oapi-codegen · gaiaz-iusipov · Mar 26, 2026 · Mar 27, 2026 · Mar 27, 2026
@@ -24,9 +24,11 @@ import (
 	"go/scanner"
 	"io"
 	"io/fs"
+	"maps"
 	"net/http"
 	"os"
 	"runtime/debug"
+	"slices"
 	"sort"
 	"strings"
 	"text/template"
@@ -103,11 +105,8 @@ func constructImportMapping(importMapping map[string]string) importMap {
 	)
 
 	{
-		var packagePaths []string
-		for _, packageName := range importMapping {
-			packagePaths = append(packagePaths, packageName)
-		}
-		sort.Strings(packagePaths)
+		packagePaths := slices.Collect(maps.Values(importMapping))
+		slices.Sort(packagePaths)
 
 		for _, packagePath := range packagePaths {
 			if _, ok := pathToImport[packagePath]; !ok && packagePath != importMappingCurrentPackage {
@@ -255,7 +254,7 @@ func Generate(spec *openapi3.T, opts Configuration) (string, error) {
 		if err != nil {
 			return "", fmt.Errorf("error getting type definition imports: %w", err)
 		}
-		MergeImports(xGoTypeImports, imprts)
+		maps.Copy(xGoTypeImports, imprts)
 	}
 
 	var serverURLsDefinitions string
@@ -626,11 +625,7 @@ func GenerateConstants(t *template.Template, ops []OperationDefinition) (string,
 		}
 	}
 
-	var providerNames []string
-	for providerName := range providerNameMap {
-		providerNames = append(providerNames, providerName)
-	}
-
+	providerNames := slices.Collect(maps.Keys(providerNameMap))
 	sort.Strings(providerNames)
 
 	constants.SecuritySchemeProviderNames = append(constants.SecuritySchemeProviderNames, providerNames...)
@@ -944,7 +939,7 @@ func resolvedNameForComponent(section, name string, contentType ...string) strin
 	}
 	if len(matches) > 0 {
 		if len(matches) > 1 {
-			sort.Strings(matches)
+			slices.Sort(matches)
 		}
 		return globalState.resolvedNames[matches[0]]
 	}
@@ -1243,14 +1238,14 @@ func OperationSchemaImports(s *Schema) (map[string]goImport, error) {
 		if err != nil {
 			return nil, err
 		}
-		MergeImports(res, imprts)
+		maps.Copy(res, imprts)
 	}
 
 	imprts, err := GoSchemaImports(&openapi3.SchemaRef{Value: s.OAPISchema})
 	if err != nil {
 		return nil, err
 	}
-	MergeImports(res, imprts)
+	maps.Copy(res, imprts)
 	return res, nil
 }
 
@@ -1263,7 +1258,7 @@ func OperationImports(ops []OperationDefinition) (map[string]goImport, error) {
 				if err != nil {
 					return nil, err
 				}
-				MergeImports(res, imprts)
+				maps.Copy(res, imprts)
 			}
 		}
 
@@ -1272,7 +1267,7 @@ func OperationImports(ops []OperationDefinition) (map[string]goImport, error) {
 			if err != nil {
 				return nil, err
 			}
-			MergeImports(res, imprts)
+			maps.Copy(res, imprts)
 		}
 
 		for _, b := range op.Responses {
@@ -1281,7 +1276,7 @@ func OperationImports(ops []OperationDefinition) (map[string]goImport, error) {
 				if err != nil {
 					return nil, err
 				}
-				MergeImports(res, imprts)
+				maps.Copy(res, imprts)
 			}
 		}
 
@@ -1316,7 +1311,7 @@ func GetTypeDefinitionsImports(swagger *openapi3.T, excludeSchemas []string) (ma
 	}
 
 	for _, imprts := range []map[string]goImport{schemaImports, reqBodiesImports, responsesImports, parametersImports} {
-		MergeImports(res, imprts)
+		maps.Copy(res, imprts)
 	}
 	return res, nil
 }
@@ -1343,14 +1338,14 @@ func GoSchemaImports(schemas ...*openapi3.SchemaRef) (map[string]goImport, error
 				if err != nil {
 					return nil, err
 				}
-				MergeImports(res, imprts)
+				maps.Copy(res, imprts)
 			}
 		} else if t.Is("array") {
 			imprts, err := GoSchemaImports(schemaVal.Items)
 			if err != nil {
 				return nil, err
 			}
-			MergeImports(res, imprts)
+			maps.Copy(res, imprts)
 		}
 	}
 	return res, nil
@@ -1371,7 +1366,7 @@ func GetSchemaImports(schemas map[string]*openapi3.SchemaRef, excludeSchemas []s
 		if err != nil {
 			return nil, err
 		}
-		MergeImports(res, imprts)
+		maps.Copy(res, imprts)
 	}
 	return res, nil
 }
@@ -1389,7 +1384,7 @@ func GetRequestBodiesImports(bodies map[string]*openapi3.RequestBodyRef) (map[st
 			if err != nil {
 				return nil, err
 			}
-			MergeImports(res, imprts)
+			maps.Copy(res, imprts)
 		}
 	}
 	return res, nil
@@ -1408,7 +1403,7 @@ func GetResponsesImports(responses map[string]*openapi3.ResponseRef) (map[string
 			if err != nil {
 				return nil, err
 			}
-			MergeImports(res, imprts)
+			maps.Copy(res, imprts)
 		}
 	}
 	return res, nil
@@ -1424,7 +1419,7 @@ func GetParametersImports(params map[string]*openapi3.ParameterRef) (map[string]
 		if err != nil {
 			return nil, err
 		}
-		MergeImports(res, imprts)
+		maps.Copy(res, imprts)
 	}
 	return res, nil
 }

@@ -1,14 +1,18 @@
 package codegen
 
 import (
+	"cmp"
 	"fmt"
-	"sort"
+	"slices"
 	"strings"
 
 	"github.com/getkin/kin-openapi/openapi3"
+
 	"github.com/oapi-codegen/oapi-codegen/v2/pkg/util"
 )
 
+var _ fmt.Stringer = (*SchemaPath)(nil)
+
 // SchemaPath represents the document location of a schema, e.g.
 // ["components", "schemas", "Pet", "properties", "name"].
 type SchemaPath []string
@@ -18,6 +22,8 @@ func (sp SchemaPath) String() string {
 	return strings.Join(sp, "/")
 }
 
+var _ fmt.Stringer = (*SchemaContext)(nil)
+
 // SchemaContext identifies where in the OpenAPI document a schema was found.
 type SchemaContext int
 
@@ -82,13 +88,13 @@ func (sc SchemaContext) Suffix() string {
 // GatheredSchema represents a schema discovered during the gather pass,
 // along with its document location and context metadata.
 type GatheredSchema struct {
-	Path        SchemaPath
-	Context     SchemaContext
-	Ref         string           // $ref string if this is a reference
-	Schema      *openapi3.Schema // The resolved schema value
-	OperationID string           // Enclosing operation's ID, if any
-	ContentType string           // Media type, if from request/response body
-	StatusCode  string           // HTTP status code, if from a response
+	Path           SchemaPath
+	Context        SchemaContext
+	Ref            string           // $ref string if this is a reference
+	Schema         *openapi3.Schema // The resolved schema value
+	OperationID    string           // Enclosing operation's ID, if any
+	ContentType    string           // Media type, if from request/response body
+	StatusCode     string           // HTTP status code, if from a response
 	ParamIndex     int              // Parameter index within an operation
 	ComponentName  string           // The component name (e.g., "Bar" for components/schemas/Bar)
 	GoNameOverride string           // x-go-name override from the component or its parent container
@@ -105,11 +111,13 @@ func GatherSchemas(spec *openapi3.T, opts Configuration) []*GatheredSchema {
 	var schemas []*GatheredSchema
 
 	if spec.Components != nil {
-		schemas = append(schemas, gatherComponentSchemas(spec.Components)...)
-		schemas = append(schemas, gatherComponentParameters(spec.Components)...)
-		schemas = append(schemas, gatherComponentResponses(spec.Components)...)
-		schemas = append(schemas, gatherComponentRequestBodies(spec.Components)...)
-		schemas = append(schemas, gatherComponentHeaders(spec.Components)...)
+		schemas = slices.Concat(
+			gatherComponentSchemas(spec.Components),
+			gatherComponentParameters(spec.Components),
+			gatherComponentResponses(spec.Components),
+			gatherComponentRequestBodies(spec.Components),
+			gatherComponentHeaders(spec.Components),
+		)
 	}
 
 	// Gather client response wrapper types for operations that will generate
@@ -268,10 +276,8 @@ func gatherComponentHeaders(components *openapi3.Components) []*GatheredSchema {
 // `<OperationId>Response`. These don't correspond to a real schema in the
 // spec but they need names that don't collide with real types.
 func gatherClientResponseWrappers(spec *openapi3.T) []*GatheredSchema {
-	var result []*GatheredSchema
-
 	if spec.Paths == nil {
-		return result
+		return nil
 	}
 
 	// Collect all operations sorted for determinism
@@ -296,10 +302,11 @@ func gatherClientResponseWrappers(spec *openapi3.T) []*GatheredSchema {
 	}
 
 	// Sort by operationID for determinism
-	sort.Slice(ops, func(i, j int) bool {
-		return ops[i].op.OperationID < ops[j].op.OperationID
+	slices.SortFunc(ops, func(a, b opEntry) int {
+		return cmp.Compare(a.op.OperationID, b.op.OperationID)
 	})
 
+	result := make([]*GatheredSchema, 0, len(ops))
 	for _, entry := range ops {
 		result = append(result, &GatheredSchema{
 			Path:        SchemaPath{"paths", entry.path, entry.method, "x-client-response-wrapper"},

@@ -3,6 +3,7 @@ package codegen
 import (
 	"errors"
 	"fmt"
+	"maps"
 	"strings"
 
 	"github.com/getkin/kin-openapi/openapi3"
@@ -87,14 +88,10 @@ 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]any)
-	for k, v := range s1.Extensions {
-		result.Extensions[k] = v
-	}
-	for k, v := range s2.Extensions {
-		// TODO: Check for collisions
-		result.Extensions[k] = v
-	}
+	result.Extensions = make(map[string]any, len(s1.Extensions)+len(s2.Extensions))
+	maps.Copy(result.Extensions, s1.Extensions)
+	// TODO: Check for collisions
+	maps.Copy(result.Extensions, s2.Extensions)
 
 	result.OneOf = append(s1.OneOf, s2.OneOf...)
 
@@ -195,14 +192,10 @@ func mergeOpenapiSchemas(s1, s2 openapi3.Schema, allOf bool) (openapi3.Schema, e
 	result.Required = append(s1.Required, s2.Required...)
 
 	// We merge all properties
-	result.Properties = make(map[string]*openapi3.SchemaRef)
-	for k, v := range s1.Properties {
-		result.Properties[k] = v
-	}
-	for k, v := range s2.Properties {
-		// TODO: detect conflicts
-		result.Properties[k] = v
-	}
+	result.Properties = make(map[string]*openapi3.SchemaRef, len(s1.Properties)+len(s2.Properties))
+	maps.Copy(result.Properties, s1.Properties)
+	// TODO: detect conflicts
+	maps.Copy(result.Properties, s2.Properties)
 
 	if isAdditionalPropertiesExplicitFalse(&s1) || isAdditionalPropertiesExplicitFalse(&s2) {
 		result.WithoutAdditionalProperties()