oapi-codegen · mromaszewicz · Feb 21, 2026 · Feb 18, 2026
@@ -29,7 +29,7 @@ import (
 	"github.com/oapi-codegen/oapi-codegen/v2/pkg/util"
 )
 
-func errExit(format string, args ...interface{}) {
+func errExit(format string, args ...any) {
 	if !strings.HasSuffix(format, "\n") {
 		format = format + "\n"
 	}
@@ -272,12 +272,13 @@ func main() {
 	}
 
 	if warnings := opts.Generate.Warnings(); len(warnings) > 0 {
-		out := "WARNING: A number of warning(s) were returned when validating the GenerateOptions:"
+		var out strings.Builder
+		out.WriteString("WARNING: A number of warning(s) were returned when validating the GenerateOptions:")
 		for k, v := range warnings {
-			out += "\n- " + k + ": " + v
+			out.WriteString("\n- " + k + ": " + v)
 		}
 
-		_, _ = fmt.Fprint(os.Stderr, out)
+		_, _ = fmt.Fprint(os.Stderr, out.String())
 	}
 
 	// If the user asked to output configuration, output it to stdout and exit

@@ -29,48 +29,48 @@ const (
 	extOapiCodegenOnlyHonourGoName = "x-oapi-codegen-only-honour-go-name"
 )
 
-func extString(extPropValue interface{}) (string, error) {
+func extString(extPropValue any) (string, error) {
 	str, ok := extPropValue.(string)
 	if !ok {
 		return "", fmt.Errorf("failed to convert type: %T", extPropValue)
 	}
 	return str, nil
 }
 
-func extTypeName(extPropValue interface{}) (string, error) {
+func extTypeName(extPropValue any) (string, error) {
 	return extString(extPropValue)
 }
 
-func extParsePropGoTypeSkipOptionalPointer(extPropValue interface{}) (bool, error) {
+func extParsePropGoTypeSkipOptionalPointer(extPropValue any) (bool, error) {
 	goTypeSkipOptionalPointer, ok := extPropValue.(bool)
 	if !ok {
 		return false, fmt.Errorf("failed to convert type: %T", extPropValue)
 	}
 	return goTypeSkipOptionalPointer, nil
 }
 
-func extParseGoFieldName(extPropValue interface{}) (string, error) {
+func extParseGoFieldName(extPropValue any) (string, error) {
 	return extString(extPropValue)
 }
 
-func extParseOmitEmpty(extPropValue interface{}) (bool, error) {
+func extParseOmitEmpty(extPropValue any) (bool, error) {
 	omitEmpty, ok := extPropValue.(bool)
 	if !ok {
 		return false, fmt.Errorf("failed to convert type: %T", extPropValue)
 	}
 	return omitEmpty, nil
 }
 
-func extParseOmitZero(extPropValue interface{}) (bool, error) {
+func extParseOmitZero(extPropValue any) (bool, error) {
 	omitZero, ok := extPropValue.(bool)
 	if !ok {
 		return false, fmt.Errorf("failed to convert type: %T", extPropValue)
 	}
 	return omitZero, nil
 }
 
-func extExtraTags(extPropValue interface{}) (map[string]string, error) {
-	tagsI, ok := extPropValue.(map[string]interface{})
+func extExtraTags(extPropValue any) (map[string]string, error) {
+	tagsI, ok := extPropValue.(map[string]any)
 	if !ok {
 		return nil, fmt.Errorf("failed to convert type: %T", extPropValue)
 	}
@@ -85,16 +85,16 @@ func extExtraTags(extPropValue interface{}) (map[string]string, error) {
 	return tags, nil
 }
 
-func extParseGoJsonIgnore(extPropValue interface{}) (bool, error) {
+func extParseGoJsonIgnore(extPropValue any) (bool, error) {
 	goJsonIgnore, ok := extPropValue.(bool)
 	if !ok {
 		return false, fmt.Errorf("failed to convert type: %T", extPropValue)
 	}
 	return goJsonIgnore, nil
 }
 
-func extParseEnumVarNames(extPropValue interface{}) ([]string, error) {
-	namesI, ok := extPropValue.([]interface{})
+func extParseEnumVarNames(extPropValue any) ([]string, error) {
+	namesI, ok := extPropValue.([]any)
 	if !ok {
 		return nil, fmt.Errorf("failed to convert type: %T", extPropValue)
 	}
@@ -109,11 +109,11 @@ func extParseEnumVarNames(extPropValue interface{}) ([]string, error) {
 	return names, nil
 }
 
-func extParseDeprecationReason(extPropValue interface{}) (string, error) {
+func extParseDeprecationReason(extPropValue any) (string, error) {
 	return extString(extPropValue)
 }
 
-func extParseOapiCodegenOnlyHonourGoName(extPropValue interface{}) (bool, error) {
+func extParseOapiCodegenOnlyHonourGoName(extPropValue any) (bool, error) {
 	onlyHonourGoName, ok := extPropValue.(bool)
 	if !ok {
 		return false, fmt.Errorf("failed to convert type: %T", extPropValue)

@@ -39,7 +39,7 @@ func Test_extTypeName(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			// kin-openapi no longer returns these as RawMessage
-			var extPropValue interface{}
+			var extPropValue any
 			if tt.args.extPropValue != nil {
 				err := json.Unmarshal(tt.args.extPropValue, &extPropValue)
 				assert.NoError(t, err)
@@ -93,7 +93,7 @@ func Test_extParsePropGoTypeSkipOptionalPointer(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			// kin-openapi no longer returns these as RawMessage
-			var extPropValue interface{}
+			var extPropValue any
 			if tt.args.extPropValue != nil {
 				err := json.Unmarshal(tt.args.extPropValue, &extPropValue)
 				assert.NoError(t, err)

@@ -87,7 +87,7 @@ func mergeAllOf(allOf []*openapi3.SchemaRef) (openapi3.Schema, error) {
 func mergeOpenapiSchemas(s1, s2 openapi3.Schema, allOf bool) (openapi3.Schema, error) {
 	var result openapi3.Schema
 
-	result.Extensions = make(map[string]interface{})
+	result.Extensions = make(map[string]any)
 	for k, v := range s1.Extensions {
 		result.Extensions[k] = v
 	}

@@ -1067,7 +1067,7 @@ func GenerateClientWithResponses(t *template.Template, ops []OperationDefinition
 }
 
 // GenerateTemplates used to generate templates
-func GenerateTemplates(templates []string, t *template.Template, ops interface{}) (string, error) {
+func GenerateTemplates(templates []string, t *template.Template, ops any) (string, error) {
 	var generatedTemplates []string
 	for _, tmpl := range templates {
 		var buf bytes.Buffer

@@ -2,23 +2,19 @@ package codegen
 
 import (
 	"fmt"
+	"slices"
 
 	"github.com/getkin/kin-openapi/openapi3"
 )
 
 func stringInSlice(a string, list []string) bool {
-	for _, b := range list {
-		if b == a {
-			return true
-		}
-	}
-	return false
+	return slices.Contains(list, a)
 }
 
 type RefWrapper struct {
 	Ref       string
 	HasValue  bool
-	SourceRef interface{}
+	SourceRef any
 }
 
 func walkSwagger(swagger *openapi3.T, doFn func(RefWrapper) (bool, error)) error {

@@ -102,7 +102,7 @@ type Property struct {
 	ReadOnly      bool
 	WriteOnly     bool
 	NeedsFormTag  bool
-	Extensions    map[string]interface{}
+	Extensions    map[string]any
 	Deprecated    bool
 }
 
@@ -270,11 +270,11 @@ func (u UnionElement) String() string {
 
 // Method generate union method name for template functions `As/From/Merge`.
 func (u UnionElement) Method() string {
-	var method string
+	var method strings.Builder
 	for _, part := range strings.Split(string(u), `.`) {
-		method += UppercaseFirstCharacter(part)
+		method.WriteString(UppercaseFirstCharacter(part))
 	}
-	return method
+	return method.String()
 }
 
 func PropertiesEqual(a, b Property) bool {

@@ -20,6 +20,7 @@ import (
 	"net/url"
 	"reflect"
 	"regexp"
+	"slices"
 	"sort"
 	"strconv"
 	"strings"
@@ -205,7 +206,7 @@ func LowercaseFirstCharacters(str string) string {
 
 	runes := []rune(str)
 
-	for i := 0; i < len(runes); i++ {
+	for i := range runes {
 		next := i + 1
 		if i != 0 && next < len(runes) && unicode.IsLower(runes[next]) {
 			break
@@ -224,25 +225,25 @@ func LowercaseFirstCharacters(str string) string {
 func ToCamelCase(str string) string {
 	s := strings.Trim(str, " ")
 
-	n := ""
+	var n strings.Builder
 	capNext := true
 	for _, v := range s {
 		if unicode.IsUpper(v) {
-			n += string(v)
+			n.WriteString(string(v))
 		}
 		if unicode.IsDigit(v) {
-			n += string(v)
+			n.WriteString(string(v))
 		}
 		if unicode.IsLower(v) {
 			if capNext {
-				n += strings.ToUpper(string(v))
+				n.WriteString(strings.ToUpper(string(v)))
 			} else {
-				n += string(v)
+				n.WriteString(string(v))
 			}
 		}
 		_, capNext = separatorSet[v]
 	}
-	return n
+	return n.String()
 }
 
 // ToCamelCaseWithDigits function will convert query-arg style strings to CamelCase. We will
@@ -407,12 +408,7 @@ func schemaXOrder(v *openapi3.SchemaRef) (int64, bool) {
 // StringInArray checks whether the specified string is present in an array
 // of strings
 func StringInArray(str string, array []string) bool {
-	for _, elt := range array {
-		if elt == str {
-			return true
-		}
-	}
-	return false
+	return slices.Contains(array, str)
 }
 
 // RefPathToObjName returns the name of referenced object without changes.
@@ -1074,7 +1070,7 @@ func ParseGoImportExtension(v *openapi3.SchemaRef) (*goImport, error) {
 
 	goTypeImportExt := v.Value.Extensions[extPropGoImport]
 
-	importI, ok := goTypeImportExt.(map[string]interface{})
+	importI, ok := goTypeImportExt.(map[string]any)
 	if !ok {
 		return nil, fmt.Errorf("failed to convert type: %T", goTypeImportExt)
 	}
@@ -1126,12 +1122,7 @@ func isAdditionalPropertiesExplicitFalse(s *openapi3.Schema) bool {
 }
 
 func sliceContains[E comparable](s []E, v E) bool {
-	for _, ss := range s {
-		if ss == v {
-			return true
-		}
-	}
-	return false
+	return slices.Contains(s, v)
 }
 
 // FixDuplicateTypeNames renames duplicate type names.

@@ -160,7 +160,7 @@ func TestSortedSchemaKeysWithXOrder(t *testing.T) {
 	withOrder := func(i float64) *openapi3.SchemaRef {
 		return &openapi3.SchemaRef{
 			Value: &openapi3.Schema{
-				Extensions: map[string]interface{}{"x-order": i},
+				Extensions: map[string]any{"x-order": i},
 			},
 		}
 	}