Fix schema shadowing issue by enums (deepmap#833)

This fixes deepmap#832 by creating errors upon type conflict, and allowing
renaming enum types via `x-go-name`.

Co-authored-by: marcinromaszewicz <marcinromaszewicz@deepmap.ai>

internal/test/issues/issue-832/config.yaml

@@ -0,0 +1,5 @@
+package: issue_832
+generate:
+  models: true
+  embedded-spec: true
+output: issue.gen.go

internal/test/issues/issue-832/generate.go

@@ -0,0 +1,3 @@
+package issue_832
+
+//go:generate go run github.com/deepmap/oapi-codegen/cmd/oapi-codegen --config=config.yaml spec.yaml

internal/test/issues/issue-832/spec.yaml

@@ -0,0 +1,43 @@
+openapi: 3.0.2
+info:
+  version: '0.0.1'
+  title: example
+  description: |
+    Make sure that recursive types are handled properly
+paths:
+  /example:
+    get:
+      operationId: exampleGet
+      responses:
+        '200':
+          description: "OK"
+          content:
+            'application/json':
+              schema:
+                $ref: '#/components/schemas/Document'
+  /example2:
+    get:
+      operationId: exampleGet2
+      responses:
+        '200':
+          description: "OK"
+          content:
+            'application/json':
+              schema:
+                $ref: '#/components/schemas/DocumentStatus'
+components:
+  schemas:
+    Document:
+      type: object
+      properties:
+        name:
+          type: string
+        status:
+          type: string
+          x-go-name: Document_Status
+          enum: [one, two, three, four]
+    DocumentStatus:
+      type: object
+      properties:
+        value:
+          type: string

pkg/codegen/codegen.go

@@ -592,14 +592,17 @@ func GenerateTypes(t *template.Template, types []TypeDefinition) (string, error)
 	m := map[string]bool{}
 	ts := []TypeDefinition{}
 
-	for _, t := range types {
-		if found := m[t.TypeName]; found {
-			continue
+	for _, typ := range types {
+		if found := m[typ.TypeName]; found {
+			// We want to create an error when we try to define the same type
+			// twice.
+			return "", fmt.Errorf("duplicate typename '%s' detected, can't auto-rename, "+
+				"please use x-go-name to specify your own name for one of them", typ.TypeName)
 		}
 
-		m[t.TypeName] = true
+		m[typ.TypeName] = true
 
-		ts = append(ts, t)
+		ts = append(ts, typ)
 	}
 
 	context := struct {

pkg/codegen/schema.go

@@ -220,7 +220,7 @@ func PropertiesEqual(a, b Property) bool {
 func GenerateGoSchema(sref *openapi3.SchemaRef, path []string) (Schema, error) {
 	// Add a fallback value in case the sref is nil.
 	// i.e. the parent schema defines a type:array, but the array has
-	// no items defined. Therefore we have at least valid Go-Code.
+	// no items defined. Therefore, we have at least valid Go-Code.
 	if sref == nil {
 		return Schema{GoType: "interface{}"}, nil
 	}
@@ -438,7 +438,18 @@ func GenerateGoSchema(sref *openapi3.SchemaRef, path []string) (Schema, error) {
 			}
 		}
 		if len(path) > 1 { // handle additional type only on non-toplevel types
-			typeName := SchemaNameToTypeName(PathToTypeName(path))
+			// Allow overriding autogenerated enum type names, since these may
+			// cause conflicts - see https://github.com/deepmap/oapi-codegen/issues/832
+			var typeName string
+			if extension, ok := schema.Extensions[extGoName]; ok {
+				typeName, err = extTypeName(extension)
+				if err != nil {
+					return outSchema, fmt.Errorf("invalid value for %q: %w", extGoName, err)
+				}
+			} else {
+				typeName = SchemaNameToTypeName(PathToTypeName(path))
+			}
+
 			typeDef := TypeDefinition{
 				TypeName: typeName,
 				JsonName: strings.Join(path, "."),
@@ -447,7 +458,6 @@ func GenerateGoSchema(sref *openapi3.SchemaRef, path []string) (Schema, error) {
 			outSchema.AdditionalTypes = append(outSchema.AdditionalTypes, typeDef)
 			outSchema.RefType = typeName
 		}
-		// outSchema.RefType = typeName
 	} else {
 		err := oapiSchemaToGoType(schema, path, &outSchema)
 		if err != nil {