaNOrInf = errors.New("value is NaN or Inf")
 
-func ConvertToFloat(i interface{}) (float64, error) {
+func ConvertToFloat(i any) (float64, error) {
 	switch v := i.(type) {
 	case float64:
 		return v, nil
@@ -58,7 +58,7 @@ func FloatToTime(v float64) (*time.Time, error) {
 	return &t, nil
 }
 
-func HumanizeDuration(i interface{}) (string, error) {
+func HumanizeDuration(i any) (string, error) {
 	v, err := ConvertToFloat(i)
 	if err != nil {
 		return "", err
@@ -105,7 +105,7 @@ func HumanizeDuration(i interface{}) (string, error) {
 	return fmt.Sprintf("%.4g%ss", v, prefix), nil
 }
 
-func HumanizeTimestamp(i interface{}) (string, error) {
+func HumanizeTimestamp(i any) (string, error) {
 	v, err := ConvertToFloat(i)
 	if err != nil {
 		return "", err

helpers/templates/time_test.go

@@ -23,7 +23,7 @@ import (
 func TestHumanizeDuration(t *testing.T) {
 	tc := []struct {
 		name     string
-		input    interface{}
+		input    any
 		expected string
 	}{
 		// Integers
@@ -81,7 +81,7 @@ func TestHumanizeDurationErrorString(t *testing.T) {
 func TestHumanizeTimestamp(t *testing.T) {
 	tc := []struct {
 		name     string
-		input    interface{}
+		input    any
 		expected string
 	}{
 		// Int

model/labels.go

@@ -124,7 +124,7 @@ func (ln LabelName) IsValidLegacy() bool {
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
-func (ln *LabelName) UnmarshalYAML(unmarshal func(interface{}) error) error {
+func (ln *LabelName) UnmarshalYAML(unmarshal func(any) error) error {
 	var s string
 	if err := unmarshal(&s); err != nil {
 		return err

model/labelset.go

@@ -16,6 +16,7 @@ package model
 import (
 	"encoding/json"
 	"fmt"
+	"maps"
 	"sort"
 )
 
@@ -107,23 +108,17 @@ func (ls LabelSet) Before(o LabelSet) bool {
 // Clone returns a copy of the label set.
 func (ls LabelSet) Clone() LabelSet {
 	lsn := make(LabelSet, len(ls))
-	for ln, lv := range ls {
-		lsn[ln] = lv
-	}
+	maps.Copy(lsn, ls)
 	return lsn
 }
 
 // Merge is a helper function to non-destructively merge two label sets.
 func (ls LabelSet) Merge(other LabelSet) LabelSet {
 	result := make(LabelSet, len(ls))
 
-	for k, v := range ls {
-		result[k] = v
-	}
+	maps.Copy(result, ls)
 
-	for k, v := range other {
-		result[k] = v
-	}
+	maps.Copy(result, other)
 
 	return result
 }

model/metric.go

@@ -17,6 +17,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"maps"
 	"regexp"
 	"sort"
 	"strconv"
@@ -258,9 +259,7 @@ func (m Metric) Before(o Metric) bool {
 // Clone returns a copy of the Metric.
 func (m Metric) Clone() Metric {
 	clone := make(Metric, len(m))
-	for k, v := range m {
-		clone[k] = v
-	}
+	maps.Copy(clone, m)
 	return clone
 }
 

model/metric_test.go

@@ -844,7 +844,7 @@ func TestEscapeMetricFamily(t *testing.T) {
 		},
 	}
 
-	unexportList := []interface{}{dto.MetricFamily{}, dto.Metric{}, dto.LabelPair{}, dto.Counter{}, dto.Gauge{}}
+	unexportList := []any{dto.MetricFamily{}, dto.Metric{}, dto.LabelPair{}, dto.Counter{}, dto.Gauge{}}
 
 	for _, scenario := range scenarios {
 		t.Run(scenario.name, func(t *testing.T) {

model/signature_test.go

@@ -281,7 +281,7 @@ func benchmarkMetricToFastFingerprintConc(b *testing.B, ls LabelSet, e Fingerpri
 	end.Add(concLevel)
 	errc := make(chan error, 1)
 
-	for i := 0; i < concLevel; i++ {
+	for range concLevel {
 		go func() {
 			start.Wait()
 			for j := b.N / concLevel; j >= 0; j-- {